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The spring tripole sea surface temperature (SST) anomalies in North Atlantic are an outstanding regional mode of interannual variability. Based on the observed and reanalyzed datasets during 1979–2019, this study reveals the relationship and linking mechanism between the spring tripole North Atlantic SST anomalies and the central China July precipitation (CCJP). Results show that the tripole SST anomalies, especially the warm SST anomalies in the tropical North Atlantic (TNA) and the subpolar North Atlantic (SNA), often cause surplus CCJP through the tropical and extratropical pathways. On the one hand, the spring TNA SST warming induces a pan-tropical climate response with the cooling in the central equatorial Pacific and the warming in the Indo-western Pacific until the following July through a series of air–sea interactions, helping maintain an anomalous anticyclone over the northwest Pacific and transport more warm humid flows to central China. On the other hand, the spring TNA and SNA SST warming persist into the following July and then emanate a wave train extending from the SNA throughout the Eurasian continent to East Asia, which induces an anomalous anticyclone over North China with its southeast flank transporting more cold air to central China. The warm humid flows from the south against the cold air from the north are conductive to the local ascending motion, favoring the increased CCJP. Our results highlight both the tropical and extratropical teleconnection pathways of the North Atlantic SST anomalies affecting the CCJP. This suggests an important seasonal predictor of the regional climate. Significance Statement July is the peak rainy month of central China, with heavy precipitation occurring frequently and often causing serious impacts on the local production and livelihood of millions of people. This study finds that the spring tripole sea surface temperature anomalies in North Atlantic induced by the North Atlantic Oscillation can exert significant impacts on the following July precipitation over central China through both the tropical and extratropical pathways. This improves our understanding of the causes of the surplus July precipitation over central China and has important implications for the seasonal predictability of the regional climate.

The central China summer precipitation (CCSP) is of great importance to the people’s livelihood of this densely populated region, including the agriculture, ecosystems, water resources, economies, and health. Based on the observed precipitation, sea surface temperature (SST), and atmospheric reanalysis datasets, the present study investigates the effects of El Nino in the developing stage on the CCSP during 1960–2014. The results show that the CCSP anomalies exhibit significant negative correlations with the El Nino-related SST anomalies in both the simultaneous summer and the following winter, implying that the developing El Nino is important for modulating the CCSP. However, this climatic teleconnection of El Nino is unstable, with an obvious interdecadal change around the late 1980s. Specifically, the negative correlation is not statistically significant in the previous epoch before the late 1980s (1960–1988), but dramatically strengthens since the late 1980s (the post epoch for 1989–2014). Such an interdecadal change is closely associated with the change of the El Nino-related SST anomaly pattern. Compared to the previous epoch, the central Pacific El Nino occurs more frequently in the post epoch, leading to an interdecadal shift of the maximum warm SST anomalies from the eastern Pacific to the central Pacific. The resultant westward extension of the atmospheric circulation responses induces an anomalous low-level cyclone covering South China in the post epoch. It would prevent the southwest monsoon from delivering the moisture to the north and hence reduce the CCSP. While, in the previous epoch, the anomalous cyclone locates east of South China, exerting insignificant influence on the CCSP. This work highlights a strengthening effect of El Nino on the CCSP since the late 1980s, with great implications for the regional seasonal climate prediction.

El Niño is a dominant source of interannual climate variability around the world. Based on the observed and reanalyzed datasets for the period of 1958-2019, this study explores the influence of El Niño on the spring precipitation over the Indo-China Peninsula (ICP). The results show that El Niño has a significant negative correlation with the following spring precipitation over the ICP. However, this climatic teleconnection of El Niño was unstable, with an obvious interdecadal strengthening since the early 1990s. During the decaying spring, the El Niño-related sea surface temperature (SST) anomalies would induce an abnormal downward motion along with an anomalous low-level anticyclone over the western North Pacific. Before the early 1990s, such El Niño-induced atmospheric circulation anomalies were located to the east of the ICP, exerting little influence on the spring ICP precipitation. In contrast, since the early 1990s, the abnormal downward motion and anomalous low-level anticyclone extended westwards covering the whole ICP, hampering local spring precipitation. This interdecadal change is owing to a relatively stronger intensity and longer duration of the El Niño-related warm SST anomalies over the tropical central Pacific in the epoch after the early 1990s (1992-2019) than in the previous decades (1958-1991). Our findings highlight a strengthening effect of El Niño on the following spring climate over the ICP since the early 1990s, which has great implications for the regional climate prediction.

