Eastern Northwest China Research Articles

Spatiotemporal Dynamics of Hot-Dry Winds in Northern China: A Multidimensional Analysis Using Gridded Datasets

Abstract Hot-dry winds (HDWs), characterized by simultaneous high temperature, low humidity, and strong wind speed, represent prevalent agrometeorological hazards in northern China. To date, our comprehension of HDWs has been constrained to regional scales due to the dependence upon in situ meteorological observations and the lack of a universal definition of HDWs. In this study, we leveraged a gridded dataset to elucidate the spatiotemporal dynamics of HDWs in northern China from 1961 to 2022. We also introduced a standardized HDW index (sHDWI) to investigate HDW severity. The results indicated more HDW occurrences in eastern Northwest China (NW) and western Inner Mongolia (IM). While there were declining trends in HDW frequency, extent, and severity on average in northern China from 1961 to 1993, these trends were reversed by an overall increase afterward. Intriguingly, regions spanning from NW to IM exhibited significant upward trends in HDW severity according to sHDWI. The spatial extents of light, moderate, and heavy HDWs consistently decreased in North China (NC), with notable expansions over IM, NW, and Northeast China (NE) from 2001 to 2022. Importantly, the increased frequency, expanded extent, and intensified severity of HDWs, particularly, the heavy ones, underscored the escalation of HDW events in recent decades over the arid IM and hyperarid NW, known for their fragile ecological environment. The findings from this research carry significant implications for agricultural production and water management in northern China influenced by the changing patterns of HDWs in the context of climate change. Significance Statement This study aims to enhance our understanding of the large-scale spatiotemporal dynamics of hot-dry winds (HDWs) in northern China using a 0.25° × 0.25° gridded dataset spanning the period from 1961 to 2022. The adoption of the gridded dataset enables a multidimensional exploration of HDWs, encompassing their frequency, extent, and severity which cannot be fully captured by in situ observations. Meanwhile, to quantify changes in HDW severity, we introduce a standardized HDW index that surpasses existing HDW definitions relying on absolute thresholds or relative percentiles of maximum air temperature, relative humidity, and wind speed. Our results reveal a consistent reversal in HDW frequency, extent, and severity around 1993 in northern China and highlight the intensification of heavy HDWs, particularly in the arid and hyperarid regions within the study area.

Impacts of increasing compound hot-dry events on vegetation under the warming-wetting trend in Northwest China

In the warming world, climate extremes tend to be more frequent and intensive. The exceptional response of ecosystems triggered by extreme events under a warmer and wetter climate in northwest China (NWC) has aroused growing concern. However, understanding the responses of vegetation to climate extremes from a compound perspective remains challenging. In this study, we identify the climate dynamics in NWC during 1971–2020 based on daily meteorological observations, focusing on the changes in compound hot-dry events (CHDEs) during the warmer and wetter period. We further explore the effects of CHDEs on vegetation by examining vegetation anomalies and recovery time using daily gross primary productivity (GPP) data. The results show a clearly warmer and wetter period in NWC during 2000–2020. No signs of a stalled increase in CHDEs are observed during this period, and even the duration of CHDEs in western NWC keeps showing an increasing tendency. Vegetation in eastern NWC, with a lower probability of GPP anomalies, exhibits stronger resistance of ecosystems to CHDEs than in western NWC. In NWC, vegetation typically returns to its normal state in 5.50 days on average, but exhibits greater resilience in the western region, where it takes less recovery time (4.82 days). Vegetation in central region shows the lowest probability of GPP anomalies and relatively long recovery time, likely due to its higher altitudes. Our research underscores the imperative to address the considerable impacts of CHDEs on vegetation growth even as the regional climate tends to be warmer and wetter.

Summertime compound heat wave and drought events in China: interregional and subseasonal characteristics, and the associated driving factors

This study investigates the characteristics of compound heat wave and drought events (CHDEs) across various subregions of China from 1961 to 2022 by utilizing a monthly probability-based index. The results uncover significant interregional and subseasonal variations. The trend analysis of CHDEs reveals statistically significant increases in most regions of China; however, there is no significant trend in the JiangHuai region throughout the entire summer season. The trends across regions exhibited subseasonal differences, especially in the eastern regions (Northeast China, North China, and South China (SC)). Furthermore, the occurrence of severe CHDEs (SCHDEs) in China has significantly increased in both frequency and extent since the 1990s. Southwest China and eastern Northwest China have witnessed the highest frequency of SCHDEs, while SC has remained relatively unaffected compared to other regions. The occurrences of SCHDE demonstrate a higher frequency occurred in June than in July and August, especially in the southern regions. The local driving factors are further explored. The incidence of CHDEs in eastern China is significantly influenced by anticyclonic circulation anomalies, which span from the upper to the lower troposphere. These anomalies are crucial in shaping the dynamic and moisture conditions necessary for CHDE formation. Their specific locations dictate the unique atmospheric conditions that lead to the regional characteristics of CHDEs across eastern China.

