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This paper presents an analysis of the relationships between soil moisture, cloud cover, solar radiation, air temperature and humidity, and precipitation during the warm half of the year in East‐Central Europe over the years 1971–2020. The temporal and spatial variability of these meteorological elements is presented in association with the occurrence of anticyclonic blocking events over the study area. It demonstrates that changes in soil moisture in East‐Central Europe point to the combined influence of many meteorological factors resulting from the atmospheric circulation, and are an indicator of the comprehensive relationships among those factors. The main factors affecting soil water content are precipitation and evapotranspiration, which in turn depend on air humidity, cloudiness, intensity of solar radiation and air temperature. The increase in the frequency and duration of sequences of days with blocking events in East‐Central Europe has contributed to an increased probability of longer periods with soil moisture negative anomalies. [ABSTRACT FROM AUTHOR]

The influence of soil moisture (SM) on atmospheric precipitation has been extensively studied, but few of these studies have considered the role of land‐atmosphere (L‐A) coupling in afternoon precipitation events (APEs) at a sub‐daily timescale. Here, using in‐situ observations and reanalysis data sets, we investigated the effect of the soil moisture anomaly (SMA) on warm seasons' afternoon precipitation in the North China Plain (NCP), identified as a strong L‐A coupling region. APEs were separated from all precipitation events in the NCP during the warm seasons of 2010–2019. It follows from a comparative analysis that an APE is more likely to be initiated on drier soil, which has little dependence on the thresholds used for identifying an APE. However, no affirmative relationship is found between precipitation amount in the first hour of an APE (APE1hour) and the SMA. Further analyses indicate that larger amounts of APE1hour result from higher convective available potential energy (CAPE), higher moist static energy (MSE), or weaker vertical shear of horizontal wind. When considering the joint effects of SMA and atmospheric variables, APEs tend to occur on drier (wetter) soil with lower (higher) lower‐tropospheric stability, CAPE, or MSE. This study highlights the significant roles of L‐A interactions on local atmospheric precipitation, especially the joint roles of SM and atmospheric variables on precipitation. Plain Language Summary: Atmospheric precipitation events (APEs) are mostly the consequence of atmospheric circulation anomalies and water vapor and energy transport supplies from the atmosphere and land surface. Previous studies have reported the important role of the soil moisture anomaly (SMA) on convective precipitation events, but how SMA influences the subsequent convective precipitation remains highly uncertain. In this work, we focus on the impact of morning SMA on subsequent local‐scale afternoon precipitation during warm seasons. Using in‐situ observations, we identified the North China Plain as a strong land‐atmosphere (L‐A) coupling area in China, further finding that warm seasons' APEs tend to occur on dry soil. However, the precipitation amount associated with an APE is almost independent of SMA. A joint analysis indicates that larger precipitation amounts result from higher moist static energy, convective available potential energy, or weaker vertical shear of horizontal wind. This study highlights the significant roles of L‐A interactions on local atmospheric precipitation. Key Points: The North China Plain is a strong land‐atmosphere coupling area during warm seasonsIn general, afternoon precipitation events (APEs) are more likely to be initiated over dry soilHowever, for more stable and moister atmosphere, APEs are more likely to occur on wet soil [ABSTRACT FROM AUTHOR]

Southeastern South America (SESA) is a highly productive agricultural region and a hot spot for land‐atmosphere interactions. To evaluate the impact of dry soil moisture anomalies (SMAs) on SESA climate and the sensitivity of the regional climate response to the location of SMAs, we perform three experimental simulations using the Community Earth System Model (CESM) with prescribed dry SMAs over (a) SESA, (b) western SESA, and (c) eastern SESA. The dry SESA and eastern SESA simulations show widespread negative precipitation anomalies. In contrast, the dry western SESA simulation shows positive precipitation anomalies over northeastern Argentina, which are associated with the enhanced southward moisture flux co‐located with the South American low‐level jet exit region. A composite analysis of extremely dry cases over western SESA using reanalysis data agrees with the findings from our CESM experiment. These findings have potential implications for subseasonal forecasting in this region. Plain Language Summary: Large‐scale soil moisture anomalies evolve slowly and can provide an opportunity for better weather forecasting at timescales longer than 2 weeks. Therefore, it is critical to understand the causal physical mechanism and evaluate whether the regional climate response is sensitive to the location of soil moisture anomalies, especially in a productive agricultural region like southeastern South America (SESA). Using a numerical climate model, we simulate the impacts of dry soil over (a) SESA, (b) western SESA, and (c) eastern SESA. The simulations show that dry soil over western SESA can alter regional atmospheric circulation in the proximity of the existing corridor of poleward moisture transport, hence enhancing rainfall over northeastern Argentina. Conversely, dry soil over eastern SESA or the entire SESA region results in less precipitation because enhanced northerly transport is not co‐located with the low‐level wind corridor. Analysis of a dataset that incorporates observations supports our findings from numerical simulations. Key Points: The impact of dry soil moisture anomalies (SMAs) on southeastern South America (SESA) regional climate is sensitive to the location of SMAsThis study provides a causal mechanism linking soil moisture to precipitation via atmospheric circulationWhen western SESA has dry soil, it generates anomalous geostrophic wind, which is co‐located with the low‐level jet exit region [ABSTRACT FROM AUTHOR]