Previous studies suggested that the dry–wet surface state over the Indo-China Peninsula (ICP), closely associated with the local spring precipitation, is an important seasonal predictor for the East Asian summer monsoon and extreme climate. Hence, this work investigates the inter-annual variability of spring precipitation over the ICP and its relationship with El Nino-Southern Oscillation (ENSO) during 1958–2019. The results show that the spring precipitation anomalies over the ICP are highly linked to the ENSO-induced atmospheric circulation anomalies. In particular, there are large asymmetries in the precipitation anomalies for the spring following ENSO. During the decaying spring of the El Nino events, the precipitation decrease mainly occurs over the Western ICP associated with an anomalous low-level anticyclone over the western North Pacific. In contrast, during the decaying spring of the La Nina events, a stronger precipitation increase broadly extends into the Southeastern ICP. This is owing to a nonlinear effect of ENSO on the atmospheric circulation. Compared to El Nino, the abnormal center of La Nina extends too far westwards, inducing a westward movement of the anomalous atmospheric circulation, which results in a stronger effect on the spring ICP precipitation. Our findings emphasize the nonlinear responses of the spring ICP precipitation to ENSO. This has important implications for the seasonal climate prediction over the ICP, especially for the Southeastern ICP countries/regions.

This study investigated the relationship between the pre-summer soil moisture (SM) over the Indo-China Peninsula (ICP) and the summer precipitation in the middle and lower reaches of the Yangtze River basin (MLR-YRB) under different SST backgrounds. When spring soil over the ICP was dry (wet), summer precipitation in most parts of the MLR-YRB was significantly higher (lower) under normal SST backgrounds (in the inner-quartile years). However, the SM anomalies produced a limited influence on summer precipitation under strong SST conditions (in the outer-quartile years). Further analysis indicates that in the inner-quartile years, the thermal heating anomalies induced by abnormal SM evidently increased (decreased) the geopotential heights above the western tropical Pacific, and enhanced (weakened) the low-level anticyclonic circulation, thereby increasing (decreasing) the warm and moist southerly flow from the ICP and western Pacific regions to the MLR-YRB, which was conducive to more (less) precipitation in the MLR-YRB. In the outer-quartile years, thermal anomalies of the ICP had very weak effects on both the wind fields above the western Pacific and the water vapor flux to the MLR-YRB, thereby leading to a limited increase (decrease) in summer precipitation. The different responses of the local and surrounding atmospheric circulations to pre-summer SM anomalies over the ICP against different SST backgrounds produced distinct impacts on the distribution of summer precipitation in the MLR-YRB. The dry (wet) anomalies of spring SM in the ICP could also increase (decrease) the zonal thermal contrast between the ICP and the South China Sea (SCS) and impact the SCS summer monsoon differently in the inner-quartile and outer-quartile years. Based on numerical experiments with the Community Earth System Model (CESM), this work further confirmed the observational results and explored the physical mechanism by which the ICP spring soil moisture affects the MLR-YRB summer precipitation under various SST backgrounds. The simulation results show that a dry (wet) ICP spring soil significantly increased (decreased) the MLR-YRB rainfall in the following summer. This negative correlation was stronger in the inner-quartile years. The atmospheric response to changes in the surface thermal conditions was more significant in the inner-quartile years. This surface heating anomaly over the ICP led to anomalous southwest wind over the SCS, which could enhance the Asian summer monsoon and increase summer precipitation in the MLR-YRB.

The seasonal prediction of precipitation extremes over the Yangtze River basin (YRB) has always been a great challenge. This study investigated the effects of spring soil moisture over the Indo-China Peninsula (ICP) on the following summer mei-yu front and YRB precipitation extremes during 1961–2010. The results indicated that the frequency of summer YRB precipitation extremes was closely associated with the mei-yu front intensity, which exhibited a strong negative correlation with the preceding spring ICP soil moisture. However, the lingering climate influence of the ICP soil moisture was unstable, with an obvious weakening since the early 1990s. Due to its strong memory, an abnormally lower spring soil moisture over the ICP would increase local temperature until the summer by inducing less evapotranspiration. Before the early 1990s, the geopotential height elevation associated with the ICP heating affected the western Pacific subtropical high (WPSH), strengthening the southwesterly summer monsoon. Consequently, the mei-yu front was intensified as more warm, wet air was transported to the YRB, and local precipitation extremes also occurred more frequently associated with abnormal ascending motion mainly maintained by the warm temperature advection. In the early 1990s, the Asian summer monsoon underwent an abrupt shift, with the changing climatological states of the large-scale circulations. Therefore, the similar ICP heating induced by the anomalous soil moisture had different effects on the monsoonal circulation, resulting in weakened responses of the mei-yu front and YRB precipitation extremes since the early 1990s.

