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Stable oxygen isotopes records (δ18O) in tree-rings are commonly used to assess the response of trees to environmental variability being a valuable tool for studying past climate at different temporal and spatial scales. This is particularly relevant in semi-arid regions like the southern Tropical Andes, where ongoing environmental changes coincide with a rapidly increasing demand for hydrological resources, presenting a challenge for ecosystem dynamics and water resource management. In this study, we aim to determine the main spatio-temporal variability of a new network of δ18O Polylepis tarapacana chronologies during the last century, and their relationships with hydroclimate and tropical circulation at local to subcontinental scales throughout the Tropical Andes. For this purpose, we develop six δ18O P. tarapacana tree-ring chronologies across a 450 km latitudinal moisture gradient in the southern Tropical Andes adjacent to the Atacama Desert, covering the period 1900–2007. Results show a clear latitudinal gradient in the δ18O values across the network and significant relationships are observed with other δ18O tree-ring chronologies in Tropical South America, demonstrating clear regional climate influences at a subcontinental scale. A principal component analysis of the δ18O tree-ring chronologies demonstrate a strong regional environmental signal contained in the network, exhibiting a main temporal pattern (PC1 δ18O) that explains 63% of the total variance during the period 1900–2007. Comparisons between PC1 δ18O and environmental variables showed significant negative relationships with precipitation and soil moisture, and positive relationships with temperature and vapor pressure deficit (VPD) during summer when the South American monsoon occurs. The main δ18O tree-ring network signal clearly records tropical atmospheric and circulation patterns across South America. The easterly wind flux conditions from the Amazon basin favor lower δ18O values, and the PC1 δ18O exhibit significant positive correlations with VPD across the entire Tropical Andes and the northern portion of the Amazon basin, and as well as outgoing longwave radiation across the southern Tropical Andes and part of the Amazon basin. The close relationships between the regional signals from our δ18O tree-ring network with the previously mentioned parameters, highlight the potential to develop future hydroclimatic-related reconstructions with these δ18O records to assess climate variability and change across the Tropical Andes. • A δ18O Polylepis tarapacana tree-ring network is developed in the Southern Tropical Andes. • The δ18O chronologies highlight a strong common signal. • Hydroclimate variability controls δ18O P. tarapacana content across our network. • Tropical atmospheric and circulation patterns show a close relation with δ18O tree-rings. [ABSTRACT FROM AUTHOR]

In the springs of 2021 and 2023, northern East Asia experienced intense dust activities resulting in significant environmental and ecological impacts. This study explores the climate factors responsible for these strong dust activities in both springs. Results show that the anomalous surface warming during the late winter and early spring and the anomalous dry surface soil moisture in the spring are the underlying surface factors contributing to the occurrence of intense dust activities in these two years. Furthermore, we find that the anomalous wave patterns over the Eurasian continent are dynamic factors driving the initiation of dust activities in these two springs. The intensified north-south pressure gradient in Gobi Desert (GD) associated with the wave patterns significantly increases near-surface wind speeds, favoring the occurrence of dust activities. The sea surface temperature (SST) anomalies in the North Atlantic and tropical eastern Pacific can significantly influence the wind speed anomalies in northern East Asia, thereby impacting dust activities. In 2021, the increase in wind speed in the GD was influenced by both the warm SST anomalies in the North Atlantic and the cold SST anomalies in the tropical eastern Pacific. Nevertheless, in 2023, the predominant influence came from the exceptionally strong warming in the North Atlantic, offsetting the opposing effect of warm SST anomalies in the tropical eastern Pacific. Sensitivity experiments confirm the important role of the SST anomalies in the North Atlantic and tropical eastern Pacific on the dust activities in GD. These findings play an insight into understanding of the mechanisms behind the recent variations in dust activities in northern East Asia. • Surface warming and drier soils are the surface factors responsible for the intense dust activities in 2021 and 2023. • SST anomalies in the North Atlantic and tropical Pacific can influence the wind speed in Gobi Desert (GD), thereby impacting dust activities. • Sensitivity experiments confirm the important role of the SST anomalies in the key regions on the dust activities in GD. [ABSTRACT FROM AUTHOR]

