The role of land-atmosphere coupling for climate variability and extremes over East Asia

The Global Land-Atmosphere Coupling Experiment (GLACE) and other Atmospheric General Circulation Model (AGCM) studies demonstrated that land-atmosphere coupling plays an important role in influencing summer climate variations and variability. However, large uncertainties exist in AGCM simulations of land-atmosphere interactions on local-to-regional scales. In this study, two long-term regional climate model simulations with the Weather Research and Forecasting (WRF) model are performed to assess how land-atmosphere coupling affects summer climate variability and extremes over East Asia. The Control experiment (CTL) uses a fully coupled land surface model while an additional experiment uncouples the land surface from the atmosphere by replacing soil moisture evolution at each time step with the climatology of CTL. Results indicate that land-atmosphere coupling plays a critical role in influencing summer climate variability, in particular over the climatic and ecological transition zones. Soil moisture-temperature interactions strongly increase interannual variability of daily mean temperature over southern Siberia-northern Mongolia region, the region from Northeast China to Central China, and eastern part of South Asia, accounting for half or more of the total variance. Soil moisture, through its enhancement of convection, makes a dominant contribution to precipitation variability over the climatic and ecological transition zones of southern Siberia-northern Mongolia region and northern China, and many areas of Northwest China. We further assess the role of land-atmosphere coupling for temperature and precipitation extremes, and discussed the mechanisms involved.