The land surface energy exchange over the Indo-China Peninsula (ICP) is important for regulating regional weather and climate. This work investigates the effect of spring soil moisture (SM) over the ICP on the following summer precipitation over the Yangtze River basin (YRB) during 1961–2010. The results show that the spring SM over the ICP has a significant negative correlation with the following summer YRB precipitation. However, this relationship experiences an obvious interdecadal change with a much stronger correlation in the epoch before the early 1990s (1961–91) than in the later decades (1992–2010). In spring, an abnormally lower SM over the ICP could induce less surface evapotranspiration, increasing local temperature until the summer. Before the 1990s, the resultant anomalous ICP heating raises the local geopotential height, resulting in an excessive westward extension of the western Pacific subtropical high (WPSH). Accordingly, the enhanced southwesterly summer monsoon would transport more moisture to the YRB, intensifying the mei-yu front and local precipitation. In the early 1990s, the East Asian summer monsoon underwent an abrupt change with an interdecadal westward extension of the climatic WPSH. Consequently, the similar abnormal ICP surface heating induced by the anomalous SM would have different influences on the monsoonal circulation, causing a much weaker effect on the YRB precipitation in the recent decades.

Extreme precipitation events (EPEs) over the Yangtze River basin (YRB) exert widespread impacts on regional ecological environment and people’s life. Using observed precipitation, atmospheric reanalysis, and land assimilation datasets, the present study explores the relationship between the summer EPEs over the YRB and the Meiyu front and their possible linkages with the preceding spring soil moisture anomalies over the Indo-China Peninsula (ICP). The analyses show that both the frequency and intensity of summer EPEs over the YRB are closely associated with the mean intensity of the Meiyu front, which exhibits a significant negative correlation with the soil moisture anomalies in the preceding spring over the ICP. An abnormally drier soil over the ICP in spring would evidently raise air temperature by suppressing local evapotranspiration, and vice versa. Owing to a strong memory of the ICP soil moisture, the persistent anomalous heating would elevate local geopotential height in summer, inducing an excessive westward extension of the Western Pacific subtropical high. Accordingly, a strengthened southwesterly wind at the lower troposphere brings abundant warm–wet air to the YRB, intensifying the mean Meiyu front. This is also verified by the diagnosis of vertical motion (omega) equation. As a result, the risk of summer EPEs (both the frequency and intensity) over the YRB would increase (decrease) with an abnormally drier (wetter) ICP soil during the preceding spring. For the summer EPEs over the YRB, our results suggest that the spring ICP soil moisture can be used as an important seasonal predictor.

Land–atmosphere interaction plays an important role in regional weather and climate. Using the soil moisture (SM) data from the Global Land Data Assimilation System V2.0, the present study examines the land–atmosphere interaction during spring over the Indo-China Peninsula (ICP) and its effect on the following summer climate over the Yangtze River basin. The analyses show that the abnormal SM over the ICP in spring would significantly change the local surface air temperature by affecting the evapotranspiration. In particular, such a SM effect on the local air temperature can persist to the following summer owing to a strong ICP SM memory, which can in turn influence the East Asian summer monsoon as well as the remote precipitation and temperature over the Yangtze River basin. The persistent abnormally lower (higher) SM over the ICP induces less (more) local evapotranspiration, increasing (decreasing) the surface temperature. The resultant anomalous heating (cooling) over the ICP raises (lowers) the local geopotential height, which attracts (repels) the Western Pacific Subtropical High (WPSH) extending westward. Accompanied by an excessive westward extension of the summer WPSH, an anomalously enhanced southwesterly wind would bring more moisture to the Yangtze River basin at the lower troposphere. This situation intensifies the Meiyu front and precipitation over the Yangtze River basin. Further thermodynamic and dynamic analyses support that the monsoonal circulation anomalies associated with the westward extension of the WPSH mainly contribute to the summer precipitation anomalies over the Yangtze River basin. In addition, more precipitation accompanied with more cloud cover and less downward solar radiation that reduce the local air temperature, and vice versa. This highlights that the spring SM over the ICP is an important predictor for the following summer climate over the East Asia. The implication for predicting extreme weather events in summer over the Yangtze River basin is also discussed.

