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From summer to autumn in 2022, a severe drought lasted in southern China, posing serious effects on economic growth and ecological systems. This study explored the atmospheric circulations accounting for this persistent drought event. It shows that the drought in southern China during the summer of 2022 was strongly linked to the divergence of water vapor flux and descending motions, which were respectively caused by the anomalous anticyclone over the western North Pacific and the northward movement of the East Asian subtropical jet (EASJ). Differently, the atmospheric background responsible for the sustained drought in autumn is manly featured by a cyclonic circulation anomaly over the region from the Bay of Bengal to the South China Sea, which led to decreased moisture and descending motions in southern China. Further investigation suggests that the rarely strong surface warming over northern Eurasia and the extreme La Niña-like pattern over the tropical Pacific jointly resulted in the anomalous anticyclone over the western North Pacific and the northward shift of the EASJ in the summer of 2022, while the cyclonic circulation anomaly prevailing over the region from the Bay of Bengal to the South China Sea in autumn was largely attributed to the extremely negative anomalies of the tropical Indian Ocean sea surface temperature. [ABSTRACT FROM AUTHOR]

Heavy precipitation events can exert greater impact than general precipitation on the economy, ecology, and people's livelihoods. Based on CN05.1 daily precipitation data and the NCEP/NCAR global daily reanalysis dataset, this study analyzes the characteristics of clustered heavy precipitation (CHP) events during summer in Northeast China (NEC) during 1961–2020, with consideration of associated atmospheric circulations and moisture transport. Results indicate that CHP events occurred mainly during midsummer, especially in July. Both the frequency and the intensity of CHP events decrease after the mid-1970s, increase after the early 1980s, and then diminish again after the 2000s. The CHP events occur in association with an anomalous lower-tropospheric cyclone centered over NEC, northward and westward shifts of the western North Pacific subtropical high in the middle troposphere, and northward shift of an intensified westerly jet in the upper troposphere, in conjunction with strengthened local convective motion. Additionally, the net moisture budget begins to increase 2 days before the occurrence of CHP and peaks 6 h earlier than the CHP. Further results indicate that net moisture influx across the southern boundary of NEC made a dominant contribution to the net moisture budget. The results of this study have importance regarding the prediction of CHP events over NEC. [ABSTRACT FROM AUTHOR]

This study investigated the contribution of Arctic sea ice concentration (SIC) on decadal variations of the dominant mode of summer precipitation over eastern China during 1981–2020. The spatial pattern of leading empirical orthogonal function mode has changed from a dipole pattern with negative anomalies over Jianghuai Valley and positive anomalies over southern China during 1981–2001 to the Yangtze River Valley (YRV) pattern during 2002–2020. Spring SIC over Kara Sea was significantly related to the dipole pattern, through influencing Eurasian snow depth. The associated anomalous temperature gradient and atmospheric circulation affected the meridional displacement of the East Asian subtropical jet, which favored the dipole pattern of summer precipitation. For the YRV pattern, spring SIC over Greenland Sea has an impact on the sea surface temperature anomalies in the western Pacific by triggering a wave train that influenced the precipitation through the establishment of the Pacific–Japan pattern. The results of this study may provide reference value for the prediction of summer precipitation over eastern China. Plain Language Summary: As Eastern China has a high level of national economic development and experiences significant variations in summer precipitation, it is crucial to comprehend the patterns and trends of rainfall. However, it is challenging to accurately predict the decadal variations of precipitation due to the intricate physical processes involved. Therefore, we consider exploring the causes of the decadal variations from the perspective of Arctic SIC. The study demonstrates the dominant mode of eastern China summer precipitation (ECSP) undergone a decadal variation at the early 2000s, and spring SIC over Kara Sea and Greenland Sea play great impacts on it. These results may have potential implications for ECSP forecasting. Key Points: Dominant mode of the summer precipitation over eastern China (ECSP) experienced a decadal variation at the early 2000sSpring sea ice concentration (SIC) over Kara Sea contributed to the dipole pattern of ECSP by influencing the Eurasian snow depth during 1981–2001Spring SIC over Greenland Sea impacted the Yangtze River Valley pattern through the western Pacific sea surface temperature during 2002–2020 [ABSTRACT FROM AUTHOR]

Assessing the capability of sub-seasonal rainfall forecast of dynamic model and proposing correction method is quite an important topic in current climate research field. From the perspective of rainfall amount, rainy days and rainfall-belt evolution, the sub-seasonal forecast ability of the European Centre for Medium-Range Weather Forecasts (ECMWF) model for the main rainy-season rainfall in eastern China is evaluated. Evaluation results show that the forecast biases increase gradually with the increase of forecast lead time, characterized by the predicted rainfall amount being obviously higher and the rainy days being much longer than observation. In order to reduce the forecast biases of sub-seasonal rainfall forecast of ECMWF model, the rainy day-based correction (RDC) method is proposed in this study. Cross validation results indicate that RDC method can modify the number of rainy days forecast of ECMWF model with the SCC of rainy days increasing by 12.96% ~ 18.62%, and the RMSE decreasing by 56.49% ~ 63.78%. The problem of maximum continuous rainy days being too long in the model forecast can be also improved. Meanwhile, the spatial correlation coefficient (SCC) of rainfall amount forecast of the ECMWF model with the observation weakly increases by 0.61% ~ 1.56% and the root mean square error (RMSE) decreases by 3.50% ~ 7.60% after the RDC treatment. Therefore, RDC method presents a good performance on improving the sub-seasonal forecast of rainy days, and maximum continuous rainy days, which can be further applied in other models' sub-seasonal forecast error correction. [ABSTRACT FROM AUTHOR]

Using the standardized precipitation evapotranspiration index, this article demonstrates that the intensity of interannual variability (IIV) of May drought in Northeast China has enhanced remarkably after entering into the 21st century. Relative to 1980–1999, the percentage increase of IIV reaches 70% during 2000–2016. Such an enhancement is well supported by the intensification of IIVs in the East Asian polar front jet stream (EAPJ), East Asian subtropical jet stream (EASJ), and lower‐level anticyclonic circulation anomaly over Northeast China. Remarkable impact from the Barents Sea ice in April is also highlighted. With respect to the former period, a substantial increase occurs as well in the IIV of April Barents Sea ice during 2000–2016. Due to larger IIV in the latter period, the decline of April Barents Sea ice can exert evident effects on heat fluxes, consequently resulting in a significant increase of surface air temperature (SAT) in situ in May. The increased SAT further induces a wave train propagating southeastward to the East Asian region from the Barents Sea, which leads to a strengthened EAPJ and a weakened EASJ in the upper level, concomitant with an anomalous anticyclonic circulation covering Northeast China in the lower level. These atmospheric circulation anomalies link to the drought variability over Northeast China. Thus, the increase in the IIV of April Barents Sea ice favors the enhanced IIV of May drought in Northeast China. Plain Language Summary: Northeast China serves as an important granary in China. In recent decades, frequent occurrences of drought exert adverse effects on agriculture production and human lives in this region. Thus, better understanding of drought variability in Northeast China is an urgent need. In this study, we revealed an increase in the intensity of interannual variability (IIV) of May drought in Northeast China after 2000, which is well supported by the increased IIVs of the East Asian polar front jet stream, East Asian subtropical jet stream, and lower‐level anticyclonic circulation anomaly over Northeast China. Further examination suggested that the April Barents Sea ice with larger IIV after 2000 plays a pronounced role, by means of modulating the thermal conditions and associated wave train. The results are encouraging to improve the understanding about the interannual variability of drought in Northeast China, and act as a scientific basis for food security and human lives. Key Points: The intensity of interannual variability of May drought in Northeast China has enhanced after 2000Such an enhancement is supported by the intensified interannual variability of associated atmospheric circulationsThe Barents Sea ice variability in April plays a role through effects on the thermal condition [ABSTRACT FROM AUTHOR]

