Increasing Compound Heat and Precipitation Extremes Elevated by Urbanization in South China

Abstract

Compared with individual events, compound weather and climate extremes may impose more serious influences on natural systems and human society, especially in populated areas. In this study, we examine the changes in the compound precipitation events that follow extremely hot weather within several days during 1961–2017 in South China by taking the Guangdong Province as an example. Additionally, we assess the impacts of urbanization on these changes. It is found that extreme precipitation events in Guangdong are often preceded by hot weather, with an average fraction of 28.25%. The fraction of such compound events is even larger in more populated and urbanized areas such as the Pearl River Delta (PRD) region. Moreover, our results reveal significant increases in the frequency and fraction of the compound extreme heat and precipitation events. These increases are especially stronger in more developed areas (e.g., PRD), and their increasing trends tend to accelerate in recent decades. Furthermore, the local urbanization contributes to 40.91 and 49.38% of the increases in the frequency and fraction of the compound events, respectively. Our findings provide scientific references for policy-makers and urban planners to mitigate the influences of the compound heat and precipitation extremes by considering their increasing risks under the context of global climate change and local urbanization.

Substantial Increase in Heavy Precipitation Events Preceded by Moist Heatwaves Over China During 1961–2019

“…Stations with high fractional contributions are mainly located in North China (43%/37% for HWHP_HI/ HWHP_TW), Northeast China (40%/34%), and the East arid zone (39%/34%), while low values are found in central China (23%/24%), South China (28%/30%) and the West arid zone (22%/22%) (Figures 3A,C). The spatial patterns of fractional contributions are consistent with those shown in previous studies (Wu et al, 2021;You and Wang, 2021;Ning et al, 2022). The linkage between hot-humid HW and HP events is preliminarily explained as follows: HWs warm the atmosphere (characterized by high sensible heat) and provide abundant vapor (high specific humidity), and then enhance the atmospheric instability (large convective available potential energy), which favors the formation of HP (Zhang and Villarini, 2020;You and Wang, 2021).…”

“…An HW_HI/HW_TW event occurring prior to an HP event, within a given time window, is defined as an HWHP event (noted as HWHP_HI and HWHP_TW, respectively) (Lombardo and Ayyub, 2015;Zhang and Villarini, 2020;Chen et al, 2021;Liao et al, 2021;Wu et al, 2021;You and Wang, 2021;Gu et al, 2022;Ning et al, 2022). The window is chosen as 3 days in this study, which is the same as previous studies (Lombardo and Ayyub, 2015;Zhang and Villarini, 2020;Chen et al, 2021;Liao et al, 2021;Wu et al, 2021;You and Wang, 2021;Gu et al, 2022;Ning et al, 2022). In the following analyses, we also examine whether our results are sensitive to the choice of the time window (e.g., 2, 4, and, 7 days).…”

“…Although changes in HWs and HP have been investigated individually at global and regional scales, few studies have focused on sequential heatwave-heavy precipitation (HWHP) events (i.e., an HP event occurring within several days after an HW event) (Lombardo and Ayyub, 2015;Zhang and Villarini, 2020;Chen et al, 2021;Liao et al, 2021;Wu et al, 2021;You and Wang, 2021;Gu et al, 2022;Ning et al, 2022). In the last decade, rare rainstorms tightly following the record-breaking HWs have been reported in some areas.…”

“…Given that both HWs and HP are becoming more extreme and more frequent, the increased risk of HW accompanied by HP is expected to rise. Thus, these HWHP events have been the topic of recent studies (Lombardo and Ayyub, 2015;Zhang and Villarini, 2020;Chen et al, 2021;Liao et al, 2021;Wu et al, 2021;You and Wang, 2021;Gu et al, 2022;Ning et al, 2022).…”

“…Since both HWs and HP over China occur mostly in summer (June-August), joint events are highly likely. Although recent studies have investigated compound flooding and hot extremes over China (Wu et al, 2021;You and Wang, 2021;Gu et al, 2022;Ning et al, 2022), the following questions remain unknown:…”