Analyzing the Contribution of Moisture Sources to Precipitation Changes Under 1.5/2.0°C Stabilized Warming Scenarios: A Study Over Northwest China

AbstractChanges in precipitation and its causes under future warming scenarios in Northwest China are of great concern. Based on the dynamical downscaling results of the Weather Research and Forecasting model (WRF), this study quantitatively identified the contribution of local evaporation and external moisture transport to future precipitation changes in western and eastern Northwest China (WNWC and ENWC) by calculating the precipitation recycling ratio (PRR). The results showed that the WRF could reasonably reproduce the observed spatial and temporal distribution of precipitation and evaporation during the historical reference period of 1985–2014. Under the 1.5 and 2.0°C stabilized warming scenarios from 2071 to 2100, there is a stronger precipitation growth in WNWC than in ENWC, and the PRR generally increases in WNWC and decreases in ENWC. Further analysis indicates that external moisture transport is the dominant contributor to the increased precipitation in all cases with its contribution exceeding 70%, while the difference of precipitation growth in two sub‐regions arises from the summer moisture transport at the southern boundary as the inflow in WNWC and outflow in ENWC. Compared to the negligible contribution of evaporation in ENWC (less than 7%), evaporation contributes more than 23% to the precipitation increase in WNWC under future warming scenarios, which may be related to the strong land‐atmosphere coupling there. Furthermore, an additional warming of 0.5°C leads to an increase in precipitation for both sub‐regions, which is mainly due to the contribution of external moisture transport.

Effects of global warming on drought onset in China

This study investigated the effects of warming on the drought onset in China using meteorological data and soil moisture data from 1980 to 2020. The variation characteristics of drought onset time and onset speed were analyzed systematically. The differences in drought onset time and onset speed during the period 1995–2020 and the period 1980–1994 were compared, and possible impact factors were analyzed. Results indicated that the spatial distribution of drought onset time decreased with an increase in regional wetness in China. In arid regions, onset time at 73 % of sites was over 35 days, and about 13 % was among 60–90 days. In semi-arid and sub-humid regions, the onset time was 25–40 days, and in humid regions, it was 20–30 days. After 1994, namely the significant temperature rise period, the onset time has remarkably shortened in parts of the southern Northeast, North China, the eastern Northwest, the western Southwest, the middle of Tibet, the lower reaches of the Yangtze River, and the coastal region of South China. The shortening was most obvious in sub-humid regions. The greater the warming magnitude, the wetter the region, the faster the drought onset speed. Drought onset speed (γ) was higher in the southern humid region than that in the northern region, and γ for southern Northeast China, northern North China, and eastern Northwest China was higher than that for the rest of North China. After 1994, drought onset speed was accelerated in most regions, especially in the semi-arid and sub-humid regions with precipitation in the range of 300–600 mm. Under the combined effect of increased evapotranspiration and reduced precipitation, the region has been the hot spot with increased drought speed after obvious warming in China.

Identifying regional patterns of extreme wet events in mainland China

Study RegionThe study region of this research is mainland China. With an improved Otsu method, the study region is clustered into 7 regions based on the spatial characteristics of the precipitation data. Study FocusThis research focuses on the mechanisms and predictions of extreme wet events in mainland China. In this paper, the drivers, regional patterns, and near-future trends of extreme wet events in mainland China are analyzed and discussed. New Hydrological Insights for the RegionThe three major drivers of extreme wet events, identified using principal component analysis (PCA), are the Atlantic Multidecadal Oscillation (AMO), Northern Hemisphere Average Temperature (NH temp), and Pacific Decadal Oscillation (PDO). Increasing trends of extreme wet events are identified in the Northeast China, North China, Southeast China, and Western Northwest China regions. In the Eastern Northwest China region, extreme wet events are decreasing. In the Southwest China region and the Tibetan Plateau region, the frequencies of extreme wet events remain the same. The results show that changes of one standard deviation in the three drivers roughly lead to a 10% increase in extreme wet events in the Northeast, Southeast and Western Northwest regions and a 10% decrease in the Eastern Northwest region.

