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Separating existing historical precipitation data into solid and liquid precipitation remains a challenge in the study of climate change, extreme precipitation, and hydrological modelling. Based on historical daily air temperature and precipitation data, as well as visual observations of precipitation phase (weather phenomena records) in China mainland, this study proposed a snow‐day direct definition method (SDDM) to determine the threshold air temperature (TAT) of rainfall and snowfall, and analysed the spatial pattern and its influential factors. The main findings include: (1) the TAT based on the SDDM varied from −1.2 to 6.3°C, with a mean value of 2.8°C for the entire study region; (2) TAT was generally higher and more variable in the low‐latitude areas, and the Qinghai‐Tibet Plateau was characterized by an abnormally high average TAT of 5.2°C, almost twice as large as that of the eastern monsoon region; (3) TAT exhibited a significant positive correlation with altitude and negative correlation with precipitation and relative humidity. The results presented in this paper have potential application for studies of large‐scale snowfall climatology and climate change, weather forecasting techniques, and hydrological model parameterization in areas with complex and diverse geographical and climatic conditions. [ABSTRACT FROM AUTHOR]

While previous studies have largely focused on anthropogenic warming characterized by surface air temperature, little is known about the behaviors of human‐perceived temperature (HPT), which describe the "feels‐like" equivalent temperature by considering the joint effects of temperature, humidity and/or wind speed. Here we adopted an optimal fingerprinting method to compare seasonal mean HPTs in China with those from simulations conducted with multiple climate models participating in the Coupled Model Intercomparison Project Phase 6. We found clear anthropogenic signals in the observational records of changes in both summer and winter HPTs over the period 1971–2020. Moreover, the anthropogenic greenhouse gas influence was robustly detected, with clear separation from natural and anthropogenic aerosol forcings. The anthropogenic greenhouse gas forcing plays the dominant role (>90%) of human‐perceived warming. Urbanization effects contribute slightly and moderately to the estimated trends in summer and winter HPTs, respectively, in addition to the effects of external forcing. Plain Language Summary: Human influences have been identified in the observed warming quantified by surface air temperature (SAT), but SAT alone is inadequate as a metric for human thermal comfort. Here we focus on human‐perceived temperature (HPT), which describes the "feels‐like" equivalent temperature by considering the joint effects of temperature, humidity, and/or wind speed. We isolate anthropogenic impacts on the observed increase in summer and winter HPTs in China during 1971–2020 by comparing observations with state‐of‐the‐art climate models. Results show that the influence of anthropogenic greenhouse gas is detected, with clear separation from other external forcings such as solar and volcanic activities and anthropogenic aerosols. The human‐induced greenhouse gas increases are also found to explain most (>90%) of the observed human‐perceived warming. Along with the effects of large‐scale anthropogenic forcing, urbanization effects also have a slight to moderate influence on the estimated trends in summer and winter HPTs. Our work is an early attempt to provide quantitative evidence for the physiological impacts of anthropogenic global warming and local urbanization on human beings. Key Points: The warming is quantified by human‐perceived temperature that considers the joint effects of temperature, humidity and/or wind speedHuman influence could be robustly detected in both summer and winter human‐perceived warmingThe observed increase in human‐perceived temperature is mostly attributed to anthropogenic greenhouse gas increases [ABSTRACT FROM AUTHOR]

Using the drought and flood grades, the historical co‐drought probabilities of the water source area (i.e., the Upper Hanjiang River or UH) and the receiving area (i.e., North China or NC) of the Middle Route of the South‐to‐North Water Diversion project from 1470 to 2017 were analyzed. It was found that there is relatively high possibility for co‐droughts to occur in the UH and NC at interannual to multi‐decadal time scales. When extreme drought occurred in NC, there was a 52% probability that the UH was on the drier side and even a 40% probability of severe drought. During the three typical severe drought events that occurred mainly in NC (i.e., 1637–1643, 1877–1878, and 1997–2002), severe droughts also appeared in the UH, with 1877–1878 even more severe than in NC. Among the seven driest years of the study period in NC (i.e., 1640, 1641, 1832, 1920, 1965, 1968, and 1997), only 1832 was wet in the UH, and 1920 even experienced the same severe region‐wide drought as NC did. Furthermore, when severe consecutive droughts occurred in NC, there was at least a 66% probability that the UH was also experiencing a drought. In addition, there were obvious cycles of drought and flood variability of around 3–6 years, 10 years, 30 years, and 55–80 years in both the UH and NC. These findings are of importance to in‐depth understanding of the regional drought variability and its mechanism at varied temporal scales and the effective management of the world‐class hydro project. Plain Language Summary: The co‐drought probabilities of the water source area (the Upper Hanjiang River) and receiving area (North China) of the Middle Route of the South‐to‐North Water Diversion project at different time scales from 1426 to 2017 were analyzed. It was found that there is relatively high possibility for co‐droughts to occur in both areas at interannual to multi‐decadal time scales. Particularly, when extreme droughts occurred in North China, there was a 52% probability that the Upper Hanjiang River was also dry and even a 40% probability of severe droughts. When severe consecutive droughts occurred in North China, there was at least a 66% probability that the Upper Hanjiang River was also experiencing a drought. In addition, there are similar drought and flood variability cycles on different time scales in North China and the Upper Hanjiang River. Key Points: There is a relatively significant co‐drought in North China and the Upper Hanjiang River at multi‐time scalesWhen extreme droughts occurred in North China, there was a 52% probability that the Upper Hanjiang River was drySimilar drought and flood variability cycles exist on different time scales in North China and the Upper Hanjiang River [ABSTRACT FROM AUTHOR]

Increasing of evidence suggests that rapid urbanization modifies precipitation and increases atmospheric instability in urban areas mainly due to urban heat island (UHI)-induced thermal effects and urban building-induced dynamic effects. However, few studies focus on the impact of urbanization on the diurnal variations in urban rainfall in terms of initiating time, frequency, amount, and intensity. Here, six years of hourly data from a relatively dense meteorological observation network in the Wuhan area in central China are used to quantify the issue of urbanization-induced diurnal variations in hourly rainfall and short-duration rainfall (SDR) events by comparing urban and surrounding rural stations during the summer dry period (13 July to 4 August), corresponding to hot weather with little rainfall and high evaporation. The results indicate that: (i) A higher frequency of hourly rainfall appears during night-time and afternoon over urban areas as compared to rural areas. The urban rainfall is more concentrated during the night-time; (ii) More and stronger urban SDR events are triggered during the night-time over urban areas, especially in terms of amount and intensity of rainfall events. A greater diurnal urban–rural difference in SDR events is detected than that in hourly mean rainfall; (iii) There is an enhancement in the night-time and afternoon urban SDR events when UHI intensity increases before they are initiated, and this is detectable in the frequency, amount, and intensity of SDR events. It is also found that the UHI-induced thermal effects are the main reason for the stronger nocturnal SDR events in Wuhan during the summer dry period, which is caused by increases in the convection current and water vapor flux convergence in the urban areas. [ABSTRACT FROM AUTHOR]

A Lagrangian model—the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT)—is used to quantify changes in moisture sources and paths for precipitation over North China's Henan Province associated with tropical cyclone (TC) over the western North Pacific (WNP) during July–August of 1979–2021. During TC-active periods, an anomalous cyclone over the WNP enhances southeasterly and reduces southwesterly moisture transport to Henan. Accordingly, compared to TC-inactive periods, moisture contributions from the Pacific Ocean (PO), eastern China (EC), and the local area (Local) are significantly enhanced by 48.32% (16.73% versus 11.28%), 20.42% (9.44% versus 7.84%), and 2.89% (4.91% versus 4.77%), respectively, while moisture contributions from the Indian Ocean (IO), Southwestern China (SWC), Eurasia (EA), and the South China Sea (SCS) are significantly reduced by −31.90% (8.61% versus 12.64%), −16.27% (4.60% versus 5.50%), −8.81% (19.10% versus 20.95%), and −6.92% (12.18% versus 13.09%). Furthermore, the moisture transport for a catastrophic extreme rainfall event during 17–22 July ("21⋅7" event) influenced by Typhoon Infa is investigated. Compared to the mean state during TC-active periods, the moisture contribution from the PO was substantially increased by 126.32% (37.87% versus 16.73%), while that from IO significantly decreased by −98.26% (0.15% versus 8.61%) during the "21⋅7" event. Analyses with a bootstrap resampling method show that moisture contributions from the PO fall outside the +6σ range, for both the TC-active and TC-inactive probability distributions. Thus, the "21⋅7" event is rare and extreme in terms of the moisture contribution from the PO, with the occurrence probability being less than 1 in 1 million times. Significance Statement: Henan, one of the most populated provinces in China, experienced a catastrophic extreme precipitation event in July 2021 (the "21⋅7" event), coinciding with the activity of a tropical cyclone (TC) over the western North Pacific, which helps establish the moisture channel. Using a Lagrangian model, we provide a better understanding of how moisture transport changes associated with TC for the mean state of 1979–2021, and reveal how extreme is the moisture transport for the "21⋅7" event with the bootstrap technique. It is found that during active TC periods, the moisture contribution from the Pacific Ocean (the Indian Ocean) is significantly enhanced (reduced). For every 1 000 000 six-day events, less than one instance like the "21⋅7" event should be expected. [ABSTRACT FROM AUTHOR]

