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The description and analysis of compound extremes affecting mid and high latitudes in the winter requires an accurate estimation of snowfall. Such variable is often missing for in-situ observations, and biased in climate model outputs, both in magnitude and number of events. While climate models can be adjusted using bias correction (BC), snowfall presents additional challenges compared to other variables, preventing from applying traditional univariate BC methods. We extend the existing literature on the estimation of the snowfall fraction from near-surface temperature, which usually involves binary thresholds or fitting parametric nonlinear functions. We show that, combining breakpoint search algorithms to define threshold temperatures and segmented regression models, it is possible to obtain accurate out-of-sample estimates of snowfall over Europe in ERA5 reanalysis, and to perform effective BC on the IPSL-WRF high resolution EURO-CORDEX climate model only relying on bias adjusted temperature and precipitation. This method offers a feasible way to reconstruct or adjust snowfall observations without requiring multivariate or conditional bias correction and stochastic generation of unobserved events. [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]

We perform simulations with the WRF regional climate model at 12 and 3 km grid resolution for the current and future climates over Central Europe and evaluate their added value with a focus on the daily cycle and frequency distribution of rainfall and the relation between extreme precipitation and air temperature. First, a 9 year period of ERA-Interim driven simulations is evaluated against observations; then global climate model runs (MPI-ESM-LR RCP4.5 scenario) are downscaled and analyzed for three 12-year periods: a control, a mid-of-century and an end-of-century projection. The higher resolution simulations reproduce both the diurnal cycle and the hourly intensity distribution of precipitation more realistically compared to the 12 km simulation. Moreover, the observed increase of the temperature–extreme precipitation scaling from the Clausius–Clapeyron (C–C) scaling rate of ~ 7% K−1 to a super-adiabatic scaling rate for temperatures above 11 °C is reproduced only by the 3 km simulation. The drop of the scaling rates at high temperatures under moisture limited conditions differs between sub-regions. For both future scenario time spans both simulations suggest a slight decrease in mean summer precipitation and an increase in hourly heavy and extreme precipitation. This increase is stronger in the 3 km runs. Temperature–extreme precipitation scaling curves in the future climate are projected to shift along the 7% K−1 trajectory to higher peak extreme precipitation values at higher temperatures. The curves keep their typical shape of C–C scaling followed by super-adiabatic scaling and a drop-off at higher temperatures due to moisture limitation. [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]

The article analyzes continentality changes in Europe in the period between 1938 and 2018. We use the raw data of monthly air temperature averages, obtained from the website: European Climate Assessment & Dataset, collected by 443 climate stations. The data is processed with the program MATLAB and the results are plotted with Excel and ArcGIS. The results show that there are differences between the Supan, Gorczynski and Conrad Continentality Indices. We also found that in the period from 1938 to 2018, the trends of continentality indices have changed. Our results have shown that the climate in some parts of Europe is becoming more maritime, especially in the Northern and Eastern regions, while in other territories it is becoming more continental, especially in the Mediterranean coastal regions. [ABSTRACT FROM AUTHOR]

ABSTRACT Due to imperfections inherent to numerical climate simulations, projections of climate change need to be accompanied with an uncertainty estimate, typically derived from multi-model ensembles. Here, an analysis of regional climate model outputs spread and its temporal evolution is presented, for the European air temperatures simulated over the 21st century. To quantify the overall uncertainty, standard deviation (sd) is used and compared to median absolute deviation and inter-quartile range. The outcomes are shown for annual and seasonal means of air temperature at 2 m, 850 hPa, 700 hPa, 500 hPa and 300 hPa levels, simulated by ENSEMBLES regional climate models for eight geographical areas across Europe. Our results indicate that the estimated uncertainty of simulated air temperature changes over Europe generally increases during the 21st century, and typically decreases with height of the studied vertical level. The influence of driving global climate model on the regional simulation generally increases with height of the studied vertical level. In lower tropospheric levels, the clustering of regional climate models according to driving global climate model is stronger in winter than in summer. [ABSTRACT FROM AUTHOR]

