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The Younger Dryas-Holocene transition represents a period of significant thermal change, comparable in magnitude to modern warming, yet in a colder context and without the effect of anthropogenic disturbance. This is useful as a reference to tackle how biodiversity is affected by temperature in natural conditions. Here, we addressed the thermal change during this period in a southern Baltic coastal lake (Konarzewo Lake, Poland), as inferred by chironomid remains. We evaluated changes in chironomid communities and used Hill numbers to explore how commonness and rarity underlie biodiversity changes attributable to warming. We found evidence of warming at Konarzewo Lake during the Younger Dryas-Holocene transition, with inferred temperatures in the Younger Dryas period supporting the NW–SE gradient in Younger Dryas summer temperatures across Europe. Chironomid communities drastically changed during the thermal transition. However, Hill numbers showed no response to temperature when rare morphotypes were emphasized (order q = 0) or a weak response when they were balanced with common morphotypes (order q = 1). Hill number of order q = 2, emphasizing the most common morphotypes, consistently increased with temperature across different sample sizes or coverages. This illustrates how common morphotypes, rather than the rare ones, may boost biodiversity facing warming. [ABSTRACT FROM AUTHOR]

Irrigation is a crucial land use practice to adapt agriculture to unsuitable climate and soil conditions. Aiming to improve the growth of plants, irrigation modifies the soil condition, which causes atmospheric effects and feedbacks through land–atmosphere interaction. These effects can be quantified with numerical climate models, as has been done in various studies. It could be shown that irrigation effects, such as air temperature reduction and humidity increase, are well understood and should not be neglected on local and regional scales. However, there is a lack of studies including the role of vegetation in the altered land–atmosphere interaction. With the increasing resolution of numerical climate models, these detailed processes have a chance to be better resolved and studied. This study aims to analyze the effects of irrigation on land–atmosphere interaction, including the effects and feedbacks of vegetation. We developed a new parameterization for irrigation, implemented it into the REgional climate MOdel (REMO2020), and coupled it with the interactive MOsaic-based VEgetation module (iMOVE). Following this new approach of a separate irrigated fraction, the parameterization is suitable as a subgrid parameterization for high-resolution studies and resolves irrigation effects on land, atmosphere, and vegetation. Further, the parameterization is designed with three different water application schemes in order to analyze different parameterization approaches and their influence on the representation of irrigation effects. We apply the irrigation parameterization for southwestern Europe including the Mediterranean region at a 0.11 ∘ horizontal resolution for hot extremes. The simulation results are evaluated in terms of the consistency of physical processes. We found direct effects of irrigation, like a changed surface energy balance with increased latent and decreased sensible heat fluxes, and a surface temperature reduction of more than -4 K as a mean during the growing season. Further, vegetation reacts to irrigation with direct effects, such as reduced water stress, but also with feedbacks, such as a delayed growing season caused by the reduction of the near-surface temperature. Furthermore, the results were compared to observational data, showing a significant bias reduction in the 2 m mean temperature when using the irrigation parameterization. [ABSTRACT FROM AUTHOR]

Vertical temperature profiles influence the wind power generation of large offshore wind farms through stability-dependent effects such as blockage and gravity waves. However, numerical tools that are used to model these effects are often computationally too expensive to cover the large variety of atmospheric states occurring over time. Generally, an informed decision about which representative nonidealized situations to simulate is missing because of the lack of easily available information on representative vertical profiles, taking into account their spatiotemporal variability. Therefore, we present a novel framework that allows a smart selection of vertical temperature profiles. The framework consists of an improved analytical temperature model for the atmospheric boundary layer and lower troposphere, a subsequent clustering of these profiles to identify representatives, and last, a determination of areas with similar spatiotemporal characteristics of vertical profiles. When applying this framework on European ERA5 data, physically realistic representatives were identified for Europe, excluding the Mediterranean. Two or three profiles were found to be dominant for the open ocean, whereas more profiles prevail for land. Over the open ocean, weak temperature gradients in the boundary layer and a clear capping inversions are widespread, and stable profiles are absent except in the region of the East Icelandic Current. Interestingly, according to the ERA5 data, at its resolution, coastal areas and seas surrounded by land behave more similar to the land areas than to the open ocean, implying that a larger set of model integrations are needed for these areas to obtain representative results for offshore wind power assessments in comparison with the open ocean. SIGNIFICANCE STATEMENT: Numerical tools used to simulate the effect of large, offshore wind farms on neighboring farms and the atmosphere are very expensive. Therefore, they can only be computed for a limited number of cases. As temperature is one of the most important parameters in these kinds of simulations, this work provides a new vertical temperature model and an analysis framework that allows for a smart selection of these cases such that they ideally represent the full variation of the atmosphere's temperature profiles. [ABSTRACT FROM AUTHOR]

North Atlantic Oscillation (NAO) has a significant impact on surrounding winter weather and climate. However, the causes of its occasional reversal between early and late winter remain unclear. This study proposes a mechanism for the mid‐winter reversal of NAO from the perspective of local midlatitude air‐sea interaction. Strong sea surface temperature (SST) tripole events, which are defined by empirical orthogonal function of winter‐mean interannual North Atlantic SST anomalies, are primarily induced by NAO in early winter and peak in January. In late winter, the persistent SST tripole exerts active feedback on atmosphere through diabatic heat and transient eddy forcing. The resulting atmospheric circulation anomalies exhibit an almost reversed NAO pattern in February, which forms a wavetrain originating above the Gulf Stream and propagating to the Middle East and weakens the former SST tripole. Consequently, significant reversals of air temperature anomalies occur in Europe and the Caspian Sea area between February and December. Plain Language Summary: The North Atlantic Oscillation (NAO) is a crucial atmospheric system that significantly impacts the weather and climate of the surrounding regions during winter. However, it often reverses between early and late winter, and the reasons for its mid‐winter reversal remain unclear. The NAO behavior can be influenced by multiple factors, such as atmospheric internal processes, underlying surface, and remote climate system, which makes the issue more complex. This study highlights the role of underlying sea surface temperature anomalies (SSTAs) in the mid‐winter reversal of NAO. The North Atlantic SSTAs are closely associated with the NAO and exhibit a tripole pattern. For strong sea surface temperature (SST) tripole events, the NAO primarily induces the early winter North Atlantic SST tripole. The SSTAs develop in early winter, peak in January, and feedback on the atmospheric circulation in late winter. The atmospheric circulation anomalies exhibit an almost reversed NAO pattern in February, forming a wavetrain that propagates above the Gulf Stream to the Middle East. As a result, during the warm phase of the SST tripole, Europe experiences colder temperatures, and the Caspian Sea experiences warmer temperatures in February than usual, as opposed to the positive NAO's control over warm Europe and cold Caspian Sea in December. Key Points: In early winter, North Atlantic Oscillation (NAO) forces a North Atlantic sea surface temperature (SST) tripole, which persists and tends to induce a nearly reversed NAO pattern in FebruarySST tripole induces a wavetrain over the Gulf Stream to the Middle East via diabatic heating and transient eddy forcing in FebruaryAs a result, there are remarkable reversals of air temperature anomalies in Europe and Caspian Sea area between February and December [ABSTRACT FROM AUTHOR]

Intra-Annual Density Fluctuations (IADFs) are an important wood functional trait that determine trees' ability to adapt to climatic changes. Here, we use a large tree-ring database of 11 species from 89 sites across eight European countries, covering a climatic gradient from the Mediterranean to northern Europe, to analyze how climate variations drive IADF formation. We found that IADF occurrence increases nonlinearly with ring width in both gymnosperms and angiosperms and decreases with altitude and age. Recently recorded higher mean annual temperatures facilitate the formation of IADFs in almost all the studied species. Precipitation plays a significant role in inducing IADFs in species that exhibit drought tolerance capability, and a growth pattern known as bimodal growth. Our findings suggest that species with bimodal growth patterns growing in western and southern Europe will form IADFs more frequently, as an adaptation to increasing temperatures and droughts. [ABSTRACT FROM AUTHOR]

Time-varying relationships between two atmospheric oscillation modes and precipitation (rainfall and snow) in the western portion of the Carpathian Mountains and the northern part of the Pannonian Plain are investigated in this paper. The Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) modes were used to explain the intra-annual variability of monthly rainfall totals and new snow over a 36-year period (1981-2017) observed at a dense network of 177 rain gauges and 33 snow rods located throughout the investigated area, respectively. The Continuous Wavelet Transform (CWT) was deployed as a band-pass fllter to quantify the spectral coherence and attribution (based on signal-to-noise ratio) of the NAO and AO modes to the precipitation variability. The temporal and spatial patterns of NAO and AO-related signal variance in monthly rainfall totals and fresh snowpack were evaluated on seasonal and monthly bases. The NAO mode explained the major historically observed snow calamities, such as the snowy cold spell of January 1985 that hit central and southern Europe, bringing heavy snowfall to the investigated region and many other parts of Europe. This event was the beginning of a prolonged cold wave in Europe, with extremely low air temperatures across the continent. Our analyses showed that the AO mode appears to have only a limited effect on the overall variability of new snowpack in late winter. The attribution of NAO and AO modes to the variability of monthly rainfall totals is less pronounced compared to new snowpack. [ABSTRACT FROM AUTHOR]