• Precipitation seasonality determines the main types of evapotranspiration coupling. • Hydrological memory influences evapotranspiration in some regions of the basin. • Water feedback increases with distance from the Atlantic Ocean. The hydrological cycle of the Amazon Basin is characterized by a multitude of interactions between the atmosphere and surface processes, involving several temporal and spatial scales. Evapotranspiration is a key variable in the water and energy balance, particularly in this watershed that is home to the world largest rainforest. This study analyzed evapotranspiration in the Amazon Basin using the concepts of Coupling (one way relationship between two variables), Memory (temporal permanence of a state or anomaly in the behavior of one variable) and Feedback (two way relationships between two variables), during a 62-year period (12/1959–11/2021). This study found that the seasonality of precipitation, mainly due to the South American Monsoon, determines when evapotranspiration is mainly driven by (or coupled with) net radiation at the surface or soil moisture. Moreover, in the regions where seasonality of precipitation is strong, the previous hydroclimatic conditions due to hydrological memory (reaching just over 90 days in shallow soils) influences the evapotranspiration during the relatively dry season. Regarding water feedback, this study found that the dependence of seasonal precipitation of the Amazon Basin from their hydrobiological processes (fraction of precipitation recycled by Amazonian evapotranspiration) increases with the distance from the Atlantic Ocean, mainly during the non-monsoonal circulation. This process is particularly remarkable in the Amazon-Andes transition zone. However, the spatial pattern and height of water recycled in this watershed is mainly determined by the dominant circulation pattern of atmospheric fluxes in each season. [Display omitted] [ABSTRACT FROM AUTHOR]

• Most of the Euro-Mediterranean region affected by drought conditions during 2021/22. • Recursive high-pressure systems & a poleward jet shift explain rainfall deficits. • Most severe drought since at least 1891 when considering evaporative demand (AED) • Enhanced AED caused unprecedented low soil moisture & runoff since at least 1965. • Potential worst-case droughts if historic rainfall deficits occur with current AED. The Euro-Mediterranean region experienced a remarkable drought during the hydrological year 2021/22. Substantial and widespread impacts on water supply systems, agricultural crops, and the production of hydroelectric power were observed. This assessment characterises the drought from a long-term perspective using a multi-index approach and analyses the associated atmospheric circulation at the annual and monthly time scales. The main dynamical forcing of the drought was the unusual recurrence of high-pressure systems over western Europe, at least partly due to an anomalous southward shift in blocking activity and a remarkable occurrence of low-latitude blocks. This led to record-breaking positive geopotential height anomalies over western Europe and a poleward displacement of the North Atlantic eddy-driven jet. Although most of the region was affected by mild drought conditions, the 2021/22 event was not unprecedented in terms of precipitation deficits since other periods of the 20th century (e.g., in the 1920s, 1940s and 1970s) displayed moderate and severe drought conditions over larger areas. However, the 2021/22 drought has been the most intense since at least 1891 because of high atmospheric evaporative demand (AED) values associated with extreme temperatures, especially during the summer of 2022. This enhanced AED also contributed to depleting soil moisture and reducing runoff generation, leading to unprecedented deficits since at least 1965. Finally, we find important differences in the 2021/22 event as compared to other major historical droughts over the Euro-Mediterranean region. In particular, the contrasting effect of AED evidences its increasing role over the last decades and warns about the current risk of experiencing unprecedented droughts. [ABSTRACT FROM AUTHOR]

• The vegetation drought was alleviating during 1982–2020 across China. • Spring drought and summer drought were more likely to occur in South China. • NPI-NAO-AO had the most significant impact on vegetation drought. • Soil moisture was the primary driving factor of vegetation drought. Vegetation drought can reduce the net ecosystem productivity, resulting in disturbances to the sustainable development of humans and nature. In this study, Vegetation Health Index (VHI) was used to identify vegetation drought. The spatial and temporal evolution of vegetation drought was characterized using the Pixel-based Trend Identification Method (PTIM) in China from 1982 to 2020. Moreover, multiple cross-wavelet techniques were used for revealing the correlations between atmospheric circulation factors and their combinations with vegetation drought. The results indicates that: (1) there is a decreasing trend of vegetation drought in China during the study period, while it will show an increasing trend in the future; (2) the South China is prone to spring drought and summer drought, and the Sichuan Basin is prone to autumn drought and winter drought; (3) in spring, the most obvious trend of vegetation drought mitigation appears; (4) a combination of atmospheric circulation factors, North Pacific Index (NPI)-North Atlantic Oscillation (NAO)-Arctic Oscillation (AO), has the most significant impact on vegetation drought across China. [ABSTRACT FROM AUTHOR]

In recent years, studies have found that drought can occur rapidly under anomalous atmospheric circulation patterns and underlying surface conditions. This type of drought is defined as "flash drought". It is more sensitive to global warming compared to traditional drought and may become a common drought phenomenon in the future and require intensive research. But the characteristics and development mechanism of flash drought in northern China has been studied much less than in southern China, and thus deserve further study. Based on the daily station data and GLDAS grid data from 1978 to 2020, this paper identified the flash drought in northern China, analyzed its evolution of temporal-spatial characteristics and explored the meteorological driving factors of flash drought. The main results are as follows: (1)The frequency of flash drought in the year is the highest in WNW (West of Northwest), followed by ENW (East of Northwest), NC (North China) and NE (Northeast China), while the frequency in the plant growing season is the highest in the south of NE and the south of NC, and low in the other regions. (2)The hotspot areas of flash drought showed an obvious eastward trend from WNW to ENW in northern China from the 1980s to 2010s. (3) There is a good relationship between soil moisture and precipitation in WNW and ENW, while the soil moisture is affected by both temperature and precipitation in NC and NE. (4) Flash drought could occur all through the year in WNW and NC, while it mainly occurred in the summer half-year and summer in EWN and NE. The main high occurrence period of flash drought in each region is in late spring and early summer, while a second high occurrence period appears from early September to late October in WNW. (5) From the perspective of the driving of water vapor changes, the flash drought in WNW and ENW is mainly driven by water vapor advection, while that in NC and NE is mainly driven by wind field divergence. • The hotspot areas of flash drought showed an obvious eastward movement from WNW to ENW in northern China. • The main high occurrence period is around early May to early July in northern China, with a second one in WNW. • Flash drought in WNW and ENW (NC and NE) is mainly driven by water vapor advection (wind field divergence). [ABSTRACT FROM AUTHOR]

