Abstract
The Asian Summer Monsoon (ASM) onset occurs between late April and early May over inland Indochina, before any transitions occur along the coast. The influence of orography and soil moisture on sub-continental-scale hydrological processes was elucidated by using a regional climate model. The model reproduced many elements of the onset of the Southeast Asia Monsoon (SEAM) associated with land surface conditions, including the early and abrupt onset observed when mountain effects and relatively dry soil conditions were included in the simulations. The nonlinear effects of mountains and ground wetness, combined with realistic increases in precipitation, can modify the hydrological cycle through changes in the surface energy budget. A positive feedback between soil moisture and precipitation increases the moisture source for further precipitation in the transition period.