Hibernation is one of the most important behaviours of bats of the temperate zone. During winter, when little food or liquid water is available, hibernation in torpor lowers metabolic costs. However, the timing of emergence from hibernation is crucial for the resumption of the reproductive process in spring. Here, we investigate the spring emergence of six bat species or pairs of bat species of the genera Myotis and Plecotus at five hibernation sites in Central Europe over 5 years. Using generalized additive Poisson models (GAPMs), we analyze the influence of weather conditions (air and soil temperature, atmospheric pressure, atmospheric pressure trend, rain, wind, and cloud cover) as predictors of bat activity and separate these extrinsic triggers from residual motivation to emerge from hibernation (extrinsic factors not studied; intrinsic motivation). Although bats in a subterranean hibernaculum are more or less cut off from the outside world, all species showed weather dependence, albeit to varying degrees, with air temperature outside the hibernaculum having a significant positive effect in all species. The residual, potentially intrinsic motivation of species to emerge from their hibernacula corresponds to their general ecological adaptation, such as trophic specialization and roosting preferences. It allows the definition of three functional groups (high, medium and low residual activity groups) according to the degree of weather dependence of spring activity. A better knowledge of the interplay of extrinsic triggers and residual motivation (e.g., internal zeitgebers) for spring emergence will help to understand the flexibility of a species to adapt to a changing world. [ABSTRACT FROM AUTHOR]

A suitable indoor climate positively affects the lifespan of historical building structures. The path to an agreeable climate begins with monitoring current conditions. Considerable attention is given to monitoring the indoor climate of historical buildings. The motivation for monitoring air temperature and surface temperatures, relative air humidity or airflow can be, for example, the installation of heating, the occurrence of biotic damage, and others. Through the analysis of the most frequently used keywords, a strong connection was found, for example, between thermal comfort and the church. This review also summarises the various reasons for conducting microclimate monitoring studies in historical religious buildings on the European continent. It is supplemented with an evaluation of the monitoring methodology from the chosen period of the year point of view, the measured parameters, and the length of the interval between the recordings of quantities. It was found that in more than one-third of the cases, the recording time was less than or equal to 15 min, but mostly less than or equal to 1 h. Quite often, monitoring results are used to calibrate a simulation model describing the hydrothermal behaviour of a historical object under various operation alternatives (e.g., influence of ventilation, climate change, occupancy, etc.). This way, it is possible to test various intelligent systems in the virtual world without much risk before they are used in an actual building application. [ABSTRACT FROM AUTHOR]

Condensation trails (contrails) from aircraft exhausts and contrail cirrus clouds play a significant role in the atmosphere's radiation balance and the climate. The aim of this study is to analyse the physical properties of contrails with the use of satellite data and determine the atmospheric conditions favoring their formation and persistence. The contrails are detected on satellite images provided by the Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) radiometer onboard the Meteosat Second Generation (MSG) satellites, using a modified version of the contrail detection algorithm by Mannstein et al. Int J Remote Sens 20(8):1641–1660. (1999) for the year 2016. The study area covers central and western Europe. Five contrail detection hotspots are located, with contrail density depending on time of day and season. The length of the detected contrails ranges between 225 and 292.5 km and the mean width between 5.1 and 8.1 km. The spatial contrail cover reaches up to 0.085% of the scene, with larger values being detected between 8 and 10 UTC and during winter. Results of the comparison with the ERA-5 reanalysis database show that contrail formation and persistence is favored in ice saturated areas (RHI≈100%), when the air temperature is between 204 and 232 Κ (− 69.2 to − 41.2 °C) and the specific humidity between 0.025 and 0.0625 g/kg. The favorable wind direction and speed lie between W and SW (240–300°) and 10 and 30 m/s, respectively. [ABSTRACT FROM AUTHOR]

The study discusses changes in the average annual air temperature over Europe in the years 1931-2020. The results of the research show that in 1987-1989, there was a sudden change in the thermal regime over Europe and a discontinuity appeared in the course of this climatic element. In the years 1931-1988, despite the high inter-annual variability, the temperature trend was zero. A positive, statistically significant, temperature trend appeared after 1988. The entire warming in Europe, which can be estimated at ~2.3 deg, occurred after 1988. The discontinuity in the course was caused by an abrupt change in macro-circulation conditions in the Atlantic-Eurasian circulation sector, which manifests itself as a fundamental change in the frequency of the macrotypes of the mid-tropospheric circulation (500 hPa) according to the Wangengejm-Girs classification, causing an equally fundamental change in the weather structure. The change in macro-circulation conditions was forced by a change in the thermal state of the North Atlantic - a sharp increase in the intensity of oceanic heat transport to the north. The analysis showed that the annual variability of temperature over Europe was mainly influenced by natural processes, the variability of which explains ~65% of its variance. Radiative forcing, which is a function of anthropogenic increase in CO2 concentration in the atmosphere, explains only 7-8% of the variability of the average annual temperature over Europe, being a secondary or tertiary factor in shaping its changes. [ABSTRACT FROM AUTHOR]

The response of the Euro‐Atlantic wintertime circulation to climate change is deeply uncertain. The Atlantic jet is caught in a "tug‐of‐war" between rapid warming trends in both the tropics and the Arctic leading to debate over the changing "waviness" of the jet, which is subject to strong non‐linearity and internal variability. From the complementary perspective of weather regimes, there is considerable uncertainty in how atmospheric blocking will alter under climate change. By applying the hybrid approach of geopotential‐jet regimes to 6th phase of the coupled model inter‐comparison project projections, we show that the centers of action of anticyclonic regimes hardly alter even under severe warming. Instead, regimes are expected to become less persistent, with zonal flow conditions becoming more prevalent, although models disagree on the details of regime changes. Finally, we show the regime response can be captured qualitatively in a simple Lorenz‐like model, emphasizing the conceptual link between observed regimes and those in basic mathematical systems. Plain Language Summary: The impact of climate change on European weather can be broken into two components: a thermodynamic part relating to increasing air temperature and humidity, and a dynamic part relating to changes in the atmospheric circulation such as the direction and strength of prevailing winds. While the thermodynamic part is relatively well understood, the dynamic part is very uncertain and this is a major problem in constraining European climate projections. Looking at the winter season, we study the dynamic response of CMIP6 models under climate change using so‐called "regimes," and show that the types of prevailing circulation are not predicted to change strongly. However the regimes are projected to be less long lived. We also show that these features can be well captured in a simple 5 equation model of regime dynamics, providing a potentially useful tool for understanding regime systems in more detail. Key Points: The spatial structure of anticyclonic circulations over Europe are projected to stay the same under climate changeThe persistence of anticyclonic circulations are in general expected to decrease, although there is considerable inter‐model variabilityWe show that these qualitative features of the atmospheric response can be reproduced in a simple forced regime model [ABSTRACT FROM AUTHOR]

Afforestation is an important mitigation strategy to climate change due to its carbon sequestration potential. Besides this positive biogeochemical effect on global CO2 concentrations, afforestation also affects the regional climate by changing the biogeophysical land surface characteristics. In this study, we investigate the effects of an idealized global CO2 reduction to pre-industrial conditions by a Europe wide afforestation experiment on the regional longwave radiation balance, starting in the year 1986 from a continent entirely covered with grassland. Results show that the impact of biogeophysical processes on the surface temperatures is much stronger than of biogechemical processes. Furthermore, biogeophysically induced changes of the surface temperatures, atmospheric temperatures and moisture concentrations are as important for the regional greenhouse effect as the global CO2 reduction. While the greenhouse effect is strengthened in winter, it is weakened in summer. On annual total, a Europe-wide afforestation has a regional warming effect, despite reduced CO2 concentrations. Thus, even for an idealized reduction of the global CO2 concentrations to pre-industrial levels, the European climate response to afforestation would still be dominated by its biogeophysical effects. [ABSTRACT FROM AUTHOR]