Examining large-scale characteristics of the difference between ground surface temperature (GST) and surface air temperature (SAT) and its long-term trend will help understand land surface energy exchange and the effect of land-atmosphere interaction on climate change and variability. Based on a homogenized monthly dataset of GST and SAT from 1961 to 2018, this study analyzes the spatial distribution and long-term trend of the difference between ground surface temperature and surface air temperature (GST–SAT) in the warm season (April to October) over China mainland. The results show that the warm-season mean GST–SAT in the Qinghai-Tibet Plateau and the northwestern deserts have the largest GST–SAT. On average, the GST–SAT in China is the greatest in summer, with the maximum monthly value occurring in July. During 1961–2018, the warm-season mean GST–SAT undergoes a significant increasing trend (0.04 °C/10yr, p < 0.01), with the largest increase seen in mid-late spring (April and May), and the smallest increase in August. Spatially, the GST–SAT increases significantly in the northern region, decreases slightly in the southern region, and remains unchanged in the Qinghai-Tibet Plateau. The warm-season mean GST–SAT is significantly positively correlated with altitude and sunshine duration (R = 0.50, 0.40; p < 0.05), and significantly negatively correlated with relative humidity and precipitation (R = 0.48, −0.42; p < 0.05), in the country on a whole in the analysis period. [ABSTRACT FROM AUTHOR]

Tropical cyclone (TC) translation distance, proportional to its duration and translation speed, basically determines the spatial extent of TC-impacted marine and terrestrial areas. Although a long-term slowdown of TCs has recently been reported, changes in translation distance of TCs over the western North Pacific (WNP) and their driving mechanisms remain poorly understood. Using multiple TC datasets, here we find that the trends are opposite in overland translation distance of landfall WNP TCs over China and excluding China, with the number of landfalls in the two groups being almost the same. However, the increase in overland translation distance of landfall TCs over China is offset by a greater decrease in that excluding China, with the result that the overland translation distance of TCs over the WNP has declined (−4.0% decade−1). The oversea translation distance of TCs over the WNP also shows a decreasing trend (−2.4% decade−1), and thus the genesis-to-demise translation distance of TCs over the WNP has significantly decreased (by 17.7%) during 1961–2019. The shorter duration and reduced translation speed of TCs directly and jointly contribute (by 76.9% and 23.1%, respectively) to their shortened translation distance. The gradual increase in westerly and northerly winds and weaker moisture transport during the days following TC generation tend to inhibit long-distance travel after TC genesis. Declining TC translation distance is likely associated with the long-term increases in genesis potential index and an anomalous cyclonic steering flow over the WNP. Our findings suggest that these changes in TC translation distance may alter regional patterns of TC-related drying and wetting of the WNP. Significance Statement: The spatial extent affected by a tropical cyclone (TC) is largely determined by TC translation distance. For example, TCs passing through marine areas could cool sea surface temperature and modulate local air–sea heat fluxes exchange; TCs with longer translation distances over land are more likely to trigger widespread flooding or terminate droughts in inland areas. Over the western North Pacific (WNP), we find that observational evidence supports opposite trends in overland translation distance of landfall TCs over China and excluding China. Nevertheless, the genesis-to-demise translation distance of TCs shows a significant decline over the WNP during the past six decades. Understanding the impacts of changes in TC translation distance has particular importance given the extensive footprint of TC-related drying and wetting of the marine and terrestrial areas. [ABSTRACT FROM AUTHOR]

The major droughts and floods in the Hanjiang River Basin, central China, have a significant impact on flood prevention and control in the middle reaches of the Yangtze River and water resources management in the areas of the South–North Water Diversion Middle Line Project. However, there is a lack of understanding of the multi-decadal to centennial-scale patterns of extreme droughts and floods in the area. Applying the yearly drought and flood records from historical documents and precipitation data in the period of instrumental measurements, this study constructs a time series of extreme droughts and floods in the Hanjiang River Basin from 1426–2017 and analyzes the temporal and spatial characteristics of the extreme drought and flood event variations. The results show that there were a total of 45 extreme droughts and 52 extreme floods in the basin over the past 592 years. Extreme droughts and floods were highly variable on a multi-decadal to centennial scale, and the frequencies were higher in the first and last 100 years or so of the study period and lower in between. Spatially, the frequencies of extreme droughts and floods were generally higher in the middle and lower reaches than in the upper reaches. It was also found that there is a good correlation of drought and flood frequencies between the upper Hanjiang River Basin and North China. These results are informative for the study of mechanisms and predictability of multi-decadal to centennial-scale variability of extreme hydroclimatic events in the river basin. [ABSTRACT FROM AUTHOR]

The intensity and direction of elevation-dependent warming (EDW) could vary in different parts of the mountain, while less attention is paid to the local EDW effect. The Tibetan Plateau (TP) and the T'ai-hang & Lvliang Mountains in Shanxi Province of China (TLMsx) were taken as cases to examine the relationship between EDW and the long-term trend of surface air temperature (SAT) lapse rate (SATLR). For the observed data, the intensity of regional EDW (I EDW) was estimated with linear regression model, while the SATLR was estimated with geographically weighted regression (GWR) model. The long-term trend of SATLR was estimated applying the modified Theil-Sen method, and the regional average SATLR trend (k SATLR ¯) was calculated and analyzed. Both observed data and simulation experiment revealed that there was not significant difference between I EDW and − k SATLR ¯ , with a little difference caused by the noise in the SAT trends. As the SATLR trend measured the difference in the surface air warming rate within 1-km vertical distance, i.e. the intensity of EDW in a small spatial scale, in the context of climate warming, it could be used to estimate the intensity of local EDW. The SATLR trend thus provided a new perspective to study the EDW effect in the future, and facilitated the quantitative analysis on the mechanisms of EDW. • Two kinds of elevation-dependent warming (EDW) effect, positive EDW and negative EDW, are found. • The regional average surface air temperature lapse rate (SATLR) trend (k SATLR ¯) was broadly opposite to that of the intensity of EDW (I EDW). • There was not significant difference between I EDW and − k SATLR ¯. [ABSTRACT FROM AUTHOR]

Two catastrophic extreme precipitation events in July 2021 and August 1975 caused tremendous damages and deaths in Henan, one of the most populated provinces in China. Revealing the relationship between large‐scale circulation patterns and precipitation extremes is vital for understanding the physical mechanisms and providing potential value for improving prediction and hence reducing impacts. Here, nine large‐scale circulation patterns are identified for July–August using the self‐organizing map. We find daily precipitation extremes under the fifth pattern (P5), characterized with the strongest easterly wind anomalies in Henan, feature the highest frequency and the largest intensity. Seven out of total 11 days in the two catastrophic extreme precipitation events belong to P5, and the top two maximum hourly precipitation extremes over continental China occurred under P5. The larger intensity of precipitation extremes is attributed to the dynamical contribution, suggesting more‐intense precipitation extremes under P5 are largely dominated by stronger ascending motions. Plain Language Summary: Henan is one of the most populated provinces in China. Two catastrophic extreme precipitation events in July 2021 and August 1975 caused devastating catastrophes, such as flooding and urban waterlogging, which resulted in widespread impacts on agricultural production, human livelihood, and economic development. We used a clustering method called self‐organizing map to link large‐scale circulation patterns with daily precipitation extremes in Henan Province. Our results show that the fifth pattern (P5), associated with the strongest easterly wind anomalies over Henan Province, is most conducive to extreme rainfall. Precipitation extremes under P5 exhibit the highest occurrence frequency and the largest mean intensity. Seven out of total 11 days for the two catastrophic extreme precipitation events belong to P5, while the top two maximum hourly precipitation extremes over continental China occurred under P5. The larger mean intensity of precipitation extremes under P5 is mainly caused by strong ascending motions. This work provides important implications for understanding the physical mechanisms and also providing potential value for the forecasting of precipitation extremes in Henan Province. Key Points: The circulation pattern (P5) most conducive to the occurrence of daily precipitation extremes is identified using self‐organizing mapSeven out of total 11 days in the "21·7" and "75·8" catastrophic extreme precipitation events belong to P5 patternThe dynamical processes, that is, the stronger ascending motions, dominate the more‐intense precipitation extremes in P5 pattern [ABSTRACT FROM AUTHOR]