The Tibetan Plateau and the Himalayas influence monsoonal circulation patterns and represent the water towers of humanity. Modern coupling of atmospheric circulation and the hydrological cycle over and on the plateau can be observed and delineated, and the factors that control lake levels can be identified. Recent monitoring of lakes has shown that many have grown for decades due to higher meltwater inflow or stronger rainfall from different sources, depending on the location. The long-term dynamics of lakes, however, can be best described by using high-resolution climate archives. We focus here on the often controversial discussion of Holocene lake development and use the Bangong Co drainage basin on the western Tibetan Plateau as a case study. We aim to identify the factors that influence lake level, such as monsoonal or convective precipitation and meltwater. To accomplish this, shells of the aquatic gastropod genus Radix were collected from an early Middle Holocene sediment sequence in the Nama Chu subcatchment of the eastern Bangong Co, and sclerochronlogical isotope patterns for five shells were obtained at a weekly to submonthly resolution. Our data suggest that at ca. 7.5 ka, monsoonal rainfall was higher than it is today. However, summer precipitation was not continuous but occurred as extended moisture pulses. This result implies that the northern boundary of the SW Asian monsoon was similar to that today. We identify convective rainfall events significantly stronger than today and relate these events to higher soil moisture and larger lake surface areas under higher insolation conditions. The regional amount of meltwater corresponds with the westerly derived winter snowfall. Exceptionally heavy δ13C values archived in the shells were likely, at least partly, triggered by biogenic methane production. We suggest that our approach is suitable for studying other lake systems on the Tibetan Plateau from which fossil Radix shells can be obtained. [ABSTRACT FROM AUTHOR]

In this study, the influence of the large-scale circulation patterns on temperature in Europe and Serbia is examined. Among the large-scale circulation patterns in the Northern Hemisphere, less attention has been paid to the impact of the East Atlantic/West Russia pattern (EA/WR). The relationship between the EA/WR pattern and geopotential height at 500 hPa is investigated using reanalysis data from National Centres for Environmental Prediction – National Centre for Atmospheric Research. Temperature anomalies have been explored in relation to strong positive and negative phases of the EA/WR pattern for all months. Analyzing the correlation between the EA/WR index (EA/WRI) and geopotential height at 500 hPa, a centre with negative correlation has been found throughout the year over Russia, north of the Caspian Sea. Positive (negative) temperature anomalies prevailed over Eastern (Western) Europe for the strong negative EA/WR phase (EA/WRI < −1). The temperature anomalies associated with the strong positive phase of the EA/WR pattern (EA/WRI > 1) reflect below-average temperatures over Eastern Europe. In addition, we explored the combined effects of positive and negative phases of the North Atlantic Oscillation (NAO) or East Atlantic (EA) pattern with the EA/WR pattern on temperature variations in Europe and Serbia. We find that the effect of the EA/WR pattern on temperature changes is dependent of the EA phase but not of the NAO phase over Serbia. When the EA/WRI is negative and EA pattern or NAO are in positive phase, the positive temperature anomalies prevailed over most of Europe, including Serbia. The highest values of temperature anomalies exist over Serbia for EA/WRI < −1 and EA index > 1. It is found that this case appears more frequently in the last 20 years, contributing to the warming in Europe and Serbia. [ABSTRACT FROM AUTHOR]