Land surface‐atmosphere coupling and soil moisture memory are shown to combine into a distinct temporal pattern for wildfire incidents across the western United States. We investigate the dynamic interplay of observed soil moisture, vegetation water content, and atmospheric dryness in relation to fuel loading, fire ignition and post‐fire recovery. We find that positive soil moisture anomalies around 5 months before fire ignition increase biomass growth in the subsequent months, thereby shaping fire‐prone vegetation conditions. Then, concurrent decrease in soil moisture, vegetation dehydration, and atmospheric dryness collectively contribute to the occurrence of fire ignition events. This is followed by a rapid recovery in both soil and atmospheric moisture within several weeks after the fire incidents. Our findings provide insights into understanding of wildfire ignition dynamics, supporting fire modeling and enabling improved fire predictions, early warning systems, and mitigation strategies. Plain Language Summary: We find that wildfire are part of a distinct temporal pattern of soil moisture, vegetation water content and atmospheric dryness dynamics that begin about 5 months before the incidents. We analyze anomalies in soil moisture, vegetation water content, vapor pressure deficit and precipitation before and after large wildfires during the warm season across various US climate regions. We document distinct patterns in soil aridity and atmospheric dryness, fuel load, and vegetation dehydration that contribute to the occurrence of wildfires. Our observation‐based analyses show that soil moisture anomalies significantly control the growth of biomass several months before the fire occurrence, which in turn affects the availability of fire fuel. Notable dry anomalies with fuel accumulation in the dry western climate regions are observed approximately 4 to 5 months before the fires, followed by a quick recovery trend several weeks after the fire in wet regions. Our results indicate that in the majority of the climate regions, there are significant dry anomalies preceding the occurrence of wildfires. Understanding the dynamics of these environmental variables can be the basis for improved wildfire hazard predictions and mitigation strategies. Key Points: Wetter‐than‐average soil moisture 4–5 months before wildfires results in increased aboveground biomass accumulationSoil moisture decrease and atmospheric drying after peak biomass lead to dry fuel availability at the time of wildfire ignitionThe temporal pattern is evident in mapped data on soil moisture, vegetation water content and wildfire incidents across western United States [ABSTRACT FROM AUTHOR]

The changes of annual average, minimum and maximum temperature (Tavg, Tmin and Tmax) in China over 1961–2020 were examined based on the Chinese gridded observation dataset (CN05.1), and the relative contributions of Tmin and Tmax to the tendency of Tavg were addressed. The results show that the nationwide mean warming rate reached 0.29°C·decade−1 for Tavg, 0.39°C·decade−1 for Tmin and 0.24°C·decade−1 for Tmax, respectively, from 1961 to 2020, which depended on temporal windows. The relative contributions of Tmin and Tmax to the trends of Tavg over China during 1961–2020 are 56% and 44%, respectively. On the spatial scale, the majority of China exhibits a greater relative contribution of Tmin than Tmax, except for some areas along the Hu Huanyong Line. As in the case of the warming rate, the temporal patterns of the magnitude of the relative contribution of Tmin and Tmax are also identified. For the first 30 years (1961–1990), Tmin is the primary contributor to changes in the trend of Tavg over a broad area excluding the Qinling Mountain‐Huai River to the Nanling Mountain. The national average magnitudes of the relative contribution of Tmax is slightly larger than Tmin in the latter 30 years (1991–2020). The areas with larger contributions of Tmax are mainly scattered along Hu Huanyong Line, the southern part of the Qinghai‐Tibet Plateau and the patchy parts of Northwest China. Changes in downward longwave radiation, solar radiation, cloud cover, land use, soil moisture, atmospheric circulation and urbanization likely accounted for much of the trend difference of Tmin and Tmax, thereby leading to various relative contributions across different regions during different periods. The warming mechanisms in China have been subjected to novel changes. The study could provide information for decision making on scientific response to warming. [ABSTRACT FROM AUTHOR]

The Central American Dry Corridor experienced five consecutive years of drought from 2015 to 2019. Here, we find that the severity of this drought was driven primarily by rainfall deficits in July–August. To determine if the magnitude of this event was outside the range of natural variability, we apply a statistical resampling method to observations that emulates internal climate variability. Our analyses show that droughts similar to the 2015–2019 event are possible, although extremely rare, even without anthropogenic influences. Persistent droughts in our ensemble are consistently linked to stronger easterly winds associated with the Caribbean Low‐Level Jet. We also examine the effects of temperature on soil moisture during this drought using the Palmer Drought Severity Index and show that anthropogenic warming increases the likelihood of severe deficits. Multi‐year droughts are likely to worsen by the end of the 21st century due to the compound effects of anthropogenic climate change. Plain Language Summary: Climate models project that Central America is one of the global hotspots for future decreases in precipitation as a result of human‐caused climate change. This is particularly concerning for the Dry Corridor region, which is already prone to frequent droughts and high levels of food insecurity among households. Much of this region experienced severe rainfall deficits between 2015 and 2019, provoking the question of whether or not this drought was caused by climate change or if it could have occurred because of natural climate variability alone. Using a statistical model, we show that while 2015–2019 was the driest period in the observational record, droughts as bad as this one are possible even without the influence of human‐caused climate change. We examine the additional role of temperature since it can modulate drought severity through its influence on soil moisture. We find warming temperatures increase the occurrences of greater soil moisture deficits. We also determine that the strength of the Caribbean Low‐Level Jet, which transports moisture from the Caribbean Sea into Central America, is strongly associated with persistent dry conditions in the region. Key Points: The 2015–2019 drought was severe, but it falls within the range of natural climate variabilityJuly–August deficits were the most significant drivers of overall droughtPositive easterly zonal wind anomalies associated with the Caribbean Low‐Level Jet are strongly linked to regional precipitation deficits [ABSTRACT FROM AUTHOR]

Both snow and precipitation are vital components of the water cycle and hydrological system, so the snow–precipitation feedback could be crucial for investigating land–atmosphere interaction and climate variability. Seldom studies have focused on the contributions of snow variations to precipitation anomalies over the Tibetan Plateau (TP). In this study, spring snowmelt (SSD, Spring Snow water equivalent Differences) variations over the TP and its influences on spring and summer precipitation and the associated physical mechanisms during 1979–2014 are investigated. Results show that the leading mode of the interannual SSD over the TP exhibits a same‐sign anomaly pattern, with an intense centre over the western TP. The SSD shows significant relations to spring and summer precipitation over the TP. In spring, when larger SSD appears over the western TP, an anomalous cyclone occupies the northwestern TP, and the central and eastern TP lies between an anomalous cyclone and an anomalous anticyclone. There is an anomalous convergence (divergence) and ascending (descending) motion of airflows over the northwestern (central and eastern) TP. Concurrently, sufficient moisture occurs over the northwestern TP due to evaporation and atmospheric circulations. As a result, precipitation anomalously increases over the northwestern TP, and decreases over the central and southeastern TP. The SSD‐related soil moisture anomalies over the western TP can persist into summer, and larger SSD corresponds to excessive summer soil moisture. The central and eastern TP lies between two anticyclones, leading to convergence of airflows and thereby ascending motions. Simultaneously, excessive moisture appears over the TP owing to atmospheric circulation transportation. Hence, precipitation anomalously increases over the central and eastern TP. [ABSTRACT FROM AUTHOR]