Compared with individual extreme events, compound events have more severe impacts on humans and the natural environment. This study explores the change in severity of compound extreme high temperature and drought/rain events (CHTDE/CHTRE) and associated influencing factors. The CHTDE and CHTRE intensified in most areas of China in summer (June–July August) during 1961–2014. Under global warming, the increased water-holding capacity of the atmosphere and the decreased relative humidity led to an increase in the severity of CHTDE. The severity of CHTRE is increased because of enhanced transient water vapor convergence and convective motion. Anthropogenic climate change, especially greenhouse gas forcing, which contributes 90% to the linear change in the severity of CHTDE and CHTRE, is identified as the dominant factor affecting the severity of CHTDE in China. In addition, the historical natural forcing (hist-NAT) may be related to the interannual-to-decadal variability in the severity of CHTDE/CHTRE. [ABSTRACT FROM AUTHOR]

Based on 20 models from phase 6 of the Coupled Model Intercomparison Project (CMIP6), this article explored possible reasons for differences in simulation biases and projected changes in precipitation in northern China among the all-model ensemble (AMME), "highest-ranked" model ensemble (BMME), and "lowest-ranked" model ensemble (WMME), from the perspective of atmospheric circulations and moisture budgets. The results show that the BMME and AMME reproduce the East Asian winter circulations better than the WMME. Compared with the AMME and WMME, the BMME reduces the overestimation of evaporation, thereby improving the simulation of winter precipitation. The three ensemble simulated biases for the East Asian summer circulations are generally similar, characterized by a stronger zonal pressure gradient between the mid-latitudes of the North Pacific and East Asia and a northward displacement of the East Asian westerly jet. However, the simulated vertical moisture advection is improved in the BMME, contributing to the slightly higher performance of the BMME than the AMME and WMME on summer precipitation in North and Northeast China. Compared to the AMME and WMME, the BMME projects larger increases in precipitation in northern China during both seasons by the end of the 21st century under the Shared Socioeconomic Pathway 5–8.5 (SSP5–8.5). One of the reasons is that the increase in evaporation projected by the BMME is larger. The projection of a greater dynamic contribution by the BMME also plays a role. In addition, larger changes in the nonlinear components in the BMME projection contribute to a larger increase in winter precipitation in northern China. [ABSTRACT FROM AUTHOR]

Based on the standardized precipitation evaporation index and reanalysis data, this article reveals that the relationship between the North Pacific Oscillation (NPO) and the drought over southern China in summer shifts from an insignificant correlation to a significant negative correlation after 2000. During the significant period (2001–2018), the positive NPO phase corresponds to an anomalous anticyclonic circulation dominating the mid‐low latitude North Pacific, which suppresses the moisture transport into southern China. Meanwhile, the easterly anomalies south of the anomalous anticyclonic circulation prevailing in the equatorial Pacific are coupled with a cooling of sea surface temperature in the central tropical Pacific, which enhances the Walker circulation and further induces an anomalous meridional circulation with the descending anomalies over southern China. Such moisture and dynamical conditions favor the occurrence of drought in southern China. During the former period (1983–2000), however, the NPO‐related atmospheric circulations over the North Pacific shift northward. In this case, the NPO shows insignificant relations with the moisture and dynamical conditions over southern China, thereby diluting the linkage of the NPO to the drought in southern China. The interdecadal strengthening in the relationship between the NPO and above atmospheric conditions is attributed to the westward (southward) extension of the NPO northern (southern) center. The larger interannual variability of spring sea ice in the Bering Sea and the southward movement of summer storm track over the North Pacific are hypothesized to account for the expansion of the NPO structure. Plain Language Summary: Southern China is an economically developed region with a large population. In recent decades, droughts frequently occurred in this region and severely affected agriculture production, forest‐fire prevention, and human lives. Therefore, it is very necessary to understand the physical mechanisms underlying the variability of droughts in southern China. In this study, we addressed the relationship of summer drought in southern China with the North Pacific Oscillation (NPO), which is characterized by the north–south seesaw pattern in sea level pressure over the North Pacific. We revealed that their relationship exhibits an interdecadal change around 2000, from an insignificant correlation to a significant negative correlation. Such an interdecadal strengthening is due to the expansion of the NPO structure, which may result from the changes of the spring sea ice in the Bering Sea and the summer storm track over the North Pacific. These findings are expected to deepen our understanding for the variation of drought in southern China and are also important for disaster prevention and mitigation. Key Points: Relationship between the summer drought in southern China and the North Pacific Oscillation (NPO) has strengthened after 2000Such a strengthening is attributed to the westward (southward) extension of the NPO northern (southern) centerThe expansion of the NPO structure is related to changes of spring sea ice in the Bering Sea and summer storm track over the North Pacific [ABSTRACT FROM AUTHOR]

Analyses of the standardized precipitation evaporation index (SPEI), using the season-reliant empirical orthogonal function (S-EOF) method, indicate that the second leading mode of drought over Northeast China features an in-phase variation from spring to summer. Such an in-phase change is closely connected to the persistence of geopotential height anomalies around Lake Baikal. The positive height anomalies around Lake Baikal, with an equivalent barotropic structure in the troposphere, can decrease water vapor transport into Northeast China and induce anomalous descending motion over Northeast China during both seasons, favoring precipitation deficit and high temperature in situ and hence resulting in the synchronous variations of spring and summer droughts. Further investigation reveals that the spring North Atlantic Oscillation (NAO) plays a notable role in the in-phase change of spring–summer droughts over Northeast China. The positive phase of spring NAO could induce spring drought over Northeast China directly through its influence on the above atmospheric circulations via a zonal wave train emanating from the North Atlantic. Meanwhile, it can also increase the soil moisture in central Siberia by enhancing the local snow depth. The wetter soil moisture in the following summer, in turn, increases the meridional temperature gradient between the middle and high latitudes and then forces westerly anomalies around 60°N, consequently yielding positive height anomalies around Lake Baikal that favor the occurrence of summer drought over Northeast China. Therefore, the spring NAO is hypothesized to contribute to the in-phase variations of spring–summer droughts over Northeast China through the combined roles of zonal wave train and central Siberian soil moisture. Significance Statement: Northeast China suffers from frequent droughts severely in recent decades. Thus, it is urgent to understand the physical mechanisms of drought in Northeast China. Using the season-reliant empirical orthogonal function (S-EOF) analysis, this study indicates that the second mode of S-EOF shows an in-phase change of drought from spring to summer over Northeast China, which is associated with the persistence of geopotential height anomalies around Lake Baikal. Our study further reveals that the spring NAO plays a pronounced role in the in-phase change of spring–summer droughts over Northeast China, through the combined roles of zonal wave train and the soil moisture in the central Siberian plateau. These findings are encouraging for better understanding of drought in Northeast China and are also important for disaster prevention and mitigation. [ABSTRACT FROM AUTHOR]