Variations of sea ice can exert significant impacts on the atmospheric general circulation, temperature and precipitation, resulting in anomalous land surface conditions such as snow cover. In this study, we explored the possible impacts of the abnormal late autumn Arctic sea ice on winter snow depth over the Eurasia, especially the mechanism responsible for regional response of the snow cover to the sea ice anomalies through both observational analysis based on multi-source snow depth data and numerical sensitivity experiments. Results show that with decreasing sea ice in the Barents and Kara Seas (BKS) region, the snow depth exhibits evident regional responses, which are featured by decreased snow depth in the North Eurasia but increased in central Europe. Further analysis suggests that the Arctic Oscillation (AO) is an important connection between the BKS sea ice and anomalous winter snow depth, which affect both the temperature and the precipitation in winter over the Eurasia. The regional difference mainly comes from significant differences in regional atmospheric general circulation anomalies as well as the various controlling factors affecting the formation of the snowfall. In North Eurasia, water vapor plays a decisive role in the formation of the winter snowfall and further the winter snow depth. Positive (negative) BKS sea ice anomaly generally induces positive (negative) AO pattern, which can enhance (weaken) the zonal wind and increase (decrease) water vapor transportation to the North Eurasia, causing increased (decreased) winter snow depth. In contrast, in Europe, temperature is the dominant factor affecting the formation of the snowfall and the snow depth. Positive (negative) AO pattern, enhances (weakens) the warm moist advection and thus leads to increased (decreased) temperatures in the Europe, consequently resulting in reduced (increased) winter snow depth.

Soil moisture (SM) feedback on climate variables especially temperature is an important aspect in land-atmosphere coupling. Based on the Global Land Data Assimilation System (GLDAS) V2.0 SM data and the gridded observational temperature data, we statistically analyze the thermal feedback of SM over North China (NC). The results show that SM exerts a decreasing trend under the background of evident warming over NC, inducing a decadal enhancement of SM feedbacks on the local temperature and extreme hot events. The SM feedback contributes 6% of the total air temperature variation during 1961–2012, while it reaches 36% after the regional warming during 1994–2012. Such SM affecting temperature is mainly reflected in its feedback on daily maximum temperature, which is also intensified during the warm period. The decadal intensification is also found in the feedback of SM on hot extremes. Further analyses show that the abnormal changes of the latent and sensible heat fluxes caused by the SM anomaly are the main reasons that affect the thermal conditions. Besides, the rising Bowen ratio indicates that upward thermal transfer on the land surface is enhanced in recent years, which suggests that the atmosphere is more sensible to the abnormal heating on the ground. This consequently translates into the decadal intensification of the local thermal feedback of SM in summer over NC.

South China is one of the most densely populated and agriculture-based regions in China. Local spring precipitation is crucial to the people’s livelihood and social economic development. Using the observed and reanalysis datasets for the period 1958–2019, this study revealed an asymmetric effect of El Niño—Southern Oscillation (ENSO) on the following spring precipitation over South China. During the years with positive ENSO phases, a strong positive correlation between spring precipitation and the preceding winter ENSO sea surface temperature (SST) anomalies existed over Guangdong province. For the years with negative ENSO phases, such a strong positive correlation shifts westwards to Guangxi province. To be specific, the El Niño events usually result in a precipitation surplus in the decaying spring over Guangdong province, while the La Niña events usually lead to a precipitation deficit in the decaying spring over Guangxi province. This is attributed to the nonlinear effects of ENSO on the atmospheric circulation. Compared with El Niño, the abnormal center of La Niña evidently extends westwards, inducing a westward movement of the anomalous low-level atmospheric circulation, which eventually results in a westward-shifted effect on the following spring precipitation over South China. Our findings emphasize the nonlinear responses of spring precipitation over South China to ENSO. This has important implications for the seasonal climate predictions over South China.

