Evaluation of severity changes of compound dry and hot events in China based on a multivariate multi-index approach

Compound dry and hot events have received increasing attention due to their serious impacts on different sectors of the society. Understanding their variability is of critical importance for developing adaptation measures to reduce their adverse impacts. Previous studies have shown increased frequency of these compound events in past decades at regional and global scales; however, the investigation of changes in their severity has been rather rare. The objective of this study is to evaluate severity changes of compound dry and hot events for the warm season during the period 1961–2012 in China using two indices, namely, Standardized Compound Event Indicator (SCEI) and Standardized Dry Hot Index (SDHI), based on monthly precipitation and temperature. Results show a significant increase in the severity of compound dry and hot events in most parts of China, which is mainly dominated by temperature compared to precipitation. In addition, significant increase of the spatial extent of compound dry and hot events at different severity levels in China is observed, with more areas affected by these compound events after the 1990s. For large regions from northeast to southwest China, severe conditions of compound dry and hot events are shown to be associated with high risk of agricultural droughts. Both the two indices show similar trends in the severity of compound dry and hot events, which indicates the robustness of increased spatial and temporal patterns, highlighting the pressing need for improved understanding to reduce their adverse impacts.