The variability and inhomogeneity of solar energy limits the development of solar heating systems (SHS) in many fields. In order to improve the utilization efficiency of SHS, this paper takes three typical cities (Xi'an, Dunhuang, Lhasa) as the research object, studies the operation state of SHS in student dormitory buildings, and puts forward a corresponding optimization strategy. The research shows that the reduction of water supply temperature will improve the operation efficiency and energy saving effect of a spontaneous combustion heat pump and that there is an optimal volume of heat storage water tank (HSWT), which can make the energy saving effect of SHS run better. The optimization of the SHS shows the water supply temperature is 35 °C, and the optimal volume of HSWT is 15 m3 in the "Resource-general area (Ⅲ)" represented by Xi'an, 25 m3 in the "Resource-rich area (Ⅱ)" represented by Dunhuang, and 40 m3 in the "Resource-richer area (Ⅰ)" represented by Lhasa. With the increase in the abundance of solar energy resources in the region, the optimal volume of HSWT also increases. Meanwhile, the solar energy contribution rate of the three regions in descending order is 61.3% (Lhasa), 32.8% (Dunhuang), and 25.9% (Xi'an). After optimization, the contribution of SHS increased by about 5%. The research results will help improve the efficiency of SHS in cold areas of China and make the system more efficient and energy efficient during operation. [ABSTRACT FROM AUTHOR]

The South Asian high (SAH) experienced a decadal weakening in the late 1970s under global warming. Based on an evaluation of the historical runs from CMIP6 models, we quantitatively assessed the contributions of different external forcing using "good" models that reasonably simulated the decadal decline of the SAH. All‐forcing runs yielded the weakened SAH after the late 1970s, albeit the decadal decline was underestimated by most models. Compared to the insignificant contributions of greenhouse gas and natural forcing, anthropogenic aerosol played a dominant role in the decadal decline of the SAH. The increased aerosol likely drove a cooling surface over the Tibetan Plateau (TP) and East China via its effect on radiation. Consequently, the weakened heat source over the TP and associated thermodynamic effects over East China would have driven a cooling of eddy temperature and cyclonic anomalies in the upper troposphere, respectively, thereby causing the decline of the SAH. Plain Language Summary: Under global warming, the South Asian high (SAH) measured by eddy geopotential height experienced a decadal decline in the late 1970s. However, the mechanism responsible for the decadal decline of the SAH has not been investigated. In this study, the contributions of external forcing to the decadal decline of the SAH are accessed using "good" CMIP6 models that can reasonably simulate the decadal changes of SAH. Results indicate that anthropogenic aerosol plays an important role in weakening the SAH. The increased aerosol emission over the Tibetan Plateau (TP) and East China cools the ground through the radiation effect. The weakened heat effect of TP and East China can contribute to the weakening of SAH. By contrast, the contributions of greenhouse gas and natural forcing are almost completely insignificant due to their homogenized and only very slight effects on the upper‐tropospheric eddy temperature over the SAH region, respectively. Key Points: ALL forcing can yield a weakening of the South Asian high (SAH), and anthropogenic aerosol provided the dominant contributionAnthropogenic aerosol drove the decline of the SAH by weakening the effect of the heat source over the Tibetan PlateauThe contribution of greenhouse gas and natural external forcing to the decadal decline of the SAH is insignificant [ABSTRACT FROM AUTHOR]

Haze pollution frequently occurs in North China almost every winter month. However, many previous studies pointed out that the interannual–decadal variations of haze in February were inconsistent with that in early winter, which demonstrated an evident subseasonal change in haze pollution. In this study, we found a close relationship between the "warm Arctic–cold Eurasia" (WACE) pattern in January and the weakened February haze pollution in North China according to monthly composites from 1980 to 2019. Associated with the warming signal in sea ice and the cooling signal in Eurasian soil temperatures, the WACE pattern sustained from January to February. The combined signal of sea ice and soil temperature anomalies and its associated anomalous cyclonic circulations over North China provided an environment conducive to the dispersion of pollutants. The relationship between the WACE pattern and the cyclonic circulation anomaly could also be detected from the large-ensemble CMIP6 simulations. Furthermore, the relationship between the January WACE pattern and the reduction of February haze pollution has been prominently enhanced since the late 1990s, which accurately corresponds to the deep Arctic warming that has emerged since the late 1990s. Significance Statement: Haze pollution frequently occurs in North China almost every winter month, but with an apparent subseasonal change. Climate anomalies in the mid- to high latitudes could regulate the variations in haze through atmospheric teleconnection. Our study found a relationship between the "warm Arctic–cold Eurasia" (WACE) pattern in January and the weakened February haze pollution in North China. The lingering signal of the WACE was associated to the anomalous cyclonic circulations over North China in February, which was conducive to the dispersion of pollutants. Furthermore, the relationship between the WACE pattern and February haze pollution has been prominently enhancing since the late 1990s, which accurately corresponds to the emergence of the deep Arctic warming accompanied by the strengthened Eurasian cooling. This investigation is of great significance for subseasonal haze prediction. [ABSTRACT FROM AUTHOR]

Evaluating the responses of net primary productivity (NPP) to climate change is essential for regional ecosystem management and adaptations to climate change. The Yangtze River Economic Belt (YREB) is a key ecological functional area and hotspot of carbon sequestration in China due to the high degree of forest coverage. We used a process-based ecosystem model to project terrestrial NPP and analyzed the response to climate change over the 21st century in the YREB under two representative concentration pathway (RCP) scenarios using the regional climate model. The results show that the projection of NPP generally increased by 13.5% under RCP4.5 and 16.4% under RCP8.5 in the middle of the century, by 23% under RCP4.5, and by 35% under RCP8.5 in the late term of the century compared with that from a reference period of current climate conditions (1985–2006). The rate of NPP change under the RCP8.5 scenario is higher than that under the RCP4.5 scenario. Similarly, the NPP is also projected to increase both with 1.5 and 2 °C global warming targets in the YREB. The magnitudes of NPP increment are approximately 14.7% with 1.5 °C and 21% with 2 °C warming targets compared with the current climate, which are higher than the average increments of China. Although NPP is projected to increase under the two scenarios, the tendency of NPP increasingly exhibits a slowdown after the 2060 s under the RCP4.5 scenario, and the growth rate of NPP is projected to drop in more than 31% of regional areas with the additional 0.5 °C warming. In contrast, under the RCP8.5 scenario, the trend in NPP keeps rising substantially, even above 2 °C global warming. However, the NPP in some provinces, including Jiangxi and Hunan, is projected to reduce at the end of the 21st century, probably because of temperature rises, precipitation decreases, and water demand increases. Generally, the NPP is projected to increase due to climate change, particularly temperature increase. However, temperature rising does not always show a positive effect on NPP increasing; the growth rate of NPP will slow down under the RCP4.5 scenario in the mid-late 21st century, and NPP will also reduce by the end of this century under the RCP8.5 scenario in some places, probably presenting some risks to terrestrial ecosystems in these areas, in terms of reduced functions and service decline, a weakened capacity of carbon sequestration, and reduced agricultural production. [ABSTRACT FROM AUTHOR]

