Amplification of soil moisture deficit and high temperature in a drought-heatwave co-occurrence in southwestern China

Co-occurrence events of droughts and heatwaves characterized by abnormal low soil moisture (SM) and high temperatures may cause more significant impacts on society and natural ecosystems than their individual occurrences. In addition to large-scale weather systems, regional land–atmosphere interactions significantly affect the development of co-occurrence events. In this study, weather research and forecasting model (WRF) was employed to evaluate the contributions of land–atmosphere interactions to a short-term drought-heatwave co-occurrence, which was the onset of the 2009/2010 extreme drought in southwestern China. The numerical experiments with perturbed SM show that the drought with SM deficit amplifies the heatwave severity, especially the afternoon's high temperature, by reducing latent cooling. The drought also tends to self-enhance through SM-precipitation feedback, as the simulated precipitation given lower SM is consistently less than the control run. The hotter/colder atmosphere experiments show that the heatwave also substantially affects the drought by altering land surface fluxes and atmospheric fields. Increases in latent heat in a hotter atmosphere reduce SM. Compared to the simulations for a colder atmosphere, simulated precipitation under a hotter atmosphere tends to be lower in a longer period before stronger precipitation occurs at the late stage of the concurrent event.