Decrease in light precipitation (LP) frequency has been reported in many regions. However, reason for the decrease remains poorly understood. Here, we quantify urbanization effect on LP (< 3.0 mm day−1) trend in China over the period 1960–2018. We show that urbanization has significantly affected the decreasing LP trend. The urbanization effect becomes more significant as the definition of LP becomes stricter, with the largest effect appearing in trace precipitation change (< 0.3 mm day−1) (LP0.3) during summer and autumn. We estimate that at least 25% of the decreases in LP0.3 days and amount are due to urbanization near the observational stations. Our analysis thus confirms that urbanization has largely contributed to the observed downward trend in LP, and the large-scale change in LP is less than previously believed. [ABSTRACT FROM AUTHOR]

Under global warming, projected changes in precipitation have shown an asymmetrical shift from light to heavy precipitation over China. However, the role of urbanization in this shift remains unknown. Here, we show that increases in total rainy‐season (May‐September) precipitation over the Yangtze River Delta (YRD) urban agglomeration of East China are characterized by decreasing light precipitation and increasing heavy precipitation during 1961–2019. This asymmetrical shift toward heavier precipitation is even more prominent in urban than rural areas. Areas with faster urban expansion rates exhibit stronger negative (positive) trends in light (heavy) precipitation. Urbanization contributes to 44.4% (26.4%) of the decreasing (increasing) light (heavy) precipitation in the urban areas of the YRD. We suggest that urban managers should consider potential adverse impacts of this asymmetrical shift, which may favor increases in both the frequency of heatwaves and waterlogging. Plain Language Summary: China has experienced rapid urbanization in recent decades, alongside decreases in light precipitation and increases in heavy precipitation. This shift in precipitation patterns is also observed in the Yangtze River Delta (YRD), a typical densely populated region of China. Over the period 1961–2019, urban areas of the YRD have witnessed intensifying precipitation characterized by sharper decreases in light precipitation as well as sharper increases in heavy precipitation than rural areas. We estimate that 44.4% of the decrease in light precipitation and 26.4% of the increase in heavy precipitation in urbanized areas can be attributed to urbanization. Key Points: Changes in rainy‐season precipitation over the YRD show an asymmetrical shift toward less light and more heavy precipitationThis asymmetrical shift has been amplified by rapid urban expansion in recent decadesUrbanization contributes to 44.4% of the decrease in light precipitation and 26.4% of the increase in heavy precipitation [ABSTRACT FROM AUTHOR]

This study discussed the mechanism of Fe-modified biochar (FeBC) derived from rice straw biochar (BC) as an adsorbent for removing Cr(VI) from aqueous solution and assessed its applicability in actual industrial wastewater. The Cr(VI) removal percentage increased with the FeBC dose, which achieved a removal of 99.5% at 8.0 g/L FeBC. Increasing the solution pH from 2 to 10 slightly reduced Cr(VI) adsorption by 6.6%. Coexisting ions such as Ca2+, Na+ and Cl− inhibited the removal of Cr(VI); the removal rate decreased to 60% at their concentration of 0.25 mol/L. The adsorption isotherm and kinetics were better described by the Langmuir isotherm and pseudo-second-order kinetic models, respectively. Through scanning electron microscopy with energy dispersive X-ray, the Brunauer–Emmett–Teller method, Fourier transform infrared, X-ray diffraction and X-ray photoelectron spectroscopy, the analysis revealed that FeBC with iron oxides loaded onto its surface had more active sites than BC; the surface functional groups changed; the removal of Cr(VI) by FeBC was mainly attributed to electrostatic adsorption; the redox reaction of Cr, and Fe loaded onto BC enhanced Cr(VI) reduction process. FeBC showed a good removal performance on actual industrial wastewater with the concentration of both total Cr and Cr(VI) meeting the integrated wastewater discharge standard of China. [ABSTRACT FROM AUTHOR]

Soil moisture is an important variable of the climate system and is used to measure dry–wet change in hydroclimate. The warming trend has slowed in China over the past 20 years since 1998, and how the soil moisture changes in this period deserves our attention. With North China as a research region, this study uses the Global Land Data Assimilation System and ground observations to investigate the causes of changes in soil moisture during 1998–2017 versus 1961–97. The results show that 1) annual mean soil moisture experienced an almost continued decrease from the 1960s to 2010s, and no pause in the decrease of soil moisture over the regional warming slowdown of the past 20 years could be detected; 2) with the stabilization or even increase in solar radiation and wind speed as well as the continuous increase of land surface air temperature, the impact of potential evapotranspiration on soil moisture gradually became prominent, and the impact of precipitation decreased, since 1998; 3) the percent contribution of annual potential evapotranspiration to soil moisture variation increased by 26% during 1998–2017 relative to that in 1961–97, and the percent contribution of summer potential evapotranspiration even increased by 45%. Our results will provide insight into the land surface water budget and mechanism involved in drought development in North China. [ABSTRACT FROM AUTHOR]

Previous studies indicated that numbers of meso‐micro scale severe convective weather exhibited a significant decrease over China's mainland in the past decades. However, the possible mechanism of the decrease has not been well understood. This paper analyzes the changes in frequency of thunderstorm and lightning days using an updated data set of denser national observational stations and theirs links to the atmospheric circulation and regional environmental factors. The results confirm the highly significant decreasing trend of frequency of thunderstorm and lightning days during 1961–2013, with the decreasing rates of −2.6 days/10 years and −6.5 days/10 years in the warm season, respectively. The decrease of geopotential height difference between south and north, the weakening of westerly jet strength at 200 hPa and the decline of zonal wind speed of high level are found to be the direct reasons for the wide‐spread decrease of thunderstorm and lightning days across the country. Meanwhile, there is a significant positive correlation between thunderstorm days and convective available potential energy (CAPE), indicating a reduction of potential atmospheric instability accompanying the decline of thunderstorm days especially in the south of China. The decrease in the relative humidity at the lower troposphere, the weakening of 0–6 km vertical wind shear and the accompanying slackening of actual convective activity, may have also contributed to the downward trends of the severe convective weather. Our analysis shows a strong link of the decreasing thunderstorm and lightning days to the long‐term changes of the atmospheric circulation and environmental factors. Further investigation is needed to examine what have driven the changes of the environmental factors over the time period. Key Points: The results confirm the highly significant decreasing trend of frequency of thunderstorm and lightning during 1961∼2013The decrease of geopotential height difference, the weakening of westerly jet strength and the decline of zonal wind have influenceCAPE, relative humidity and 0–6 km vertical wind shear have a significant positive correlation with change of thunderstorm and lightning days [ABSTRACT FROM AUTHOR]

Precipitation accumulations, integrated over rainfall events, are investigated using hourly data across continental China during the warm season (May–October) from 1980 to 2015. Physically, the probability of precipitation accumulations drops slowly with event size up to an approximately exponential cutoff scale sL where probability drops much faster. Hence sL can be used as an indicator of high accumulation percentiles (i.e., extreme precipitation accumulations). Overall, the climatology of sL over continental China is about 54 mm. In terms of cutoff changes, the current warming stage (1980–2015) is divided into two periods, 1980–97 and 1998–2015. We find that the cutoff in 1998–2015 increases about 5.6% compared with that of 1980–97, with an average station increase of 4.7%. Regionally, sL increases are observed over East China (10.9% ± 1.5%), Northwest China (9.7% ± 2.5%), South China (9.4% ± 1.4%), southern Southwest China (5.6% ± 1.2%), and Central China (5.3% ± 1.0%), with decreases over North China (−10.3% ± 1.3%), Northeast China (−4.9% ± 1.5%), and northern Southwest China (−3.9% ± 1.8%). The conditional risk ratios for five subregions with increased cutoff sL are all greater than 1.0, indicating an increased risk of large precipitation accumulations in the most recent period. For high precipitation accumulations larger than the 99th percentile of accumulation s99, the risk of extreme precipitation over these regions can increase above 20% except for South China. These increases of extreme accumulations can be largely explained by the extended duration of extreme accumulation events, especially for "extremely extreme" precipitation greater than s99. [ABSTRACT FROM AUTHOR]