Impacts of Tibetan Plateau Spring Snowmelt on Spring and Summer Precipitation in Northwest China

Snow on the Tibetan Plateau (TP) is an important signal for the prediction of East Asian climate. In this study, the relationship between the TP spring snowmelt and spring and summer precipitation in Northwest China (NWC) was investigated, along with the possible mechanisms linked to the impacts of snowmelt on precipitation. The results showed that the TP spring snowmelt had significant impacts on spring and summer precipitation in NWC. For example, when there was a large spring snowmelt in the central- eastern TP, the spring and summer precipitation in the Hexi Corridor and southeast NWC was excessive, especially in summer; when there was a large spring snowmelt in the northern TP, the spring and summer precipitation was deficient across the whole of NWC, while a large spring snowmelt in the western TP led to deficient spring and summer precipitation in eastern NWC but excessive precipitation in western NWC. The possible mechanisms for this included the fact that more spring snowmelt over the TP led to higher soil moisture contents, which further resulted in weakened subtropical westerly and enhanced ridge over Xinjiang. By changing the TP thermal forcing, these anomalous atmospheric circulation conditions transported water vapor into NWC, thus creating excessive summer precipitation in that region.

Significant Increases in Wet Nighttime and Daytime–Nighttime Compound Heat Waves in China from 1961 to 2020

Heat waves (HWs) with high humidity are dangerous to human health. However, existing studies on different types of HWs considering the effect of humidity are still limited. This study defines three types of wet summer HWs (that is, wet independent daytime and nighttime HWs and wet daytime-nighttime compound HWs) and investigates their spatial-temporal changes across China during 1961–2020. Results show significant upward trends of wet nighttime and compound HWs in terms of frequency, occurring days, duration, intensity and spatial extent, while changes for wet daytime HWs are weak and insignificant in nearly all sub-regions of China except for southwest and eastern northwest China. Compared with wet compound and daytime HWs, wet nighttime HWs accompanied by more elevated relative humidity exhibit larger growth rates in frequency, occurring days, duration and affected areas. Additionally, most wet nighttime and compound HWs with the longest duration and/or the maximum intensity are found to occur after the mid-1990s, compared to fewer than half for wet daytime HWs. Our findings emphasize the prominent intensifying trends in wet nighttime HWs across China for the last 60 years, and suggest more efforts on exploring humid HWs.

Spatiotemporal variations of precipitation concentration influenced by large-scale climatic factors and potential links to flood-drought events across China 1958–2019

Understanding the irregularity of precipitation variations at both temporal and spatial scales is critical for assessing flood and drought risks. In this study, the statistical characteristics of precipitation variations in eight subregions were detected based on daily precipitation records from 798 meteorological sites during 1958–2019, and Long-term precipitation Concentration Index (LCI), Annual precipitation Concentration Index (ACI) and Seasonal precipitation concentration index (SPCI) values were used to analyse temporal heterogeneity of precipitation concentrations. Results showed that the LCI and ACI values were generally characterized by “high in southwest, low in Tibet, high in summer, and low in winter.” Specifically, ACI presented significant increasing trends in 5 regions (Northeast, North, Tibetan Plateau, Western Northwest, and Eastern Northwest), insignificant increasing trends in 2 regions (Jianghuai and Southwest), and a significant decreasing trend in 1 region (South), indicating the potential of increased drought and flood risks. SPCI exhibited an increasing trend in the spring months in Northeast China (p < 0.01), and significant increasing trends in the Tibetan Plateau and Western Northwest China during autumn months (p < 0.05). Attribution analyses on 11 large-scale climatic factors showed that the El Nino-Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO), and Arctic Oscillation (AO) strongly influenced the precipitation concentration indices with distinct zonal characteristics. ENSO, which is the most significant factor affecting the precipitation concentrations, had the strongest positive effect in South China and coastal areas. Meanwhile, the NAO presented a notable negative influence on the ACI, while the AMO exhibited a positive impact in Northern China. Our work added to the body of evidence that the extreme rainfall events have been significantly increasing in the Tibetan Plateau, Western Northwest China, and Eastern Northwest China (p < 0.05), and that the north-western regions of China have been experiencing significant wetting trends. Furthermore, climate change would potentially lead to more extreme drought-flood events in the future.

