Identification and analysis of evolution characteristics of flash drought based on three-dimensional perspective: A case study in the Jialing River basin

Flash drought is an extreme hydrological event, with a short foreseeable period and high destructive force, and it is difficult to monitor. Flash drought aggravates the risk of extreme disasters and seriously threatens agricultural production and urban water security. To explore the temporal and spatial dimension evolution and identifiable characteristics of flash drought, the present study proposed a comprehensive flash drought intensity (FDI) index to evaluate the severity of flash drought in the Jialing River Basin (JRB) based on the standardized evaporative stress ratio (SESR) method. In addition, the Normalized Area -Time Accumulation (NATA) curve was used to describe the three-dimensional continuous spatiotemporal evolution process of flash drought in the basin. The results showed that flash droughts lasted longer and were more severe in the highly urbanized southern part of the basin. In the past 40 years (1980-2020), the frequency, duration, and severity of flash droughts in the JRB increased. According to the susceptibility to flash drought, the JRB can be divided into four drought centers. Drought Center No. 1 is situated in the mountainous region in the northwest of the basin, exhibiting a high frequency of occurrence but affecting a relatively small area. In contrast, Drought Centers No. 2, 3, and 4 are located within urban areas, showing lower occurrence frequency but affecting a wider geographical expanse. Drought events with different developmental characteristics were compared using the NATA curve. Overall, the FD1 flash drought type, occurring in the early stages of drought, accounted for a significant proportion. Meanwhile, the accumulated area affected by FD3 and FD4 flash drought events in the later stages exceeded that of the FD2 flash drought type. In the later period, FD3 and FD4 flash drought events exhibited stronger growth momentum, thereby increasing the complexity and challenges of drought monitoring. The present study provides a theoretical basis for understanding the process, shape and evolution model of drought development under environmental changes as well as enables an enhanced early warning for flash droughts to improve management of water resources.