Accurate information on snowpack conditions is crucial for understanding changes in the hydrological cycle and its impacts on the climate system, especially at the middle and high latitudes. Two satellite-derived products that cover Eurasia from 1979 to 2006, i.e., the snow water equivalent (SWE) data provided by the National Snow and Ice Data Center (NSIDC; SWENSIDC) and the GlobSnow dataset provided by the Finnish Meteorological Institute (FMI) (SWEGS) are selected for examination in the present study. The performances of these datasets in representing snowpack conditions are evaluated by comparing the datasets with the observations of snow depth (SD) recorded in the Historical Soviet Daily Snow Depth (HSDSD; SDHSDSD) dataset. The results indicate that the SWEGS dataset is more consistent with the SDHSDSD dataset over northern Eurasia than the SWENSIDC dataset. In particular, the SWENSIDC dataset exhibits large discrepancies in northern Europe and western Siberia (NE-WS), indicating problems or even errors in the SWENSIDC dataset. Based on snow formation criteria (e.g., temperature and precipitation), we further explore and confirm the existence of problems in the SWENSIDC dataset. These problems may be associated with the retrieval method used to generate this dataset; this method is based on a static algorithm. Our findings suggest that satellite-derived SWE datasets (e.g., SWENSIDC) should be used with caution when investigating the impacts of snow in different research fields (e.g., climatology, hydrology, and ecology).

Land–atmosphere coupling is a key process of the climate system, and various coupling mechanisms have been proposed before based on observational and numerical analyses. The impact of soil moisture (SM) on evapotranspiration (ET) and further surface temperature (ST) is an important aspect of such coupling. Using ERA-Interim data and CLM4.0 offline simulation results, this study further explores the relationships between SM/ST and ET to better understand the complex nature of the land–atmosphere coupling (i.e., spatial and seasonal variations) in eastern China, a typical monsoon area. It is found that two diagnostics of land–atmosphere coupling (i.e., SM–ET correlation and ST–ET correlation) are highly dependent on the climatology of SM and ST. By combining the SM–ET and ST–ET relationships, two “hot spots” of land–atmosphere coupling over eastern China are identified: Southwest China and North China. In Southwest China, ST is relatively high throughout the year, but SM is lowest in spring, resulting in a strong coupling in spring. However, in North China, SM is relatively low throughout the year, but ST is highest in summer, which leads to the strongest coupling in summer. Our results emphasize the dependence of land–atmosphere coupling on the seasonal evolution of climatic conditions and have implications for future studies related to land surface feedbacks.

This study assesses the performance of 22 Coupled Model Intercomparison Project Phase 5 (CMIP5) historical simulations of rainfall over East Africa (EA) against reanalyzed datasets during 1951–2005. The datasets were sourced from Global Precipitation Climatology Centre (GPCC) and Climate Research Unit (CRU). The metrics used to rank CMIP5 Global Circulation Models (GCMs) based on their performance in reproducing the observed rainfall include correlation coefficient, standard deviation, bias, percentage bias, root mean square error, and trend. Performances of individual models vary widely. The overall performance of the models over EA is generally low. The models reproduce the observed bimodal rainfall over EA. However, majority of them overestimate and underestimate the October–December (OND) and March–May (MAM) rainfall, respectively. The monthly (inter-annual) correlation between model and reanalyzed is high (low). More than a third of the models show a positive bias of the annual rainfall. High standard deviation in rainfall is recorded in the Lake Victoria Basin, central Kenya, and eastern Tanzania. A number of models reproduce the spatial standard deviation of rainfall during MAM season as compared to OND. The top eight models that produce rainfall over EA relatively well are as follows: CanESM2, CESM1-CAM5, CMCC-CESM, CNRM-CM5, CSIRO-Mk3-6-0, EC-EARTH, INMCM4, and MICROC5. Although these results form a fairly good basis for selection of GCMs for carrying out climate projections and downscaling over EA, it is evident that there is still need for critical improvement in rainfall-related processes in the models assessed. Therefore, climate users are advised to use the projections of rainfall from CMIP5 models over EA cautiously when making decisions on adaptation to or mitigation of climate change.

During the last decade, several high intensity and long duration droughts happened in Southwest China (SWC) and resulted in tremendous socioeconomic losses. Meanwhile, it is well known that soil moisture (SM) plays a key role in land–atmosphere interaction and weather/climate prediction and is a direct drought index. Thus, a general analysis of SM is beneficial to drought research and prediction over this region. Based on the SM data of Global Land Data Assimilation System V2.0, we examined the temporal variations in SM in SWC during 1961–2012. Results show that significant soil drying trend happened in autumn accompanied by an evident abrupt change in 1991. Moreover, SM exhibits a strong and season-dependent persistence. Particularly, the autumn SM anomaly shows the strongest memory that can be sustained to the next spring. Along with the decadal shift of SM, the memory time of autumn SM can extend from 3 months before 1991 to 6 months in recent years. We further used the Standardized Precipitation Evapotranspiration Index (SPEI) at multiple time scales to identify the droughts in different seasons over SWC, and the inter-annual change patterns of autumn SM and SPEIs are generally in agreement with each other, which confirms that SM is suitable for indicating the droughts. Our results suggest that the autumn SM can be a potential predictor of persistent droughts over SWC, especially for those multi-season persistent drought events started in autumn.

