Evidence for Intensification in Meteorological Drought since the 1950s and Recent Dryness-Wetness Forecasting in China

Drought is one of the major environmental stressors; drought is increasingly threatening the living environment of mankind. The standardized precipitation evapotranspiration index (SPEI) with a 12-month timescale was adopted to monitor dry-wet status over China from 1951 to 2021. The modified Mann-Kendall (MMK) and Pettitt tests were used to assess the temporal trend and nonlinear behavior of annual drought variability. The analysis focuses on the spatio-temporal structure of the dry-wet transition and its general connections with climate change processes. In addition, the seasonal autoregressive integrated moving average (SARIMA) model was applied to forecast the dry-wet behavior in the next year (2022) at 160 stations, and the hotspot areas for extreme dryness-wetness in China were identified in the near term. The results indicate that the dry-wet climate in China overall exhibits interannual variability characterized by intensified drought. The climate in the Northeast China (NEC), North China (NC), Northwest China (NWC), and Southwest China (SWC) has experienced a significant (p < 0.05) drying trend; however, the dry-wet changes in the East China (EC) and South Central China (SCC) are highly spatially heterogeneous. The significant uptrend in precipitation is mainly concentrated to the west of 100 degrees E; the rising magnitude of precipitation is higher in Eastern China near 30 degrees N, with a changing rate of 20-40 mm/decade. Each of the sub-regions has experienced significant (p < 0.01) warming over the past 71 years. Geographically, the increase in temperature north of 30 degrees N is noticeably higher than that south of 30 degrees N, with trend magnitudes of 0.30-0.50 degrees C/decade and 0.15-0.30 degrees C/decade, respectively. The response of the northern part of Eastern China to the warming trend had already emerged as early as the 1980s; these responses were earlier and more intense than those south of 40 degrees N latitude (1990s). The drying trends are statistically significant in the northern and southern regions, bounded by 30 degrees N, with trend magnitudes of -0.30--0.20/decade and -0.20--0.10/decade, respectively. The northern and southwestern parts of China have experienced a significant (p < 0.05) increase in the drought level since the 1950s, which is closely related to significant warming in recent decades. This study reveals the consistency of the spatial distribution of variations in precipitation and the SPEI along 30 degrees N latitude. A weak uptrend in the SPEI, i.e., an increase in wetness, is shown in Eastern China surrounding 30 degrees N, with a changing rate of 0.003-0.10/decade; this is closely associated with increasing precipitation in the area. Drought forecasting indicates that recent drying areas are located in NWC, the western part of NC, the western part of SWC, and the southern part of SCC. The climate is expected to show wetting characteristics in NEC, the southeastern part of NC, and the eastern part of EC. The dry-wet conditions spanning the area between 30-40 degrees N and 100-110 degrees E exhibit a greater spatial variability. The region between 20-50 degrees N and 80-105 degrees E will continue to face intense challenges from drought in the near future. This study provides compelling evidence for the temporal variability of meteorological drought in different sub-regions of China. The findings may contribute to understanding the spatio-temporal effect of historical climate change on dry-wet variation in the region since the 1950s, particularly in the context of global warming.