In China and East Asia, the long-term continuous observational data at daily resolution are insufficient, and thus there is a lack of good understanding of the extreme climate variation over the last 100 years plus. In this study, the extreme temperature indices defined by ETCCDI (Expert Team on Climate Change Detection and Indices) and local meteorological administrations were analyzed for Changchun City, Northeast China, by using the daily maximum temperature (Tmax) and daily minimum temperature (Tmin) over 1909–2018. The results showed that extreme cold events, such as cold days, cold nights, frost days, icing days, and low temperature days, decreased significantly at rates of −0.41 d (10 yr)−1, −1.45 d (10 yr)−1, −2.28 d (10 yr)−1, −1.16 d (10 yr)−1 and −1.90 d (10 yr)−1, respectively. Warm nights increased significantly at a rate of 1.71 d (10 yr)−1, but warm days decreased slightly and the number of high temperature days decreased at a rate of −0.20 d (10 yr)−1. The frequency of cold surge events increased significantly at a rate of 0.25 d (10 yr)−1, occurring mainly from the mid-1950s to late-1980s. The average Tmax, average Tmin and extreme Tmin increased at rates of 0.09°C (10 yr)−1, 0.36°C (10 yr)−1 and 0.54°C (10 yr)−1, respectively; and extreme Tmax decreased significantly at a rate of −0.17°C (10 yr)−1. In 1909−2018, 1951−2018 and 1979−2018, the indices related to cold events decreased, while the trends of the indices related to warm events were different for different periods. [ABSTRACT FROM AUTHOR]

As semi‐enclosed and shallow seas, the Bohai and Yellow Seas (hereafter, BYS) marine ecosystems are more easily affected by natural and anthropogenic climate changes than those in the open oceans. An accurate assessment of sea surface temperature (SST) change is crucial for the near‐shore water environment. In this work, new high‐quality monthly mean SST time series from 11 in situ coastal hydrological stations at BYS for the period of 1960–2012 have been generated. Monthly mean SST time series were initially subjected to penalized maximal t (PMT) test, using homogeneous monthly mean surface air temperature (SAT) series as references. Homogenized monthly mean SST series were obtained by adjusting all significant change points which have been supported by historic metadata. Our study shows that there are 29 significant change points in these 11 SST series. The majority of them are caused by instrument changes and station relocations—both account for about 51.7 and 31%, respectively. Then, homogeneous SST series are used to assess the long‐term trends. As the regional average, the annual mean homogeneous SST series shows a rapid warming trend, with the rate of 0.21°C/decade. Compared to the homogeneous SST series, the original SST series underestimate the long‐term trend (only 0.13°C/decade), indicating the artificial change points usually result in a warm‐bias in the early period measurements. Seasonally, the most significant warming occurs in boreal winter during the period analysed. The relationships of the significant warming in boreal winter and atmospheric circulation modes have also been investigated. Results reflect the remarkable and direct influence of the East Asian Trough (EAT) on SST along the coastal BYS. [ABSTRACT FROM AUTHOR]

The anthropogenic‐induced global warming and local urbanization exert important influences on temperature extremes in Eastern China. Here we use China station observations and climate models to investigate their effects on the warm and cold days and nights simultaneously. We quantified the contribution from these two factors based on an optimal fingerprinting method. We find that both anthropogenic and urbanization signals can be clearly detected and separated from each other in the nighttime temperature extremes. The effect of urbanization may explain as much as one third of the observed changes in cold and warm nights while the urbanization signal is weak in the daytime extremes. The results are robust against sampling uncertainty in the estimate of urbanization signal, but uncertainty due to collinearity between the urbanization signal and global warming is difficult to assess. Plain Language Summary: Understanding the causes behind changes in temperature extremes is of significance for reliably projecting future climate change. Previous studies have separately shown that global warming and the urbanization effects are the two important drivers for the increase of warm extremes and decrease of cold extremes in Eastern China. In this study, we consider these two factors simultaneously using an optimal fingerprinting method. We find that climate models can well reproduce the observed changes in extreme temperature when the urbanization effects are included. Both global warming and urbanization have contributed to changes in nighttime temperature extremes, with global warming contributing slightly more. On the other hand, changes in daytime temperature extremes seem to be predominantly due to global warming. Key Points: Global warming and urbanization exert important influences on both warm and cold days and nights in Eastern ChinaBoth anthropogenic and urban signals are detected in nighttime extreme temperatures while only the former is detected in daytime extremesThe effect of urbanization is estimated to have contributed as much as one third of the observed warming in nighttime temperature extremes [ABSTRACT FROM AUTHOR]

The systematic bias of the estimated average temperature using daily Tmax and Tmin records relative to the standard average temperature of four time-equidistant observations and its effect on the estimated trend of long-term temperature change have not been well understood. This paper attempts to evaluate the systematic bias across mainland China using the daily data of national observational stations. The results revealed that the positive bias of annual mean temperature was large, reaching 0.58°C nationally on average; regional average bias was lowest in the northwest arid region and highest in the Qinghai–Tibetan Plateau; the bias was low in spring and summer and high in autumn and winter, reaching its lowest point in mid- and late May and highest point in early November. Furthermore, the bias showed a significant upward trend in the past 50 years, with a rising rate of 0.021°C (10 yr)−1, accounting for about 12% of the overall warming as estimated from the data of the observational network; the largest positive trend bias was found in the northwest arid region, while the east monsoon region experienced the smallest change; the most remarkable increase of the bias occurred after early 1990s. These results indicate that the customarily applied method to calculate daily and monthly mean temperature using Tmax and Tmin significantly overestimates the climatological mean and the long-term trend of surface air temperature in mainland China. [ABSTRACT FROM AUTHOR]

The Qinghai Lake is the largest saltwater lake in the Tibetan Plateau and in mainland China. Effects of the lake on surface climate of the coastal areas, however, are not well understood. This article utilizes hourly observation data of warm season from 17 automatic weather stations to analyze the diurnal and seasonal variations in air temperature in different coastal zones of the Qinghai Lake. The EOS/MODIS data was also used to analyze the surface temperature differences between the lake and its surrounding areas. The results show a few unique characteristics of the plateau lake: (1) based on the satellite data, lake surface temperature is lower than its surrounding areas (4.9~25.1 °C and 12.2~35.6 °C respectively) in the daytime, while it is obviously higher than that in the surrounding areas (1.9~10.5 °C and − 13.1~6.3 °C respectively) at the nighttime. Daily mean water surface temperature is higher than that in the surrounding areas, which is 7.8~17.9 °C and − 2.6~17.9 °C respectively; (2) based on data of meteorological stations, coastal zones closer to the shoreline have a higher air temperature during the warm season largely due to the much warmer nighttime near the shoreline than those in deep inland zones. For the on-shore, near-shore, and far-shore zones, mean daytime air temperature is 8.7~9.6 °C, 9.5~11.1 °C, and 10.0~10.7 °C, respectively, and the mean nighttime air temperature is 2.9~4.1 °C, 1.3~12.3 °C, and − 0.2~0.4 °C respectively. The hourly mean diurnal temperature range (DTR) increases with distance to the shoreline, which is 8.6 °C, 10.9 °C, and 12.3 °C in the on-shore, near-shore, and far-shore zones respectively; (3) differences between maximum and minimum 5-day mean daily maximum (minimum) air temperature during the warm season are 20.3 °C (23.3 °C), 21.7 °C (25.6 °C), and 22.6 °C (26.7 °C) for the on-shore, near-shore, and far-shore zones, respectively, indicating an asymmetrical effect on daytime and nighttime air temperature in the on-shore zone; (4) daily maximum air temperature of the on-shore zone is lower before early October, but it is slightly higher afterward and occurs later; (5) daily minimum air temperature of the on-shore zone is on average higher than that of the far-shore zone, especially after the mid-September, and it also appears later in autumn than in summer. [ABSTRACT FROM AUTHOR]

Typical rain gauge measurements have long been recognized to underestimate actual precipitation. Long-term daily precipitation records during 1961–2013 from a dense national network of 2379 gauges were corrected to remove systematic errors caused by trace precipitation, wetting losses, and wind-induced undercatch. The corrected percentage was higher in cold seasons and lower in warm seasons. Both trace precipitation and wetting loss corrections were more important in arid regions than in wet regions. A greater correction percentage for wind-induced error could be found in cold and arid regions, as well as high wind speed areas. Generally, the annual precipitation amounts as well as the annual precipitation intensity increased to varying degrees after bias correction with the maximum percentage being about 35%. More importantly, the bias-corrected snowfall amount as well as the rainstorm amount increased remarkably by percentages of more than 50% and 18%, respectively. Remarkably, the total number of actual rainstorm events during the past 53 years could be 90 days more than the observed rainstorm events in some coastal areas of China. Therefore, the actual amounts of precipitation, snowfall, and intense rainfall were much higher than previously measured over China. Bias correction is thus needed to obtain accurate estimates of precipitation amounts and precipitation intensity. [ABSTRACT FROM AUTHOR]