Based on the Gini-coefficients, this study has presented an analysis of the impacts of anthropogenic forcing on the temporal inequality (i.e., increase in unevenness or disparity) of precipitation amounts (PRCPTOT), intensity (SDII), and extremes (R95p and RX5day) at national and regional scales (eight regions) in China. A positive anthropogenic influence on the temporal inequality is found for precipitation extremes over China, especially in southern regions during the period 1961–2005. Projections of future precipitation indices except R95p have a stepped upward trend in temporal precipitation variability with increasing anthropogenic forcing in most regions of China under SSP126, SSP370, and SSP585 scenarios. Except for Southern China (SC) and SWC2, R95p has a significant decrease in the future, and the largest decrease is up to 29.5% in Northwest China under SSP370. Results obtained from this study offer insights into temporal variability of precipitation extremes and help policy makers for managing water-related disasters. [ABSTRACT FROM AUTHOR]

The effect of soil moisture (SM) on precipitation is an important issue in the land–atmosphere interaction and shows largely regional differences. In this study, the SM of the ERA-Interim reanalysis and precipitation data of the weather stations were used to investigate their relationship over eastern China during July and August. Moreover, the WRF model was applied to further validate the effect of SM on rainfall. In the observations, a significantly negative relationship was found that, when the soil over southern China is wet (dry) in July, the rainfall decreases (increases) over the Huang–Huai–River basin (hereafter HHR) in August. In the model results, the soil can "memorize" its wet anomaly over southern China from July to August. In August, the wet soil increases the latent heat flux at surface and the air moisture at lower levels of the atmosphere, which is generally unstable due to the summer monsoon. Thus, upward motion is prevailing over southern China in August, and the increased surface air moisture is transported upwards. After that, the condensation of water vapor is enhanced at the middle and upper levels, increasing the release of latent heat in the atmosphere. The heat release forms a cyclonic circulation at the lower levels over eastern China, and induces the transport and convergence of water vapor increased over southern China in August. This further strengthens the upward motion over southern China and the cyclonic circulation at the lower levels. Therefore, positive feedback appears between water vapor transport and atmospheric circulation. Meanwhile, the cyclonic circulation over southern China results in a response of water vapor divergence and a downward motion over HHR. Consequently, the negative anomalies of precipitation occur over HHR in August. When the July soil is dry over southern China, the opposite results can be found through the similar mechanism. [ABSTRACT FROM AUTHOR]

The Eurasian continent experienced significant warming during the past decades. West Asia is located in an arid/semiarid zone, and its warming amplification has drawn considerable attention. However, the climatic effect of such a warming is not clear yet. In this study, we explored the possible impacts of recent land surface warming over West Asia on the atmospheric general circulation and climate. Results show that abnormal spring land surface warming over West Asia tends to increase precipitation over North China and decrease (increase) precipitation (air temperature) over Northeast China in early summer (June). It is noted that the precipitation anomalies are much stronger over the eastern region of North/Northeast China. Further analysis suggests that abnormal spring land surface warming can trigger eastward-propagating disturbances via diabatic heating, which intensifies the atmospheric circumglobal teleconnection (CGT) pattern, causing anomalous circulation and climate in early summer over northern China. Sensitivity experiments demonstrate that abnormal spring land surface warming can increase the atmospheric baroclinic instability and trigger Rossby waves that propagate along the westerly jet stream (WJS), resulting in the formation of CGT. Due to persistent land surface thermal forcing and the interaction between the basic flow (especially the WJS) and CGT, the CGT tends to be intensified. The anomalous wave center over East Asia in early summer is responsible for the precipitation increases (decreases) over North (Northeast) China and the evident warming in Northeast China. Our results suggest that the spring land surface thermal anomalies over West Asia can be a potential signal for short-term prediction of early summer climate over northern China. [ABSTRACT FROM AUTHOR]

Using the dynamical downscaling by the regional climate model RegCM4 from four global climate models, future changes in heat waves (HWs) over China under the RCP4.5 scenario are projected in terms of frequency and magnitude. The magnitude combines the duration and intensity together to characterize HW severity. The ensemble of RegCM4 downscaling simulations indicates a substantial increase in the frequency and magnitude of HWs over China toward the end of the 21st century relative to the current climate (1986–2005). The considerable changes occur in Southwest, South, North, and Northeast China for the frequency and in South, Southwest, East, and Central China for the magnitude. The prolonged HW duration plays a leading role in the enhancement of HW severity. In particular, an accelerated aggravation of the risk of extreme HWs is anticipated. Unusual HWs that never occurred in the current climate are expected to be usual phenomenon. For instance, by the end of the 21st century, the risks of the occurrence of extreme HWs (above the 99th percentile) in Southwest and South China are 64 and 53 times of the current, respectively, while the projected risks of the occurrence of mild HWs (below the 60th percentile) are much smaller and comparable in China. The HW frequency above the maximum of the current would appear once almost every year, and South, Central, and East China (North and Northeast China) would experience more severe HWs than the most extreme of the present every 1–2 (2–4) years. [ABSTRACT FROM AUTHOR]

This article evaluates the performance of 20 Coupled Model Intercomparison Project phase 6 (CMIP6) models in simulating temperature and precipitation over China through comparisons with gridded observation data for the period of 1995–2014, with a focus on spatial patterns and interannual variability. The evaluations show that the CMIP6 models perform well in reproducing the climatological spatial distribution of temperature and precipitation, with better performance for temperature than for precipitation. Their interannual variability can also be reasonably captured by most models, however, poor performance is noted regarding the interannual variability of winter precipitation. Based on the comprehensive performance for the above two factors, the "highest-ranked" models are selected as an ensemble (BMME). The BMME outperforms the ensemble of all models (AMME) in simulating annual and winter temperature and precipitation, particularly for those subregions with complex terrain but it shows little improvement for summer temperature and precipitation. The AMME and BMME projections indicate annual increases for both temperature and precipitation across China by the end of the 21st century, with larger increases under the scenario of the Shared Socioeconomic Pathway 5/Representative Concentration Pathway 8.5 (SSP585) than under scenario of the Shared Socioeconomic Pathway 2/Representative Concentration Pathway 4.5 (SSP245). The greatest increases of annual temperature are projected for higher latitudes and higher elevations and the largest percentage-based increases in annual precipitation are projected to occur in northern and western China, especially under SSP585. However, the BMME, which generally performs better in these regions, projects lower changes in annual temperature and larger variations in annual precipitation when compared to the AMME projections. [ABSTRACT FROM AUTHOR]

