Compound hot droughts over China: Identification, risk patterns and variations

Abstract

The increasing concentration of atmospheric greenhouse gases results in not only the consistent tendency of rising temperature but also changes in intensity and frequency of extreme climatic events, and may thereby impact the structure and functioning of terrestrial ecosystems. Increasing concern on increasing global warming has triggered research on extreme climatic events across the globe. In China, existing studies generally focused on single climatic extreme events while the combinations of different climatic events (e.g., high temperatures and droughts) and relevant impacts are rarely studied. To provide a better understanding of compound hot and dry events, in this study we first examined spatial characteristics of the correlations between temperature and drought conditions in the warm season over four different periods (i.e., 1901–1950, 1951–2015, 1951–1980, and 1981–2015). Our results show the negative connection between temperature and droughts encompasses most of China, indicating that high temperatures and droughts are generally concurrent in these regions. We then present a joint dependence model to estimate the occurrence probability of compound hot droughts over the four different periods across the country. Our results demonstrate that likelihood patterns of compound hot droughts vary among different periods. During 1901–1950, the occurrence probability of the compound hot droughts in the eastern part of the country is generally higher than the western part while the likelihood increased significantly in 1951–2015 as compared to pre-1950s over much of western China. A comparison also presents a distinct change in risk patterns between the two sub-periods (1951–1980 and 1981–2015). Given the impact of temperature extremes and drought stress on vegetation and ecosystems, we further examined variations in the likelihood of compound hot droughts regarding different climate zones and terrestrial ecosystems over various periods. Our findings may provide additional insights regarding the climate extremes and risk evaluation over China in a warming world. The proposed framework to evaluate the compound drought and occurrence probability over different climate zones and terrestrial ecosystems could also offer a valuable reference to other regions worldwide.