Based on a homogenized data set of monthly mean temperature, minimum temperature, and maximum temperature at Shijiazhuang City Meteorological Station (Shijiazhuang station) and four rural meteorological stations selected applying a more sophisticated methodology, we reanalyzed the urbanization effects on annual, seasonal, and monthly mean surface air temperature (SAT) trends for updated time period 1960–2012 at the typical urban station in North China. The results showed that (1) urbanization effects on the long-term trends of annual mean SAT, minimum SAT, and diurnal temperature range (DTR) in the last 53 years reached 0.25, 0.47, and − 0.50 °C/decade, respectively, all statistically significant at the 0.001 confidence level, with the contributions from urbanization effects to the overall long-term trends reaching 67.8, 78.6, and 100%, respectively; (2) the urbanization effects on the trends of seasonal mean SAT, minimum SAT, and DTR were also large and statistically highly significant. Except for November and December, the urbanization effects on monthly mean SAT, minimum SAT, and DTR were also all statistically significant at the 0.05 confidence level; and (3) the annual, seasonal, and monthly mean maximum SAT series at the urban station registered a generally weaker and non-significant urbanization effect. The updated analysis evidenced that our previous work for this same urban station had underestimated the urbanization effect and its contribution to the overall changes in the SAT series. Many similar urban stations were being included in the current national and regional SAT data sets, and the results of this paper further indicated the importance and urgency for paying more attention to the urbanization bias in the monitoring and detection of global and regional SAT change based on the data sets. [ABSTRACT FROM AUTHOR]

Northwest China forms the main part of the arid and semiarid areas in China, and even includes some extremely arid areas. This zone of interaction is affected by the westerlies and monsoons making it sensitive to global climate change. Drought is the main type of natural disaster affecting northwest China. Global warming has caused a gradual strengthening of the frequency and intensity of hot extremes, when dry conditions and heatwaves occur simultaneously or successively; as a result, that socioeconomic risks can increase considerably. The present study examined changes in concurrent droughts and hot extremes in northwest China during 1961–2017 based on data from 119 meteorological stations. The result shows that the frequency of concurrent droughts and hot extremes exhibited an increasing trend over most parts of northwest China, while a negative trend occurred in western Xinjiang and at some sites in Qinghai. Concurrent droughts and hot extremes appeared more often in May in western Xinjiang, and in summer in other parts of northwest China. Overall, the trends of such concurrent events, regardless of different definitions, increased from 1961–2017 over northwest China. In particular, from 1981–2017, the trend rose more significantly than in other decades, and reached an abrupt point of change in 1996. Although the trend changed from a positive significant signal to a negative one from 2001–2017, the trend grew 2–3 times from 1997–2017. Changes in large‐scale atmospheric circulation show that an anticyclonic circulation strengthened, increasing in geopotential height over the midhigh latitudes of Eurasia and was centred on Mongolia and Lake Baikal. This enhanced relative humidity in western Xinjiang and eastern Qinghai, and weakened it elsewhere from 1997–2017. These changes have contributed to the changes in the spatial distribution and trends in concurrent droughts and hot extremes in northwest China. Variations in the number of concurrent droughts and hot extremes for the period of 1961–2017 in northwest China. Red line for DH85, blue line for DH90. DH85 and DH90 indicate simultaneous a month 3‐month SPEI < −1.0 and hot extremes during which the daily maximum temperature exceeded the 85th and 90th percentiles for at least three consecutive days, respectively. [ABSTRACT FROM AUTHOR]

Human-induced environmental and climate change are widely blamed for causing rapid global biodiversity loss, but direct estimation of the proportion of biodiversity lost at local or regional scales are still infrequent. This prevents us from quantifying the main and interactive effects of anthropogenic environmental and climate change on species loss. Here, we demonstrate that the estimated proportion of species loss of 252 key protected vertebrate species at a county level of China during the past half century was 27.2% for all taxa, 47.7% for mammals, 28.8% for amphibians and reptiles and 19.8% for birds. Both human population increase and species richness showed significant positive correlations with species loss of all taxa combined, mammals, birds, and amphibians and reptiles. Temperature increase was positively correlated with all-taxa and bird species loss. Precipitation increase was negatively correlated with species loss of birds. Human population change and species richness showed more significant interactions with the other correlates of species loss. High species richness regions had higher species loss under the drivers of human environmental and climate change than low-richness regions. Consequently, ongoing human environmental and climate changes are expected to perpetuate more negative effects on the survival of key vertebrate species, particularly in high-biodiversity regions. [ABSTRACT FROM AUTHOR]

Climate plays an important role in heating energy consumption owing to the direct relationship between space heating and changes in meteorological conditions. To quantify the impact, the Transient System Simulation Program software was used to simulate the heating loads of office buildings in Harbin, Tianjin, and Shanghai, representing three major climate zones (i.e., severe cold, cold, and hot summer and cold winter climate zones) in China during 1961-2010. Stepwise multiple linear regression was performed to determine the key climatic parameters influencing heating energy consumption. The results showed that dry bulb temperature (DBT) is the dominant climatic parameter affecting building heating loads in all three climate zones across China during the heating period at daily, monthly, and yearly scales (R2 ≥ 0.86). With the continuous warming climate in winter over the past 50 years, heating loads decreased by 14.2, 7.2, and 7.1 W/m2 in Harbin, Tianjin, and Shanghai, respectively, indicating that the decreasing rate is more apparent in severe cold climate zone. When the DBT increases by 1 °C, the heating loads decrease by 253.1 W/m2 in Harbin, 177.2 W/m2 in Tianjin, and 126.4 W/m2 in Shanghai. These results suggest that the heating energy consumption can be well predicted by the regression models at different temporal scales in different climate conditions owing to the high determination coefficients. In addition, a greater decrease in heating energy consumption in northern severe cold and cold climate zones may efficiently promote the energy saving in these areas with high energy consumption for heating. Particularly, the likely future increase in temperatures should be considered in improving building energy efficiency. [ABSTRACT FROM AUTHOR]

While the land-surface temperature (LST) observed at meteorological stations has significantly increased over the previous few decades, it is still unclear to what extent urbanization has affected these positive trends. Based on the LST data recorded at an urban station in Shijiazhuang in North China, and two rural meteorological stations, the effect of urbanization at the Shijiazhuang station for the period 1965-2012 is examined. We find, (1) a statistically-significant linear trend in annual mean urban-rural LST difference of $$0.27\,^{\circ }\hbox {C}$$ $$\hbox {(10 year)}^{-1}$$ , with an urbanization contribution of 100% indicating that the increase in the annual mean LST at the urban station is entirely caused by urbanization. The urbanization effects in spring, summer and autumn on the trends of mean LST are also significant; (2) the urbanization effect is small for time series of the annual mean minimum LST, and statistically marginal for the trend in annual mean maximum LST [ $$0.19\,^{\circ }\hbox {C}\,\hbox {(10 year)}^{-1}$$ ]; (3) the urbanization effect on the annual mean diurnal LST range ( $$\Delta {LST}$$ ) at the urban station is a strongly significant trend of $$0.23\,^{\circ }\hbox {C (10\,year)}^{-1}$$ , with an urbanization contribution of 21%. The urbanization effects on trends in the spring and autumn mean $$\Delta {LST}$$ are also larger and more significant than for the other seasons; (4) the urbanization effects on the long-term LST trends are remarkably different from those on the near-surface air temperature at the same urban station. Nonetheless, the significant warming of the urban boundary layer is expected to affect the urban environment and ecosystems. However, the problem of data representativeness at an urban station for the monitoring and investigation of large-scale climate change remains. [ABSTRACT FROM AUTHOR]

The spatial and temporal pattern of sub-daily temperature change in mainland China was analysed for the period from 1973 to 2011 using a 3-hourly dataset based on 408 stations. The increase in surface air temperature was more significant by night between 1973 and 1992, with the fastest upward trend around local midnight being about 0.27 °C/decade, while it was more significant by day between 1992 and 2011, with the fastest upward trend being about 0.46 °C/decade in mid-late morning. The season with rapid temperature increase also shifted from winter in 1973-1992 (the largest increase happened near midnight in December, 0.75 °C/decade) to spring in 1992-2011 (the largest increase happened at in the early afternoon in March, 0.82 °C/decade). The change in the spatial distributions of the sub-daily temperature trends shows that Northeast China warmed more significantly in 1973-1992 than elsewhere, but it cooled in 1992-2011, when Southwest China was the new focus of temperature increase whereas it had previously been cooling. A preliminary analysis of the possible causes implies that changes in solar radiation, cloud cover, aerosols and the observational environments near the stations might have contributed to these observed temperature changes. [ABSTRACT FROM AUTHOR]