Highlights • The dependence between flow and hydroclimatic factors in Baden-Württemberg is modeled. • The probabilities of droughts and floods under various hydroclimatic scenarios is examined. • The links between flow variability and atmospheric circulation are explored. Abstract This study presents an investigation of probabilistic relationships between streamflow and hydroclimatic variables (including precipitation, temperature and soil moisture) and the potential links to large-scale atmospheric circulation over Baden-Württemberg, Southwest Germany. First, the joint dependence between seasonal streamflow and hydroclimatic variables was established by using copulas. On the basis of the joint dependence structure, we estimated the probabilities of hydrological droughts and prolonged high-streamflow events conditioned upon two different scenarios (high and low) of hydroclimatic variables for various seasons over the study area. The results indicate that both precipitation and soil moisture are positively related to the streamflow variation in Baden-Württemberg for each season and strongly impact the likelihoods of hydrological droughts and high-streamflow events. Temperature tends to have less impact on the streamflow variation, and an inverse connection between streamflow and temperature is found in spring and summer. Then, the connections between streamflow variability and large-scale atmospheric circulation in summer and winter were explored by using composite analysis. Although the atmospheric circulation patterns vary in each season, it can be found that in summer high streamflow anomalies over Baden-Württemberg are related to a cyclonic activity over central Europe while low streamflow anomalies are linked to anticyclonic patterns over western Ireland. The high streamflow anomalies in winter are strongly impacted by the westerlies that play an important role in favoring warm and moist airstreams from the Atlantic Ocean towards the study area, while an opposite atmospheric pattern is found for the years with low streamflow anomalies. The presented probabilistic methodology could also be applied in other regions worldwide. [ABSTRACT FROM AUTHOR]

• The path analysis method is proposed to explain the interplay of drivers in soil moisture drought. • Precipitation deficits dominates the interannual variation of soil moisture drought while potential evapotranspiration impacts are magnified by drought deterioration. • Atmospheric movement and temperate indirectly affects soil moisture drought through precipitation and potential evapotranspiration. • Proportion of drought explanation decreased with increasing soil depth. Soil moisture drought, as one of the most important drought categories, is determined by both water supply (e.g., precipitation) and demand (e.g., potential evapotranspiration). To shed light on the underlying mechanisms driving soil moisture drought, the statistical multiple linear regression, machine learning, and modeling experiments methods have been pervasively used in early studies. However, these methods neglect the collinearity and interactions of climate variables, and thus cannot reflect the direct and indirect interaction of factors leading to soil moisture drought. To reveal the synergistic effects of water supply and demand on soil moisture drought, this study quantified the contributions of key drivers to the change of soil moisture drought by a path analysis method to exhibit the relationships between atmospheric movement state and soil moisture drought. Prior to applying the systematic path analysis model, we identified the spatial patterns of soil moisture droughts at different depths by using a state-of-art three-dimensional drought recognition method in China. Our results showed that precipitation deficits dominated the interannual variation of soil moisture drought while increasing potential evapotranspiration only had marginal intensification in drought. The response of soil moisture drought to potential evapotranspiration was magnified by drought deterioration, especially in basically severe drought conditions. The total column water vapor and the horizontal divergence of the vapor flux, as well as temperature, directly affected precipitation and potential evapotranspiration and led to soil moisture drought through various direct and indirect processes. This study highlighted that the interactions among precipitation, potential evapotranspiration, and atmospheric vapor movement state in space and time were important for understanding the drought development mechanisms. [ABSTRACT FROM AUTHOR]

This paper examines the local and non-local climatic effects of wetter arid areas of Northwestern China (ANWC) in summer using a fully coupled climate model. In response to soil moisture increase, the local air temperature significantly decreases, and precipitation increases in summer. The wetter ANWC results in a warmer and rainless climate over the Central part of North China Plain (CNCP). While the influence of increasing soil moisture on the Tibetan Plateau (TP) precipitation is negligible due to the high altitude. A cooler climate over ANWC leads to an abnormal descending motion occurring. Meanwhile, an anomalous high pressure and an abnormal anticyclonic circulation occurs in 500 hPa over the west of ANWC. Correspondingly, a huge anomalous cyclone circulation occurs over the northeastern part of China and Mongolia, which can hinder the northward movement of the East Asian summer Monsoon (EASM) and reduce the water vapor transport into Central China Plain. As a result, the weakened EASM thus leads to rainless over CNCP. As soil moisture increases over ANWC is stronger, the magnitudes of the influence on the atmospheric field become larger. This study highlights the wetter ANWC effect on local climate and provides more information about the mechanism of wetter ANWC remote effect on non-local climate. • This paper examines the local and non-local climatic effects of wetter arid areas of Northwestern China (ANWC) in summer using a fully coupled climate model. • It finds that the wetter ANWC can result in a warmer and rainless climate over the Central part of North China Plain (CNCP) through a complex atmospheric circulation response. • A cooler climate leads to an abnormal descending motion occurring over ANWC. • A huge anomalous cyclone circulation over the northeastern part of China and Mongolia can block the East Asian summer Monsoon northward and decrease the water vapor transport into Central China Plain. • This study highlights the wetter ANWC effect on local climate and provides more information about the mechanism of wetter ANWC remote effect on non-local climate. [ABSTRACT FROM AUTHOR]