Soil moisture (SM) affects weather through its impact on surface flux partitioning, influencing vertical atmospheric profiles and circulations driven by differential surface heating. In West Africa, observational studies point to a dominant negative SM‐precipitation feedback, where dry soils help to initiate and maintain convection. In this context, serious concerns exist about the ability of models with parameterised convection to simulate this observed sensitivity of daytime convection to SM. Here, we evaluate the effect of initial SM perturbations in a short‐range ensemble forecast over West Africa, comparing the UK Met Office Global and Regional Ensemble Prediction System (MOGREPS) with parameterised convection (GLOB‐ENS) to its regional convection‐permitting counterpart (CP‐ENS). Results from both models suggest SM perturbations introduce considerable spread into daytime evaporative fraction (EF) and near‐surface temperatures. This spread is still evident on Day 3 of the forecast. Both models also show a tendency to increased afternoon rainfall frequency over negative EF anomalies, reproducing the observed feedback. However, this effect is more pronounced in CP‐ENS than GLOB‐ENS, which illustrates the potential for process‐based forecast improvements at convection‐permitting scales. Finally, we identify persistent biases in rainfall caused by land cover mapping issues in the operational GLOB‐ENS setup, emphasising the need for careful evaluation of different mapping strategies for land cover. [ABSTRACT FROM AUTHOR]

Land–atmosphere coupling is a crucial factor influencing extreme weather and climate. Based on the ERA5‐Land reanalysis data set and sensitivity experiments with the CESM1.2.2 model, this study investigated the possible impacts of land–atmosphere coupling on low temperature extremes (LTEs) during fall and winter over southern Eurasia (SEA). The results suggested that LTEs show evident interdecadal variations in recent 60 years (1958–2017) and exhibit significant positive correlations with soil moisture anomalies based on the ERA5‐Land data set. Numerical simulations (the control run and sensitivity run with prescribed climatological soil moisture) isolated the effects of soil moisture‐related land surface processes and demonstrated that land–atmosphere coupling explains around 70% of temperature variability, increases the near‐surface air temperature by 0.81 K, and favors the reduction of LTEs by 8.20 d·yr−1. In the perturbation scenarios, the impacts of coupling on the frequency and spatial coverage of LTEs are more prominent. Further analysis revealed that the thermal cooling anomalies induced by the coupling could alter the atmospheric circulation, thereby affecting the frequency and intensity of LTEs. When the land–atmosphere interactions are weakened, the surface latent heat flux increases accompanied by intense evapotranspiration, while the sensible heat flux and net infrared radiation decrease. Land surface cooling is apparent, and it weakens with increasing altitude, along with geopotential height anomalies that are positive in the lower troposphere and weaker at higher altitudes. The northeasterly wind anomalies over the East European Plain facilitate the development of cold advection, providing a favorable circulation background for the generation of LTEs over SEA. Plain Language Summary: As a key land surface variable, soil moisture can affect the surface thermal conditions and regulate the surface energy exchange, further trigger anomalous atmospheric circulation, and lead to extreme weather and climate events. In recent 60 years (1958–2017), low temperature extremes (LTEs) have occurred at times over southern Eurasia (SEA) and exhibit close relationships with soil moisture anomalies. Several simulations were conducted to isolate the effects of soil moisture‐related land surface processes on LTEs. When the land–atmosphere interactions are restricted, the frequency and intensity of LTEs in fall and winter consistently increase over SEA. The effects of land–atmosphere coupling on LTEs are spatially consistent under different backgrounds, albeit with certain differences in the magnitude of increase. Further analysis revealed that land surface cooling is evident when land–atmosphere interactions are weakened. The surface latent heat flux increases accompanied by strong evapotranspiration, while the sensible heat flux and net infrared radiation decrease. The positive geopotential height anomalies and northeasterly wind anomalies over SEA facilitate the development of cold advection, which can contribute to more frequent and intense LTEs over SEA. Key Points: Low temperature extremes (LTEs) over southern Eurasia are closely related to soil moisture anomalies and land–atmosphere couplingLand–atmosphere coupling is conducive to LTEs reduction, and the stronger variations the coupling has, the greater impact on LTEs it exertsThermal effects of land–atmosphere coupling and their influence on atmospheric circulation are the key factors affecting LTEs [ABSTRACT FROM AUTHOR]

This study examines the European heatwaves' predictability at subseasonal timescales. Land surface feedbacks and tropical convection, due to their variability at intraseasonal timescales, are taken into consideration and their potential role in extending the predictability beyond the medium range (10 days) is explored. A classification of European heatwaves into five heatwave types is used to discriminate the effects of surface feedbacks and of tropical variability among the different heatwave types. The classification is computed in terms of circulation patterns. By inferring the near‐surface temperature through atmospheric circulation, we aim to identify the predictable component of the heatwave events. All five heatwave circulation patterns are characterized by persistent anticyclonic anomalies located over the region with maximum temperatures. We show that soil moisture deficit is not a required precondition for the occurrence of heatwaves over most of Europe. However, heatwave events over southern Europe exhibit some sensitivity to dry conditions. We use a simplified index to describe the dominant mode of tropical convection at intraseasonal timescales. The index, based on precipitation anomalies, represents the evolution of the Boreal Summer Intraseasonal Oscillation (BSISO). We find that episodes with strong BSISO amplitudes characterized by enhanced convection over India, Bay of Bengal and China sea favour the occurrence of heatwave events over Russia. The results highlight the role of tropical intraseasonal variability in enhancing the predictability of some extreme temperature events over Europe. [ABSTRACT FROM AUTHOR]