Recent years have seen a significant increase in weather anomalies in Central Europe (51°22′ N, 22°64′ E), which makes it more difficult to predict yields of winter wheat and to estimate prices on world exchanges. Eight-year (2007–2015) field observations of winter wheat cv. Turnia were carried out in order to determine the relationship between selected meteorological indicators (e.g., the values of average daily air temperature, daily sums of precipitation, and the number of days with precipitation) and the biometric traits and seed yield of winter wheat. In addition, an attempt was made to identify the meteorological parameters that determine an increase in stem elongation during the growing season. The relationship between yield parameters and biometric parameters was evaluated using Spearman's non-parametric correlation coefficients. The regression models for analysis of the dependence of yield parameters and biometric parameters on meteorological elements (temperature, precipitation totals, and days with precipitation) in each development period was used. The study showed that from the beginning of vegetative growth to the flowering stage, growth and development were most advanced in plants for which the average temperature was about 8–9 °C, and the number of days with precipitation was about 41. During generative growth, spike length is 80% determined by the precipitation total. Grain weight is 68% negatively determined by the temperature during dormancy (the higher the temperature during dormancy, the lower the weight of the kernel). A positive relationship was shown between yield and the precipitation total during the period from sowing to the onset of dormancy (r = 0.37). Winter wheat yield was 69% dependent on the density at harvest (the greater the density, the higher the final yield). On the basis of the 8-year results of the study, we conclude that the weather is highly variable from year to year, and therefore breeders should direct their research towards creating variants with much greater plasticity and high tolerance for unfavourable weather patterns. [ABSTRACT FROM AUTHOR]

Variability of the North Atlantic Oscillation (NAO) drives wintertime temperature anomalies in the Northern Hemisphere. Dynamical seasonal prediction systems can skilfully predict the winter NAO. However, prediction of the NAO‐dependent air temperature anomalies remains elusive, partially due to the low variability of predicted NAO. Here, we demonstrate a hidden potential of a multi‐model ensemble of operational seasonal prediction systems for predicting wintertime temperature by increasing the variability of predicted NAO. We identify and subsample those ensemble members which are close to NAO index statistically estimated from initial autumn conditions. In our novel multi‐model approach, the correlation prediction skill for wintertime Central Europe temperature is improved from 0.25 to 0.66, accompanied by an increased winter NAO prediction skill of 0.9. Thereby, temperature anomalies can be skilfully predicted for the upcoming winter over a large part of the Northern Hemisphere through increased variability and skill of predicted NAO. Plain Language Summary: Wintertime temperature in the Northern Hemisphere is regulated by the variations of atmospheric pressure, represented by the so‐called North Atlantic Oscillation (NAO). The NAO's phase—negative or positive—is associated with the pathways of cold and warm air masses leading to cold or warm winters in Europe. While the NAO phase can be predicted well, predictions of the NAO‐dependent air temperature remain elusive. Specifically, it is challenging to predict the strength of the NAO, the most important requirement for the accurate prediction of wintertime temperature. Here, we improve wintertime temperature prediction by increasing the strength of the predicted NAO. We use observation based autumn Northern Hemisphere ocean and air temperature, as well as ice and snow cover for statistical estimation of the first guess NAO for the upcoming winter. Then, we sub‐select only those simulations from the multi‐model ensemble, which are consistent with our first guess NAO. As a result, based on these selected members, the wintertime temperature prediction is substantially improved over a large part of the Northern Hemisphere. Key Points: Amplitude and skill of predicted North Atlantic Oscillation (NAO) improve significantly by subsampling of ensemble of existing seasonal prediction systemsAmplified NAO variability leads to significant improvement in predicting the upcoming winter temperature anomalies in the Northern Hemisphere [ABSTRACT FROM AUTHOR]

Since our climate is in a rapid changing phase, it is crucial to get information about the regional patterns of basic climatic parameters and indices. The EURO-CORDEX project provides high-quality regional climate model outputs, but these raw datasets are not convenient for the application in wider geoscience studies. According to the authors' knowledge, there is a lack of published spatial information about basic climate parameters and indices in Central Europe and especially in the broader Carpathian region therefore the basic aim of this study to fill this gap. The study presents the future trends in daily air temperature and precipitation and various climatic indices in the broader Carpathian Basin region during the 21st century. The indices are calculated using multi-model average temperature and precipitation data from EURO-CORDEX model simulations for the future time periods (2021-2050, 2071-2100) and emission scenarios (RCP4.5, RCP8.5). The indices present the future trends of the heat load, energy demand as well as extreme precipitation and drought characteristics. Based on the results the temperature increase is obvious and the heat load and energy demand quantifying indices follow the temperature trend. However, the trend is difficult to evaluate in the case of precipitation. The changes in the precipitation and the related indices can be considered small and appear within the regions. The future changes are the most considerable in the Carpathian Basin, but the entire examined region faces crucial changes in the following decades. [ABSTRACT FROM AUTHOR]

Long‐term satellite land surface temperature (LST) data are desirable to augment 2m air temperatures (T2m) measured in situ and as an independent measure of surface temperature change. However, previous studies show variable agreement between LST and T2m time series. The objective of this study is to assess the stability and trends in six new LST data sets from the European Space Agency's Climate Change Initiative for LST (LST_cci). LST anomalies are compared with homogenized station T2m anomalies over Europe, which verifies all six data sets are well coupled (LST vs T2m anomaly correlations and slopes: 0.6–0.9). The temporal stability of the LST_cci data is assessed through a comparison with the T2m anomaly time series. Only the LST_cci data sets for the MODerate resolution Imaging Spectroradiometer (MODIS) onboard Aqua and the Advanced Along‐Track Scanning Radiometer (AATSR) appear stable; the MODIS/Terra, ATSR‐2, and multisensor InfraRed and MicroWave data sets show non‐climatic discontinuities associated with changes in sensor and/or drift over time. For MODIS/Aqua (2002–2018), significant trends in LST of 0.64–0.66 K/decade compare well with the equivalent T2m trends of 0.52–0.59 K/decade. The LST and T2m trends for AATSR (2002–2012) are found to be statistically insignificant, likely due to the comparatively short study period and specific years available for analysis. No evidence is found to suggest that trends calculated using cloud‐free InfraRed observations are affected by clear‐sky bias. This study suggests that satellite LST data can be used to assess warming trends over land and for other climate applications if the required homogeneity is assured. Plain Language Summary: Long‐term changes in surface temperature due to climate change are usually studied using near‐surface air temperatures (T2m) from weather stations. However, these data are not available everywhere and changes in T2m are poorly understood in some regions (e.g., parts of Africa). This study assesses the potential for satellite‐observed land surface temperatures (LST) to help fill these gaps. The study finds that LST and T2m provide very similar information on surface temperatures and therefore LST can provide useful information where T2m data are unavailable. However, some of the LST data sets are found to be "unstable" and suffer from jumps and changes over time that result from for example, changes in satellite instrument or a change in the orbit of the satellite platform. These unstable LST data sets cannot be used to measure changes in surface temperature. However, the study finds that for "stable" LST data sets, which do not suffer from these non‐climatic jumps and changes, the changes in LST over time are very similar to, or even the same as, the changes in T2m. Therefore, this work suggests that satellite LST data could be used to measure changes in surface temperature where there are not enough stations to make these measurements using T2m. Key Points: The stability of six satellite land surface temperature data sets is assessed using homogenized station air temperatures over EuropeOnly two data sets are stable; the other four show non‐climatic discontinuities associated with a change in sensor and/or drift over timeSignificant trends in land surface temperature of ∼0.65 K/decade over Europe are found for one of the stable data sets over 2002–2018 [ABSTRACT FROM AUTHOR]

[Display omitted] • The model performs good in capturing the seasonal pattern and peak values of river water temperature. • Air temperature and day of year are the major factorson modeling river water temperature. • The model is a promising tool to investigate the impact of climate change on river thermal dynamics. Water temperature is an important physical indicator of rivers because it impacts many other physical and biogeochemical processes and controls the metabolism of aquatic species in rivers. Having a good knowledge of river thermal dynamics is of great importance. In this study, an advanced machine learning based model that is fast, accurate and easy to use, namely the nonlinear autoregressive network with exogenous inputs (NARX) neural network, was coupled with Bayesian Optimization (BO) algorithm for optimizing the number of NARX hidden nodes and lagged input/target values and the Bayesian Regularization (BR) backpropagation algorithm for the NARX training, to forecast daily river water temperatures (RWT). Long-term observed data from 18 rivers of the Vistula River Basin, one of the largest rivers in Europe, were used for model testing, and model performance was compared with the air2stream model. The results showed that the NARX-based model performs significantly better than the air2stream model in the calibration and validation stages, and can better capture the seasonal pattern and peak values of RWT. Input combinations impact the performance of the NARX-based model in RWT modeling, and air temperature and the day of the year (DOY) are the major inputs, while streamflow and rainfall play a minor role on modeling RWT at the Vistula River Basin. Considering that future times series of air temperatures are easily accessible from climate models and DOY is easy to be considered in the model, the NARX-based model can serve as a promising tool to investigate the impact of climate change on river thermal dynamics. [ABSTRACT FROM AUTHOR]

