Abstract
The frequency, duration, and magnitude of heatwaves and droughts are expected to increase in a warming climate, which can have profound impacts on the environment, society, and public health, and these may be severely affected specifically by compound droughts and heatwaves (CDHWs). On the basis of daily maximum temperature data and the one-month standardized precipitation evapotranspiration index (SPEI) from 1961 to 2018, the Gan River Basin (GRB) was taken as a case here to construct CDHW identification indicators and quantify the population exposure to CDHWs. We found that ERA5 reanalysis data performed well in overall simulating temperature, precipitation, one-month SPEI, heatwaves, and CDHWs in the GRB from 1961 to 2018. CDHWs during the period from 1997 to 2018 were slightly higher than that in 1961–1997. CDHWs were more likely to occur in the southern parts of the basin due to the relatively high values of drought–heatwave dependence indices. Atmospheric circulation analysis of the 2003 CDHW in the GRB showed a relatively long-lasting anomalous high pressure and anticyclonic circulation system, accompanied by the positive convective inhibition and surface net solar radiation anomalies. These circulating background fields eventually led to the exceptional 2003 CDHW occurrence in the GRB. The population exposure to CDHWs basically increased, especially for the moderate CDHWs in ERA5. The change in total exposure was mainly due to climate change. Compared with the period from 1989 to 1998, the contributions of the population change effect in 2009–2018 gradually increased with the increase in the CDHW magnitude both in the observations and ERA5 reanalysis data.
Highlights
A combination of climate extremes have received much attention due to their disproportionate and amplified impacts on the ecosystems and societies across the world [1,2,3,4,5,6,7,8]
The special report by the Intergovernmental Panel on Climate Change (IPCC) remarked that a combination of multiple climate events can be termed as a compound event [13], and recommended three general definitions to describe it as such: (a) two or more extreme events occurring simultaneously or successively, (b) a combination of multiple extremes with underlying conditions that amplify the impact of the individual extremes, and (c) a combination of multiple events that are not extremes at their individual level but lead to an extreme event or impact when they combined
We investigated the annual variability of the overall population exposure to the Compound droughts and heatwaves (CDHWs) frequency and compound drought and heatwave magnitude index (CDHMI) in the Gan River Basin (GRB)
Summary
A combination of climate extremes (e.g., low precipitation and high temperatures) have received much attention due to their disproportionate and amplified impacts on the ecosystems and societies across the world [1,2,3,4,5,6,7,8]. Compound events were further divided into four categories based on the weather/climate drivers and hazards/risks [2,5]: (a) preconditioned events due to one or more hazards under particular pre-existing conditions (e.g., floods may arise from a combination of extreme precipitation and “preconditioned” saturated soils), (b) multivariate events occurring simultaneously in the same region (e.g., concurrent droughts and heatwaves), (c) temporally compounding events, for example, a succession of hazards (the same or different events) that affect a given region (e.g., a flood followed by heatwaves), and (d) spatially compounding events occurring in connected areas that are affected by the same or different hazards within a limited time window (e.g., synchronous crop failures due to heatwaves and/or droughts). Exploring the changes in CDHWs based on the severity (CDHW magnitude index) may prove to be useful for understanding CDHW characteristics
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