Flash Drought Characteristics by Different Severities in Humid Subtropical Basins: A Case Study in the Gan River Basin, China

Abstract

It is essential to assess flash drought risk based on a reliable flash drought intensity (severity) index incorporating comprehensive information of the rapid decline (“flash”) in soil moisture towards drought conditions and soil moisture thresholds belonging to the “drought” category. In this study, we used the Gan River Basin as an example to define a flash drought intensity index that can be calculated for individual time steps (pentads) during a flash drought period over a given grid (or station). The severity of a complete flash drought event is the sum of the intensity values during the flash drought. We explored the spatial and temporal characteristics of flash droughts with different grades based on their respective severities. The results show that decreases in total cloud cover, precipitation, and relative humidity, as well as increases in 500 hPa geopotential height, convective inhibition, temperature, vapour pressure deficit, and wind speed can create favorable conditions for the occurrence of flash droughts. Although flash droughts are relatively frequent in the central and southern parts of the basin, the severity is relatively high in the northern part of the basin due to longer duration. Flash drought severity shows a slightly downward trend due to decreases in frequency, duration, and intensity from 1961 to 2018. Extreme and exceptional flash droughts decrease significantly while moderate and severe flash droughts trend slightly upward. Flash drought severity appears to be more affected by the interaction between duration and intensity as the grade increases from mild to severe. The frequency and duration of flash droughts are higher in July to October. The southern part of the basin is more prone to moderate and severe flash droughts, while the northern parts of the basin are more vulnerable to extreme and exceptional flash droughts due to longer durations and greater severities than other parts. Moderate, severe, extreme, and exceptional flash droughts occurred approximately every 3-6, 5-15, 10-50, and 30-200 year intervals, respectively, based on the copula analysis.

Flash drought: A state of the science review

“…Numerous studies have examined flash drought over China (a total of 48; Table 1), including 29 that focused on their climatological characteristics. Ten of these studies quantified a climatology of flash drought across all of China, while 19 studies examined flash drought within individual basins, plateaus, or subregions, including Horqin Sandy Land (Hu et al, 2023), the Huaibei Plain (Gou et al, 2022), the Loess Plateau (Hu et al, 2021; Zhang, Liu, et al, 2022; Zheng et al, 2022), the Pearl River basin (Li et al, 2020a; Yang, Wang, & Wei, 2023; Zha et al, 2023; Zhong et al, 2022), provinces in southern China (Li et al, 2022), Xilinguole (Liu et al, 2022), the Yellow River basin (Liu et al, 2020b), the province of Guangxi (Yang, Yang, et al, 2023; Yun‐chuan et al, 2023), the Hai River basin (Yao et al, 2022), the Gan River basin (Zhang et al, 2017; Zhang et al, 2021), the Qilian Mountains (Yin et al, 2023), and the Yangtze River basin (Liang et al, 2023).…”

The severity of heat and cold waves amplified by high relative humidity in humid subtropical basins: a case study in the Gan River Basin, China

“…1a), with an area of 80,948 km 2 that is controlled by the Waizhou hydrological station (outlet). The GRB receives approximately 678×10 8 m 3 of annual stream ow on average, representing the largest sub-basin both in area (51%) and runoff (50%) of the Poyang Lake Basin (Zhang et al 2021d). The topography of the GRB is relatively high in the south and low in the north.…”

Drought Assessment Using Two-Variate Modelling

“…Drought is considered the most complex and costly natural hazard which affects economic, agriculture and environment [1]. Drought effects are cumulative, extending for months or years over a large spatial extent [2,3]. Drought assessing is important in water resources planning and management [4].…”