The North Atlantic Oscillation (NAO) index is often characterized by independent positive and negative NAO events with a characteristic spatial pattern and a typical lifetime of around 1 week. These events are separated by periods of near‐neutral NAO conditions. Here, we challenge this view by showing in reanalysis and observed data that the strength and spatial shape of NAO events depends on the NAO index prior to the window of 1 week and this dependency is most pronounced for negative NAO events. The influence is seen in the mean sea level pressure, and in other important features, including blocking frequency and jet stream characteristics, and also in air surface temperature and precipitation in parts of Europe. This new appreciation is important for efforts to improve methods for subseasonal‐to‐seasonal predictions of NAO. Plain Language Summary: Northern European winters differ. Some are mild and moist with prevailing westerly winds and some are cold and dry, dominated by the Siberian air masses from East. When the Northern European winters are mild, the winter in Greenland is cold, and vice versa. This is the North Atlantic Oscillation (NAO) and its companion, the Europe–Greenland temperature seesaw. They were described in qualitative terms already in the late eighteenth century. Nowadays, the NAO is often described as a series of independent positive or negative events with a duration of around 1 week with intermittent periods of near‐neutral conditions and variable duration. The net result of these events determines the NAO strength of the winter. We show that this picture is too simplified because the NAO outside the time horizon of 1 week influences the strength of the individual NAO events. This is most pronounced for the negative events where this influence can both distort and amplify or diminish the pattern of the event. Also the typical temperatures and precipitation patterns associated with NAO are influenced significantly by this effect. One important consequence for our discovery is the improved prospects of doing subseasonal‐to‐seasonal predictions. Key Points: The daily North Atlantic Oscillation (NAO) index consists of positive and negative events of duration around 1 week separated by periods of near‐neutral conditionsThe strength and spatial shape of negative NAO events depends on NAO‐index values prior to the eventBlocking frequencies, jet strength and position, and surface temperature and precipitation have similar dependencies [ABSTRACT FROM AUTHOR]

Climate change increases the frequency and intensity of heat waves, bringing along multiple adverse impacts on ecosystems, human health, societies, and the economy. Groundwater influences the near surface air temperature evolution through land–atmosphere interactions. Using simplified and shallow groundwater representations, reproducing heat waves in a regional climate model (RCM) is challenging. Currently, RCMs applied over Europe exhibit a warm bias. This study analyzes heat waves over a 13‐year evaluation period, comparing the terrestrial systems modeling platform (TSMP) with an explicit groundwater representation to a EURO‐CORDEX RCM ensemble, the ERA5 reanalysis, and observations. The TSMP multiannual heat wave statistics are consistent with observations and reanalysis data. We attribute the lower absolute deviations of heat wave metrics simulated by TSMP to the improved hydrology including 3D groundwater flow. The findings emphasize the importance of hydrological process representation in RCMs. Plain Language Summary: Heat waves severely impact the ecosystem, society, and the economy. Climate change will amplify these events in the near future, urging a correct representation of heat waves in climate models. Especially during warm and dry periods, there is a strong connection from the groundwater stored in the subsurface through the land surface to the atmosphere. Commonly applied models have a simplified representation of groundwater and cannot establish a correct connection to the atmosphere, simulating too high temperatures over Europe. To show the advantage of a model with a complex groundwater representation, we compare such a model with 12 representative climate models. The results indicate lower deviations from heat wave statistics of observations with the inclusion of complex groundwater. Our findings emphasize the importance of including groundwater dynamics representation in climate models. Key Points: Multiannual heat wave statistics from a regional climate model including groundwater dynamics are consistent with observationsRegional climate models with simplified groundwater representations overestimate observed multiannual heat wave statisticsExplicit groundwater treatment increases the reliability of heat wave simulations with implications for regional climate projections [ABSTRACT FROM AUTHOR]

Peatlands perform many important ecosystem functions at both the local and global scale, including hydrologic and climatic regulation. Although peatlands often act as climatic microrefugia, they have rarely been the subject of long-term microclimatic studies. In this study, we aimed to compare the local climatic conditions of a mid-forest mire to that of an open area and examine the differences in microclimates within the mire based on plant community diversity, shading, and water table depths. The peatland studied in this work was significantly cooler than the reference site, mainly due to a higher decline in nighttime air temperatures. However, the daily maximum air temperature near the ground was often higher. We also noticed that microclimates significantly differed within the studied peatland. Wet and shaded microsites were cooler than the sites having a lower water level and receiving higher amounts of solar radiation. The results of the study suggest that peatlands have locally cooler climates, and thus can serve as climate change refugia. These findings can help us interpret reconstructed data from the peat archive, and, when combined with experiments, identify tipping points for peatland ecosystems. [ABSTRACT FROM AUTHOR]

The quantification of land–atmosphere coupling strength is still challenging, particularly in the atmospheric segment of the local coupling process chain. This is in part caused by a lack of spatially comprehensive observations of atmospheric temperature and specific humidity which form the verification basis for the common process-based coupling metrics. In this study, we aim at investigating where uncertainty in the atmospheric temperature and moisture affects the land–atmosphere coupling strength over Europe, and how changes in the mean temperature and moisture, as well as their vertical gradients, influence the coupling. For this purpose, we implemented systematic a posteriori modifications to the temperature and moisture fields from a regional climate simulation to create a spread in the atmospheric conditions. Afterwards, the process-based coupling metric convective triggering potential – low-level humidity index framework was applied to each modification case. Comparing all modification cases to the unmodified control case revealed that a strong coupling hotspot region in northeastern Europe was insensitive to temperature and moisture changes, although the number of potential coupling days varied by up to 20 d per summer season. The predominance of positive feedbacks remained unchanged in the northern part of the hotspot, and none of the modifications changed the frequent inhibition of feedbacks due to dry conditions in the atmosphere over the Mediterranean and the Iberian Peninsula. However, in the southern hotspot region in the north of the Black Sea, the dominant coupling class frequently switched between wet soil advantage and transition zone. Thus, both the coupling strength and the predominant sign of feedbacks were sensitive to changes in temperature and moisture in this region. This implies not only uncertainty in the quantification of land–atmosphere coupling strength but also the potential that climate-change-induced temperature and moisture changes considerably impact the climate there, because they also change the predominant atmospheric response to land surface wetness. [ABSTRACT FROM AUTHOR]

The occurrence of long-lasting severe heat stress, such as in July–August 2003, July 2010, or in April–May 2018 has been one of the biggest meteorological threats in Europe in recent years. The paper focuses on the biometeorological and mortality effects of the hot June that was observed in Central Europe in 2019. The basis of the study was hourly and daily Universal Thermal Climate Index (UTCI) values at meteorological stations in Poland for June 2019. The average monthly air temperature and UTCI values from 1951 to 2018 were analysed as background. Grosswetterlagen calendar of atmospheric circulation was used to assess synoptic conditions of heat wave. Several heat strain measures were applied : net heat storage (S), modelled heart rate (HR), sultriness (HSI), and UTCI index. Actual total mortality (TM) and modelled strong heat-related mortality (SHRM) were taken as indicators of biometeorological consequences of the hot June in 2019. The results indicate that prolonged persistence of unusually warm weather in June 2019 was determined by the synoptic conditions occurring over the European region and causing advection of tropical air. They led to the emergence of heat waves causing 10% increase in TM and 5 times bigger SHRM then in preceding 10 years. Such increase in SHRM was an effect of overheating and overload of circulatory system of human organism. [ABSTRACT FROM AUTHOR]

The current warming of climate has led to an enhancement of the extreme temperature risks threatening various systems. Following that, we analysed the progress of the main type of the temperature-extreme weather events—heatwaves (HWs). We focused on the area of the Western Carpathians (Central Europe), since the Carpathian Mountains are widely recognised as an important biodiversity hot-spot particularly for mountain species in Europe. The HWs were identified for a range of elevations from low to high altitudes including a high mountain station. We used the percentile threshold-based calculation of HW, which in comparison to those using absolute thresholds allows for revealing the possible threats of climate warming extremes at the range of altitudes. We observed the HWs based on the maximum (HWMAX) and average (HWAVG) daily air temperatures in June–August during the period of 30 years (1989–2018) and we characterised them by the strength, frequency, and duration of the longest HW event. The Mann-Kendal trend test of these heatwave characteristics was significantly positive (p < 0.05) at most of stations throughout the region of Western Carpathians. At the high mountain station, particularly the maximum temperature exceedance increased, indicated by significant positive trends of HWMAX in strength (p = 0.02), frequency (p = 0.01), and duration of the longest event (p = 0.02). The majority of the strongest HWs occurring across Europe over the last three decades hit the area of Western Carpathians. More importantly, the area experienced the regional HWs, severity of which was comparable to those of exceptionally strong HWs, although these regional HWs were less important from the large-scale aspect. The greatest intensification of HWs is evident particularly in the last decade, although the longest HWMAX event from 1994 was not exceeded. Our results show potentially enhanced HW-induced stress to organisms as a consequence of the coincidence of HWMAX and HWAVG of the comparable strength during the last decade. [ABSTRACT FROM AUTHOR]

