Spatial and Temporal Evolution Patterns of Droughts in China over the Past 61 Years Based on the Standardized Precipitation Evapotranspiration Index

The SPEI-12 values of 2254 meteorological stations in China were interpolated by inverse distance weight space in ArcGIS 10.8.1 software, and the spatial distribution (Figure 5a–f) and average SPEI spatial distribution (Figure 5g) of each decadal drought in China over the past 61 years were obtained, as shown in Figure 5. In the 1960s, droughts were most severe in the Xinjiang region of China, followed by east-central Qinghai Province and western Gansu Province. Mild droughts were experienced in eastern and northeastern China, while Tibet, northern central China, and western Yunnan Province were wetter (Figure 5a). By the 1970s, droughts gradually expanded in Xinjiang, with droughts also occurring in northern Tibet and western Qinghai; widespread droughts in eastern China shifted northward, with most of central China being affected by drought; drought conditions increased in Heilongjiang Province in northeastern China; while the Guangdong–Guangxi region in southern China shifted from droughts to wet conditions (Figure 5b). In the 1980s, droughts gradually weakened in Xinjiang and Heilongjiang, while drought intensity increased in Tibet, Guizhou, Shandong, and northern Guangxi, with the highest decadal average drought intensity of −1.09106; meanwhile, Shaanxi, eastern Sichuan, and southern Gansu were wet, with the highest moisture intensity of 1.15548 (Figure 5c). In contrast, the spatial distribution of drought in the 1990s was quite different from that of the previous decade, with droughts converging toward the center; stronger droughts occurred in southern Gansu, Shaanxi, Shanxi, eastern Sichuan, Qinghai, and eastern Tibet, while Xinjiang exhibited a moist climate (Figure 5d). By the 21st century, stronger droughts shifted to northeastern China, with higher intensity droughts occurring over large areas in eastern Inner Mongolia, Heilongjiang, and western Jilin provinces, and the highest decadal mean drought index was −1.14854, and minor droughts also occurring in central and southern China (Figure 5e). In the last decade, 2010–2021, the spatial pattern of drought changed again, with high-intensity droughts shifting to southwestern China, with the most severe in Yunnan Province and parts of southern Tibet, where the highest decadal mean drought intensity was −1.10677; in this decade, the wettest areas were central Qinghai Province and southeastern Xinjiang, while parts of Heilongjiang and Jiangsu–Zhejiang also shifted to wetter conditions. At the same time, Heilongjiang and parts of Jiangsu and Zhejiang also changed to wet (Figure 5f).

As shown by the spatial and temporal evolutions of droughts over the 61 years, the average drought intensity was highest in northwestern Qinghai Province, while high moisture intensity occurred in the western part of Inner Mongolia Autonomous Region (Figure 5g). In terms of the changes in the spatial pattern of drought over the six decades in China, the areas experiencing high-intensity droughts generally show a pattern of initially moving from the northwest to the southwest, then from the southwest to central China, later from central China to the northeast, and finally back to the southwest.