Spatiotemporal evolution characteristics of compound drought and heatwave events in Dongting Lake Basin

Abstract

[Objective] In the context of global climate warming, extreme weather events occur with increasing frequency in the Dongting Lake Basin, and compound drought and heatwave events(CDHEs) exacerbate their influence on socioeconomy and the ecological environment. Analyzing the spatiotemporal evolution patterns of the CDHEs in the Dongting Lake Basin and their response to atmospheric circulation factors is of great significance for regional disaster prevention and mitigation. [Methods] Based on daily maximum temperatures, Standardized Precipitation Evapotranspiration Index(SPEI), and atmospheric circulation indices from 1971 to 2020, trend analysis and wavelet coherence analysis were employed to analyze the spatiotemporal evolution patterns and atmospheric circulation driving mechanisms of CDHEs in the Dongting Lake Basin. [Results] The results showed that from 1971 to 2020, the annual maximum daily temperature in the Dongting Lake Basin showed a significant increasing trend, with a rate of 0.28 ℃/10 a. The SPEI showed substantial interannual fluctuations, with no clear pattern. Droughts were relatively frequent and persistent, occurring during 1983—1988 and 2003—2009. The number of days and duration of CDHEs in the river basin demonstrated increasing trends, with the number of days increasing at rates of 2.2 d/10 a, 1.3 d/10 a, 0.3 d/10 a, and the duration increasing at 0.9 d/10 a, 0.6 d/10 a, 0.2 d/10 a, respectively, exhibiting significant interdecadal variation characteristics. Seasonally, CDHEs mainly occurred in July and August. In the latter 25 years, the number of days and duration of these events increased compared to the former 25 years. Spatial frequency variations exhibited an “increase in the east and decrease in the west” pattern. The northeastern region showed the most significant increase, exceeding 200%. The frequency of CDHEs was influenced by multi-scale atmospheric circulation factors, among which the El Ni1o-Southern Oscillation(ENSO), Pacific Decadal Oscillation(PDO), North Atlantic Oscillation(NAO), and Western Pacific Subtropical High(WPSH) demonstrated more significant influence. [Conclusion] From 1971 to 2020, the number of days and duration of CDHEs in the Dongting Lake Basin showed increasing trends, with significant spatial distribution differences. An overall increasing trend was observed in the east, while the decreasing areas were mainly located in the west. Atmospheric circulation factors such as ENSO, PDO, and NAO were important influencing factors of the occurrence of CDHEs. These findings provide a scientific basis for regional compound disaster risk assessment and adaptive management.

Keywords

Dongting Lake Basin / compound drought and heatwave events / daily-scale SPEI / spatiotemporal variation / atmospheric circulation factors / wavelet coherence analysis / extreme high temperature / influencing factor