The potential effects of climate change on plant reproductive phenology include asynchronies with pollinators and reductions in plant fitness, leading to extinction and loss of ecosystem function. In particular, plant phenology is sensitive to extreme weather events, which are occurring with increasing severity and frequency in recent decades and are linked to anthropogenic climate change and shifts in atmospheric circulation. For 15 plant species in a Venezuelan cloud forest, we documented dramatic changes in monthly flower and fruit community composition over a 35‐year time series, from 1983 to 2017, and these changes were linked directly to higher temperatures, lower precipitation, and decreased soil water availability. The patterns documented here do not mirror trends in temperate zones but corroborate results from the Asian tropics. More intense droughts are predicted to occur in the region, which will cause dramatic changes in flower and fruit availability. [ABSTRACT FROM AUTHOR]

Soil moisture as a key variable of land processes greatly influences the weather and climate. This study investigates the observed linkage between Tibetan Plateau (TP) spring soil moisture and summer precipitation and floods in the Yangtze River basin during 1988–2008 using satellite and in‐situ observations. A significant (p = 1%) proportion of interannual variations of summer precipitation (about 25%) in the Yangtze River basin can be attributed to spring TP soil moisture anomalies which show a dipole pattern. When spring soil moisture anomalies are positive (negative) over eastern (western) TP, there is more summer precipitation and consequently river discharge in the Yangtze River basin, or vice versa. The possible mechanisms can be explained from the perspectives of surface energy balance and atmospheric thermodynamics. More (less) spring soil moisture over the eastern (western) plateau enhances summer diabatic heating, which may be related to soil moisture memory. The enhanced summer diabatic heating stimulates vigorous ascending motions over TP, which diverge in the upper troposphere (200 hPa) and descend over the western Pacific. This is conducive to the enhancement and mutual proximity of the South Asian High (SAH) and the Western Pacific Subtropical High (WPSH). As a result, the warm and humid air flows from the Bay of Bengal and the western Pacific and the cold and dry air flows from the boreal continent converge in the Yangtze River basin, causing excessive summer precipitation. Therefore, TP spring soil moisture can be considered a seasonal predictor of summer precipitation and possible subsequent floods in the Yangtze River basin. Plain Language Summary: Spring soil moisture over the Tibetan Plateau (TP) explains a significant proportion of interannual variations of summer precipitation (about 25%) in the Yangtze River basin. When spring soil moisture anomalies are positive (negative) over the eastern (western) TP, there is more summer precipitation and consequently river discharge in the Yangtze River basin, or vice versa. The possible mechanisms can be attributed to the perspectives of surface energy balance and atmospheric thermodynamics. More (less) spring soil moisture over the eastern (western) plateau enhances summer diabatic heating. The diabatic heating controls the atmospheric circulation changes over the TP and surrounding regions associated with the enhancement and eastward (westward) stretching of the South Asian High (Western Pacific Subtropical High), favoring the convergence of the warm and humid (cold and dry) air flows from Tropical Ocean (boreal continent) to the Yangtze River basin, resulting in excessive summer precipitation. Key Points: Spring soil moisture over the Tibetan Plateau (TP) explains about 25% of interannual variations of summer precipitation in the Yangtze River basinPositive (negative) soil moisture anomalies over eastern (western) TP lead to more precipitation and discharge in the Yangtze River basinMore precipitation is due to moisture‐rich airflow convergence linked to South Asian High and Western Pacific Subtropical High affected by soil moisture‐induced diabatic heating [ABSTRACT FROM AUTHOR]

Land surface heterogeneity in conjunction with ambient winds influences the convective atmospheric boundary layer by affecting the distribution of incoming solar radiation and forming secondary circulations. This study performed coupled large‐eddy simulation (ICON‐LEM) with a land surface model (TERRA‐ML) over a flat river corridor mimicked by soil moisture heterogeneity to investigate the impact of ambient winds on secondary circulations. The coupled model employed double‐periodic boundary conditions with a spatial scale of 4.8 km. All simulations used the same idealized initial atmospheric conditions with constant incident radiation of 700 W⋅m−2 and various ambient winds with different speeds (0 to 16 m⋅s−1) and directions (e.g., cross‐river, parallel‐river, and mixed). The atmospheric states are decomposed into ensemble‐averaged, mesoscale, and turbulence. The results show that the secondary circulation structure persists under the parallel‐river wind conditions independently of the wind speed but is destroyed when the cross‐river wind is stronger than 2 m⋅s−1. The soil moisture and wind speed determine the influence on the surface energy distribution independent of the wind direction. However, secondary circulations increase advection and dispersive heat flux while decreasing turbulent energy flux. The vertical profiles of the wind variance reflect the secondary circulation, and the maximum value of the mesoscale vertical wind variance indicates the secondary circulation strength. The secondary circulation strength positively scales with the Bowen ratio, stability parameter (−Zi/L), and thermal heterogeneity parameter under cross‐river wind and mixed wind conditions. The proposed similarity analyses and scaling approach provide a new quantitative perspective on the impact of the ambient wind under heteronomous soil moisture conditions on secondary circulation. [ABSTRACT FROM AUTHOR]

Heatwaves of different spatial types can cause various impacts. Based on the spatial heatwave intensity, 47 North China heatwaves from 1961 to 2019 could be classified into two categories: the S‐type with a centre in the south and the N‐type in the north. There were more N‐type events (36) than the S‐type (11). Observational analysis indicated that under atmospheric circulations favourable to North China heatwaves (e.g. the enhanced continental high), there is a linkage between the sea ice concentration (SIC) changes in the Barents‐Kara Sea (BKS) and these two types of heatwaves. Relative to high BKS SIC, the reduction of SIC would strengthen the cyclonic circulation over the Siberian‐BKS, which could coordinate with the continental high to enhance the cyclonic over the Jianghuai region. A cyclonic‐anticyclonic‐cyclonic pattern is present over the BKS‐North China‐Jianghuai. The cyclonic circulation over the Jianghuai region would push the continental high northerly, resulting in the heatwave centre to the north. It would also cause favourable conditions for precipitation over southern North China, reducing temperatures and raising soil moisture, not conducive to the heatwave. Therefore, the heatwave intensity in southern North China would weaken and the heatwave centre would locate in the north, making the N‐type. Conversely, when the BKS SIC increases, the upper cyclonic over the Siberian‐BKS would not get strengthened, indicating entire North China would be controlled by continental high, and the heatwaves would be southerly relative to the N‐type, namely the S‐type. A series of numerical experiments using NCAR CAM5.3 confirm the above observational results, whereby if the BKS SIC reduces (increases), the North China heatwave is likely to be the N‐type (S‐type). [ABSTRACT FROM AUTHOR]