Differences in drought evolution as portrayed for China using various evapotranspiration models and drought indices

AbstractDrought, a slow‐growing natural disaster that affects large areas worldwide, has serious social and economic consequences. There is compelling evidence to suggest that drought will be more prevalent in various regions in the future, due to the impact of climate change. Evapotranspiration is an important drought evolution control factor, and various evapotranspiration models show different drought evolution trends. In the study described here, meteorological data from 840 Chinese weather stations, for 1960–2018, were used to estimate potential evapotranspiration (PET), using the Thomthwaite (TH), Hargreaves (HG), Priestley–Taylor (PT), Penman and Penman–Monteith (PM) models. We then compared various drought indices (the standardized precipitation index [SPI], the standardized precipitation evapotranspiration index [SPEI], and the Palmer drought severity index [PDSI]), calculated using inputs from the five evapotranspiration models. The results showed that (a) evapotranspiration means and trends, as estimated by the five PET models, were significantly different, with Penman giving the highest estimate while TH the lowest. Differences between the PET model outcomes reduced under climate warming scenarios; (b) significantly different evapotranspiration models and drought indices can give rise to varied results, with the climate becoming wetter under the Penman and PM models (especially in western northwest China and eastern south China), and drier under the TH model; (c) the different drought forecasts obtained using the evapotranspiration models decreased with increasing precipitation, for all regions; (d) the SPEI is more suitable for drought monitoring compared with PDSI due to the higher sensitive to the choice of evapotranspiration model of SPEI; and (e) SPEI‐PM and SPEI‐Penman is the best drought indices in all regions. SPEI‐PT and SPEI‐HG can be applied in regions with relatively abundant precipitation (northern north China, southern north China, eastern south China, western south China, and Tibetan Plateau), and SPEI‐PM and SPEI‐Penman can be suitable for drought monitoring in arid and semi‐arid regions (western northwest China and eastern northwest China). The results presented herein are expected to aid in the selection of a proper drought index for disaster assessment.

Projected changes and uncertainty in cold surges over northern China using the CMIP6 weighted multi-model ensemble

Cold surge (CS) events are the most serious extreme cold events in winter in China, causing large economic losses and casualties. The occurrence of CS events has slightly increased since the 1990s. However, the possible future changes in these events remain unclear, and quantifying robust projected changes in CS events is important for developing adaptation and policy planning. Here, we project the occurrence of CS events and strong CS (SCS) events using the weighted multi-model ensemble (MME) of the Coupled Model Intercomparison Project 6 (CMIP6) through the application of the rank-based weighting (RBW) approach under three shared socioeconomic pathway (SSP126, SSP245, and SSP585) scenarios. The corresponding weights of each model were obtained depending on the comprehensive historical performance from three aspects: climatology, spatial variation, and interannual variability. The results show that the RBW approach can reduce the relative bias by approximately 50% compared to the unweighted MME. The occurrence of CS and SCS events shows a decreasing trend during 2015–2099 over northern China under the three SSP scenarios. There are also robust change projections during the long-term (2080–2099) and 2015–2099 periods under SSP245 and SSP585, especially in the NEC region, which exhibits a signal-to-noise ratio (SNR) that is >1. However, the occurrence of SCS events shows slight increases of 1.18% and 3.55% over northern China (notably western and eastern Northwest China) during the near-term (2020–2039) under SSP126 and SSP245, respectively. Obvious reductions in projected uncertainty are widespread throughout northern China after applying the RBW approach compared to the unweighted MME, which mainly depends on the scenario, region, and term variation. Then, a robust decreased frequency may contribute to projected changes in large-scale atmospheric circulation (a more positive AO and weaker SH and EAT) under SSP585. Our results emphasize that the weighted MME can be taken into account when projecting future extreme climate change in some areas to enhance reliability.