This study investigates the variability of extreme rainfall (temperature) events in the twenty-first century based on 18 (24)-member multimodel simulations of models participating in phase 5 of the Couple Model Intercomparison Project (CMIP5). The study employed extreme indices defined by the WMO’s Experts Team on Climate Change Detection Indices, under two radiative forcing scenarios: RCP4.5 and RCP8.5. Two 30-year time periods, mid- (2021–2050) and end (2071–2100) of the twenty-first century, are considered for investigation of extremes, relative to the baseline period (1961–1990). Mann–Kendall test statistic and Sen’s slope estimator are used to investigate trend. Temperature shows a remarkable increase with an increase in radiative forcing. A sharp augmentation in temperature is projected towards the end of the twenty-first century. There will be almost zero cool days and cold nights by the end of the century. Very wet and extremely very wet days increase, especially over Uganda and western Kenya. Variation in maximum 1-day precipitation (R × 1 day) and maximum 5-day precipitation amount shows a remarkable increase in variance towards the end of the twenty-first century. Although the results are based on relatively coarse resolution data, they give likely conditions that can be utilized in long-term planning and be relied on in advanced studies.

This study presents potential future variations of mean rainfall and temperature over East Africa (EA) based on five models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) and representative concentration pathways (RCPs): 4.5 and 8.5. In this study, climate simulations of two timeframes, a baseline period (1961–1990) and projection period (2071–2100), are compared. The models reproduce EA's bimodal rainfall pattern but overestimate and underestimate seasonal rainfall of October–December (OND) and March–May (MAM), respectively. Rainfall is projected to increase under the two scenarios. Larger increases in rainfall will occur during the OND season than during the MAM season and in RCP8.5 than in RCP4.5. During the last half of the 21st century, EA is likely to warm by 1.7–2.8 and 2.2–5.4 °C under the RCP4.5 and RCP8.5 scenarios, respectively, relative to the baseline period. Scenario uncertainty is projected to exceed model uncertainty from the middle to the end of the 21st century. The central parts of Kenya and the Lake Victoria Basin will witness the highest increases in seasonal rainfall. The probability density functions (PDFs) of future seasonal rainfall show a positive shift and a statistically insignificant increase in variance relative to the baseline. Thus, EA is likely to experience an increase in extreme rainfall events. Understanding the future climate variability in EA is important for planning purposes but these results are based on relatively course resolution models prone to bias and therefore should be used with caution. There is a need for further research on climate projections over EA, including determining the causes of the poor performance of global models in reproducing rainfall climatology and trends over the region.

Updated information on trends of climate extremes is central in the assessment of climate change impacts. This work examines the trends in mean, diurnal temperature range (DTR), maximum and minimum temperatures, 1951–2012 and the recent (1981–2010) extreme temperature events over Kenya. The study utilized daily observed and reanalyzed monthly mean, minimum, and maximum temperature datasets. The analysis was carried out based on a set of nine indices recommended by the Expert Team on Climate Change Detection and Indices (ETCCDI). The trend of the mean and the extreme temperature was determined using Mann-Kendall rank test, linear regression analysis, and Sen’s slope estimator. December–February (DJF) season records high temperature while June–August (JJA) experiences the least temperature. The observed rate of warming is + 0.15 °C/decade. However, DTR does not show notable annual trend. Both seasons show an overall warming trend since the early 1970s with abrupt and significant changes happening around the early 1990s. The warming is more significant in the highland regions as compared to their lowland counterparts. There is increase variance in temperature. The percentage of warm days and warm nights is observed to increase, a further affirmation of warming. This work is a synoptic scale study that exemplifies how seasonal and decadal analyses, together with the annual assessments, are important in the understanding of the temperature variability which is vital in vulnerability and adaptation studies at a local/regional scale. However, following the quality of observed data used herein, there remains need for further studies on the subject using longer and more data to avoid generalizations made in this study.

