Co-occurrence of droughts and heat waves under the changing climate in the Pearl River Basin: Variations, interactions and impacts

Increases in air temperature and changes in precipitation regimes caused by global warming lead to considerable variations in heat waves and droughts, two of the most costly natural hazards for society. Droughts and heat waves are mainly caused by large- scale abnormal weather systems, such as ENSO and Atlantic Multi-decadal Oscillation. At the same time, the land-atmosphere interactions between droughts and heat waves can enhance each other. Such co-occurrences of droughts and heat waves are self- perpetuating and often associated with record-breaking drought-heat wave events. Although investigations of co-occurrence events have been conducted over Europe and the United States, similar studies for the Pearl River Basin (PRB), which is under a different climate system, are very limited. The PRB is located in the south China under subtropical monsoon climate and plays an indispensable role in providing water resources for the socioeconomic development of the Pearl River Delta (PRD), Hong Kong and Macau. Although the PRB is usually considered as with abundant precipitation, the high water demand and large population coupled with the changing climate make the PRB vulnerable to both droughts and heat waves. Droughts can cause salinity intrusion by seawater as water tables fall and thus causes threats to coastal drinking water supply, as well as adverse impacts on agricultural productivity, shipping and hydropower generation across the PRB, and heat waves can trigger heat-related diseases and deaths. The proposed study will investigate the changes, interactions and impacts of the co- occurrence of droughts and heat waves across the PRB under the changing climate. Datasets for observations, reanalysis data and Global Climate Model (GCM) outputs will be developed. The Variable Infiltration Capacity (VIC) and Weather Research and Forecasting model (WRF) will be configured for the PRB to simulate droughts and heat waves and conduct sensitivity experiments of the land-atmosphere interactions. The objectives of the proposed study are three-fold: (1) to characterize the spatio-temporal changes in the duration, intensity and joint return period of the co-occurrence across the PRB during the 21st century; (2) to analyze the sensitivity of land-atmosphere interactions to the development and evolution of the co-occurrence events under the changing climate, and; (3) to evaluate the impacts of the co-occurrence on society in terms of affected areas and heat stress to humans with the consideration of humidity. The expected outcomes of the proposed study will help decision makers to make predictions, give early warning, and plan for potential extreme drought-heat wave events.