Much attention has been given to the large-scale anthropogenic influence on extreme temperature changes. However, the possible effects of atmospheric factors and the role of the locally anthropogenic driver on the observed regional change in extreme temperatures have not been well understood. Datasets of the China Meteorological Administration (CMA) were used to examine the possible influence. The data include the homogenized surface air maximum/minimum temperature, surface sunshine duration (SSD), water vapor pressure (VAP), and total cloud cover (CLO) during 1961–2020. We calculated the seasonal means of maximum temperature (Tx (mean)), minimum temperature (Tn (mean)) and diurnal temperature range (DTR) to analyze the characteristics of extreme surface air temperature (ESAT) changes in winter and summer, and their relationship to SSD, VAP , and CLO , as well as the urbanization effect in the extreme temperature indices series. The changes in the trends for SSD and VAP were more closely correlated with ESAT in winter and summer, respectively. The decreasing of SSD led to a slowing of the ESAT warming, while an increase of the VAP led to the intensification of ESAT warming. In addition, CLO also had an important role in the change of ESAT. The seasonal mean correlation coefficient over China mainland between Tn (mean) and VAP were statistically significant and higher than those with SSD and CLO. The seasonal mean correlation between Tx (mean) / DTR and SSD were also statistically significant. The SSD and VAP strongly influenced the Tx (mean) in winter. The urbanization contribution to the DTR trends reached >25% in both winter and summer. SSD strongly influenced the trend of ESAT in urban area whereas CLO/VAP had larger influence on the trend of ESAT in rural area, which were all related to the urbanization effect as observed in the data series. • The decreasing of sunshine duration and increasing of the water vapor led to a slowing and the intensification of the extreme temperature warming, respectively. • The correlation coefficient between minimum temperature and water vapor were statistically significant. The correlation between maximum temperature / diurnal temperature range and sunshine duration were statistically significant. • The trend of sunshine duration strongly influenced on the trend of extreme temperature in urban area, whereas the trend of cloud cover and water vapor had more influence in rural area. [ABSTRACT FROM AUTHOR]

The summer of 2013 was the hottest on record in Eastern China. Severe extended heatwaves affected the most populous and economically developed part of China and caused substantial economic and societal impacts. The estimated direct economic losses from the accompanying drought alone total 59 billion RMB (ref. ). Summer (June-August) mean temperature in the region has increased by 0.82 °C since reliable observations were established in the 1950s, with the five hottest summers all occurring in the twenty-first century. It is challenging to attribute extreme events to causes. Nevertheless, quantifying the causes of such extreme summer heat and projecting its future likelihood is necessary to develop climate adaptation strategies. We estimate that anthropogenic influence has caused a more than 60-fold increase in the likelihood of the extreme warm 2013 summer since the early 1950s, and project that similarly hot summers will become even more frequent in the future, with fully 50% of summers being hotter than the 2013 summer in two decades even under the moderate RCP4.5 emissions scenario. Without adaptation to reduce vulnerability to the effects of extreme heat, this would imply a rapid increase in risks from extreme summer heat to Eastern China. [ABSTRACT FROM AUTHOR]

The aim of the study is to estimate the trend in extreme temperature events in the northern part of Korean Peninsula during 1960–2019, as well as to conduct a comparison experiment with the other representative results, all trends are examined based on quality-controlled daily maximum and minimum temperature data from 37 weather stations. Results are as follows. First, frost days (FD0) and ice days (ID0) showed a clear downward trend, whereas warm days (SU25) and warm nights (TR20) experienced an obvious uptrend, with SU25 exceeding TR20, while very hot days (TX35), extreme hot days (TX37) and very extreme hot days (TX39) showed abrupt increasing trends, especially twice in TX37 and six times in TX39, respectively. Both of cold nights (TN10) and cold days (TX10) decreased by about −0.7d/decade, hot nights (TN90) and hot days (TX90) increased by 0.6d and 1.0d/decade, respectively. Second, as compared with to representative results in global by the relevant reference and study period, all uptrends in TR20, SU25 and annual maximum of daily maximum temperature (TXx) were significantly higher than those in most regions in China, SU25 and TR20 were mostly greater than those in most regions, except for some regions in Europe. In particular, TR20 upward trend exceeded any other region's results. Meanwhile, TX10 and TNn experienced stronger downward and upward tendencies than those in whole China respectively. Especially, TNn experienced the strongest upward trend in comparing with the others. Overall, results revealed hot weather frequency and nighttime warm events over the study area have experienced a larger increasing trend than those in global land. • Cold-Cool extreme events represented downtrends, the crosscurrents in Hot-Warm ones. • Extreme hot weather events during summer had experienced a strong uptrend. • Uptrends in some extreme events were the largest in comparative regions in global. [ABSTRACT FROM AUTHOR]

Abstract: Based on monthly mean HadISST data, climatological characteristics and long-term changes of sea surface temperature (SST) over marginal seas of China are analyzed for the time period 1870–2011. The results show that (1) The smallest and largest spatial SST differences among various areas are seen in August and January respectively, with the coolest month occurring in February for all of the seas and the warmest month occurring in August for all but South China Sea (SCS); (2) The warming trends of the marginal seas of China during the time periods analyzed are generally larger than the global and hemispheric averages, with the East China Sea seeing the largest warming of all seas; (3) All of the sea areas see significant rising trends of annual mean SST in the last 140 years and the last 50 years, with larger and more significant warming generally occurs in autumn and winter; (4) The last 30 years especially the last 14 years undergo a slowdown of warming in the marginal seas of China, and the slowdown in the last 14 years is more evident than the global and northern hemispheric averages; (5) A weak upwelling current exists in western SCS, and the upwelling intensity has a significant positive correlation with the SCS summer monsoon index, with both seeing a decreasing trend in the last 64 years. [Copyright &y& Elsevier]

Marine heatwaves (MHWs) are becoming more frequent and intense in many regions around the world. However, the MHWs over China's marginal seas and associated physical drivers are largely unknown. During August 2016, the Yellow Sea experienced the most intense MHW on record since 1982. Here, we used a set of high-resolution satellite data and reanalysis products to examine the characteristics of the MHW in August 2016 and analyze the potential influencing factors from atmospheric perspective. MHW was directly caused by great-than-normal solar radiation and much weaker wind speeds which reduced upper oceanic mixing and caused substantial warming of the stratified surface layer. These anomalies were associated with an unusually fractured western Pacific subtropical high (WPSH) and the distinctly more active transmission of Madden-Julian Oscillation (MJO) eastward to the western Pacific in August 2016. The MJO triggered more frequent tropical cyclones, splitting the WPSH into two parts. The western segment of the WPSH combined with the continental high to form an abnormally positive geopotential height at the west of 120°E, causing strong subsiding flows at its east and extremely high solar radiation. An unambiguous cyclonic circulation anomaly in the lower troposphere, encompassing much of the northwestern Pacific, reduced the surface wind speed in the Yellow Sea. Therefore, MJO was critical to driving the extreme MHW in August 2016 in the Yellow Sea. • During August 2016, the Yellow Sea experienced the most intense MHW on record since 1982. • The MHW was directly driven by more solar radiation and weaker wind speeds. • The unusually fractured WPSH and active transmission of MJO played the critical role in leading anomalous heat and wind. [ABSTRACT FROM AUTHOR]

Cold and warm temperature extremes predominantly occurring in winter gained much more attention than mean temperatures. On the basis of daily maximum and minimum surface air temperature records at 303 meteorological stations in China, the spatial and temporal distributions of five indices for winter (DJF: December, subsequent January and February) temperature extremes are analysed during 1961-2003. For the majority of stations, the frequency of cold days/nights decreases by − 1.33/− 2.98 and warm days/nights increases by 0.92/2.35 d/decade, respectively. Cold days/nights are significantly negatively correlated with the Arctic Oscillation (AO) index, while warm days/nights are positively correlated with the AO. The diurnal temperature range (DTR) has a declining trend with rate of − 0.25 °C/decade and positive correlation with the AO index. Compared with other regions in China, stations in the northern China have larger trend magnitudes and stronger correlations with the AO index, and the AO can explain more than 50% of winter temperature extreme change in China. Compared with the annual basis, the winter temperature extremes have larger trend magnitudes, which reflect the rapid warming. During strongly positive AO index years, enhanced contrast tropospheric temperature (defined as the average of air temperature vertically integrated between 200 hPa and 1000 hPa based on the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis) between the north of China and the southern China weakens the East Asian winter monsoon which in turn reduces cold outbreaks in the northern and eastern China. The composites of large-scale atmospheric circulation are consistent with the asymmetrical changes of the geopotential height, zonal and meridional winds at high and mid latitudes at troposphere. Meanwhile, the linkage between the AO and solar activity also modulates the winter temperature extremes, while the mechanism needs to be investigated. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