Little use has been made up till now of the concept of climate analogues to link the present and the past, i.e. places whose current climate ('target' locations) is similar to that experienced some decades ago at distant locations ('reference' sites). Indeed, most research up till now has focused on analogues between present and future climates. Here we assess at what period of time the climate at a target station in Europe has reached-or will reach-that of a reference location, and show that the velocity of northward-moving isotherms can attain 15 km year−1. Such displacements in space imply that temperatures at many target sites in Europe have already exceeded those experienced by stations located 300-500 km to the south in the last half-century. Such results can serve to better portray what a rapidly changing climate means to a lay audience, and can provide useful information to the policy-making community. [ABSTRACT FROM AUTHOR]

Much progress has recently been made in reconstructing European temperature variability over centuries to millennia. In contrast, there are only a few attempts at long-term precipitation and/or drought reconstruction, which are spatially less significant. Here we discuss the possibility of using climate reconstructions from tree-ring density and width to make spatially explicit estimates of European temperature and drought variability, respectively. Four experiments were performed to assess spatial field correlations of (1) parameter-specific mean reconstructions, (2) individual site reconstructions, (3) instrumental stations, and (4) model analogues. The simple mean of 4 temperature reconstructions from northern Scandinavia and high-elevation sites in the Tatra, Alps, and Pyrenees revealed a significant positive correlation (r > 0.4) with the gridded Central European summer temperature south of 55° N and west of 25° E. In contrast, the mean of 11 hydro-climatic reconstructions located between Sweden and Turkey had a significant positive correlation with only a handful of small patches scattered along an east-west corridor from the British Isles over Germany to the Baltic. The significant positive correlation increased to 71% of the European landmass between 35-70° N and 10° W 40° E when using the individual 4 temperature reconstructions instead. The 11 individual hydro-climatic reconstructions had a significant positive correlation with summer drought over only 16% of the area. The proxy-based correlation fields are greatly supported by the spatial significance of instrumental station measurements and model analogues corresponding to the initial tree-ring site locations. [ABSTRACT FROM AUTHOR]

Anomalies of mean air temperature of 12 consecutive months were detected recently at a number of spatial scales: from local via national and continental, to hemispheric. At all these spatial scales, pre-2007 records were exceeded by considerable margins. The recent rise in the mean temperature of 12 consecutive months at several scales has remained largely unnoticed, because the 12-month means are seldom analyzed. Broad attention is typically focused on monthly, seasonal and annual temperatures. Analysis of shifted 12-month periods helps spot peculiar 12-month episodes with remarkable temperature anomalies that do not coincide with a calendar year. Introducing 12-month running mean temperatures into the global warming debate can prove useful. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of principal component (PC) regression and regularized expectation maximization (RegEM) to reconstruct European summer and winter surface air temperature over the past millennium. Reconstruction is performed within a surrogate climate using the National Center for Atmospheric Research (NCAR) Climate System Model (CSM) 1.4 and the climate model ECHO-G 4, assuming different white and red noise scenarios to define the distortion of pseudoproxy series. We show how sensitivity tests lead to valuable “a priori” information that provides a basis for improving real world proxy reconstructions. Our results emphasize the need to carefully test and evaluate reconstruction techniques with respect to the temporal resolution and the spatial scale they are applied to. Furthermore, we demonstrate that uncertainties inherent to the predictand and predictor data have to be more rigorously taken into account. The comparison of the two statistical techniques, in the specific experimental setting presented here, indicates that more skilful results are achieved with RegEM as low frequency variability is better preserved. We further detect seasonal differences in reconstruction skill for the continental scale, as e.g. the target temperature average is more adequately reconstructed for summer than for winter. For the specific predictor network given in this paper, both techniques underestimate the target temperature variations to an increasing extent as more noise is added to the signal, albeit RegEM less than with PC regression. We conclude that climate field reconstruction techniques can be improved and need to be further optimized in future applications. [ABSTRACT FROM AUTHOR]

The article outlines the study conducted by Nicoletta Cannone and colleagues on evaluating the impact of climatic changes in the European Alps. Researchers found that the stronger ice mass loss affects Sforzellina Glacier during 1996 to 2006 was attributed to the local summer warming combined with reduced precipitation and shortening of snow season. Such changes in climatic temperature results in changes in vegetation of glacier forefield due to the increase of colonization rates. The found that their is a strong link between the abiotic and biotic components of high altitude ecosystems, the impacts of climate change undergone dramatic acceleration during the last 35 years.