This study investigated the relationship between extreme precipitation and near‐surface temperature (precipitation–temperature relation) from two different perspectives, the rate of change of precipitation with temperature and dynamic (i.e., effect of the change in atmospheric motion) and thermodynamic (i.e., effect of the change in atmospheric moisture content) aspects, using a 5‐km dynamical downscaled hundreds‐year data set for past climate condition (PAST; from 1951 to 2010) and future climate condition (FUTURE; 4°C warmer than the preindustrial condition). Initially, using the observation and the PAST and FUTURE data sets, it was found that the 99th and 99.9th percentile hourly precipitation for each temperature bin (P99 and P99.9, respectively) paralleled the slope of the Clausius–Clapeyron (C–C) relation for a certain temperature range over the Tokachi River basin in Hokkaido, the northern island of Japan; however, both P99 and P99.9 decreased in the high‐temperature range. Next, we examined the cause of the P99 and P99.9 differences between PAST and FUTURE for each temperature bin by classifying dynamic and thermodynamic factors. The result showed that the thermodynamic effect dominates the differences in P99 and P99.9 between PAST and FUTURE, which means that the thermodynamic effect is the main component of the precipitation–temperature relation. Similar analyses were applied to the whole river basin, including the mountainous area. The results showed that the differences in P99 and P99.9 between PAST and FUTURE are mainly due to the thermodynamic contribution, regardless of plain or mountain area. Using such large model data sets, we could make a robust assessment of the precipitation–temperature relation and the dynamic and thermodynamic contributions to precipitation changes. Moreover, using the 5‐km resolution hundreds‐year data set enabled us to quantify the spatial distribution of such precipitation characteristics over a thousands of square kilometer catchment. [ABSTRACT FROM AUTHOR]

The present study utilizes the standard precipitation index (SPI) to differentiate Asian summer droughts that are associated with variations of precipitation over periods of 3, 9 and 24 months (termed as short‐term, medium‐term and long‐term droughts, respectively). Then, the relationships between these droughts and atmospheric circulation, sea surface temperature (SST), and soil moisture are investigated. While the spatial and temporal characteristics of short‐term and medium‐term droughts are fairly similar, long‐term droughts display different spatial and temporal features. The leading spatial mode of short‐term and medium‐term droughts exhibits a dipole pattern with opposite loading north and south of approximately 30°N. The second spatial mode displays a tripole pattern with the same sign of loading over India and north‐northeast China–Mongolia and opposite loading in between. Temporal variations of short‐term and medium‐term droughts are dominated by interannual variabilities. For long‐term droughts, the first two spatial modes switch their order, and the long‐term trends are as important as the interannual and interdecadal variabilities. The droughts of the dipole mode are associated with SST anomalies featuring an El Niño‐like pattern in the tropical Indo‐Pacific Ocean that affect the drought variations through inducing large‐scale divergence and convergence. The interannual variability of the droughts with the dipole mode is also associated with the SST anomalies in the North Atlantic Ocean that affect the North Atlantic‐Eurasian atmospheric circulation. Local soil moisture conditions are more important for the formation of long‐term droughts than short‐term and medium‐term droughts. [ABSTRACT FROM AUTHOR]

This study investigates the variability of summer surface air temperature (SAT) over northern Eurasia and its precursory signals in the tropical Atlantic and northern Asian land. The leading mode of summer SAT variations features a northern Eurasian SAT tripole (NEST) pattern, with two same‐sign SAT anomaly regions over eastern Europe–western Siberia and the Far East region and an opposite‐sign SAT anomaly region around the Baikal Lake. It is found that sea surface temperature (SST) or SAT anomalies in the tropical Atlantic and rainfall‐soil moisture anomalies around the Baikal Lake during May can modulate the NEST pattern. The SST anomalies in the tropical Atlantic persist from May to summer and induce a downstream zonal wave train across northern Eurasia, consequently causing the variation in the summer NEST pattern. May rainfall anomalies around the Baikal Lake affect the overlying atmospheric circulation during summer through the 'memory' effect of soil moisture and the soil moisture‐rainfall interaction, correspondingly modulating the downstream wave train and the associated NEST pattern. Based on the above results, a statistical prediction model is established using the two precursory signals, that is, SAT in the tropical Atlantic and rainfall around the Baikal Lake during May. The leave‐three‐out cross‐validation shows that the model has a high skill in predicting the summer NEST pattern, with a correlation coefficient of 0.51 (significant at the 99.8% confidence level) between observation and prediction during the period 1980–2016. [ABSTRACT FROM AUTHOR]

Rapid drought intensification, or flash droughts, is often driven by anomalous atmospheric ridging and can cause severe and complex impacts on water availability and agriculture, but the full range of variability of such events in terms of intensity and frequency is unknown. New tree‐ring reconstructions of May–July mid‐tropospheric ridging and soil moisture anomalies back to 1500 CE in the central United States—a hotspot for flash drought—suggest that over the last five centuries, anomalies in these two variables combined to indicate flash‐drought conditions in ∼17% of years and exceptionally severe flash drought in ∼4% of years, similar to frequencies in recent decades. However, over one‐third of all inferred exceptional flash droughts occurred since 1900, suggesting the 20th century was highly flash‐drought prone. These results may guide future work to diagnose the roles of external, oceanic, and land‐surface forcing of warm‐season atmospheric circulation and hydroclimate over North America. Plain Language Summary: In 2012, the central United States experienced a "flash drought," when rapid soil drying due to persistently low precipitation totals and high temperatures in late spring and summer caused billions of dollars in damages and agricultural losses. Such events are difficult to forecast because flash droughts can develop in a matter of weeks, and only a handful of flash droughts have been observed in recent decades, giving high uncertainty as to their likelihood. Here, we use tree rings to create two independent annual records of central United States soil moisture and the principal atmospheric circulation pattern known to cause flash droughts that extend back to the year 1500. Taken together, these records provide a new five‐century perspective on these crucial components of flash drought and reveal for the first time the long‐term behavior of central United States flash droughts, including frequency and cyclicity of exceptional events. We find that the instrumental record is a good representation of the long‐term likelihood of flash droughts. This apparent agreement with long‐term average conditions is largely by chance; however, as the reconstructions indicate large century‐to‐century variations in flash‐drought frequency and magnitude over the past 500 years. Key Points: We developed tree‐ring reconstructions of central U.S. soil moisture and the atmospheric ridge that causes flash droughts back to 1500 CEObservations capture flash drought's long‐term probability distribution, but reconstructions reveal centennial fluctuations in variabilityCycles in reconstructed atmospheric ridging may aid diagnosis and prediction of flash drought on interannual to decadal time scales [ABSTRACT FROM AUTHOR]

