Effects of Irrigated Cropland on the Local and Regional Climate over Northeast Asia in a Regional Climate Model

摘要

The effects of land cover change (LCC), mixed woodland to irrigated cropland, on climate over Northeast Asia according to the intensity of the East Asian monsoon were investigated using a regional climate model (RegCM4.0). All model configurations were same except for the prescription of land cover over North China Plain (NCP) and South Korea (SK). Generally, LCC directly induced decreases in the leaf area index and roughness length but increases in soil moisture, and led to the increases in surface wind speed and changes in the surface energy budget (SEB) in two regions. However, these changes resulted in different effects on climate according to the region, season, and climate regime. In NCP, increased soil moisture directly caused increases in the latent heat flux, leading to cooling of daily maximum temperature in all seasons. Also, the increased soil moisture is a key role of increase of daily minimum temperature during winter with respect to the increased portion of ground heat flux with decrease of albedo. The subsidence by surface cooling over NCP during summer resulted in significant decreases in the moist static energy, bring about decreases in convective precipitation indirectly. These effects were more dominant for the weak monsoon year. In SK, direct effects of LCC on the SEB were mostly similar to those of NCP, but summer climates were largely affected by indirect effects, advection of warm and humid air masses, associated with circulation changes due to local cooling effects over NCP. Consequently, summer precipitation over SK is increased by about +60-+100mm during JJA.