Local-scale climate information is increasingly needed for the study of past, present and future climate changes. In this study we develop a non-linear statistical downscaling method to generate local temperatures and precipitation values from large-scale variables of a Earth System Model of Intermediate Complexity (here CLIMBER). Our statistical downscaling scheme is based on the concept of Generalized Additive Models (GAMs), capturing nonlinearities via non-parametric techniques. Our GAMs are calibrated on the present Western Europe climate. For this region, annual GAMs (i.e. models based on 12 monthly values per location) are fitted by combining two types of largescale explanatory variables: geographical (e.g. topographical information) and physical (i.e. entirely simulated by the CLIMBER model). To evaluate the adequacy of the non-linear transfer functions fitted on the present Western European climate, they are applied to different spatial and temporal large-scale conditions. Local projections for present North America and Northern Europe climates are obtained and compared to local observations. This partially addresses the issue of spatial robustness of our transfer functions by answering the question "does our statistical model remain valid when applied to large-scale climate conditions from a region different from the one used for calibration?". To asses their temporal performances, local projections for the Last Glacial Maximum period are derived and compared to local reconstructions and General Circulation Model outputs. Our downscaling methodology performs adequately for the Western Europe climate. Concerning the spatial and temporal evaluations, it does not behave as well for Northern America and Northern Europe climates because the calibration domain may be too different from the targeted regions. The physical explanatory variables alone are not capable of downscaling realistic values. However, the inclusion of geographical-type variables - such as altitude, advective continentality and moutains effect on wind (W-slope) - as GAM explanatory variables clearly improves our local projections. [ABSTRACT FROM AUTHOR]

The temperatures in large parts of Europe have been record high during the meteorological autumn of 2006. Compared to 1961-1990, the 2 m temperature was more than three degrees Celsius above normal from the North side of the Alps to southern Norway. This made it by far the warmest autumn on record in the United Kingdom, Belgium, the Netherlands, Denmark, Germany and Switzerland, with the records in Central England going back to 1659, in the Netherlands to 1706 and in Denmark to 1768. The deviations were so large that under the obviously false assumption that the climate does not change, the observed temperatures for 2006 would occur with a probability of less than once every 10 000 years in a large part of Europe, given the distribution defined by the temperatures in the autumn 1901-2005. A better description of the temperature distribution is to assume that the mean changes proportional to the global mean temperature, but the shape of the distribution remains the same. This includes to first order the effects of global warming. Even under this assumption the autumn temperatures were very unusual, with estimates of the return time of 200 to 2000 years in this region. The lower bound of the 95% confidence interval is more than 100 to 300 years. Apart from global warming, linear effects of a southerly circulation are found to give the largest contributions, explaining about half of the anomalies. SST anomalies in the North Sea were also important along the coast. Climate models that simulate the current atmospheric circulation well underestimate the observed mean rise in autumn temperatures. They do not simulate a change in the shape of the distribution that would increase the probability of warm events under global warming. This implies that the warm autumn 2006 either was a very rare coincidence, or the local temperature rise is much stronger than modelled, or non-linear physics that is missing from these models increases the probability of warm extremes. [ABSTRACT FROM AUTHOR]

The article investigates the number of days with snow cover at 268 Alpine climate stations during winter period, from 1961-2000, and its relation with the mean winter temperature over Europe. A physical-statistical model of snow duration, along with hyperbolic tangent function to generate the logistic curve for the snow-temperature relationship were used. Results of the study proves to be valid for the Alpine region and independent against a linear temperature trend. Findings reveal that the snow-temperature sensitivity in the Alpine region is in accordance with earlier estimates for Austria and Switzerland.