This study investigated monthly and annual reference evapotranspiration changes over southwestern China (SWC) from 1960 to 2012, using the Food and Agriculture Organization of the United Nations’ report 56 (FAO-56) Penman–Monteith equation and routine meteorological observations at 269 weather sites. During 1960–2012, the monthly and annual decreased at most sites. Moreover, the SWC regional average trend in annual was significantly negative (p < 0.05); this trend was the same in most months. A new separation method using several numerical experiments was proposed to quantify each driving factor’s contribution to changes and exhibited higher accuracy based on several validation criteria, after which an attribution analysis was performed. Across SWC, the declining annual was mainly due to decreased net radiation (RN). Spatially, the annual changes at most sites in eastern SWC (excluding southeastern West Guangxi) were generally due to RN, whereas wind speed (WND) or vapor pressure deficit (VPD) was the determinant at other sites. Nevertheless, the determinants differed among 12 months. For the whole SWC, increased VPD in February and decreased WND in April, May, and October were the determinant of decreased ; however, decreased RN was the determinant in other months. Overall, the determinant of the monthly changes exhibited a complex spatial pattern. A complete analysis of changes and the related physical mechanisms in SWC is necessary to better understand hydroclimatological extremes (e.g., droughts) and to develop appropriate strategies to sustain regional development (e.g., water resources and agriculture). Importantly, this separation method provides new perspective for quantitative attribution analyses and thus may be implemented in various scientific fields (e.g., climatology and hydrology).

Due to the close relationship of climate change with reference evapotranspiration (ETo), detecting changes in ETo spatial distribution and its temporal evolution at local and regional levels is favorable to comprehensively understand climate change-induced impacts on hydrology and agriculture. In this study, the objective is to identify whether climate change has caused variation of ETo spatial distribution in different analysis periods [i.e., long- (20-year), medium- (10-year), and short-term (5-year)] and to investigate its temporal evolution (namely, when these changes happened) at annual and monthly scales in Southwest China (SWC). First, we estimated ETo values using the United Nations Food and Agriculture Organization (FAO) Penman-Monteith equation, based on historical climate data measured at 269 weather sites during 1973–2012. The analysis of variance (ANOVA) results indicated that the spatial pattern of annual ETo had significantly changed during the past 40 years, particularly in west SWC for the long-term analysis period, and west and southeast SWC in both medium- and short-term periods, which corresponded to the percent area of significant differences which were 21.9, 58.0, and 48.2 %, respectively. For investigating temporal evolution of spatial patterns of annual ETo, Duncan’s multiple range test was used, and we found that the most significant changes appeared during 1988–2002 with the significant area of higher than 25.0 %. In addition, for long-, medium-, and short-term analysis periods, the spatial distribution has significantly changed during March, September, November, and December, especially in the corresponding periods of 1988–1997, 1983–1992, 1973–1977, and 1988–2002. All in all, climate change has resulted in significant ETo changes in SWC since the 1970s. Knowledge of climate change-induced spatial distribution of ETo and its temporal evolution would aid in formulating strategies for water resources and agricultural managements.

Under the exacerbation of climate change, climate extreme events, especially for drought, happened frequently and intensively across the globe with greater spatial differences. We used the Standardized Precipitation-Evapotranspiration Index computed from the routine meteorological observations at 269 sites in Southwest China (SWC) to study the drought characteristics (e.g., extent, duration and intensity) and their decadal variations during 1971–2012. It was revealed that the drought, in responses to the coupling between decadal precipitation and potential evapotranspiration (PET) anomalies, differed among regions and periods. For the entire SWC, droughts in 1970s and 2000s+ was generally stronger than in 1980s and 1990s with respect to their spatial extent, duration and intensity, especially in 2000s+. It was well-known that drought was closely related with a lack of precipitation; however, the impact of atmospheric demand of evaporation (reflected by PET here) on drought (e.g., duration and intensity) was rarely paid enough attentions. To that end, a spatial multi-linear regression approach was proposed in this study for quantifying the contributions of decadal PET and precipitation variations to drought duration and intensity. We have found that the contributions of decadal PET anomalies to drought duration and intensity could exceed those of precipitation, e.g., during 1980s and 1990s in SWC. Additionally, despite the strongest droughts in 2000s+, it was suggested that PET could exert comparable impacts on drought anomalies as precipitation. All these findings implied that PET plays a critical role in drought event, which acts to amplify drought duration and intensity. To sum up, this study stressed the need for enough attentions for PET processes in drought studies.