A daily drought index-based regional drought forecasting using the Global Forecast System model outputs over China

Drought is a complicated climatic phenomenon occurring in the phase of water scarcity and can have devastating ecological and social impacts. Reliable drought forecasting can benefit various sectors by allowing adequate lead times for drought mitigation efforts. However, drought forecasting, especially on a short-term lead timescale (within two weeks), is still challenging. In this study, we performed regional meteorological drought forecasting at short-term lead times based on a daily drought index (Daily Evapotranspiration Deficit drought Index, DEDI) using modeling outputs from Global Forecast System (GFS) of National Centers for Environmental Prediction in typical climatic regions of China. The skills of the 3-, 5-, 10-, and 14-day lead regional DEDI forecasts were systematically evaluated by comparing with the DEDI derived from the ERA5 reanalysis datasets of European Center for Medium-Range Weather Forecasts which was used as a proxy for observations. Results show that the GFS-based DEDI forecasts can realistically characterize the spatial and temporal variations of the regional drought events that occurred in North China, Southwest China, eastern Northwest China, and Northeast China, and compare favorably to the ERA5-based DEDI. The skill of the GFS-based drought forecasts varies at different lead days. The 3- and 5-day lead forecasts present the best skill in capturing spatio-temporal variability of droughts and generally show the highest correlations and the smallest deviations. For the 10- and 14-day lead regional drought forecasts, the smoothed GFS-based DEDI could bring substantial improvements with remarkably increased correlations and reduced biases, and have skills in forecasting the dryness or wetness tendency. Notably, the GFS-based DEDI has skills in forecasting the occurrence or evolution of the regional drought events, but with a limitation in the drought magnitude evaluation. Overall, these results could be conductive to achieve the reliable regional drought forecasting and effective drought mitigation over China.

Interdecadal Variation of the Number of Days with Drought in China Based on the Standardized Precipitation Evapotranspiration Index (SPEI)

Abstract Based on the standardized precipitation evapotranspiration index (SPEI), a significant increase after the mid-1990s is detected in the annual number of days with drought in the zonal belt from southern Xinjiang to southern Northeast China and North China. This change features the predominant mode of the annual number of days with drought in China. Meanwhile, two significant breakpoints in 1981 and 2001 indicate a continuous increase of days with drought in the meridional belt from eastern Northwest China to eastern Southwest China. The increase in days with drought is closely related to the significant warming in the zonal belt but is attributed to both the increase of temperature and the decrease of precipitation in the meridional belt. The typical circulation patterns responsible for the increase of days with drought comprise a wave train stretching from North Atlantic to East Asia, the generally anomalous high pressure over China, the northerly anomalies prevailing over northern and central China, and the suppressed convection in most of the zonal and meridional belt. Both the AMO and the PDO after the 1980s have a close relationship with the interdecadal variation of the number of days with drought. On one hand, either a positive AMO phase or negative PDO phase motivates the typical circulation patterns favorable for the occurrence of drought. On the other hand, both the AMO and PDO affect the warming in the zonal and meridional belt, and the PDO is also closely connected with the precipitation in the meridional belt.

Effects of the surface coupling strength in the WRF/Noah-MP model on regional climate simulations over China

Land–atmosphere energy and moisture exchange can strongly influence local and regional climates. However, high uncertainty exists in the representation of land–atmosphere interactions in numerical models. Parameterization of surface exchange processes is greatly affected by parameter Czil, which, however, is typically defined as a domain-wide constant value. In this study, we examine the sensitivity of regional climate simulations over China to different surface exchange strengths via three Czil schemes (default (without Czil), constant (Czil = 0.1), and dynamic canopy-height-dependent Czil-h schemes) within a 13-km-resolution Weather Research and Forecasting model coupled with the Noah land surface model with multiparameterization options (WRF/Noah-MP). Our results demonstrate that compared to the other two schemes, the Czil-h scheme substantially reduces land–atmosphere coupling strength overestimation, and comparison to Chinese terrestrial ecosystem flux research network (ChinaFLUX) observations reveals the capability of the Czil-h scheme to better match observed surface energy and water variations. The results of the application of the various Czil schemes in four typical climate zones in China demonstrate that the Czil-h simulations achieve the closest agreement with field observations. The Czil-h scheme can narrow the positive discrepancies in the simulated precipitation and surface fluxes and the negative biases of the land surface temperature in Northeast China, North China, eastern Northwest China, and Southwest China. In particular, the above remarkable improvements produced by the Czil-h scheme primarily occur in areas covered with short vegetation. Additionally, the precipitation simulated with the Czil-h scheme exhibits more intricate and uncertain changes compared with surface flux simulations due to the nonlocal impacts of the surface exchange strength resulting from atmospheric fluidity. Overall, our findings highlight the applicability of the dynamic Czil scheme as a better physical alternative to the current treatment of surface exchange processes in atmosphere coupling models.