Understanding the global soil moisture (SM) dynamics and its governing controls beyond the Darcy Scale is critical for various hydrological, meteorological, agricultural, and environmental applications. In this study, we parameterize the pathways of global surface SM (θRS) drydowns using seasonal observation from Soil Moisture Active Passive (SMAP) satellite (between 2015 and 2019) at 36 km resolution. We develop a new data‐driven nonparametric approach to identify the canonical forms of θRS drydown, followed by a nonlinear least squares parameterization of the seasonal drydown pathways at each SMAP footprint. The derived parameters provide the effective soil water retention parameters (SWRPeff), land‐atmospheric coupling strength and soil hydrologic regimes for SMAP footprint. Depending on the footprint heterogeneity, climate, and season, the characteristics curves comprising different drydown phases are discovered at SMAP footprints. Drydown curves respond to the within‐footprint changes in the meteorological drivers, land‐surface characteristics, and the soil‐vegetative and atmospheric dynamics. Drydown parameters display high interseasonal variability, especially in the grasslands, croplands, and savannah landscapes due to significant changes in the landscape characteristics and moisture patterns at the subgrid‐scale. Soil texture exerts influence on the soil water retention and drydown parameters only when the footprint mean θRS is low, specifically in arid and sparsely vegetated regions. The interseasonal variability of the SWRPeff is primarily driven by the landuse and climate of the SMAP footprint. A global understanding of the SM drydown features at SMAP footprint provides a significant step toward a scale‐specific, effective soil hydrologic parameterization for various applications. Key Points: Quantification of global soil moisture drydown patterns at SM Active Passive (SMAP) footprint using a nonparametric methodSeasonally variable soil, vegetative, and atmospheric controls are observed in effective soil water retention parameters at SMAP footprintInterseasonal variability in soil drydown parameters is governed by climate and landuse [ABSTRACT FROM AUTHOR]

The low‐latitude highlands (LLH) of China are situated in the subtropical southwest China. The spring climatic characteristics of the LLH were previously regarded as being governed by remote sea surface temperature forcing and large‐scale atmospheric circulations. Recent studies qualitatively demonstrated that the LLH is a relatively strong soil moisture (SM)‐surface air temperature (SAT) coupling region in China during spring. In this study, the quantitative spring SM‐SAT coupling (mean of March and April before wet season) is further statistically analysed using two different SM data sources (one reanalysis data set and one land surface assimilation product). The results show that significant negative SM‐SAT feedbacks mainly occur in the western and middle part of the LLH. Over these areas, 10–50% of the total SAT variance could be explained by the SM‐induced negative feedbacks with a feedback parameter of −0.2°C·(standardized SM)−1 to −0.8°C·(standardized SM)−1. Further analyses show that SM negatively impacts Bowen ratio in the western and middle part of the LLH where Bowen ratio positively affects SAT, therefore significant negative SM‐SAT feedbacks occur therein. The potential impact of India–Burma Trough (IBT) on the SM‐SAT coupling is also investigated in this study, the results of which suggest that SM‐SAT coupling and the effects of SM on land surface energy balance may be immune to the influence of the IBT. Furthermore, SM and IBT may comparably affect SAT in the western and middle part of the LLH. This highlights that SM might have prominent effects on the subseasonal predictability of spring SAT over these areas. [ABSTRACT FROM AUTHOR]

Climate change presents risks both in terms of warming and increased variability that are heightened when compounded. It is thus notable that the simulations in the Coupled Model Intercomparison Project Phase 5 (CMIP5) showing greater Northern midlatitude continental warming also show a greater increase in monthly average temperature variance, particularly in Europe. European variability increases with warming at a rate of 0.40°C2/°C (95% C.I. [0.28, 0.50]), with local warming rates explaining 71% of the intermodel difference in variability changes. Coupling between warming and variance increases the probability of high temperatures compared to a scenario where variance is stable. If warming were to reach 6°C, the risk of monthly average temperature exceeding a 30°C threshold is 4 times greater in the increased‐variance scenario. Despite the simple scaling across models suggesting some common origin, changes in model temperature and variance potentially involve a range of mechanisms whose contributions remain unclear. Plain Language Summary: Extreme and persistent summertime temperatures present risks to human health, property, and natural systems. The frequency of hot extremes increases in response to both growing mean temperature and increasing variability. Here we show that models that predict higher summertime warming also predict greater increases in temperature variability in midlatitude continents, especially in Europe. The combination of warming and increased variability makes the chances of hot extremes much greater than if temperature variance stayed constant. The reasons for increased variability may involve changes in soil moisture, variability in local radiation, and changes in atmospheric circulation, but exactly why a simple scaling between warming and increased variance emerges in Europe and elsewhere is unclear. Key Points: Summertime temperature variability and warming in NH midlatitudes covary across CMIP5 models, especially in EuropeSuch covariance between warming and increased variability accentuates risks of future high‐temperature eventsAlbeit a weaker relationship than with warming, increases in variability also scale with biases in simulated historical variability [ABSTRACT FROM AUTHOR]