In the course of analysing the annual air temperature in Wrocław (TWr), a rapid change of the thermal regime was found between 1987 and 1989. TWr increased by >1°C, a strong, statistically significant positive trend emerged. The analysis of processes showed that strong warming in the cold season of the year (December–March) occurred as a result of an increase in the NAO intensity and warming in the warm season because of increased sunshine duration in Wrocław (ShWr). Multiple regression analysis has shown that the winter NAO Hurrell's index explains 15% of TWr variance, and the ShWr of the long-day (April–August) period 49%, whereas radiative forcing 5.9%. This indicates that the factors incidental to the internal variability of the climate system explain 64% of the TWr variability and the effect of increased CO2 concentration only ~6%. The reason for this rapid change of the thermal regime was a radical change in macro-circulation conditions in the Atlantic-European circular sector, which took place between 1988 and 1989. The heat, which is the cause of warming in Wrocław, comes from an increase in solar energy inflow (April–August) and also is transported to Europe from the North Atlantic surface by atmospheric circulation (NAO). These results indicate that the role of CO2 in shaping the contemporary temperature increase is overestimated, whereas the internal variability of the climate system is underestimated. [ABSTRACT FROM AUTHOR]

The objective of research involved the comparison of daily and seasonal courses of thermal stress occurring in Central Europe depending on the inflowing air mass. The analysis used data from Warsaw (1991–2000), including air temperature (°C), water vapour pressure (hPa), wind speed (m s−1) and cloud cover (%). Universal thermal climate index was calculated and subsequently averaged for the individual months and four types of atmospheric air masses: polar maritime (mP), arctic(A), polar continental (cP) and tropical (T). The studies analysed differences in daily patterns of the averaged values of universal thermal climate index between air masses and determined the frequency of days with various types of thermal stress in individual air masses. The analyses indicated that under the conditions of Central Europe, the highest daily variance of biothermal conditions occurs between the masses of cP and T in the spring and autumn. Considerably greater diversity of biothermal conditions was observed between the masses during daytime compared with nighttime, especially in the warm half of the year. The thermal stress, which can be encountered in Central Europe, ranges from an "extreme cold stress" in winter at night and early morning hours to "very strong heat stress" in summer at noon. Extreme thermal stress is related primarily to the masses of cP, A and T. The most optimal biothermal conditions occur during the advection of mP air. [ABSTRACT FROM AUTHOR]

Aim: Distribution ranges of temperate tree species are shifting poleward and upslope into cooler environments due to global warming. Successful regeneration is crucial for population persistence and range expansion. Thus, we aimed to identify environmental variables that affect germination and seedling establishment of Europe's dominant forest tree, to compare the importance of plasticity and genetic variation for regeneration, and to evaluate the regeneration potential at and beyond the southern and northern distribution margins. Location: Europe. Time period: 2016–2018. Major taxa studied: European beech (Fagus sylvatica (L.)). Methods: We investigated how germination, establishment and juvenile survival change across a reciprocal transplantation experiment using over 9,000 seeds of beech from 7 populations from its southern to its northern distribution range margins. Results: Germination and establishment at the seedling stage were highly plastic in response to environmental conditions. Germination success increased with warmer and declined with colder air temperature, whereas establishment and survival were hampered under warmer and drier conditions. Germination differed among populations and was positively influenced by seed weight. However, there was no evidence of local adaptation in any trait. Main conclusions: The high plasticity in the early life‐history traits found irrespective of seed origin may allow for short‐term acclimatization. However, our results also indicate that this plasticity might not be sufficient to ensure the regeneration of beech in the future due to the low survival found under dry and hot conditions. The future climatic conditions in parts of the distribution centre and at the rear edge might thus become limiting for natural regeneration, as the likelihood of extreme heat and drought events will increase. By contrast, at the cold distribution margin, the high plasticity in the early life‐history traits may allow for increasing germination success with increasing temperatures and may thus facilitate natural regeneration in the future. [ABSTRACT FROM AUTHOR]

Hourly precipitation extremes can intensify with temperature at higher rates than expected from thermodynamic increases explained by the Clausius‐Clapeyron (CC) relationship (∼6.5%/K), but local scaling with surface air temperature is highly variable. Here we use daily dew point temperature, a direct proxy of absolute humidity, to estimate at‐gauge local scaling across six macro‐regions for a global data set of over 7,000 hourly precipitation gauges. We find scaling rates from CC to 2 × CC at more than 60% of gauges, peaking in the tropics at a median rate of ∼1.5CC. Moreover, regional scaling rates show surprisingly universal behavior at around CC, with higher scaling in Europe. Importantly for impacts, hourly scaling is persistently higher than scaling for daily extreme precipitation. Our results indicate greater consistency in global scaling than previous work, usually at or above CC, with positive scaling in the (sub)tropics. This demonstrates the relevance of DPT scaling to understanding future changes. Plain Language Summary: Globally, hourly precipitation extremes have increased during recent decades and are projected to intensify more in the future. Therefore, understanding the relationship of precipitation extremes with temperature may be helpful for risk assessment and in decision making for climate adaptions. Using station‐based observations of hourly precipitation and daily dewpoint temperature, we show that precipitation extremes increase with the increase in dewpoint temperature consistently at a regional scale, and even with a higher rate at the gauge‐level. This rate of increment is much higher than that for daily extreme precipitation. Our results have implications for understanding drivers of changes to extreme precipitation at different spatial scales. Key Points: Hourly extreme precipitation consistently follows at least the CC rate at a regional scale, and often a super‐CC rate at the gauge‐levelThe median scaling is greater than CC rate for gauges in wet and dry regionsRegional scaling curves consistently follow the CC rate in the temperate climate zone [ABSTRACT FROM AUTHOR]

For the first time, the Limited-Area Mode of the new ICON (Icosahedral Nonhydrostatic) weather and climate model has been used for a continuous long-term regional climate simulation over Europe. Built upon the Limited-Area Mode of ICON (ICON-LAM), ICON-CLM (ICON in Climate Limited-area Mode, hereafter ICON-CLM, available in ICON release version 2.6.1) is an adaptation for climate applications. A first version of ICON-CLM is now available and has already been integrated into a starter package (ICON-CLM_SP beta1). The starter package provides users with a technical infrastructure that facilitates long-term simulations as well as model evaluation and test routines. ICON-CLM and ICON-CLM_SP were successfully installed and tested on two different computing systems. Tests with different domain decompositions showed bit-identical results, and no systematic outstanding differences were found in the results with different model time steps. ICON-CLM was also able to reproduce the large-scale atmospheric information from the global driving model. Comparison was done between ICON-CLM and the COnsortium for Small-scale MOdeling (COSMO)-CLM (the recommended model configuration by the CLM-Community) performance. For that, an evaluation run of ICON-CLM with ERA-Interim boundary conditions was carried out with the setup similar to the COSMO-CLM recommended optimal setup. ICON-CLM results showed biases in the same range as those of COSMO-CLM for all evaluated surface variables. While this COSMO-CLM simulation was carried out with the latest model version which has been developed and was carefully tuned for climate simulations on the European domain, ICON-CLM was not tuned yet. Nevertheless, ICON-CLM showed a better performance for air temperature and its daily extremes, and slightly better performance for total cloud cover. For precipitation and mean sea level pressure, COSMO-CLM was closer to observations than ICON-CLM. However, as ICON-CLM is still in the early stage of development, there is still much room for improvement. [ABSTRACT FROM AUTHOR]

Europe has experienced many extreme heat waves over the past few decades. In this study, the physical processes underlying these long-lasting and wide-ranging heat wave events are investigated based on a case study in Europe in June 2021. Heat waves are associated with barotropic anticyclonic anomalies accompanied by positive geopotential height anomalies locally. These anomalies persist under the conditions of increased meridional air temperature gradients of the mid–upper troposphere in the high latitudes of Eurasia and the formation of the Arctic front jet. The shrinking high-latitude snow cover in April–May favors higher surface temperatures and larger meridional temperature gradients in June in the mid–upper troposphere due to the soil moisture–evaporation–temperature positive feedback process. The summer Arctic front jet is then strengthened, and the mid-latitude westerly winds are weakened. This atmospheric circulation background favors waveguide formation and wave resonance that produces high-amplitude atmospheric waves and the stagnation of ridges in the mid-latitudes. Numerical experiments using the Community Atmosphere Model version 5 verify the proposed physical mechanisms, with the climatic responses in sensitivity experiments to anomalous snowfall rates closely resembling the observational results. Therefore, in June 2021, under the identified atmospheric circulation background and the perturbation of the upstream positive phase of the North Atlantic Oscillation, the large-scale barotropic high pressure and barotropic anticyclonic circulation in the study region tended to be stable and persistent, which is favorable for the production of long-lasting and wide-ranging heat wave events. • Physical mechanisms underlying heat waves are investigated based on a case study in Europe in June 2021. • Shrinking Eurasian snow cover in spring favors the strengthened summer Arctic front jet that produces high-amplitude waves. • Upstream positive NAO in June 2021 favors a sequence of waves downstream and affect persistent anticyclone for heat waves. [ABSTRACT FROM AUTHOR]

