Agriculture Development-induced Surface Albedo Changes and Climatic Implications Across Northeastern China

To improve the understandings on regional climatic effects of past human-induced land cover changes, the surface albedo changes caused by conversions from natural vegetation to cropland were estimated across northeastern China over the last 300 years, and its climatic effects were simulated by using the Weather Research and Forecasting (WRF) model. Essential natural vegetation records compiled from historical documents and regional optimal surface albedo dataset were used. The results show that the surface albedo decreased by 0.01-0.03 due to conversions from grassland to cropland in the Northeast China Plain and it increased by 0.005-0.015 due to conversions from forests to cropland in the surrounding mountains. As a consequence, in the Northeast China Plain, the surface net radiation increased by 4-8 W/m(2), 2-5 W/m(2), and 1-3 W/m(2), and the climate was therefore warmed by 0.1 degrees C-0.2 degrees C, 0.1 degrees C-0.2 degrees C, 0.1 degrees C-0.3 degrees C in the spring, autumn and winter, respectively. In the surrounding mountain area, the net radiation decreased by less than 1.5 W/m(2), and the climate was therefore cooled too slight to be detected. In summer, effects of surface albedo changes on climate were closely associated with moisture dynamics, such as evapotranspiration and cloud, instead of being merely determined by surface radiation budget. The simulated summer climatic effects have large uncertainties. These findings demonstrate that surface albedo changes resulted in warming climate effects in the non-rainy seasons in Northeast China Plain through surface radiation processes while the climatic effects in summer could hardly be concluded so far.