The mechanisms causing European heatwaves in recent years, particularly their differences among several heatwaves, are poorly understood. Here atmospheric circulation anomalies and soil moisture‐temperature coupling during the summer 2018 heatwave are comprehensively examined and compared with the 2003 and 2010 heatwaves using ERA5 reanalysis, model simulations, and eddy covariance flux measurements. We show that the 2018 heatwave successively affected northern and central Europe, and the peak temperature in Finland and northwest Russia broke historical records of the past 40 years. Although three heatwaves were all initially triggered by atmospheric circulation anomalies, the strong moisture‐temperature coupling were found to further strengthen the 2003 and 2010 heatwaves. This coupling was also strong in central Europe during 2018 heatwave, but was weak in the northern European center of the heatwaves. The high temperature in 2018 was mainly due to increases in the amount of net surface radiation caused by the clear skies associated with reduced precipitation. Furthermore, we also find that land cover plays a critical role in determining the occurrence and strength of soil moisture‐temperature coupling. Cropland/grassland depletes soil moisture more readily than forests, thereby triggering a more rapid release of sensible fluxes as observed during 2018 heatwave. Plain Language Summary: In summer 2018, Europe was attacked by strong heatwave. This heatwave successively affected northern and central Europe, and temperature in Finland and northwest Russia broke historical records. Similar with heatwaves happened in 2003 and 2010, the 2018 heatwave was triggered by atmospheric circulation anomalies. However, different from the strong soil moisture‐temperature coupling during 2003 and 2010 heatwaves, this coupling was relative weak in northern Europe during 2018 heatwave because of the relatively small soil moisture deficits. Key Points: The 2018 heatwave successively affected northern and central Europe, and temperature in Finland and northwest Russia broke historical recordThe moisture‐temperature coupling was strong in central Europe, which was relatively weak in northern Europe during 2018 heatwaveLand cover plays a critical role in determining the occurrence and strength of soil moisture‐temperature coupling [ABSTRACT FROM AUTHOR]

Arctic and boreal ecosystems play an important role in the global carbon (C) budget, and whether they act as a future net C sink or source depends on climate and environmental change. Here, we used complementary in situ measurements, model simulations, and satellite observations to investigate the net carbon dioxide (CO2) seasonal cycle and its climatic and environmental controls across Alaska and northwestern Canada during the anomalously warm winter to spring conditions of 2015 and 2016 (relative to 2010–2014). In the warm spring, we found that photosynthesis was enhanced more than respiration, leading to greater CO2 uptake. However, photosynthetic enhancement from spring warming was partially offset by greater ecosystem respiration during the preceding anomalously warm winter, resulting in nearly neutral effects on the annual net CO2 balance. Eddy covariance CO2 flux measurements showed that air temperature has a primary influence on net CO2 exchange in winter and spring, while soil moisture has a primary control on net CO2 exchange in the fall. The net CO2 exchange was generally more moisture limited in the boreal region than in the Arctic tundra. Our analysis indicates complex seasonal interactions of underlying C cycle processes in response to changing climate and hydrology that may not manifest in changes in net annual CO2 exchange. Therefore, a better understanding of the seasonal response of C cycle processes may provide important insights for predicting future carbon–climate feedbacks and their consequences on atmospheric CO2 dynamics in the northern high latitudes. [ABSTRACT FROM AUTHOR]

Dry land surface conditions have been shown to amplify extreme heat events in Europe, but the extent to which this influence involves modification of the overlying atmospheric circulation has yet to be fully established. Here, this issue is addressed using two Community Earth System Model ensembles, with the same heatwave‐inducing atmospheric circulation pattern imposed over different land surface states. These two ensembles differ in the vertical level above which the circulation is constrained (surface vs. upper troposphere). Soil moisture anomalies are found to play an important role in dictating heatwave intensity among ensemble members. The heatwave is approximately 0.1°C hotter per standard deviation soil moisture reduction when the troposphere is free to respond to surface conditions than when it is constrained, implying that a portion of the land surface influence involves feedbacks through the atmospheric circulation. The additional atmospheric response also allows for nonlocal heatwave amplification in subsequent months. Plain Language Summary: Seasonally persistent European heatwaves are socioeconomically costly. Though established by atmospheric circulation patterns, heatwaves can be intensified by dry land surface conditions, increasing societal risks. Here, we show that the manner in which dry land surface conditions affect European heatwave intensity is twofold: through local heating and through changes to the structure of the atmosphere. The additional influence of the land surface on the atmosphere can make the same European heatwave up to 0.4°C hotter overall and can cause surface drying in other regions. This nonlocal mechanism leads to hotter conditions in those regions in subsequent months. Key Points: By constraining atmospheric circulation, a seasonally persistent European heatwave is imposed over different initial land surface statesThe prescribed heatwave is amplified by local dryness directly and indirectly through the modification of the near‐surface atmosphereThe atmospheric response to surface dryness allows for an additional 0.1°C of warming per standard deviation of soil moisture drying [ABSTRACT FROM AUTHOR]

This study investigates the atmospheric drivers of severe precipitation deficits in the Greater Alpine Region during the last 210 years utilizing a daily atmospheric circulation type reconstruction. Precipitation deficit tends to be higher during periods with more frequent anticyclonic (dry) and less frequent cyclonic (wet) circulation types, as would be expected. However, circulation characteristics are not the main drivers of summer precipitation deficit. Dry soils in the warm season tend to limit precipitation, which is particularly the case for circulation types that are sensitive to a soil moisture‐precipitation feedback. This mechanism is of specific relevance in explaining the major drought decades of the 1860s and 1940s. Both episodes show large negative precipitation anomalies in spring followed by increasing frequencies of circulation types sensitive to soil moisture precipitation feedbacks. The dry springs of the 1860s were likely caused by circulation characteristics that were quite different from those of recent decades as a consequence of the large spatial extent of Arctic sea ice at the end of the Little Ice Age. On the other hand, the dry springs of the 1940s developed under a persistent positive pressure anomaly across Western and Central Europe, triggered by positive sea surface temperatures in the western subtropical Atlantic. Key Points: Winter and spring droughts are strongly related to the Eastern Atlantic‐Western Russia atmospheric variability patternSummer droughts are enhanced by prevailing dry spring conditions through a positive soil moisture‐precipitation feedbackThe major dry episodes in the 1860s and 1940s are particularly driven by this feedback mechanismThe dry springs of the 1860s were likely caused by unusual circulation regimes, synchronized with large spatial extents of Arctic sea ice at the end of the Little Ice AgeThe dry springs of the 1940s are due to positive sea surface temperature anomalies in the western subtropical Atlantic, which are related to a positive Eastern Atlantic‐Western Russia pattern [ABSTRACT FROM AUTHOR]