Remarkable climate anomalies occurred in Europe in recent years, but the reasons are not entirely disclosed. This entails further exploring the physical mechanism of anomalous climate variability over Europe on the basis of previous studies. Using NCEP-NCAR reanalysis and CMAP precipitation datasets, we investigated the relationship between the thermal condition of the Tibetan Plateau (TP) and precipitation over Europe during summer and related mechanisms behind through observational analyses and simulation experiments. The results show that the summer TP surface air temperature (SAT) is significantly correlated with the simultaneous precipitation over the region from eastern Ukraine to the North Caucasus (EUNC; 43°–51° N, 34°–46° E) during the period 1979–2017. The effect of anomalous TP heating plays, to some extent, an active role in linking the summer TP SAT with EUNC precipitation. The variability of the TP SAT is a result of the anomalous TP heating, but it can reflect the variability in temperature of a thick tropospheric air column over the TP well. Corresponding to higher (lower) TP SAT, the higher (lower) temperature anomaly appears over the TP and extends westwards through the transport of anomalous temperature fluxes from the TP to the EUNC regions in the upper troposphere, resulting in the expansion (withdrawal) of the South Asian high (SAH) and associated less (more) precipitation over the EUNC region. Numerical simulations basically reproduce the above-mentioned physical process, which confirms that, through stimulating the variability of upper-tropospheric temperatures over the TP and a larger area to its west and associated upstream large-scale atmospheric circulation, the summer TP's thermal condition can modulate and expand the impact of the SAH to the EUNC region and therefore affect the concurrent precipitation in situ. This study implies an importance of the thermal anomaly of the TP to the variability of EUNC precipitation during summer. [ABSTRACT FROM AUTHOR]

In summer 2018, Europe experienced a record drought, but it remains unknown how the drought affected ecosystem carbon dynamics. Using observations from 34 eddy covariance sites in different biomes across Europe, we studied the sensitivity of gross primary productivity (GPP) to environmental drivers during the summer drought of 2018 versus the reference summer of 2016. We found a greater drought-induced decline of summer GPP in grasslands (−38%) than in forests (−10%), which coincided with reduced evapotranspiration and soil water content (SWC). As compared to the 'normal year' of 2016, GPP in different ecosystems exhibited more negative sensitivity to summer air temperature (Ta) but stronger positive sensitivity to SWC during summer drought in 2018, that is, a stronger reduction of GPP with soil moisture deficit. We found larger negative effects of Ta and vapour pressure deficit (VPD) but a lower positive effect of photosynthetic photon flux density on GPP in 2018 compared to 2016, which contributed to reduced summer GPP in 2018. Our results demonstrate that high temperature-induced increases in VPD and decreases in SWC aggravated drought impacts on GPP. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'. [ABSTRACT FROM AUTHOR]

Aim: A progressive increase in air temperature is recognized as the most important mechanistic driver of species range shifts. However, only a few studies have simultaneously considered the influence of both extrinsic and intrinsic mechanistic drivers; there are still no studies on the roles of extrinsic and intrinsic drivers that regulate such species changes. We investigated how species will shift their geographical ranges to cope with future climate change and analysed the relative importance of the mechanistic drivers in governing species range shifts. Location: Sixteen countries in South, West and North Europe. Methods: We used ensemble species distribution models on the European continental scale to predict 105 odonate species in response to climate change in the future decades until 2080s under three emission scenarios. We evaluated the projected changes in four community metrics (distribution area, optimum position, leading edge and trailing edge) and investigated how these changes are driven by extrinsic and intrinsic factors. Results: The odonate species were predicted to shift their range margins poleward, with a higher migration rate towards the trailing edge (2.38‒10.34 km/year) than the leading edge (1.13‒2.00 km/year). Contrary to the assumption that the response of the odonate species to climate change will linearly accelerate over time, the distribution areas of odonate species were predicted to increase until 2050s and then decline until 2080s under RCP 2.6 (representative concentration pathway). However, their distributions under RCP 4.5 and RCP 8.5 were predicted to decrease over time, with a higher rate under RCP 8.5. Overall, environmental preference and habitat override dispersal ability govern the range shift of odonate species. Main conclusions: Quantifying the relative importance of extrinsic and intrinsic factors across a large spatial scale under different emission scenarios can help understand the mechanistic processes to facilitate species range shifts. [ABSTRACT FROM AUTHOR]

This study investigates changes in seasonal runoff and low flows related to changes in snow and climate variables in mountainous catchments in Central Europe. The period 1966–2012 was used to assess trends in climate and streamflow characteristics using a modified Mann–Kendall test. Droughts were classified into nine classes according to key snow and climate drivers. The results showed an increase in air temperature, decrease in snowfall fraction and snow depth, and changes in precipitation. This resulted in increased winter runoff and decreased late spring runoff due to earlier snowmelt, especially at elevations from 1000 to 1500 m a.s.l. Most of the hydrological droughts were connected to either low air temperatures and precipitation during winter or high winter air temperatures which caused below-average snow storages. Our findings show that, besides precipitation and air temperature, snow plays an important role in summer streamflow and drought occurrence in selected mountainous catchments. [ABSTRACT FROM AUTHOR]

Forecasting atmospheric CO2 concentrations on synoptic timescales (∼ days) can benefit the planning of field campaigns by better predicting the location of important gradients. One aspect of this, accurately predicting the day-to-day variation in biospheric fluxes, poses a major challenge. This study aims to investigate the feasibility of using a diagnostic light-use-efficiency model, the Vegetation Photosynthesis Respiration Model (VPRM), to forecast biospheric CO2 fluxes on the timescale of a few days. As input, the VPRM model requires downward shortwave radiation, 2 m temperature, and enhanced vegetation index (EVI) and land surface water index (LSWI), both of which are calculated from MODIS reflectance measurements. Flux forecasts were performed by extrapolating the model input into the future, i.e., using downward shortwave radiation and temperature from a numerical weather prediction (NWP) model, as well as extrapolating the MODIS indices to calculate future biospheric CO2 fluxes with VPRM. A hindcast for biospheric CO2 fluxes in Europe in 2014 has been done and compared to eddy covariance flux measurements to assess the uncertainty from different aspects of the forecasting system. In total the range-normalized mean absolute error (normalized) of the 5 d flux forecast at daily timescales is 7.1 %, while the error for the model itself is 15.9 %. The largest forecast error source comes from the meteorological data, in which error from shortwave radiation contributes slightly more than the error from air temperature. The error contribution from all error sources is similar at each flux observation site and is not significantly dependent on vegetation type. [ABSTRACT FROM AUTHOR]

Central European weather and climate are closely related to atmospheric mass advection triggered by the North Atlantic Oscillation (NAO), which is a relevant index for quantifying internal climate variability on multi-annual timescales. It remains unclear, however, how large-scale circulation variability affects local climate characteristics when downscaled using a regional climate model. In this study, 50 members of a single-model initial-condition large ensemble (LE) of a nested regional climate model are analyzed for a NAO–climate relationship. The overall goal of the study is to assess whether the range of NAO internal variability is represented consistently between the driving global climate model (GCM; the Canadian Earth System Model version 2 – CanESM2) and the nested regional climate model (RCM; the Canadian Regional Climate Model version 5 – CRCM5). Responses of mean surface air temperature and total precipitation to changes in the NAO index value are examined in a central European domain in both CanESM2-LE and CRCM5-LE via Pearson correlation coefficients and the change per unit index change for historical (1981–2010) and future (2070–2099) winters. Results show that statistically robust NAO patterns are found in the CanESM2-LE under current forcing conditions. NAO flow pattern reproductions in the CanESM2-LE trigger responses in the high-resolution CRCM5-LE that are comparable to reanalysis data. NAO–response relationships weaken in the future period, but their inter-member spread shows no significant change. The results stress the value of single-model ensembles for the evaluation of internal variability by pointing out the large differences of NAO–response relationships among individual members. They also strengthen the validity of the nested ensemble for further impact modeling using RCM data only, since important large-scale teleconnections present in the driving data propagate properly to the fine-scale dynamics in the RCM. [ABSTRACT FROM AUTHOR]

Nearly every study dealing with temperature extremes underscores the lack of a universal and broadly used method of identifying such events. The most popular are relative methods, which are based on the empirical distribution of temperature at each location (i.e., percentiles). The aim of this study was to evaluate the effects of the various percentile-based methods of defining hot days on the analysis of their frequency of occurrence, trends, and geographic patterns in summer in Europe. The basis for the research consists of daily maximum (TX) and minimum (TN) values of air temperature for 1961–2017 for Europe obtained from the E-OBS database. A hot day occurs when air temperature exceeds the 90th percentile–based threshold. These thresholds are determined using the following: (I) various temperature metrics (TX and TN), (II) various baseline periods (1961–1990, 1971–2000, 1981–2010), and (III) different timeframes within the year that the percentile is calculated for (summer season, separate summer months, and each calendar day). Our results indicate that the use of different variants of the percentile-based definition leads to differences in the geographic patterns of frequencies of and trends in summer hot days in Europe. The differences are especially substantial within the results obtained using various temperature metrics and baseline periods, and they are relatively small when different timeframes within the year that the percentile is calculated for are considered. On the example of the case study, we also show how the use of different research approaches may affect the intensity and spatial extent of an extreme temperature event. [ABSTRACT FROM AUTHOR]

