Dry Coupling Aggravates Soil Drought and Atmospheric Aridity Over North China

The drought-prone North China (NC) is located in one of so called "hot spots" for land–atmosphere coupling. To find out the role that the dry and wet coupling plays in NC drought, land-atmosphere coupling at daily time scales is divided into four regimes: dry coupling, wet coupling, transition, and atmospherically controlled, based on the joint probability space of the low-level humidity index (HI), convective triggering potential (CTP) and surface soil moisture (SM), and then a time series of the same coupling types is created for each spatial grid and each dry or wet coupling event is identified. Results show that the initial value of HI determines the type of coupling events, and the initial SM plays an important role in the persistence of the event. In drought events, the dry coupling aggravates soil drought and atmospheric aridity concurrently and the wet coupling is beneficial for drought recovery.