Global climate change impacts can already be tracked in many physical and biological systems; in particular, terrestrial ecosystems provide a consistent picture of observed changes. One of the preferred indicators is phenology, the science of natural recurring events, as their recorded dates provide a high-temporal resolution of ongoing changes. Thus, numerous analyses have demonstrated an earlier onset of spring events for mid and higher latitudes and a lengthening of the growing season. However, published single-site or single-species studies are particularly open to suspicion of being biased towards predominantly reporting climate change-induced impacts. No comprehensive study or meta-analysis has so far examined the possible lack of evidence for changes or shifts at sites where no temperature change is observed. We used an enormous systematic phenological network data set of more than 125 000 observational series of 542 plant and 19 animal species in 21 European countries (1971–2000). Our results showed that 78% of all leafing, flowering and fruiting records advanced (30% significantly) and only 3% were significantly delayed, whereas the signal of leaf colouring/fall is ambiguous. We conclude that previously published results of phenological changes were not biased by reporting or publication predisposition: the average advance of spring/summer was 2.5 days decade−1 in Europe. Our analysis of 254 mean national time series undoubtedly demonstrates that species' phenology is responsive to temperature of the preceding months (mean advance of spring/summer by 2.5 days°C−1, delay of leaf colouring and fall by 1.0 day°C−1). The pattern of observed change in spring efficiently matches measured national warming across 19 European countries (correlation coefficient r=−0.69, P<0.001). [ABSTRACT FROM AUTHOR]

Simulations of the present-day temperature climate in Europe obtained with the dynamic regional climate model HadRM3P from the Hadley Centre are evaluated. Observed daily temperature maxima (Tx) and minima (Tn) for the 1961-1990 period at 185 stations are compared with their nearest corresponding HadRM3P grid-box data. The model generally performs well over the UK and elsewhere between latitudes 50 and 55°N, with biases mostly within ±0.5 K. In other areas coherent regions with seasonal biases up to more than ±5 K exist. In some areas, biases in climatological averages are associated with even larger errors (up to more than ±15 K) in the upper/lower extreme temperature range. Both areas with systematically overestimated and underestimated intra-seasonal daily temperature variances exist, but overestimation dominates. Too hot summerTx south of about 45°N are associated with drying soils in the model. This problem may occur further north in “future” integrations with a greenhouse-gas induced warming. Given the existence of errors in the simulations of the present-day climate, we recommend that results from future scenario integrations are treated with care. [ABSTRACT FROM AUTHOR]

European agricultural production is influenced by the space-time distribution of regional climate. Because regional distributions of temperature and precipitation in Europe are affected by changes in the wintertime atmospheric circulation, this paper aims at identifying the relationships between the wintertime Euro-Atlantic variability and wheat yield for the Member States of the European Union. An empirical orthogonal function (EOF) decomposition of the 500 hPa geo-potential height fields is used to describe the wintertime climate variability, associating the leading 4 components of the EOF decomposition into known climatic patterns (such as North Atlantic Oscillation or Eastern Atlantic patterns). Using statistical methods such as ANOVA, linear regression and 'leave-one-out' cross-validation, those patterns are related to time series of wheat yield anomalies. It is shown that, depending on the country, there is a link between wheat yield and modes of winter climate variability, and this link differs from the relationship between temperature and precipitation with the modes. Looking ahead to the improvement of seasonal climate forecasts, it is expected that such meteorological patterns may be predicted with some accuracy, which in turn could improve crop yield forecasts. [ABSTRACT FROM AUTHOR]

Trends in indices of climate extremes are studied on the basis of daily series of temperature and precipitation observations from more than 100 meteorological stations in Europe. The period is 1946–99, a warming episode. Averaged over all stations, the indices of temperature extremes indicate “symmetric” warming of the cold and warm tails of the distributions of daily minimum and maximum temperature in this period. However, “asymmetry” is found for the trends if the period is split into two subperiods. For the 1946–75 subperiod, an episode of slight cooling, the annual number of warm extremes decreases, but the annual number of cold extremes does not increase. This implies a reduction in temperature variability. For the 1976–99 subperiod, an episode of pronounced warming, the annual number of warm extremes increases 2 times faster than expected from the corresponding decrease in the number of cold extremes. This implies an increase in temperature variability, which is mainly due to stagnation in the warming of the cold extremes. For precipitation, all Europe-average indices of wet extremes increase in the 1946–99 period, although the spatial coherence of the trends is low. At stations where the annual amount increases, the index that represents the fraction of the annual amount due to very wet days gives a signal of disproportionate large changes in the extremes. At stations with a decreasing annual amount, there is no such amplified response of the extremes. The indices of temperature and precipitation extremes in this study were selected from the list of climate change indices recommended by the World Meteorological Organization–Commission for Climatology (WMO–CCL) and the Research Programme on Climate Variability and Predictability (CLIVAR). The selected indices are expressions of events with return periods of 5–60 days. This means that the annual number of events is sufficiently large to allow for meaningful trend analysis in ∼50 yr time series. Although the selected indices refer to events that may be called “soft” climate extremes, these indices have clear impact relevance. [ABSTRACT FROM AUTHOR]