The objective of the paper was the determination of the circulation conditions of occurrence of strong and very strong frost in Central Europe. A frost day was defined as a day with the minimum temperature lower than 0 °C and maximum temperature higher than 0 °C. Moreover, a division of frost was performed in terms of value of minimum temperature, resulting in the designation of mild frost (up to − 2.0 °C), moderate frost (from − 2.1 to − 4 °C), strong frost (from − 4.1 to − 6 °C) and very strong frost (< − 6 °C). The study was based on data from the years 1966–2015 from the Institute of Meteorology and Water Management—National Research Institute, Deutscher Wetterdienst and National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). The analysis of baric conditions employed values of pressure at sea level, height of isobaric surface of 500 hPa and air temperature at a level of 850 hPa, as well as their anomalies. The spatial analysis showed that the number of frost days in spring and autumn increased from the west to the east of Central Europe. A decrease in the number of frost days, however, is observed over the prevailing area. Average conditions favouring the occurrence of strong and very strong frost both in spring and autumn were related to higher than average pressure at sea level over the prevailing area of the Euro-Atlantic sector. Such baric conditions caused advections of cool air masses from the northern sector. [ABSTRACT FROM AUTHOR]

Chornohora is the highest mountain ridge in the Ukrainian Carpathians with 6 peaks of an altitude over 2,000 m above sea level (Hoverla is the highest peak, 2,061 m a.s.l). Its climate is explored less than other mountain ridges in Europe. The massif is a climatic barrier for air masses on NW-SE line. To describe the climate of this area data from the weather station at Pozhyzhevska alpine meadow for the years 1961–2010 were used. The seasonal and long-term variability of air temperature, atmospheric precipitation and snow cover were investigated on the background of air circulation types. The results show that general features of Chornohora climate depend both, on elevation above sea level and on air circulation. Lowest temperature is observed at N-NE circulation and highest precipitation – at western air inflow. Long-term changes of examined climate elements in Chornohora show significant increase in mean (0.13°/10 years) and minimum (0.22°C/10 years) air temperature as well as in snow cover depth and number of snowy days. [ABSTRACT FROM AUTHOR]

Central European weather and climate is closely related to atmospheric mass advection triggered by the North Atlantic Oscillation (NAO) which is a relevant index for quantifying natural variability on multi-annual time scales. It remains unclear, though, how large-scale circulation variability affects local climate characteristics when downscaled using a regional climate model. In this study, 50 members of a single-model initial-condition large ensemble (LE) (http://www.climex-project.org/) are analyzed for a climate-NAO relationship, especially its inter-member spread and its transfer from the driving model CanESM2 into the driven model CRCM5. The NAO pressure dipole is quantified in the CanESM2-LE by an extended station-based index; responses of mean surface air temperature and total precipitation to changes in the index value are determined for a Central European domain (CEUR) in both the CanESM2-LE and CRCM5-LE. NAO-response relationships are expressed via Pearson correlation coefficients (strength) and the change per unit index change for historical (1981-2010) and future (2070-2099) winters. Results show that (a) statistically robust NAO patterns are found in the CanESM2-LE under current forcing conditions and (b) impulses from the NAO in the CanESM2-LE produce correct responses in the high-resolution CRCM5-LE. Relationships weaken in the future period, but the amplitude of their inter-member spread shows no significant change. Among others, the results strengthen the validity of the climate module in the ClimEx model chain for further impact modelling and stress the importance of single-model ensembles for evaluating internal variability. [ABSTRACT FROM AUTHOR]

The aim of the research was to identify connections between the occurrence of heat load across Poland and large-scale factors, which will allow statistical models to be derived that are useful to describe bioclimatic conditions in Poland in the summer. Atmospheric circulation over the North Atlantic Ocean and Europe and near-surface air temperature over the central part of Europe were considered. The monthly frequency of the occurrence of combined "moderate, strong, very strong and extreme heat stress" based on the assessment scale of the Universal Thermal Climate Index (UTCI) in the summer months accounted for 6% to more than 30% of all cases. The statistical downscaling procedure of canonical correlation analysis (CCA) with respect to the period 1971–2000 was applied to extract the main modes of large-scale factors and their local responses. The greatest explained variance of local field response to atmospheric circulation as well as to near-surface air temperature is above 70%. Warm air flow from the east and from the southeast has the strongest influence on the increase in frequency of the occurrence of heat stress on human beings in Poland. The spatial differentiation of the air temperature anomaly over central Europe is an important determinant of the occurrence of heat stress in Poland. The validation of constructed models encompassed the periods 1951–1970 and 2001–2010. The best reliability of results was reached for the reconstructed series in July. The results are less useful in June and August and in the coastal region. [ABSTRACT FROM AUTHOR]

Cyclic volatile methylsiloxanes (cVMS) and short-chain chlorinated paraffins (SCCPs) use has been restricted in recent years due to environmental health concerns. Both of these classes of emerging contaminants possess long range transport potential (LRTP), highlighting the need for continuous monitoring to assess effectiveness of implemented regulations. However, emission source elucidation and understanding processes affecting atmospheric transport remain challenging. Atmospheric levels of cVMSs and SCCPs were simultaneously monitored at a background monitoring site in Norway from January–July 2020. Concentrations obtained from active air samplers ranged from 49.9 to 845 (mean: 208) pg/m3 for ƩSCCPs and from 0.4 to 3.5 (mean: 1.5), 1.1–15 (mean: 5.6) and 0.1–0.9 (mean: 0.4) ng/m3 for octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6), respectively. As SCCPs pose several challenges to analysts, different quantification methodologies and blank handling procedures were investigated to ensure reliable environmental measurements. Simulations using a Lagrangian atmospheric transport model (FLEXPART) revealed air masses impacting sampling measurements were of Oceanic origin, but periodic emission events from Europe and Russia were also observed. Seasonal pattern in cVMS concentrations was mainly driven by atmospheric degradation via hydroxyl radical reaction, whereas SCCP concentrations were more influenced by periodic anthropogenic inputs from local and continental Europe. No clear correlation could be observed with SCCP atmospheric concentrations and temperature over the entire sampling campaign. However, increased volatilization at elevated temperatures may be important with emissions originating from local sources. Higher chlorinated homologue groups dominated during the winter season and declined towards spring and summer, whereas reverse was found for the lower and more volatile chlorinated homologue groups. [Display omitted] • LRT of cVMS primarily driven by seasonal atmospheric degradation. • SCCP LRT primarily driven by anthropogenic inputs from continental Europe. • Seasonal changes in SCCP composition pattern were observed. • Proper quantification and blank handling procedures crucial for reporting SCCP. [ABSTRACT FROM AUTHOR]

Circulation in the mid-troposphere in moderate and high latitudes of the Northern Hemisphere can be characterised by the Vangenheim-Girs (VG) circulation macro-forms. The aim of the research was to analyse the VG macro-forms as a factor determining the general characteristics of the atmospheric circulation in mid-troposphere in the Euro-Atlantic region and low-troposphere airflow characteristics in the profile (zonal belt) crossing Central Europe from Ireland to Kazan in Russia (5°30'W–44°00'E). Alongside the VG macro-form calendar, ERA-INTERIM data were used. The utilised meteorological variables comprised 500hPa geopotential height, SLP and air temperature at 995 sigma level. The temporal scope of the research was 35 years (1981–2015) and the resolution was 24h (12.00 UTC). The circulation in the low-troposphere was characterised by the geostrophic wind vector characteristics directly resulting from SLP and air temperature fields. Subsequently, derived indices (e.g. wind direction stability) were used. The presented results indicate that the variability of anemological conditions at SLP in the area of 50–60°N over Europe is in direct connection with the mid-troposphere circulation features. The differences are statistically significant across nearly the entire research area. This includes the reversal of the dominant air flow direction in some areas. The greatest variability in geostrophic wind characteristics due to W, E and C VG macro-forms is revealed in the central and eastern part of the 50–60°N zone – between the southern Baltic Sea and the western border of Russia. [ABSTRACT FROM AUTHOR]