Understanding the reasons for past changes in soil moisture conditions is key to improving forecasts of this extremely important variable coupling land and atmosphere. To contribute to this understanding, we analyzed the variability of soil moisture and its relationship to regional climate features. In this study we focused on the Poyang Lake basin, which is located on the southern bank of the Yangtze River at the junction of its middle and lower reaches in Jiangxi Province. Using in situ soil moisture observations from Nankang and Hukou stations for the period from 1998 to 2012, we tested the regional applicability of the high-resolution long-term Essential Climate Variable (ECV) soil moisture (SM) dataset (1978–2013) by means of trend and correlation analyses. We only used the ECV SM product here that is based on passive microwave technology. Both observed and ECV SM data show the same variations on monthly and inter-annual time scales including identical trend direction and strong correlations. To investigate the relationship between soil moisture conditions in the Poyang Lake basin and the Western Pacific Subtropical High (WPSH), correlation coefficients were calculated between the ECV SM data, the strength index ( I S ), and the northern limit index ( I N ) of the WPSH. The I S of the last autumn and winter shows a strong positive correlation with soil moisture during the subsequent rainy season. A strong WPSH in the preceding autumn and winter could result in more humid climate conditions in the Poyang lake basin during the following rainy season. The I N shows a strong negative correlation with concurrent soil moisture from July to September. The further the WPSH extends towards the north, the drier the area. [ABSTRACT FROM AUTHOR]

The present study investigates the characteristics and factors of the variability of summer precipitation over the Tibetan Plateau (TP). It is found that interannual variations of summer precipitation tend to be opposite over the eastern and western TP, manifesting an east-west TP precipitation dipole pattern (TPPD). The summer TPPD is significantly correlated with the spring sea surface temperature (SST) in the tropical Indian Ocean, and the latter can be considered an important precursor for the former. The impacts of spring SST in the tropical Indian Ocean on summer TPPD are through oceanic and land relay effects. For the oceanic relay effect, the positive SST anomaly (SSTA) in the tropical Indian Ocean persists from spring to summer and induces the upper-tropospheric positive geopotential height anomaly and anomalous anticyclone to the south of the TP by stimulating a Rossby wave response. Winter El Niño and Indian Ocean Dipole (IOD) contribute to the persistence of the SSTA in the Indian Ocean from spring to summer through modulating a spring asymmetric mode in the Indian Ocean. The SSTAs in the Indian Ocean affect the western North Pacific anticyclone at lower troposphere through modulating the Indo-Western Pacific Ocean capacitor (IPOC) mode. These circulation anomalies adjust the variability of the summer TPPD. For the land relay effect, the SSTA in the tropical Indian Ocean induces the soil moisture (SM) anomaly in the Turan Plain through modulating atmospheric circulation around the Arabian Peninsula and the Mediterranean Sea during spring. The SM anomaly in the Turan Plain is maintained from spring to summer and induces the upper-tropospheric negative geopotential height anomaly and anomalous cyclone north of the TP during summer by stimulating an anomalous vertical motion. Through the above oceanic and land processes, a north-south opposite pattern of geopotential height anomalies around the TP appears and eventually modulates water vapor transport into the TP and hence the formation of the TPPD during summer. Further analyses reveal that the impact of the winter El Niño and IOD and spring tropical Indian Ocean SST on the summer TPPD becomes weaker when one of the abovementioned relay effects is absent. • An east-west TP precipitation dipole pattern (TPPD) during summer was revealed. • Spring tropical Indian Ocean SST can affect summer TPPD through two relay effects. • Physical process linking spring SSTA in the Indian Ocean and summer TPPD was found. [ABSTRACT FROM AUTHOR]

Highlights: [•] Identification of circulation patterns promoting dry conditions is possible. [•] Spatial differences can be explained with topography-induced phenomena. [•] No direct information about droughts from analyzing CP frequency changes. [ABSTRACT FROM AUTHOR]

This study investigates precursory signals of the June precipitation over the southern Yangtze River valley (SYRV). It is found that the synergistic anomalies of the Turan Plain soil moisture and northern Iranian Plain snow cover (TPSM-IPSC) during April can modulate the June SYRV precipitation. Through the persistence/memory effect of soil moisture anomalies, lower soil moisture around the Turan Plain-Iranian Plain region can maintain from April to June. Because of drier soil (i.e., lower soil moisture), higher surface air temperature (SAT) appears over the Turan Plain during June. The higher SAT anomaly stimulates anomalous upward motion and associated overlying and downstream atmospheric circulation anomalies through modulating the downstream dispersion of Rossby wave energy. As a part of these atmospheric circulation anomalies, the blocking-like anomaly to the west of the Okhotsk Sea facilitates more June precipitation over the SYRV. Additionally, June SYRV precipitation is significantly correlated with sea surface temperature (SST) anomalies in the tropical eastern Pacific (TEP) during the preceding winter. The TPSM-IPSC can compensate for the defect of prediction using the TEP SST (i.e., ENSO) signal in recent years since the former (latter) shows a strengthened (weakened) relationship with SYRV precipitation recently. Considering jointly the traditional pacific SST and new TPSM-IPSC precursors, we establish a physics-based statistical prediction model, which shows a good skill in predicting June SYRV precipitation. • Precursory signals of the June southern Yangtze River valley precipitation was found. • Physical process linking April TPSM-IPSC and June SYRV precipitation was revealed. • A physics-based statistical prediction model was established. [ABSTRACT FROM AUTHOR]

