Simulated effects of cropland extension on climate over Northeast China from 1980 to 2000 by WRF Model

Abstract

By using the land use/cover data for the early 1980 and 2000 in Northeast China, we carried out two 21-year(1980-2000) simulations, respectively, with the Weather Research and Forecast(WRF) model. This paper is aimed to investigate the effects of cropland extension on climate in Northeast China. In winter and spring, the replacement of natural grassland and forest by cropland enhanced land surface albedo, and surface net solar radiation was therefore reduced. As a consequence, the surface sensible heat flux decreased and the cooling effect occurred. Mostly, the local surface air temperature dropped by 0.1° C to 1.0° C. The cooling strength is comparable to the contemporaneous background temperature change which is induced by large circulation and sea surface temperature changes. In summer and autumn, the replacement of nature vegetation by cropland reduced land surface albedo, and surface net solar radiation was therefore increased. Meanwhile, the surface latent heat flux increased largely and the surface sensible heat flux decreased. As a result, there was also a cooling effect on local surface climate. These findings demonstrate detectable effects of land use/cover changes on local temperature. The effects of agricultural development on summer precipitation vary with background climate. In the South-Drought and North-Flood years, the decreased precipitation is detected in the Hulun Buir to central Heilongjiang province and central Jilin province and around the Liaodong Gulf while the precipitation increases in common boundary area of Heilongjiang, Jilin and Inner Mongolia. In the South-Flood and North-Drought years, the precipitation anomaly pattern is approximately reverse to the abovementioned South-Drought and North-Flood years with the exception that there is still decreased precipitation around the Liaodong Gulf. However, due to limited area with land use/cover changes, the impact on regional mean temperature is very limited.