Water Vapor Changes Affect Cross-Seasonal Strong Drought Events in the Eastern Region of Northwest China

Drought in eastern Northwest China (ENC) is severely affected by water vapor conditions. An in-depth study of the primary sources of water vapor and its characteristics, at intraseasonal and interannual timescales, was conducted. This information is crucial for further study of the causes and mechanisms of extreme droughts and floods in the ENC. This study evaluated the spatial distribution and transport characteristics of water vapor over ENC during the 1981–2019 period based on the fifth generation of the European Center for Medium-Range Weather Forecasts atmospheric reanalyzes data of the global climate (ERA5). We studied the water vapor transport routes, water vapor convergence, water vapor budgets as well as the changes in water vapor fluxes and budgets over time in four areas surrounding ENC. The Mediterranean Sea, Black Sea, Caspian Sea, Indian Ocean, Bay of Bengal, and the South China Sea were the main sources of water vapor in ENC, supplemented by mid to high-latitude continental sources. The monthly change in water vapor flux in ENC exhibited the peak on July. The transport of water vapor in ENC was mainly toward the east and north. For most cross-seasonal drought events, the water vapor output is the main way in the south boundary and the west boundary. However, for the longest duration of cross-seasonal strong drought events, it is characterized by that the water vapor output is the main way in the south boundary, while the water vapor input in the north boundary is obviously weak. Water vapor paths in cross-seasonal strong drought events are analyzed, by which the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT). The intensity of the subtropical high in the western Pacific is weak and the position is south, which corresponds to the occurrence of cross-seasonal strong drought in the ENC.

Climate Transition from Warm-Dry to Warm-Wet in Eastern Northwest China

During the second half of the 20th century, eastern Northwest China experienced a warming and drying climate change. To determine whether this trend has continued or changed during the present century, this study systematically analyzes the characteristics of warming and dry–wet changes in eastern Northwest China based on the latest observational data and World Climate Research Programme (WCRP) Coupled Model Intercomparison Project Phase 6 (CMIP6) collection data. The results show that eastern Northwest China has warmed continuously during the past 60 years with a sudden temperature change occurring in the late 1990s. However, the temperature in the 2000s decreased slowly, and that in the 2010s showed a warming trend. The amount of precipitation began to increase in the late 1990s, which indicates a contemporary climate transition from warm-dry to warm-wet in eastern Northwest China. The contribution of precipitation to humidity is significantly more than that of temperature. Long-term and interannual variations dominate the temperature change, with the contribution of the former much stronger than that of the latter. However, interannual variation dominates the precipitation change. The warming accelerates from period to period, and the temperature spatial consistently increased during the three most recent climatic periods. The precipitation decreased from 1961–1990 to 1981–2010, whereas its spatial consistency increased from 1981–2010 to 1991–2019. The significant warming and humidification which began in the late 1990s and is expected to continue until the end of the 21st century in the medium emission scenario. However, the current sub-humid climate will not easily be changed. The warming could cause a climate transition from warm temperate to subtropical by 2040. The dry-to-wet climate transition in eastern Northwest China could be related to a synergistic enhancement of the East Asian summer monsoon and the westerly circulation. This research provides a scientific decision-making basis for implementing western development strategies, ecological protection, and high-quality development of the Yellow River Basin Area as well as that for ecological construction planning and water resource management of eastern Northwest China.

Characteristics of spring consecutive dry days with different durations across China based on the objective zoning approach

AbstractThe duration of dry periods is closely related to drought conditions and is used to evaluate the degree of drought. In this article, using the rotated empirical orthogonal function (REOF) and K‐medoids clustering methods and considering the spatial continuity, 500 stations in China are divided into 10 clusters to analyze the variation characteristics of consecutive dry days (CDDs) with different durations in spring. In Clusters 1–5 over the middle and lower reaches of the Yangtze River, South China, North China, and eastern and western Southwest China, the contribution percentage of short‐duration CDDs to total dry days decreases, while that of medium‐ and/or long‐duration CDDs increases, which leads to an increase in the total dry days and the duration of CDDs. In Clusters 6–8, the total dry days decrease, which are mainly contributed by the decreases in medium‐duration CDDs (for Cluster 6 over southern Northeast China) or long‐duration CDDs (for Clusters 7–8 over northern Northeast China and southern Xinjiang). The total dry days change little in Clusters 9–10 over eastern Northwest China and northern Xinjiang, which is attributed to the offset among the changes in the three‐type duration CDDs. In Clusters 6–10, the duration of CDDs shortens overall. The decadal changes of spring dry days in China exhibit remarkable regional differences. The total day days and three‐type duration CDDs in some clusters (1, 4, and 8) all have significant decadal changes, but they have not in Cluster 7. And the decadal change times also exhibit regional differences. The investigation of different‐duration CDDs in this study provides more information on droughts at different time scales in China.