Abstract: In the Iberian Peninsula the raise of temperatures has been notable from mid-1970s to mid-2000s, especially in spring and summer. This study analyses spatial and temporal relationships between extreme temperatures and atmospheric circulation types (CTs) defined over the Iberian Peninsula (IP) in these seasons. Station series (29) of maximum and minimum temperature are considered, starting from 1905 until 2006. The CTs (9 for spring and 8 for summer) are derived by a cluster method applied to daily mean SLP grids covering the period 1850–2003. Changes in the seasonal frequency of extreme temperatures and of CTs are analysed. Subsequently, the CTs are examined for their effectiveness in leading to moderately extreme temperatures (at each location) using an index that measures the contribution to extreme days with respect to the contribution to non-extreme days. Correlation between regional extreme series and CTs frequency is also tested. In spring, the decrease in cold nights, which is notable in the 1970s onwards, can be partially attributable to a downtrend in the frequency of Northerly flow. High frequency of Anticyclone in North Iberia in the 1980s and 1990s has contributed to an increase in warm days in West and North stations. To the SE quadrant of the IP, a great part of warm days is related to south-westerly flow, (both) presenting a higher frequency in the 1950s and the 1960s. In summer warm nights increased remarkably to the SE and SW, and may be in part related to uptrends in Iberian thermal low pattern (1950–2003) and North Atlantic Anticyclone (1850–2003) respectively. Warm days have increased remarkably to the NE especially in the 1990s and 2000s, but this is not found to be related to changes in CTs' frequency. Furthermore, the existence of within type changes (variations in Tmax, Tmin and extreme indices within the CTs) points to the identification of other physical factors operating on inter-annual to multidecadal time scales. Thus, the consideration of Sea Surface Temperature (SST) of the East Atlantic Ocean and Iberian soil moisture conditions (by means of a drought index) helps to explain the evolution of extreme temperatures. [Copyright &y& Elsevier]

Abstract: Concern and debate about the condition of quaking aspen in the intermountain West of North America have led to many studies examining aspen recruitment at local to landscape scales. Patterns of aspen mortality and recruitment may reflect local conditions, or may show broad synchrony if regional-scale drivers are important. This paper aggregates historical aspen establishment data from 12 case studies from nine locations in a meta-analysis of emergent patterns of aspen dynamics at sub-continental or mesoscales (104–106 km2). Aspen establishment data were reported in multiple forms among studies, so the meta-analysis included two approaches (1) a quantitative analysis of percent aspen establishment in decadal time bins for 1820–1999 for six studies that reported data in a format suited for this approach and (2) a qualitative ranking of 19th and 20th century peaks in aspen establishment for all 12 studies. Aspen forests ranging from Wyoming to northern Arizona experienced two peaks in establishment between 1820 and the 1980s. The first peak began in the 1860s, reached its maximum in the 1880s, and gradually declined to an end the 1910s. The second peak began abruptly in the 1970s and continued through the 1980s. I speculate that the late-1800s peak in aspen recruitment was driven primarily by the occurrence of the last historical fires throughout the intermountain West and that the 1970s and 1980s peak was driven by improved moisture conditions brought about by a shift to a positive phase of the Pacific Decadal Oscillation and a persistent negative phase of the Atlantic Multidecadal Oscillation. The overarching implication of large-scale synchrony in aspen dynamics is that current aspen ecosystem condition is not solely the result of local-scale histories of browsing or fire, but is more likely the interwoven legacy of these local factors combined with broad factors such as climate and Euro-American settlement. [Copyright &y& Elsevier]

Abstract: Upper Permian and Lower Triassic palaeosols from northeastern Tethyan localities exposed within the Bogda Mountains, NW China, provide a wealth of information regarding long-term palaeoclimatic and palaeoenvironmental variations. Wuchiapingian palaeosols are characterized by intense redoximorphy, accumulation of vascular plant matter, accumulation of clay minerals and Fe-oxides, slickensides, and clastic dikes, suggesting a soil moisture regime that ranged from perennially wet to distinctly seasonal in soil moisture budget. Changsinghian to early Induan palaeosols include subsurface accumulations of clay and carbonate as well as surficial accumulations of organic matter, indicative of sub-humid to sub-arid soil moisture and variable soil moisture regimes. Induan to Olenekian palaeosols contain pedogenic CaCO3 accumulations and gypsum pseudomorphs, indicating a drier environment characterized by net soil moisture deficiency. Elemental composition of palaeosol matrix was used to estimate palaeoprecipitation through the chemical index of alteration minus Potassium (CIA-K) proxy. Estimates from various Wuchiapingian strata indicate relatively stable palaeoprecipitation. During the late Changsinghian and early Induan, palaeoprecipitation appears to have decreased from 1100 to 230 (±180)mm/year over less than 100m of vertical stratigraphic section. In the Induan and Olenekian, palaeoprecipitation appears much less stable than in Wuchiapingian, with values vacillating from 290 to 1014mm/year. The transition to a relatively unstable precipitation state coincides generally with the Permian–Triassic boundary, and may reflect climatic disturbances associated with the end-Permian extinction event in addition to altered atmospheric circulation patterns resulting from regional tectonics, moisture availability, and expansion of the subtropical high pressure belt. [Copyright &y& Elsevier]

