We use a case study to show that a continuous heavy rainfall process in southern China was closely related to tropical cyclone activity in the Bay of Bengal. The continuous heavy rainfall that occurred in southern China on 11–13 May 2002 can be considered as two different processes. The first process, referred to as a predecessor rain event, occurred over southwestern China before landfall of the tropical cyclone. The second process occurred after dissipation of the tropical cyclone when its remnant caused heavy rainfall that expanded from southwestern China to the middle to lower reaches of the Yangtze–Huaihe river basin. Both of the heavy rainfall processes were closely related to the transport of warm, moist air associated with a tropical cyclone originating over the Bay of Bengal, but the mechanisms in the two processes were quite different. Low-level orographic forcing was the main contributor to the predecessor rain event, whereas baroclinic frontogenesis induced by thermal advection was the main contributor to the tropical cyclone remnant event. Both heavy rainfall events occurred beneath the equatorial entrance of the upper level East Asian subtropical jet.

In recent decades, Southwest China (SWC) has experienced a series of severe and extensive droughts resulting in tremendous socioeconomic losses. The annual maximum dry spell length (AMDSL), which refers to the number of consecutive days without rainfall, or days with rainfall below a threshold, plays an important role in triggering drought. The main objective of this study is to provide a comparison of the capabilities of current regional climate models (RCMs) in simulating extreme dry spell characteristics in mountainous SWC. Five available RCM simulations utilized in the Coordinated Regional Climate Downscaling Experiment (CORDEX)-East Asia project over 1981–2005 were employed in this study; the RCMs being NIMR-HadGEM3, SNU-MM5, SNU-WRF, KNU-RegCM4, and YSU-RSM. First, it was found that all of the RCMs reasonably simulate the main seasonality features of rainfall and dry days in SWC. Furthermore, four of the RCMs, excepting YSU-RSM, can accurately capture the spatial pattern of dry-day occurrence based on Taylor diagram diagnosis. Second, we assessed the performance of the five RCMs to detect and reproduce the climatology and variability of the AMDSL. In general, the RCMs simulate the spatial pattern of long-term mean and interannual variability of the AMDSL in SWC well. Based on Taylor diagram evaluation, NIMR-HadGEM3 was the best among the five in simulating the AMDSL characteristics. Third, the generalized extreme value (GEV) distribution is considered the most suitable model for fitting the AMDSL in both observation and RCM experimental data in comparison to other three-parameter probabilistic models. Higher value centers of the scale parameter and the location parameter indicate a wider and amplified distribution of the AMDSL over the low-latitude highlands (LLH) region against other areas in SWC, which is consistent with the spatial patterns of climatological AMDSL. In addition, sensitivity analysis of different thresholds for dry days shows that the 1 mm threshold is suitable for this study and that different threshold choices have little effect on simulation ability. Overall, the results show that although significant differences are found between RCMs, the RCMs excepting YSU-RSM can reasonably reveal extreme dry spell occurrence and amplitude, along with the spatial distribution of the AMDSL at a 20-year return period in SWC. This information is useful for model evaluation and improvement, future climate projections, and water resource risk management.

According to the Sixth Assessment Report of the IPCC, the global surface temperature has been higher in each of the last 4 decades compared to any previous decade since 1850. With the ongoing intensification of global warming, the intensity and frequency of extreme drought events have significantly increased. Based on the CN05.1 observational dataset and the results of five regional simulations from RegCM4.0 under future warming scenarios from the CORDEX (Regional Climate Downscaling Experiment), extreme dry periods are characterized by the number of consecutive dry days (CDD index). The Generalized Extreme Value (GEV) distribution is used to model the probability distribution of the CDD index in China to assess the spatiotemporal variations of extreme dry periods. By analyzing the spatiotemporal trends of the CDD index in China over the past 60 years and utilizing simulation techniques to assess the probability distribution characteristics of the CDD index, the study incorporates the Taylor diagram to evaluate the simulation performance of RegCM4.0. Finally, projections of the temporal and spatial distribution of the CDD index in China under a stable 2°C warming scenario, as well as changes in the ensemble mean of the five regional simulations relative to historical climate conditions, are presented.The results indicate that the spatial distribution of the CDD index in China gradually decreases from northwest China and the Qinghai-Tibet Plateau to the eastern coastal areas. Over the past 60 years, the CDD index has decreased in northwest China and the Qinghai-Tibet Plateau, while it has increased in the eastern coastal regions, Northeast China, and North China, showing significant trends in these areas. The eastern coastal areas exhibit the lowest CDD index and minimal inter-annual variability, while northwest China and the Qinghai-Tibet Plateau show the highest CDD index values and the most significant inter-annual variability. According to the Taylor diagram, under the RCP4.5 emission scenario, the CDD index from simulations using the RegCM4.0 regional climate model, corrected by the Quantile Delta Mapping (QDM) method, shows better performance than uncorrected simulations. The corrected model results are strongly correlated with the CN05.1 observational dataset, with minimal error. Under a 2°C steady warming scenario, Generalized Extreme Value (GEV) analysis of the CDD index and return periods suggests that extreme dry periods will increase in northwest China, the Qinghai-Tibet Plateau, and Northeast China, with a growing disparity in extreme dry periods between the northern and southern regions as the return period increases. Multi-model ensemble projections for future periods under a 2°C stable warming scenario indicate a decreasing trend in the annual mean CDD index in northern China and an increasing trend in southern China.