Forty one years (1958–1998) of NCEP reanalysis data are used to perform a set of statistical analyses, investigating the interactions between the sea surface temperature (SST), the storm track activity (STA) and the time mean atmospheric circulation in the North Atlantic-Europe (NAE) region. When the atmospheric region of study is restricted to Europe, the singular value decomposition (SVD) lead-lag analysis between seasonal 500 hPa geopotential height (Z500) and SST captures a significant covariance between a summer SST anomaly and a strong winter anticyclonic anomaly over Europe. The summer SST pattern is close to the first empirical orthogonal function (EOF) of SST for the consecutive months J-A-S-O-N. The same analysis, but extending the atmospheric area of interest to the entire NAE region, points out the same signal with a phase shift of one month. A more zonally oriented North-Atlantic-Oscillation-like (NAO) pattern is then found as the SST structure remains practically unchanged. This summer SST anomaly is found to persist through surface heat fluxes exchanges until winter, when it can finally have an impact on the atmospheric circulation. Composites are made from the former SST SVD scores, showing the winter STA and different transient and stationary eddies diagnostics associated with the extreme positive and negative events of the SST anomaly. These suggest that the SST anomaly induces an anomalous stationary wave in winter, creating an initially small anticyclonic anomaly over Europe. Anomalous transient eddies located over northern Europe then strengthen this anomaly and maintain it during winter, thus acting as a positive feedback. [ABSTRACT FROM AUTHOR]

The extratropical cyclone is one of the basic systems that characterize the weather and climate in mid-latitude areas, where the mean meridional temperature gradient is large. As for in Europe's middle or higher latitude areas. Although the climatological mean meridional gradient of the air temperature there is rather weak compared to that from autumn to spring around Japan in East Asia, many extratropical cyclones appear throughout a year. Thus it would still be necessary to re-examine the seasonal cycle of the daily cyclone and anticyclone activities around Europe, paying attention also to their intraseasonal variations and the effects on the behaviors of daily cyclone and anticyclone systems together with the variety of their characteristics. Our previous case studies for 2000 (Kuwana et al., EGU2017 and 2018) pointed out that daily cyclones and anticyclones were greatly reflected by the alternation of the intraseasonal-scale ones with equivalent barotropic structure in northwestern Europe in summer. In addition, the intraseasonal and daily behaviors of the Icelandic low in the seasonal cycle showed the seasonal progression from autumn to the next spring.The present study will further examine the detailed features on the above mentioned topics, together with their relationship to the weather conditions in Europe, mainly based on the NCEP/NCAR re-analysis data. From late May to August, intraseasonal-scale low and high areas (as for the deviation fields) with the equivalent barotropic structure extended from the Norwegian Sea to Northern Germany. In the negative deviation period (stage with the intraseasonal-scale low there), baroclinic zone in the lower layer just on the south of that low was periodically enhanced. It is interesting that, in one of the negative periods, the southward shift of intraseasonal-scale baroclinic zone seemed to be related to the temporal activity of baroclinic ibstability wave cyclones, or the rather lower air temperature stage in central Europe. The detailed description on there will be made at the poster presentation. As for the asymmetric seasonal progression, not only the differences of intraseasonal features of the Icelandic lows between the former half and latter half of winter as shown in EGU2018, but also the differences of the daily variations between early summer and early autumn were notable. As for early autumn, amplitude of the short-period SLP variation in northern Europe, corresponding to the temporal appearance of the "Icelandic low-like" cyclone with relatively short persistency, increased greatly one month earlier than the formation timing of the seasonal mean Icelandic low in middle October. Interestingly, that event occurred just when the air temperature began to decrease seasonally. [ABSTRACT FROM AUTHOR]

The article reports on the maximum summer temperature changes in Europe from 1880 to 2007. Data collected from Scandinavia, Iberian Peninsula and other European regions reveals that the length of summer heat waves have already doubled. Scientists likewise found that the frequency of hot days has almost tripled over the time interval. They attribute the condition to the long-term trend towards higher temperatures and to the significant rise in the daily summer maximum temperatures in the continent.