An overview of basic research on climate change in recent years in China is presented. In the past 100 years in China, average annual mean surface air temperature (SAT) has increased at a rate ranging from 0.03°C (10 yr) to 0.12°C (10 yr). This warming is more evident in northern China and is more significant in winter and spring. In the past 50 years in China, at least 27% of the average annual warming has been caused by urbanization. Overall, no significant trends have been detected in annual and/or summer precipitation in China on a whole for the past 100 years or 50 years. Both increases and decreases in frequencies of major extreme climate events have been observed for the past 50 years. The frequencies of extreme temperature events have generally displayed a consistent pattern of change across the country, while the frequencies of extreme precipitation events have shown only regionally and seasonally significant trends. The frequency of tropical cyclone landfall decreased slightly, but the frequency of sand/dust storms decreased significantly. Proxy records indicate that the annual mean SAT in the past a few decades is the highest in the past 400-500 years in China, but it may not have exceeded the highest level of the Medieval Warm Period (1000-1300 AD). Proxy records also indicate that droughts and floods in eastern China have been characterized by continuously abnormal rainfall periods, with the frequencies of extreme droughts and floods in the 20th century most likely being near the average levels of the past 2000 years. The attribution studies suggest that increasing greenhouse gas (GHG) concentrations in the atmosphere are likely to be a main factor for the observed surface warming nationwide. The Yangtze River and Huaihe River basins underwent a cooling trend in summer over the past 50 years, which might have been caused by increased aerosol concentrations and cloud cover. However, natural climate variability might have been a main driver for the mean and extreme precipitation variations observed over the past century. Climate models generally perform well in simulating the variations of annual mean SAT in China. They have also been used to project future changes in SAT under varied GHG emission scenarios. Large uncertainties have remained in these model-based projections, however, especially for the projected trends of regional precipitation and extreme climate events. [ABSTRACT FROM AUTHOR]

Middle and eastern routes of the South-North Water Diversion Project (SNWDP) of China, which are approximately located within the area 28°-42°N and 110°-122°E, are being constructed. This paper investigates the past climatic variations on various time scales using instrumental and proxy data. It is found that annual mean surface air temperature has increased significantly during the past 50-100 years, and winter and spring temperatures in the northern part of the region have undergone the most significant changes. A much more significant increase occurs for annual mean minimum temperature and extreme low temperature than for annual mean maximum temperature and extreme high temperature. No significant trend in annual precipitation is found for the region as a whole for the last 50 and 100 years, although obvious decadal and spatial variation is detectable. A seesaw pattern of annual and summer precipitation variability between the north and the south of the region is evident. Over the last 100 years, the Haihe River basin has witnessed a significant negative trend of annual precipitation, but no similar trend is detected for the Yangtze and Huaihe River basins. Pan evaporation has significantly decreased since the mid-1960s in the region in spite of the fact that the trend appears to have ended in the early 1990s. The negative trend of pan evaporation is very significant in the plain area between the Yangtze and Yellow Rivers. There was a notable series of dry intervals lasting decades in the north of the region. The northern drought of the past 30 years is not the most severe in view of the past 500 years; however, the southern drought during the period from the 1960s to the 1980s may have been unprecedented. The dryness-wetness index (DWI) shows significant oscillations with periodicities of 9.5 and 20 years in the south and 10.5 and 25 years in the north. Longer periodicities in the DWI series include 160-170- and 70-80-yr oscillations in the north, and 100-150-yr oscillations in the south. The observed climate change could have implications for the construction and management of the SNWDP. The official approval and start of the hydro project was catalyzed by the severe multiyear drought of 1997-2003 in the north, and the operation and management of the project in the future will also be influenced by climate change-in particular by precipitation variability. This paper provides a preliminary discussion of the potential implications of observed climate change for the SNWDP. [ABSTRACT FROM AUTHOR]

In the global lands, the bias of urbanization effects still exits in the surface air temperature series of many city weather stations to a certain extent. Reliable reference climate stations need to be selected for the detection and correction of the local manmade warming bias. The underlying image data of remote sensing retrieval is adopted in this study to obtain the spatial distribution of surface brightness temperature, and the surface air temperature reference stations are determined based on the locations of the weather stations in the remote sensing surface thermal fields. Among the 672 national reference climate stations and national basic weather stations of mainland China, for instance, 113 surface air temperature reference stations are selected for applying this method. Compared with the average surface air temperature series of the reference stations obtained by a more sophisticated method developed in China, this method is proven to be robust and applicable, and can be adopted for the evaluation and adjustment study on the urbanization bias of the currently used air temperature records of surface climate stations in the global lands. [ABSTRACT FROM AUTHOR]

Holocene pollen maps of China north of the Yangtze River are presented for six time slices at 2000 year intervals and for ten taxa or taxon combinations on the basis of a data set of pollen diagrams of 142 sites. In spite of the problems with the differentiated data quality, a general correspondence of modern pollen maps with actual vegetation distribution justifies the feasibility of using the pollen maps to illustrate the past temporal and spatial patterns of vegetation change and to tentatively reconstruct palaeo-biomes for the specific time slices. The pollen maps reveal large changes in Holocene vegetation. In the southeastern half of the study area, arboreal taxa generally expanded in the early Holocene times, reaching their maximum at 6 or 4 ka BP, and then shrank during the late Holocene. An exception was found for eastern and northern Northeast China where the maximum development of arboreal taxa occurred during the last 4000 or 2000 years. The evident drop in AP percentages, and therefore the decline of forests, occurred after 6 ka BP in the most southeastern regions, especially in the middle and lower reaches of the Yellow River, and may have been caused by the expansion of farming since the Yangshao Culture period. The reconstructed biomes enable the visual expression of palaeo-vegetation change. A relatively open forest with Pinus as its dominant component developed in the southeastern Loess Plateau and western North China Plain from 8 to 6 ka BP, but it came to an end at about 4 ka BP. On the other hand, cold temperate conifer forest, and temperate mixed conifer and deciduous forest in Northeast China did not yet exist between 10 and 6 ka BP. They appeared at 4 ka BP and then continued to develop through time. Warm temperate deciduous forest experienced a remarkable reduction during the last 6000 years. Alpine valley Picea/Abies forest in the eastern Qinghai-Tibet Plateau developed in the early and mid Holocene, but started to decline at 4 ka BP, and has almost disappeared today. [Copyright &y& Elsevier]

Heatwaves are multi-day periods of extremely high-temperature weather relative to a region's average conditions and are among the deadliest natural disasters. This study was designed to evaluate changes in the characteristics of heatwaves during the periods of warming acceleration versus warming slowdown using the multivariate joint probability distributions of heatwave duration and severity. The results revealed that: (1) From the warming acceleration period (1961–1997) to the warming slowdown period (1998–2017), the return levels of heatwave duration increased by <1.0 d as the return period increased. As the return period lengthened, the return level of heatwave severity rose as well; (2) The joint occurrence probability of heatwaves with both variables exceeding the 20-yr, 50-yr, and 100-yr return levels exhibited relative increases of 3%, 8%, and 16% across China, respectively. There were greater than the joint probability of heatwaves with only 1 variable exceeding the return levels; (3) The number of heatwaves with both duration and severity exceeding the 50-yr joint return period increased in China, and this increase was dominated by heatwaves with joint return periods of 50–100 years, leading to a strengthening of heatwave severity. • The Copula function was used to connect the duration and severity of heatwaves; • The return level of heatwave severity rose more significantly than duration in China; • The probability of heatwaves with both variables exceeding the 100-yr return level exhibited a increase of 16% in China; • The increase of the joint probability of heatwaves with both variables exceeding return levels is more obvious. [ABSTRACT FROM AUTHOR]