Impacts of large-scale urbanization over eastern China on East Asian summer monsoon circulation and climate are investigated by comparing three 25-year climate simulations with and without incorporating modified land cover maps reflecting two different idealized large-scale urbanization scenarios. The global atmospheric general circulation model CAM4.0 that includes an urban canopy parameterization scheme is employed in this study. The large-scale urbanization over eastern China leads to a significant warming over most of the expanded urban areas, characterized by an increase of 3 K for surface skin temperature, 2.25 K for surface air temperature, significant warming of both daily minimum and daily maximum air temperatures, and 0.4 K for the averaged urban–rural temperature difference. The urbanization is also accompanied by an increase in surface sensible heat flux, a decrease of the net surface shortwave and long-wave radiation, and an enhanced surface thermal heating to the atmosphere in most Eastern Asia areas. It is noted that the responses of the East Asian summer monsoon circulation exhibits an evident month-to-month variation. Across eastern China, the summer monsoon in early summer is strengthened by the large-scale urbanization, but weakened (intensified) over southern (northern) part of East Asia in late summer. Meanwhile, early summer precipitation is intensified in northern and northeastern China and suppressed in south of ~35°N, but late summer precipitation is evidently suppressed over northeast China, the Korean Peninsula and Japan with enhancements in southern China, the South China Sea, and the oceanic region south and southeast of the Taiwan Island. This study highlights the evidently distinct month-to-month responses of the monsoon system to the large-scale urbanization, which might be attributed to different basic states, internal feedbacks (cloud, rainfall) as well as a dynamic adjustment of the atmosphere. Further investigation is required to understand the dynamic mechanisms by which a large-scale urbanization in China affects eastern Asian climate and summer monsoon circulation, especially possible internal feedbacks relevant to the sub-seasonal changes of the monsoon system.

The International Centre for Theoretical Physics (ICTP) regional climate model RegCM4.0 is used in this study to examine its ability to reproduce the climate of East Africa (EA) in regard to the annual cycle and June-to-August (JJA) seasonal climatology. Two domain sizes (large domain (LD) and small domain (SD)) and two cumulus convection schemes (Grell convection scheme with Fritsch-Chappell closure as- sumption (GRE scheme) and MIT scheme (EMA scheme)) are used. Simulations were done for the period 1989-2008 at a resolution of 50 km. The experiments were performed with the initial and lateral boundary conditions obtained from ERA- Interim-gridded reanalysis data at a 1.5° resolution. The vari- ables investigated are precipitation, temperature, humidity, diur- nal temperature range, and 850-hPa winds. Results show that the model realistically reproduces the East African climate, with a few discrepancies due to the different cumulus convection schemes and the domain sizes used. Grell with Fritsch- Chappell (Grell-FC) scheme captures well the observed climate in regard to the annual cycle and June-to-August seasonal cli- matology, with a tendency to underestimate rainfall over the JJA rainfall maximum region (RMR). This scheme performs better in LD than in SD. EMA scheme similarly captures well the observed climatology. It tends to overestimate rainfall over RMR. It however performs better in SD than in LD. The ensem- ble mean of simulations with GRE and EMA schemes (ENSM) tends to offer an improved representation of the observed climate, with a few discrepancies owing to the individual schemes used. In general, therefore,considering the performance of the model in both domains, the East African climate based on this study is better simulated by the Grell-FC scheme over LD. The observed biases in this study signify that the ability of the model in simulating climate over East Africa is still a significant challenge. Thus, future work must focus on improving the performance of the model in climate research over the region.

The influence of topography on east African climate is investigated using the International Centre for Theoretical Physics Regional Climate Model, with focus on October to December season. Results show that the mean rainfall (temperature) significantly reduces (increases) over the region when topography elevation is reduced. Based on the model, when topography over the selected region (KTU) is reduced to 25%, the mean rainfall (temperature) over east Africa is reduced (increased) by about 19% (1.4°C). The maximum rainfall (temperature) reduction (increase) is however observed around the region over which topography is reduced. The reduction in topography elevation resulted in an anomalous moisture divergence at low level and descending motion over the region. KTU topography enhances the surface heat flux over KTU region and tends to enhance convection over both KTU and the east African region. The topography also helps in the generation of the high frequency mesoscale and subsynoptic disturbances over the region. These disturbances produce precipitation over the region and may also enhance precipitation systems over remote areas due to propagation of the disturbances. The magnitude of the zonal wind speed at 850 hpa increases with the decrease in topography elevation.