More frequent and widespread persistent compound drought and heat event observed in China

Compound drought and heat event (CDHE) causes severe impacts on agriculture, ecosystem, and human health. Based on daily maximum surface air temperature and meteorological drought composite index data in China, changing features of CDHEs in warm season from 1961 to 2018 is explored at a daily time scale based on a strict and objective definition in this study. Results reveal that CDHEs have occurred more frequently and widely in China, especially since the late 1990s. Notably, such changes are more obvious in Southwest China, eastern Northwest China, northern North China, and the coastal area of southeastern China. A prominent feature is that persistent CDHEs on a daily scale have increased significantly. To better understand climate change of compound extreme events, further studies on the physical mechanism, especially attribution analyses at a regional scale, are urgently needed.

Spatiotemporal Variations in Drought and Wetness from 1965 to 2017 in China

Drought and extreme precipitation events can have major environmental and socioeconomic impacts. Yet, how drought and wetness are changing in China in the context of climate change is still under debate. Here, the standardized precipitation evapotranspiration index (SPEI) was calculated based on high-quality and more densely distributed daily meteorological observation data from 655 stations across China during the period of 1965–2017. National and regional trends in drought and wetness and their various characteristics, including intensity, duration, frequency, and percentage of area affected, were investigated at multiple timescales. We found that (1) China as a whole has undergone a significant (p &lt; 0.01, trend significant at the level of 0.01) wetting trend, with an annual SPEI increase of 0.5 per decade from 1965 to 2017. A seasonal wetting trend was also observed, with summer being particularly significant (p &lt; 0.01). (2) Regionally, each subregion also showed a wetting trend during the study period except for southwest China, and these wetting trends were significant in the western region of northwest China (p &lt; 0.05, trend significant at the level of 0.05), the Tibetan Plateau (p &lt; 0.05), and eastern China (p = 0.06). (3) Decadal trends in drought and wetness intensity, frequency, duration, and affected areas indicated that the drought events also became more severe and more frequent in the last two decades, and the areas showing drying trends were mainly located in southwest China (especially for the autumn drought) and the southwestern parts of eastern northwest China (spring drought). Our results highlight the fact that although a wetting trend was observed in most regions of China, the frequent occurrence of severe drought in southwest China and the southwestern parts of eastern northwest China still present a considerable threat to both the environment and society. Therefore, how to effectively coordinate the allocation of regional water resources to cope with drought risk under future climate change will be particularly important.

Observed changes in heat waves with different severities in China during 1961\u20132015

Heat waves (HWs) exert severe impacts on ecosystem, social economy, and human lives. Thus, changes in HWs under a warming climate have triggered extensive interests. In this study, the authors developed a new method to identify the HW events in China by double thresholds and further classified them into four categories (i.e., mild, moderate, severe, and extreme HWs) according to their magnitudes by using the daily maximum temperature data from 701 observation stations. On this basis, the spatiotemporal features of HWs with different severities in China from 1961 to 2015 were investigated. The results show that the high HW frequency mainly appears in Jianghuai, South China and western Northwest China. Moreover, the high frequencies of moderate, severe, and extreme HWs occur from June to August and reach the peak in July, while the mild HW frequency is compared from May to September. Since the 1960s, the frequencies of the mild, moderate, severe, and extreme HWs in China have increased significantly with rates of 7.5, 4.3, 1.4, and 1.8 events per year, respectively. The increases are the greatest in July for the moderate, severe, and extreme HWs while comparable during May to September for the mild HW. Besides, an interdecadal change is found to occur in the late 1990s. Compared with the former period (1961–1996), the occurrence of the extreme HWs during the latter period (1997–2015) has increased most significantly in eastern Northwest China and North China, while the frequency of the mild HWs increases most significantly in Jianghuai and South China.