Heavy PM2.5 (particulate matter with aerodynamic diameter equal to or less than 2.5 μm) pollution and urban heat island (UHI) pose increasing threats to human health and living environment in populated cities. However, how PM2.5 pollution affects the UHI intensity (UHII) has not been fully understood. The impacts of PM2.5 on the wintertime UHII in the Beijing‐Tianjin‐Hebei megalopolis of China are explored during 2013–2017. The results show that the UHII at the time of daily maximum/minimum temperature (UHIImax/UHIImin) exhibits a decreasing/increasing tendency as PM2.5 concentration increases, causing a continuous decrease in the diurnal temperature range. These effects are mediated via aerosol‐radiation interaction (aerosol‐cloud interaction) under clear‐sky (cloudy) condition. The changes in PM2.5 concentration further cause different relative trends of UHIImax/UHIImin/diurnal temperature range across different cities in the Beijing‐Tianjin‐Hebei region, which are likely related to the differences in both the PM2.5 composition and city size. This study provides insights on how air pollution affects urban climate and would help to design effective mitigation strategies. Plain Language Summary: A detailed understanding of the relationship between PM2.5 (particulate matter with aerodynamic diameter equal to or less than 2.5 μm) and the urban heat island (UHI) effect is significant for climate change adaption, planning, and sustainable development in urban regions. While the Beijing‐Tianjin‐Hebei (BTH) megalopolis of China is among the areas with the highest population densities and fastest urbanization rates in the world, the impacts of PM2.5 pollution on UHI, along with their regional differences in the BTH megalopolis, remain unclear. This study demonstrates that different PM2.5 concentrations in the BTH region pose various influences on the UHI intensities and their change rates in different cities of varying sizes. The UHI intensities during daytime and nighttime, respectively, exhibit weakening and strengthening tendency as PM2.5 concentration increases. These effects are mediated via aerosol‐radiation interaction under clear‐sky condition and aerosol‐cloud interaction in cloudy weather. The relative changes in the UHI magnitudes were mainly determined by PM2.5 composition and city size. The asymmetrical influences of PM2.5 on the daytime and nighttime UHI intensities caused continuous decreases in the diurnal temperature ranges in the urban areas as the pollution level increased. Our study improves the understanding of urban climate affected by air pollution and provides a scientific basis for the mitigation of UHI impacts. Key Points: Given a similar change in PM2.5 pollution levels, the relative change in UHII is determined by both PM2.5 species and city sizeWith increasing PM2.5 in the urban area, daytime UHII weakens and nighttime UHII strengthens, leading to a continuous reduction in DTRPM2.5 affects UHII via aerosol‐radiation interaction under the clear sky and via aerosol‐cloud interaction under cloudy condition [ABSTRACT FROM AUTHOR]

Heatwaves describe prolonged periods of excessive heat. The increasing trend in heatwave frequency, duration, and magnitude in a warmer future has been extensively investigated. However, the vast majority of traditional studies on heatwaves consider only the role of air temperature, which is inadequate as a metric for human heat stress. While reported worsening levels in heat stress with global warming are concerning, the changes in heatwaves may not be directly comparable to the temperature increase. The reliable information on future changes in human-perceived heatwaves is still fairly limited. Given this context, we quantified future changes in human-perceived heatwaves in eastern China, where the population is dense and the summers are often sultry, based on dynamic downscaling climate projections and a human thermal comfort index that combines the effect of temperature and humidity. We demonstrated that under the 3.0 °C of global warming (similar to late-century warming projected based on current mitigation policies), the frequency, duration, and magnitude of human-perceived heatwaves in eastern China would increase approximately 5, 4, and 20 times, respectively, relative to the reference period (1986–2005). Human-perceived heatwaves are projected to increase more rapidly than heatwaves solely based on the temperature definition, implying that the escalating heat risk for humans may have been underestimated by previous studies. Moreover, extra cautions need to be given to low-latitude regions, where the smallest changes in the mean temperature will probably be accompanied by the most pronounced increases in human-perceived heatwaves. Our results suggest the urgent demand of reducing greenhouse gas emissions toward mitigating persistent thermal discomfort in the future. Although here we focused on eastern China, our approach to assessing heatwaves can also be readily generalized to address similar problems worldwide. [Display omitted] • Wet bulb globe temperature is a better metric than T max for human heat stress. • Heatwave characteristics are defined by wet bulb globe temperature in our work. • Human-perceived heatwaves increase more rapidly than temperature-based heatwaves. • Lower latitudes in eastern China will experience the most pronounced increase. [ABSTRACT FROM AUTHOR]

• The southwesterly and northeasterly paths dominate the moisture transport. • Interannual variations of precipitation and moisture transport are closely linked. • Contribution of southwesterly path and the Indian Ocean increase during wet years. • The northeasterly path ranks the most important path during the dry years. • Flood variation is linked to moisture contribution from the Indian Ocean. This study used the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to examine the moisture sources and pathways associated with warm-season precipitation over the Sichuan Basin (SCB), southwestern China, with emphasis on the long-term mean state and interannual variability. Four groups of moisture pathways were identified over the period 1981–2017; i.e., the southwesterly, northeasterly, northwesterly, and westerly paths. With respect to the long-term mean state, the southwesterly path made the largest moisture contribution (36.0%) and, in combination with the northeasterly path (the importance of which has received little attention in previous studies), provided 70.2% of the total moisture. The Indian Ocean serves as the most important moisture source, accounting for 36.3% of the total moisture. In terms of interannual variability, compared with dry years, in wet years, the moisture contributions from the southwesterly path and the Indian Ocean increase by 18.6% (38.3% vs. 32.3%) and 20.71% (38.38% vs. 31.80%), but the contributions from the other moisture pathways and other major sources decrease. During the dry years, the northeasterly path, rather than the southwesterly path, provides the most moisture (34.6%). There are significant positive correlations between variations in runoff over the central and northern SCB and the moisture contribution from the Indian Ocean, which is associated with anomalous precipitation patterns over the SCB induced by fluctuations in the moisture contributions from the Indian Ocean. [ABSTRACT FROM AUTHOR]

Typhoons (TYs) and their interactions with large-scale ambient flow might exert an important control on moisture transport and precipitation. In this study, we used a Lagrangian model, the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT), to quantify changes in moisture pathways and sources associated with TY activity in relation to precipitation in eastern China during the three major rainy seasons. We compared TY-active and TY-inactive periods, i.e., the periods with and without TYs (maximum sustained surface wind speeds of up to 32.7 m/s), over the western North Pacific (WNP) to investigate TY-associated changes for the period 1979–2020. During the pre-summer rainy season in South China, anomalous moisture exhibited a north–south dipole pattern, with moisture contributions from the region extending from the South China Sea to the adjacent tropical WNP showing a 17.0% decrease during TY-active compared with TY-inactive periods (34.7% versus 41.8%, respectively), and contributions from the region extending from southwestern China to the northwestern North Pacific showing a 18.9% increase (17.0% versus 14.3%, respectively) and those from the Bay of Bengal showing a 16.6% increase (17.6% versus 15.1%, respectively). The moisture anomaly during the Meiyu rainy season in the Yangtze–Huaihe River Basin had an east–west dipole structure, with the moisture contribution from the Bay of Bengal reduced by 21.8% as compared with TY-inactive periods, and that from the WNP increased by 62.3%. During the rainy season of North China, the moisture contribution from the Indian Ocean decreased by 7.2%, while that from the WNP increased by 8.7% and from Northeast China increased by 10.0%. In addition, during TY-active periods, moisture contributions with local origins showed a slight increase. • Anomalous cyclone (south) and anticyclone (north) with enhanced easterly moisture transport is observed with the typhoon (TY) activities. • Typhoon-related changes in moisture sources and pathways are significant during the three rainy seasons. • Compared to TY-inactive periods, southwesterly (easterly) paths and regions contribute less (more) moisture in TY-active periods. [ABSTRACT FROM AUTHOR]

Climate change has a distinct impact on agriculture in China, particularly in the northeast, a key agriculture area sensitive to extreme hydroclimate events. Using monthly climate and agriculture data, the influence of drought on maize and soybean yields-two of the main crops in the region-in northeast China since 1961 to 2017 were investigated. The results showed that the temperature in the growing season increased by 1.0 °C from the period 1998-2017 to the period 1961-1980, while the annual precipitation decreased slightly. However, precipitation trends varied throughout the growing season (May-September), increasing slightly in May and June, but decreasing in July, August and September, associated with the weakening of the East Asian summer monsoon. Consequently, the annual and growing season drought frequency increased by 15%, and 25%, respectively, in the period 1998-2017 relative to the period 1961-1980. The highest drought frequency (55%) was observed in September. At the same time, the drought intensity during the growing season increased by 7.8%. The increasing frequency and intensity of drought had negative influences on the two crops. During moderate drought years in the period 1961-2017, 3.2% and 10.4% of the provincial maize and soybean yields were lost, respectively. However, during more severe drought years, losses doubled for soybean (21.8%), but increased more than four-fold for maize (14.0%). Moreover, in comparison to the period 1961-1980, a higher proportion of the yields were lost in the period 1998-2017, particularly for maize, which increased by 15% (increase for soybean was 2.4%). This change largely depends on increasing droughts in August and September, when both crops are in their filling stages. The impact of drought on maize and soybean production was different during different growth stages, where a strong relationship was noted between drought and yield loss of soybean in its filling stage. Given the sensitivity of maize and soybean yields in northeast China to drought, and the observed production trends, climate change will likely have significant negative impacts on productivity in the future., Competing Interests: The authors declare no conflict of interest.