This study investigates the first two leading modes of the interannual variability of frequency of snowfall events (FSE) over China in the winter during 1986–2018. The positive phase of the first leading mode (EOF1) is mainly characterized by positive FSE anomalies in northeastern–northwestern China and negative FSE anomalies in the three-river-source region. In contrast, the positive phase of the second leading mode (EOF2) is mainly characterized by positive FSE anomalies in central-eastern China (CEC). EOF1 is affected by the synoptic-scale wave activity over the midlatitudes of the East Asian continent, where active synoptic-scale wave activity over the midlatitudes may cause increased FSE over northeastern–northwestern China, and vice versa. In a winter of a negative phase of the North Atlantic Oscillation, an anomalous deep cold low may occur over Siberia, which may induce increased meridional air temperature gradient, increased atmospheric baroclinicity, and hence increased FSE over the midlatitudes of the East Asian continent. The EOF2 is affected by the interaction between anomalous northerly cold advection and anomalous southerly water vapor transport over CEC. The positive phase of EOF2 is associated with negative sea ice anomalies in the Barents Sea–Kara Sea region and negative sea surface temperature anomalies in the central-eastern tropical Pacific. Reduced sea ice in the Barents Sea–Kara Sea during January–February may cause increased northerly cold advection over CEC, while a La Niña–like condition during January may induce southerly water vapor transport anomalies over CEC. [ABSTRACT FROM AUTHOR]

China has experienced dramatic warming in summer mean temperature since the early 1990s, leading to precipitation variation across the region. We have studied the variation of rainy‐season (April–September) precipitation in eastern China during 1961–2016. Overall, we found that rainy‐season precipitation increased in the south and decreased in the north during 1992–2016 (PII) compared to 1961–1991 (PI). By defining rainfall‐belt indices of intensity and central location, we found that the southern rainfall‐belt during the main rainy‐season tends to produce much more‐intense precipitation during PI relative to PII, in contrast to the northern rainfall‐belt, which tends to have less‐intense precipitation during PII. Despite some fluctuations, the central positions of neither the northern nor the southern rainfall‐belts exhibit a statistically significant difference between the two periods. Unlike during PI, during PII, there is an obvious anticyclone over the Lake Baikal region. This anticyclone has caused anomalous north winds flowing from north‐central to southwestern China, leading to weakening of the northward moisture transport. Also, regions such as northeastern, north‐central, and southwestern China have been controlled by negative geopotential height anomalies and weak vertical air‐motion anomalies, resulting in drying from north to southwestern China. At the same time, the enhanced water‐vapour convergence in the southeastern coastal region of China favours increased precipitation there. These processes working in concert created the drying‐north–wetting‐south pattern in the main rainy‐season during 1961–2016. The change in rainfall‐belt intensity in eastern China has also shown a close relationship with the change in vapour transport from low latitudes. The weakened land‐sea thermal difference in the East Asia–Northwest Pacific region, which has weakened water‐vapour and atmospheric circulation, has also played a role in the change of rainfall‐belt intensity. [ABSTRACT FROM AUTHOR]

Previous studies detected significant negative correlations between the nonuniform land surface warming and the decadal weakened activities of the summer extratropical cyclones (ECs) over East Asia and the East Asian summer monsoon (EASM) after the early 1990s. Here such relationships are further examined and the possible mechanisms are explored via numerical sensitivity experiments with a regional climate model (RegCM4.5). The positive/negative sensible heat flux (SH) anomalies were added as a forcing to a key region near 50°N of East Asia in RegCM4.5 to simulate the observed ground surface temperature (GST) anomalies. The model results suggest that the nonuniform land surface warming over the Lake Baikal area (50°–60°N, 90°–120°E) can indeed cause the weakening of the extratropical cyclogenesis and affect the decadal weakening of the EASM. Warm (cold) GST forcing over the key GST region can lead to decreasing (increasing) atmospheric baroclinicity and related energy conversion of the EC activity over the key EC region (40°–50°N, 90°–120°E), resulting in an evidently weakening (enhancing) of the ECs over East Asia. Meanwhile, precipitation shows a dipole pattern with significantly suppressed (enhanced) precipitation in northern and northeastern China, and slightly enhanced (suppressed) rainfall south of 40°N of East Asia, mainly over the East China Sea. Lake Baikal and its adjacent areas are occupied by a strong anticyclonic (cyclonic) circulation while the southeast coastal areas of China have a relatively weak cyclonic (anticyclonic) circulation accompanied with an anomalous northeasterly (southwesterly) wind to the southeast of the anticyclonic circulation, which is opposite to (coincident with) the atmospheric circulation anomalies that are associated with the second mode of the EASM. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A severe low‐temperature snowstorm and ice freezing event occurred in China in early 2018. This event was similar to that occurred in early 2008 but with a weaker intensity and salient difference in location and extent. The reason for this discrepancy was investigated in this study using station data and atmospheric reanalysis data. The results reveal that two different circulation patterns (i.e., zonal dipole pattern and meridional dipole pattern) over the mid‐high latitudes of Eurasia played an important role. The zonal dipole pattern, which is closely related to the 2018 event, is characterized by positive anomalies over the Ural Mountains and negative anomalies over Lake Baikal in the 500 hPa geopotential height field. This pattern can cause intense low temperatures in northern China through its influence on the anomalous cyclone over Northeast Asia. The meridional dipole pattern, which is highly associated with the 2008 event, is characterized by positive anomalies over Siberia and negative anomalies over Asia in the 500 hPa geopotential height field. This pattern corresponds to a strong East Asian winter monsoon (EAWM) and can drive cold air to move further southward, causing nearly nationwide chilly weather, particularly in northwestern China and south of the Yangtze River valley. The two patterns, combined with the strengthened western Pacific subtropical high (WPSH), have a synergistic role in the occurrence of snowfall. However, these patterns have weak correlations with the number of icy days but provide favourable conditions for ice freezing events. [ABSTRACT FROM AUTHOR]

Autumn rainfall in West China, the last rainy season of China, exerts profound impacts on the economic society, therefore, researches on its changes in the context of a warmer world are crucial for better adaptation to climate change. Using the dynamical downscaling performed by the regional climate model RegCM4 from four global climate models, this study firstly evaluated the fidelity of the RegCM4 simulations on the mean and extreme aspects of autumn rainfall in West China, and then projected their changes during the middle and the end of the 21st century under the RCP4.5 scenario. The evaluations indicate a good performance of the RegCM4 downscaling simulations in reproducing the observed spatial distribution of autumn rainfall amount, wet days, maximum consecutive 5‐day precipitation (RX5day), total extremely wet‐day precipitation (R95p), and consecutive dry days (CDD). Under the RCP4.5 scenario, relative to 1986–2005, the amount of autumn rainfall and the frequency of wet days are projected to increase in the northwestern part of West China and to decrease in its southeastern flank, concurrent with greater changes by the end of the 21st century than by the middle of the 21st century. Such an increase is closely associated with the enhancement of zonal water vapour transport and atmospheric unstable stratification, while the projected decrease is largely related to the reduction of moisture supply. Similar changes are also projected for the precipitation extremes Rx5day and R95p. Corresponding to the changing pattern of autumn rainfall, the CDD is projected to decrease in the northwestern part and to increase in the southeastern part of West China. [ABSTRACT FROM AUTHOR]