Summary: The aim of this paper is to analyse the differences in the long-term regimes of extreme precipitation and floods across the Alpine–Carpathian range using seasonality indices and atmospheric circulation patterns to understand the main flood-producing processes. This is supported by cluster analyses to identify areas of similar flood processes, both in terms of precipitation forcing and catchment processes. The results allow to isolate regions of similar flood generation processes including southerly versus westerly circulation patterns, effects of soil moisture seasonality due to evaporation and effects of soil moisture seasonality due to snow melt. In many regions of the Alpine–Carpathian range, there is a distinct shift in flood generating processes with flood magnitude as evidenced by a shift from summer to autumn floods. It is argued that the synoptic approach proposed here is valuable in both flood analysis and flood estimation. [ABSTRACT FROM AUTHOR]

• Soil moisture-temperature coupling is stronger over the monsoon dominated regions of north-central India (NCI). • Significant increase of temperature extremes over NCI is dominantly influenced by soil moisture drying. • Decrease of evapotranspiration and soil moisture memory is conducive for drying of soil moisture. Soil moisture (SM) and near-surface temperature variations are known to be linked through land–atmosphere interactions. While previous investigators have examined the association between temperature extremes and large-scale atmospheric circulation variability, the role of land–atmosphere coupling on temperature extremes over the monsoon-dominated region of India is not well understood. This study presents an analysis of hydro-meteorological datasets for the 67-year period (1948–2014) to assess the impact of long-term soil moisture changes on temperature extremes over the Indian region. Firstly, our findings show that the hot-spot of land–atmosphere coupling located across north-central India (NCI) is a region where SM variations can significantly influence temperature extremes. We further note that the NCI region experienced a significant declining trend in SM (about 1.1 mm/decade) during 1948–2014, in association with the decreasing trend of monsoon precipitation. Our findings suggest that the long-term decrease of SM over the NCI has favored increased incidence of temperature extremes through strengthening (weakening) of sensible (latent) heat fluxes; while the loss of soil moisture memory has additionally promoted increased variability of temperature extremes. The frequency, duration and variability of extreme temperatures are found to increase significantly by 1–2 occurrences, 5–6 days and 43%, respectively, in association with a decrease of 10 mm SM over NCI. The Generalized Extreme Value (GEV) distributions are fitted to extreme temperature duration (ExTD) using SM as a covariate to quantify the role of SM on temperature extremes over NCI. GEV analysis reveals that drier SM conditions (10th percentile) lead to an increase in the 67-year return value of ExTD by 9–10 days, relative to wet SM conditions (90th percentile) over NCI. Furthermore, it is interesting to note that the rise in temperature extremes over NCI in the recent three decades has been more prominent during the monsoon and post-monsoon seasons as compared to the pre-monsoon months. [ABSTRACT FROM AUTHOR]

This study assesses the impact of an improved soil moisture (SM) initialization using direct insertion methodology for convection-resolving modelling of heavy precipitation events (HPEs). State-of-the-art 1 km SM data from the Soil Moisture and Ocean Salinity (SMOS) mission, SMOS-BEC L4 version 3 are used for this purpose. A strategy is developed to prepare the SMOS-L4 surface soil moisture (SSM) product for the COnsortium for Small-scale MOdelling (COSMO) model initialization by applying a cumulative density function (CDF)-matching bias-correction and the exponential filter method to calculate corresponding SM profiles (L4-Expo). The processed satellite-derived product is validated with 38 observing sites from three in-situ SM networks REMEDHUS (19), SMOSMANIA (11) and VAS (8). All networks measure at a soil depth of 5 cm, only at the SMOSMANIA network additional measurements at 10, 20 and 30 cm are available. Four HPEs are selected to evaluate the impact of the high-resolution realistic initialization. The results show a high agreement index (AI = 0.91) and a low root-mean-square deviation (0.03 m3/m3) of the high-resolution, bias-corrected SMOS-L4 SSM product compared to in-situ observations. Moreover, the derived L4-Expo SM profile field agrees with ground-based observations and successfully removes the wet bias of the original COSMO simulated SM profile. Enhanced SM initialization with the SMOS-L4 SM derived profiles improves precipitation modelling in all selected HPEs as a consequence of improved near-surface 2 m-temperature and induced changes in the pressure field (−0.5 hPa), atmospheric humidity distribution (dqs = 5–15%) as well as wind circulations (dw 700 hPa = 25%), thus convergence/divergence fields. The sensitivity study, applying the same methodology for SM initialization for a SMOS-L3 (~25 km), shows a weaker improvement of the precipitation forecast of an analysed HPE than the 1 km SMOS-L4 product. Our results highlight the benefit of high-resolution SSM remote sensing satellite data for scientific disciplines like meteorology in overcoming present limitations such as the uncertainty associated to SM initialization in models. • Novel methodology for model initialization with state-of-the-art soil moisture data • Improvement of heavy precipitation forecasts with 1 km SMOS-L4 soil initialization • Optimal time for SMOS-L4 initialization is 3 days before precipitation initiation. • Improved understanding of soil-atmosphere feedbacks and related processes [ABSTRACT FROM AUTHOR]