This study analyzes the differences and similarities of Eurasian cold air outbreaks (CAOs) under the weak (CAOW), strong (CAOS), and neutral (CAON) stratospheric polar vortex states and examines the potential links between the polar vortex and Eurasian CAOs. The results indicate that the colder surface air temperature (SAT) over Europe in the earlier stages of CAOW events is likely because the amplitude of the preexisting negative North Atlantic Oscillation pattern is larger in CAOW events than in CAON and CAOS events. Marked by the considerably negative stratospheric Arctic Oscillation signals entering the troposphere, the SAT at midlatitudes over eastern Eurasia in CAOW events is colder than in CAON events. A larger diabatic heating rate related to a positive sensible heat flux anomaly in CAOW events likely offsets, to some degree, the cooling effect caused by the stronger cold advection and makes the differences in area-averaged SAT anomalies over northern Eurasia between the CAOW and CAON events look insignificant in most stages. Massive anomalous waves from the low-latitude western Pacific merge over northeastern Eurasia, then weaken the westerly wind over this region to create favorable conditions for southward advection of cold air masses in the earlier stages of all three types of CAOs. This study further analyzes the interannual relationship between the stratospheric polar vortex strength and the intensity of Eurasian CAOs and finds that climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) relative to the reanalysis dataset tend to underestimate the correlation between them. The relationship between them is strengthening under representative concentration pathway 4.5 (RCP4.5) and 8.5 (RCP8.5) scenarios over the period 2006–60. In addition, the intensity of Eurasian CAOs exhibits a decreasing trend in the past and in the future. [ABSTRACT FROM AUTHOR]

This work presents the Guadalfeo Monitoring Network in Sierra Nevada (Spain), a snow monitoring network in the Guadalfeo Experimental Catchment, a semiarid area in southern Europe representative of snowpacks with highly variable dynamics on both annual and seasonal scales and significant topographic gradients. The network includes weather stations that cover the high mountain area in the catchment and time-lapse cameras to capture the variability of the ablation phases on different spatial scales. The data sets consist of continuous meteorological high-frequency records at five automatic weather stations located at different altitudes ranging from 1300 to 2600 m a.s.l. that include precipitation, air temperature, wind speed, air relative humidity and the short- and longwave components of the incoming radiation, dating from 2004 for the oldest station (2510 m a.s.l.) (10.1594/PANGAEA.895236); additionally, daily data sets of the imagery from two time-lapse cameras are presented, with different scene area (30 m × 30 m, and 2 km 2 , respectively) and spatial resolution, that consist of fractional snow cover area and snow depth from 2009 (10.1594/PANGAEA.871706) and snow cover maps for selected dates from 2011 (10.1594/PANGAEA.898374). Some research applications of these data sets are also included to highlight the value of high-resolution data sources to improve the understanding of snow processes and distribution in highly variable environments. The data sets are available from different open-source sites and provide both the snow hydrology scientific community and other research fields, such as terrestrial ecology, riverine ecosystems or water quality in high mountains, with valuable information of high potential in snow-dominated areas in semiarid regions. [ABSTRACT FROM AUTHOR]

The main aim of the presented investigation was to determine the effect of the air thermal conditions variability on cow's milking performance in summer in a moderate climate. The analyses covered the summer months of 2012-2013 (June-September) and shorter, several-day periods characterized by the times of elevated or high air temperatures and by the declines and increases in milking performance. The research was conducted in a free stall barn for Holstein-Friesian cows. The study showed that the thermoneutral temperature for high yielding cows decreases gradually with the registered increasingly warmer summer periods. The decreases in milk yield already commence at an air temperature equal to 20°C and also depend on the dairy cattle sensitivity. July and August, with a high number of hot days, caused that in September the cows responded faster to a worsening of thermal conditions and the decline in milking performance happened almost simultaneously with the air temperature change, at milking yield recovery after the period of 3-4 d (r=-0.84, P<0.04). The percent duration in the individual temperature ranges which caused a decrease of milk yield was also determined. In June, and at the beginning of July, this was 90% of the time with temperatures above 20°C, and simultaneously 45% above 25°C occurred to milking performance decrease (r=-0.89, P<0.02). In September, this was only 30% of the time with temperatures above 20°C (r=-0.91, P<0.01). [ABSTRACT FROM AUTHOR]

Snow plays a critical role in the water cycle of many mountain regions and heavily populated areas downstream. In this study, changes of snow water equivalent (SWE) time series from long-term stations in five Alpine countries are analyzed. The sites are located between 500 and 3000 m above mean sea level, and the analysis is mainly based on measurement series from 1 February (winter) and 1 April (spring). The investigation was performed over different time periods, including the last six decades. The large majority of the SWE time series demonstrate a reduction in snow mass, which is more pronounced for spring than for winter. The observed SWE decrease is independent of latitude or longitude, despite the different climate regions in the Alpine domain. In contrast to measurement series from other mountain ranges, even the highest sites revealed a decline in spring SWE. A comparison with a 100-yr mass balance series from a glacier in the central Alps demonstrates that the peak SWEs have been on a record-low level since around the beginning of the twenty-first century at high Alpine sites. In the long term, clearly increasing temperatures and a coincident weak reduction in precipitation are the main drivers for the pronounced snow mass loss in the past. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present the development and evaluation of neural network based identification algorithms for the prediction of outdoor air temperature using acquired data from four European cities (Ancona – Italy, Chania – Greece, Granada – Spain and Mollet – Spain). Different neural network topologies (feed forward, cascade and elman) have been tested to identify the most suitable for each city. The efficiency of the prediction is validated by comparing predicted and measured outdoor air temperature. Furthermore, statistical tools such as R 2 , and root mean square error (rmse) are used to evaluate the annual performance of the neural network. The comparison of measured and predicted outdoor air temperature ( R 2 > 0.9, rmse <2 °C) confirms the accurate training of the neural network for all four European cities. All work has been contacted using Matlab's environment. [ABSTRACT FROM AUTHOR]

Future anthropogenic climate change is likely to increase the air temperature ( T) across Europe and increase the frequency, duration and magnitude of severe heat stress events. Heat stress events are generally associated with clear-sky conditions and high T, which give rise to high radiant heat load, i.e. mean radiant temperature ( T). In urban environments, T is strongly influenced by urban geometry. The present study examines the effect of urban geometry on daytime heat stress in three European cities (Gothenburg in Sweden, Frankfurt in Germany and Porto in Portugal) under present and future climates, using T as an indicator of heat stress. It is found that severe heat stress occurs in all three cities. Similar maximum daytime T is found in open areas in all three cities despite of the latitudinal differences in average daytime T. In contrast, dense urban structures like narrow street canyons are able to mitigate heat stress in the summer, without causing substantial changes in T in the winter. Although the T averages are similar for the north-south and east-west street canyons in each city, the number of hours when T exceeds the threshold values of 55.5 and 59.4 °C-used as indicators of moderate and severe heat stress-in the north-south canyons is much higher than that in the east-west canyons. Using statistically downscaled data from a regional climate model, it is found that the study sites were generally warmer in the future scenario, especially Porto, which would further exacerbate heat stress in urban areas. However, a decrease in solar radiation in Gothenburg and Frankfurt reduces T in the spring, while the reduction in T is somewhat offset by increasing T in other seasons. It suggests that changes in the T under the future scenario are dominated by variations in T. Nonetheless, the intra-urban differences remain relatively stable in the future. These findings suggest that dense urban structure can reduce daytime heat stress since it reduces the number of hours of high T in the summer and does not cause substantial changes in average and minimum T in the winter. In dense urban settings, a more diverse urban thermal environment is also preferred to compensate for reduced solar access in the winter. The extent to which the urban geometry can be optimized for the future climate is also influenced by local urban characteristics. [ABSTRACT FROM AUTHOR]

The impact of biogenic emissions on ozone and PM 2.5 levels over Europe is assessed using CMAQ. Biogenic emissions are predicted to increase Max8hrO 3 mixing ratios by 5.7% and to decrease PM 2.5 concentrations by 1.9%, increasing PM 2.5 _ OC by 13.6% and decreasing PM 2 . 5 _SO 4 , PM 2 . 5 _NO 3 and PM 2 . 5 _NH 4 by 5.6%, 3.7% and 5.6%, respectively, on average over Europe due to their interactions with anthropogenic emissions. A suite of perturbations in temperature is imposed individually on the base case conditions in order to determine the sensitivities to air temperature changes. Temperature increases of 1, 2 or 3° K suggest an average increase in Max8hrO 3 mixing ratios of 0.9%, 1.8% or 2.9%, respectively, and an average decrease in daily average PM 2.5 concentrations of 2.5%, 4.2% and 5.8%, respectively, increasing PM 2.5 _ OC and decreasing PM 2 . 5 _SO 4 , PM 2 . 5 _NO 3 and PM 2 . 5 _NH 4 component concentrations on average over Europe. In order to examine if abatement measures for anthropogenic emissions could offset ozone increases in higher temperatures and their effect on PM 2.5 concentrations, a simulation with a domain wide reduction in anthropogenic NO x emissions of 10% is performed. This is estimated to reduce Max8hrO 3 mixing ratios by 1.3% on average over Europe. However, NO x reduction is estimated to increase Max8hrO 3 in VOCs limited areas. The reduction in anthropogenic NO x emissions is predicted to reduce PM 2.5 concentrations by 1.0% enhancing the reduction simulated, here, with temperature increase but further modifying PM 2.5 component concentrations. [ABSTRACT FROM AUTHOR]