Autumn rain of West China (ARWC), a typical climate phenomenon characterized by continuous rainfall, is prone to flooding and secondary disasters. The ARWC in 2017, the greatest one since the last 30 years, resulted in an economic loss of 1.9 billion dollars and serious social impacts. It is thus urgent to understand the cause for this anomaly. In this article, the atmospheric circulations affecting the 2017's ARWC are identified. They are (1) a dipole pattern with the blocking over Europe and the trough over Lake Balkhash, which favors the southward outbreak of cold airs into West China, (2) increased water vapor transportation toward West China from the Pacific and Indian Oceans, and (3) a strengthening and northward displacement of the East Asian jet stream. The cold sea surface temperature anomaly (SSTA) in the equatorial central Pacific provides a superimposed effect. Further analysis reveals a synergic role in the interannual variability of the ARWC from the anomalies of the atmospheric circulation over Lake Balkhash and the SST in the equatorial central Pacific. The combination of anomalous trough over Lake Balkhash with cold SSTA in the equatorial central Pacific is most favorable for the increase of ARWC, while that of anomalous ridge with warm SSTA generally results in a decrease of ARWC. The combination of anomalous ridge with cold SSTA or that of anomalous trough with warm SSTA has no specific indication for ARWC anomalies. [ABSTRACT FROM AUTHOR]

This study introduces a multivariable covariance index (MVCI) to illustrate the synoptic features of mei-yu in the Yangtze River valley (YRV) region, which contains information of three indicators of mei-yu including precipitation, surface relative humidity, and tropospheric vertical motion. The interdecadal variation in the synoptic features of mei-yu during 1961–2016 is investigated using the MVCI. The date of mei-yu peak and the intensity of mei-yu underwent noticeable interdecadal variations over past decades, which are characterized by a delayed (relatively early) mei-yu peak and a relatively large (small) mei-yu intensity during 1985–97 (1961–80 and 2006–16). The mechanisms of these interdecadal variations are further discussed. The interdecadal variation in the date of mei-yu peak is mainly modulated by the meridional water vapor transport over eastern China during June, which may be partially attributed to an influence of the Pacific decadal oscillation (PDO) on the clockwise gyre over the North Pacific during boreal summer. The interdecadal variation in mei-yu intensity is associated with the interdecadal variation of tropospheric vertical motion over the YRV region during boreal summer, which may be partially attributed to an interaction between the PDO and the large-scale tropical east–west circulation during boreal summer. In addition, the interdecadal variation in the water vapor flux budget and relative humidity over the YRV region also exerted an impact on the interdecadal variation of mei-yu intensity in the YRV region. [ABSTRACT FROM AUTHOR]

Evaluation of Chinese precipitation extremes is conducted based on large ensemble projections of the present climate and 4-K-warmer climates derived from a high-resolution atmospheric general circulation model. The model reproduced the overall trend and magnitude of total precipitation and extreme precipitation events for China reasonably well, revealing that this dataset can represent localized precipitation extremes. Precipitation extremes are more frequent and more severe in future projections under 4-K-warmer climates than in the representative concentration pathway 8.5 (RCP8.5) scenario of phase 5 of the Coupled Model Intercomparison Project (CMIP5). Our results show that using a large-ensemble simulation can improve the ability to estimate with high precision both the precipitation mean and the precipitation extremes compared with small numbers of simulations, and the averaged maximum yearly precipitation will be likely to increase by approximately 18% under a +4-K future in southern China compared with the past. Finally, uncertainty evaluation in future precipitation projections indicates that the component caused by the difference in six ΔSST patterns is more important in southern China compared with the component due to the atmospheric internal variability. All these results could provide valuable insights in simulating and predicting precipitation extremes in China. [ABSTRACT FROM AUTHOR]

As the last rain season in China, "West China Autumn Rain" (WCAR) often causes floodings and secondary disasters, severely damaging the economic society. Therefore, the variability of WCAR is an important issue for disaster prevention and mitigation. This study addressed the linkage of the WCAR variability to the early summer sea ice concentration in the Barents Sea (BSIC) over the course of 1961–2020. It is found that their relationship changes from a significant negative correlation to an insignificant one since the early 21st century. During 1961–2002, the reduction in early summer BSIC can induce anomalous warming of autumn surface air temperature over the Barents-Kara Seas through altering the surface heat fluxes. The resultant warming further triggers a meridional wave train extending from the high latitudes southeastward to the western North Pacific via the region of Lake Balkhash and Lake Baikal, leading to a northward displacement of the East Asian jet, a deepening of the Lake Balkhash trough, and a strengthening of the western North Pacific subtropical high, which favor the increase of WCAR. During 2003–2020, however, the surface thermal anomaly in autumn associated with the reduction of early summer BSIC shifts to the western flank, due to decreased climatology and interannual variability of BSIC. Correspondingly, it yields a westward-located meridional wave train, which fails to affect the above WCAR-related atmospheric circulations and hence the variability of WCAR. • Linkage of WCAR to the early summer BSIC has weakened since the early 21st century. • Weakened BSIC-WCAR linkage is supported by changes in autumn atmospheric circulations associated with the early summer BSIC. • The thermal forcing and associated wave train related to the change of early summer BSIC in the two periods are different. [ABSTRACT FROM AUTHOR]

This paper reports a comprehensive study on the observed and projected spatiotemporal changes in mean and extreme climate over the arid region of northwestern China, based on gridded observation data and CMIP5 simulations under the RCP4.5 and RCP8.5 scenarios. The observational results reveal an increase in annual mean temperature since 1961, largely attributable to the increase in minimum temperature. The annual mean precipitation also exhibits a significant increasing tendency. The precipitation amount in the most recent decade was greater than in any preceding decade since 1961. Seasonally, the greatest increase in temperature and precipitation appears in winter and in summer, respectively. Widespread significant changes in temperature-related extremes are consistent with warming, with decreases in cold extremes and increases in warm extremes. The warming of the coldest night is greater than that of the warmest day, and changes in cold and warm nights are more evident than for cold and warm days. Extreme precipitation and wet days exhibit an increasing trend, and the maximum number of consecutive dry days shows a tendency toward shorter duration. Multi-model ensemble mean projections indicate an overall continual increase in temperature and precipitation during the 21st century. Decreases in cold extremes, increases in warm extremes, intensification of extreme precipitation, increases in wet days, and decreases in consecutive dry days, are expected under both emissions scenarios, with larger changes corresponding to stronger radiative forcing. [ABSTRACT FROM AUTHOR]