Based on the European Centre for Medium‐Range Weather Forecasts (ECMWF) ERA‐Interim reanalysis data from 1979 to 2016, an index for Tibetan Plateau (TP) soil moisture (ITPSM), which could represent inter‐annual variation in spring soil moisture, is defined after removing the linear trend in soil moisture. The late spring soil moisture variation over the TP and its influences on the plateau summer monsoon are analysed. The results show that the TP soil moisture variation is non‐uniform, and spring soil moisture over the northeastern TP shows an increasing trend, while the western TP (especially the peripheral area) renders a significantly decreasing trend. When the ITPSM shows positive (negative) anomalies (i.e., spring soil moisture over the northeastern TP is higher (lower), soil moisture over the western TP is lower (higher) than normal), the plateau summer monsoon may be stronger (weaker). Anomalous variations in spring TP soil moisture can eventually affect the plateau summer monsoon by changing atmospheric circulation, diabatic heating, and water vapour transportation. It is found that when the ITPSM exhibits positive anomalies, diabatic heating over the centre and eastern TP is remarkably enhanced, and warm and humid moisture from the Bay of Bengal and Arabian Sea and cold air from high latitudes merge over the central and eastern TP; coupled with lower‐level convergence and upper‐level divergence, all these contribute to an increase in plateau summer monsoonal precipitation. When the ITPSM shows negative anomalies, diabatic heating over the centre and eastern TP is weakened, the anomalous cyclone to the south of the TP hinders warm and humid air flows transportation to the TP, and the anomalous anticyclone to the southeast of Lake Baikal weakens cold air to the south; coupled with weakened convergence and upwards motion, these factors all lead to a decrease in plateau summer monsoonal precipitation. [ABSTRACT FROM AUTHOR]

ABSTRACT We propose how seasonal climate prediction with the use of an atmospheric general circulation model ( AGCM) can be optimized. The AGCM predictive skill is extensively examined under various forecast strategies that mimic truly operational prediction. It is shown that the AGCM predictive skill is found to produce superior results given a suitable sea-surface temperatures ( SSTs) as forcing and is subject to an initialization strategy that uses realistic atmosphere and soil moisture states. Evaluation of hindcasts performed with the model further revealed that the AGCM is able to forecast anomalous upper air atmospheric dynamics (circulation) over the tropics up to several months ahead. The AGCM probabilistic forecasts for rainfall and surface air temperatures during the austral summer season are also found to be informative and useful. The contribution of the predicted SST, which is based on a multi-model approach, is shown to be of significant importance for best AGCM results. The AGCM may also benefit from the initial condition interface in the AGCM's configuration which is implicitly considered in the analysis. Notwithstanding, the AGCM's predictive skill does not vary much whether the AGCM is initialized with realistic or climatological soil moisture which is presumably suggestive of the AGCM's internal weakness. [ABSTRACT FROM AUTHOR]

[1] Observations of 408 monsoon low-pressure systems (MLPSs) including 196 monsoon depressions (MDs) that formed in the Bay of Bengal during the 1951-2007 period, and the gridded analysis of daily rainfall fields for the same period, were used to identify the association of antecedent rainfall (1 week average rainfall prior to the genesis of MLPS) with the genesis of MLPS and length of inland penetration by MDs. Prestorm rainfall is treated as a surrogate to prestorm ground wetness conditions due to unavailability of historical soil-moisture data over the monsoon region. These observations were analyzed using self-organizing maps (SOMs) to group nine different prestorm monsoon rainfall patterns into different transition states like active, active-to-break, break-to-active, break, etc. The analysis indicates that MLPS are four times more likely to form on a day during active monsoon state compared to break state. Analysis of MLPSs linked to each monsoon state represented by SOM nodes shows that MDs with higher inland penetration were associated with higher antecedent rainfall. On the other hand, there was no significant difference in low-level atmospheric circulation for MDs with shortest and longest inland penetration. [ABSTRACT FROM AUTHOR]

The late spring/early summer flooding that occurred in the American Midwest between May and June 2008 resulted from a combination of large-scale atmospheric circulation patterns that supported a steady influx of moisture into the area. A low pressure system centered over the central-western United States steered a strong jet and associated storms along its eastern edge from the west to southwest and an anomalously strong Great Plains Low Level Jet brought continuous warm and moist air into the area from the Gulf of Mexico into the area. We examine and quantify here the impact these circulation patterns had on the hydroclimatology of the Midwest highlighting the magnitude, frequency, geographic distribution, and temporal evolution of precipitation that ultimately magnified the flooding. Historical precipitation records were used to assess the regional rainfall characteristics at various geographic and time scales. Five distinct hydroclimatic characteristics contributed to the definition of the 2008 flood including persistent high surface soil moisture conditions prior to flooding exasperated by anomalously high rainfall, extreme rainfall totals covering extensive areas, increased frequency of shorter-term, smaller-magnitude events, persistent multiday heavy precipitation events, and extreme flood-producing rain storms. The major flooding lasted for approximately 24 days and most greatly impacted the state of Iowa, southern Wisconsin, and central Indiana. Its occurrence during the May-June period makes the event especially unusual for this region. [ABSTRACT FROM AUTHOR]

The article presents analysis on the relationships between the atmospheric circulation and the soil moisture availability atmospheric in Central Europe. The results reveal that the big scale droughts during spring months (MAM) were related with south, (S), east (E) and the south-east (SE) Grosswettertypen (GWT), the Central Europe high pressure systems (HM) and E GWT were contributive to drought. Statistically important drying trends were marked at a majority of the stations, particularly during MAM and JJA over the entire period for which the self-calibrated Palmer Z-index (scZ-index) and Palmer Drought Severity index (scPDSI).

Examines the interaction of large scale soil moisture anomalies and the atmospheric circulation. Anomalies of soil moisture; Nonlinear processes in the land-atmosphere system and the complex roles played by convection, cloud, circulation regimes, thermal conditions and horizontal moisture transports; Asymmetry in the transient response of the climate system.