The southeast Qaidam Basin (SQB) lies near the boundary between the modern-day Asian summer monsoon (ASM) and mid-latitude westerly jet, and the paleoclimate variation in this region can be affected by these two atmospheric circulation systems. Reconstructions of paleotemperature and palaeohydrology are therefore critical to constraining the driving forces of climate in this region, where the ecological environment is fragile. Here, we analyzed glycerol dialkyl glycerol tetraethers (GDGTs), microbial membrane lipids occurring ubiquitously in aquatic and terrestrial environments across the globe, in an aeolian sediment profile over the last 7000 years from Xiangride Town (XRD) of southeast Qaidam Basin (SQB), China. The temperature record was generated using the global calibration of MAT mr based on branched GDGTs (brGDGTs), whereas the palaeohydrological condition was reconstructed from the relative abundance of isoprenoid GDGTs vs. brGDGTs (R i/b), the cyclisation index of brGDGTs (CBT), and the brGDGT-based pH indices. The results show that the paleoclimate during the mid-Holocene was relatively warmer and wetter in the SQB. Afterwards it was a trend to a cold and dry climate. Temperature variation was highly coupled with the moisture change during the mid- to late Holocene, as opposed to some previous studies showing a warm-dry and cold-wet climate pattern in the northern Qaidam basin. The palaeohydrological evolution agrees with the precipitation pattern of the Chinese loess plateau but opposes to that in Northeastern China, the middle reaches of Yangtze river and Arid Central Asia (ACA), implying that the ASM strength is the driving force of precipitation evolution during the mid- to late Holocene in the SQB and the spatial heterogeneity of the mid- to late Holocene precipitation pattern across China is remarkable. A rapid cold and drought event at around 4 ka before present (BP) was identified, which might be a key factor that caused the decline in the agricultural civilization during the late Neolithic Age in northwestern China. • Paleotemperature and moisture in Southeast Qaidam Basin (SQB) were reconstructed by GDGT-based proxies. • A gradual shift from a warm-wet to a cold-dry climate during the mid- to late Holocene was observed in the SQB. • Coupled thermal and moisture evolution imply a dominance of Asian Summer Monsoon in the SQB during the mid- to late Holocene. • A boundary between Asian Summer Monsoon and Westerlies during the mid- to late Holocene was proposed in the Qaidam Basin. • A cold and drought event at ca. 4 ka BP caused the demise of ancient civilization. [ABSTRACT FROM AUTHOR]

• An alternative nonparametric trivariate integrated drought index was proposed. • It is easier to calculate but more reliable in capturing droughts compared with univariate and parametric ones. • The drought in an integrated manner gradually intensified in the WRB. • The non-stationarity of integrated drought series is mainly caused by human activities and sunspots. • Sunspots are the dominant teleconnection factors exerting both direct and indirect effects on drought evolution. Drought index is an important tool for drought research. The development of a reliable and simple integrated drought index is a critical step of current drought monitoring and risk assessments. The Gringorten point position formula was adopted to develop a trivariate standardized drought index (TSDI) based on precipitation (meteorology), runoff (hydrology), and soil moisture (agriculture) information in this study. This index can be used to characterize droughts from an integrated meteorological, hydrological, and agricultural point of view, and explore drought evolution characteristics. The possible driving forces of drought were explored by examining the associations between sunspot activities and large-scale atmospheric circulation anomalies. A typical Loess Plateau watershed, the Wei River Basin (WRB), was selected as a case study. Results showed that: 1) the TSDI is better at characterizing real drought conditions than other traditional single-variable indices; although it is similar to the parametric trivariate drought index based on copula function (Serinaldi and Grimaldi., 2007; Yang et al., 2018), it is much simpler to calculate and more suitable for characterizing drought of different regions; 2) the value of integrated drought index gradually increased in all areas, and its change point occurred in the early 1970s and 1990s mainly due to variations in runoff; 3) the evolution of the integrated drought appeared to be strongly influenced by sunspot activities and abnormal atmospheric circulation factors, where sunspots activities are dominant. This study provides a valuable reference for the development of an integrated drought index, which might be applied to local drought monitoring, preparedness and mitigation. [ABSTRACT FROM AUTHOR]