ABSTRACT Based on the high-resolution gridding data ( CN05) from 2416 station observations, a grid dataset of temperature and precipitation extreme indices with the resolution of 0.5° × 0.5° for China region was developed using the approach recommended by the Expert Team on Climate Change Detection and Indices. This article comprehensively presents temporal and spatial changes of these indices for the time period 1961-2010. Results showed widespread significant changes in temperature extremes consistent with warming, for instance, decreases in cold extremes and increases in warm extremes over China. The warming in the coldest day and night is larger than the warmest day and night, respectively, which is concurrent with the coldest night larger than the coldest day and the warmest night larger than the warmest day. Changes in the number of the cold and warm nights are more remarkable than the cold and warm days. Changes in precipitation extremes are, in general, spatially more complex and exhibit a less widespread spatial coverage than the temperature indices, for instance, the patterns of annual total precipitation amount, average daily precipitation rate, and the proportion of heavy precipitation in total annual precipitation are similar with negative trends in a southwest-northeast belt from Southwest China to Northeast China while positive trends in eastern China and northwestern China. The consistency of changes in climate extremes from the CN05 with other datasets based on the stations and reanalyses is also analysed. [ABSTRACT FROM AUTHOR]

Given that climate extremes in China might have serious regional and global consequences, an increasing number of studies are examining temperature extremes in China using the Coupled Model Intercomparison Project Phase 5 (CMIP5) models. This paper investigates recent changes in temperature extremes in China using 25 state-of-the-art global climate models participating in CMIP5. Thirteen indices that represent extreme temperature events were chosen and derived by daily maximum and minimum temperatures, including those representing the intensity (absolute indices and threshold indices), duration (duration indices), and frequency (percentile indices) of extreme temperature. The overall performance of each model is summarized by a 'portrait' diagram based on relative root-mean-square error, which is the RMSE relative to the median RMSE of all models, revealing the multi-model ensemble simulation to be better than individual model for most indices. Compared with observations, the models are able to capture the main features of the spatial distribution of extreme temperature during 1986-2005. Overall, the CMIP5 models are able to depict the observed indices well, and the spatial structure of the ensemble result is better for threshold indices than frequency indices. The spread amongst the CMIP5 models in different subregions for intensity indices is small and the median CMIP5 is close to observations; however, for the duration and frequency indices there can be wide disagreement regarding the change between models and observations in some regions. The model ensemble also performs well in reproducing the observational trend of temperature extremes. All absolute indices increase over China during 1961-2005. [ABSTRACT FROM AUTHOR]

This paper presents projected changes in temperature and precipitation extremes in China by the end of the twenty-first century based on the Coupled Model Intercomparison Project phase 5 (CMIP5) simulations. The temporal changes and their spatial patterns in the Expert Team on Climate Change Detection and Indices (ETCCDI) indices under the RCP4.5 and RCP8.5 emission scenarios are analyzed. Compared to the reference period 1986-2005, substantial changes are projected in temperature and precipitation extremes under both emission scenarios. These changes include a decrease in cold extremes, an increase in warm extremes, and an intensification of precipitation extremes. The intermodel spread in the projection increases with time, with wider spread under RCP8.5 than RCP4.5 for most indices, especially at the subregional scale. The difference in the projected changes under the two RCPs begins to emerge in the 2040s. Analyses based on the mixed-effects analysis of variance (ANOVA) model indicate that by the end of the twenty-first century, at the national scale, the dominant contributor to the projection uncertainty of most temperature-based indices, and some precipitation extremes [including maximum 1-day precipitation (RX1day) and maximum 5-day precipitation (RX5day), and total extremely wet day total amount (R95p)], is the difference in emission scenarios. By the end of the twenty-first century, model uncertainty is the dominant factor at the regional scale and for the other indices. Natural variability can also play very important role. [ABSTRACT FROM AUTHOR]

"West China Autumn Rain" (WCAR), as the last rainy season in China, is inclined to flooding and secondary disasters which often cause severe damages to the development of socio-economy and safety of people's lives. It is thus crucial to explore influential factors and associated physical processes for the anomalies in WCAR. In this study, based on the gridded precipitation data and reanalysis data during 1961–2013, we presented that the WCAR-AO relationship has strengthened in the mid-1980s, which varies from an insignificant correlation to a significant positive one. During the latter period (the significant period), the positive AO phase corresponds to a strong anticyclonic circulation anomaly over the region from northeast Asia extending to the North Pacific in the middle and lower troposphere, concurrent with a northward displacement of the East Asian jet (EAJ) in the upper troposphere. These atmospheric circulation situations favor the increase of WCAR, through their influences on the moisture and dynamical conditions. During the former period (the insignificant period), however, the association of the AO with above atmospheric circulations is weakened, thus diluting the WCAR-AO linkage. The unstable relationship between the AO and aforementioned atmospheric circulations may be due to the change in the AO structure. In the latter period, associated with the positive AO phase is a typical seesaw pattern featured by negative sea level pressure (SLP) anomalies in the Arctic and positive SLP anomalies in the North Atlantic and the North Pacific, whereas the anomalous center in the North Pacific becomes less pronounced in the former period. This discrepancy may be attributed to stronger wave activity arising from the SST warming from the former period to the latter period over the North Pacific. • The relationship of West China Autumn Rain (WCAR) with the Arctic Oscillation (AO) has strengthened after the mid-1980s. • The strengthened WCAR-AO relationship is well supported by the changes of the AO-related atmospheric circulation anomalies. • Changes in the spatial structure of AO over the North Pacific from the former period to the latter period may play a role. [ABSTRACT FROM AUTHOR]

West China Autumn Rain (WCAR), the last rainy season in China associated with the East Asian summer monsoon, is prone to flooding and secondary disasters and has profound impacts on the economic society. Thus, it is of great interest to understand its variability. Through an analysis with gridded rainfall data and reanalysis data, this study reveals that the variability of WCAR is positively correlated to the boreal summer (austral winter) sea ice concentration (SIC) in the Southern Indian and Pacific Ocean basins. Such a relationship is supported by the SIC-related changes in atmospheric circulations and water vapor transport. Corresponding to a high summer SIC, both the Lake Balkhash trough and the Asian low pressure are deepened, the East Asian jet shifts northward, and the water vapor transport to West China is enhanced during the boreal autumn, providing a favorable background for the increase of WCAR, and vice versa. The potential mechanism of how the boreal summer SIC affects the autumn atmospheric situation is further investigated. Results show that the atmospheric circulation in the high latitudes of the Southern Hemisphere possesses a seasonal persistence from the boreal summer to autumn due to the sea ice persistence. Thus, the boreal summer SIC-related anomalies in the upper-tropospheric winds over the Southern Indian and Pacific Ocean basins can persist to the following autumn and subsequently exert substantial influences on the Eurasian atmospheric circulations via two meridional teleconnections. The counterpart in the lower troposphere contributes to the water vapor transport toward West China. Certainly, this candidate mechanism is a preliminary explanation, and other processes may also act in their linkage. • Boreal summer sea ice in the Southern Indian and Pacific Ocean basins is positively correlated to West China autumn rain. • Their linkage is well supported by changes of autumn atmospheric circulation and water vapor conditions. • Sea ice resultant upper-tropospheric wind anomalies may affect Eurasian atmospheric circulations via two teleconnections. [ABSTRACT FROM AUTHOR]

Considering impacts of elevated CO 2 -induced increases in surface resistance on potential evapotranspiration (PET), to revisit and attribute the changes in dryness/wetness is necessary for accurately understanding evolutions of the historical and future drying and wetting conditions. Therefore, we comprehensively investigated the historical (1965–2011) and future (2019–2098; including four scenarios) annual dryness/wetness changes through incorporating CO 2 effect into the Food and Agriculture Organization of the United Nations' report 56 (FAO-56) Penman-Monteith and the self-calibrating Palmer Drought Severity Index. During the historical and future periods, China experienced significant wetting (p < 0.05), and moreover the wetting trends prevailed across most (> 70%) of China, especially for each future scenario with >50% of China with significant (p < 0.05) wetting. A joint-solution method with multiple sensitivity experiments was used to separate each driving factor's contribution to annual dryness/wetness changes. Results showed that for the whole China increased precipitation was responsible for the historical and future wetting trends. However, the determinant factors varied spatially. Across China, the historical major contributors were precipitation, wind speed, air temperature and net solar radiation, totally accounting for 97.6% of China. The annual dryness/wetness across China could be attributed to precipitation, air temperature and net solar radiation for SSP1–2.6 and SSP2–4.5, but precipitation and air temperature for SSP3–7.0 and SSP5–8.5. Moreover, through comparing attributions of the annual dryness/wetness changes with and without CO 2 effect, we found that the CO 2 effect could change the determinant factors mainly in eastern China, and the corresponding area percentages increased with the gas emissions, particularly for SSP3–7.0 and SSP5–8.5 with the largest values above 42%. This finding highlighted that the CO 2 effect should be considered when conducting attribution analysis of the changes in dryness/wetness. [Display omitted] • Impacts of the CO 2 effect on surface resistance were incorporated in this study. • The historical and future dryness/wetness changes in China were attributed. • The historical dominant factors were generally precipitation and wind speed at space. • The future dominant factors were generally temperature and precipitation at space. • The CO 2 effect should be considered when attributing dryness/wetness changes. [ABSTRACT FROM AUTHOR]

Studying impacts of the CO 2 effect on potential evapotranspiration (PET) and offline drought indices from surface resistance perspective is significant for understanding and accessing droughts. This study comprehensively investigated impacts of the CO 2 effect on PET and Standardized Precipitation-Evapotranspiration Index (SPEI) over China during 1971–2010 based on two simulations with and without CO 2 effect, respectively. We found that the CO 2 effect led to decreased PET and increased SPEI , and decreased drought, which showed strong spatial variations with the greatest impact over northern China (excluding westernmost part for PET). Such spatial variations had functional relationships not only with CO 2 concentration but also climatological conditions, i.e., climatological wind speed (U) and slope of vapour pressure curve (s) for PET , but climatological U , s and precipitation (P) for SPEI. Further analyses implied that climatological U (climatological U and P) determined the spatial variations in the CO 2 effect-induced PET (SPEI) changes over China during 1971–2010. [ABSTRACT FROM AUTHOR]

• A probability-based index is calculated to represent concurrent heatwaves and droughts. • Physical mechanisms of concurrent heatwaves and droughts are recognized. • Independent predictors are used to construct a physical-empirical prediction model. Concurrent heatwaves and droughts that occur over northeastern China (NEC) bring severe threats to human lives and crop production. Despite the great efforts taken in previous studies, realistic prediction of these concurrent extreme events remains a challenge. In the present study, a probability-based index that simultaneously considers precipitation deficiency and high temperature is calculated to represent concurrent heatwaves and droughts in July–August over NEC. Based on this index, the characteristics of concurrent heatwaves and droughts over NEC in July–August are investigated using the year-to-year increment approach. The results indicate that the occurrence of concurrent heatwaves and droughts over NEC is closely related to the Polar-Eurasian teleconnection pattern and the Pacific-Japan teleconnection pattern. Further analyses indicate that the sea ice content in the Barents Sea in March ( SICBS ), the La Niña-like sea surface temperature (SST) in February ( SST-PC1 ), and the northwestern Siberia soil moisture in April ( SM ) are coincidently linked to the two teleconnection patterns mentioned above. Based on their corresponding physical mechanisms, these three independent predictors are chosen to construct a physical-empirical prediction model for the prediction of concurrent heatwaves and droughts over NEC. Results suggest that this physical-empirical prediction model performs well with a high correlation coefficient and a low root mean squared error between the observed and predicted concurrent heatwaves and droughts over NEC during the period of 1979–2018. Moreover, the cross-validation test and independent hindcasts both suggest that the physical-empirical model proposed in the present study with the three independent predictors has good prediction skills. [ABSTRACT FROM AUTHOR]

• Causes of the annual evapotranspiration (ET) and water yield trends over vegetated mainland China were investigated. • Vegetation and precipitation dominated ET trends over 55% and 32% of study area, respectively. • Human-distributed vegetation and natural vegetation combined explained water yield trends over 30% areas. • Vegetation (particularly for human-distributed vegetation) greening was crucial for the hydrological cycle changes. Quantifying the contributions of climate and vegetation to the dynamics of evapotranspiration (ET) and water yield (i.e., precipitation minus ET) will help us better understand the changes in the water budget. In this study, we identified the contributions of climate variables (including precipitation, radiation, temperature, and relative humidity), human-disturbed vegetation, and natural vegetation to the trends in annual ET and water yield over vegetated mainland China during 2001–2020, using a process-based terrestrial ecosystem model and a joint-solution method with multiple sensitivity numerical experiments. Results showed that 46% of the study area experienced significant (p <0.05) increases in ET, with an overall increase of 2.32 mm y−1. Meanwhile, the overall trend in water yield was 2.56 mm y−1 but insignificant. Spatially, vegetation and precipitation are the dominant factors for ET trends over 55% and 32% of vegetated mainland China, respectively. Over the regions where vegetation dominates the ET trends, nearly half of these regions are covered by human-disturbed vegetation (e.g., cropland or regions with land cover changes), suggesting that anthropogenic activities play a crucial role in the hydrological cycle there. Concerning the trends in water yield, precipitation is the dominant factor over 64% areas. Human-disturbed vegetation and natural vegetation play similar roles and combined can explain the water yield trends over 30% areas. Our study highlights the spatial variations in the mechanisms behind changes in the water budget over mainland China, particularly in regions covered by human-disturbed vegetation. This finding should be considered in the existing and future national ecological recovery policies to maximize its eco-hydrological benefits. [ABSTRACT FROM AUTHOR]