地表反照率直接影响地表辐射平衡,进而改变当地温度(2m气温,下同),然后还可能通过大气平流过程影响下游地区的温度。为揭示利用实时更新的地表反照率替换WRF(Weather Research and Forecasting)模式的静态地表反照率对中国大陆温度模拟结果的影响,本文进行了两组为期6年(2002-2007年)的连续积分试验:控制试验(CT试验)采用短波波段地表反照率,取自WRF模式推荐的地表参数数据集;敏感试验(MD试验)采用分波段的(可见光和近红外)地表反照率,取自MODIS BRDF/Albedo数据产品。试验结果表明,CT试验能够模拟中国温度的基本空间格局,但是模拟温度相对于观测温度有明显偏差,青藏高原南部的模拟温度偏低(负偏差),最大偏低幅度为1.03℃,出现在秋季,东部地区的模拟温度偏高(正偏差),最大偏高幅度达3.4℃,出现在春季;MD试验模拟结果的正、负偏差格局与CT试验基本相似,但是与CT试验相比,MD试验模拟的青藏高原南部温度的负偏差更大,最大为1.32℃,而模拟的东部地区温度的正偏差明显减小,最大为2.97℃,这说明MD试验比CT试验模拟的温度普遍偏低。在青藏高原,这主要归因于MD试验比CT试验的地表反照率大,使得地表净辐射少,地表感热少,致使温度偏低;在中国东部的黄淮海至江南丘陵区,这主要归因于MD试验中北方蒙古高原的地表反照率比CT试验的大,使得MD试验中该地区的地表净辐射少,地表感热少,温度低,然后通过南下冷平流过程致使位于其下游的黄淮海至江南丘陵区温度降低。
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simulated by using the Weather Research and Forecasting (WRF) model.Essential natural vegetation records compiled from historical documents and regional optimal surface albedo dataset were used.The results show that the surface albedo decreased by 0.01-0.03 due to conversions from grassland to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℃-0.2℃、0.1℃-0.2℃、 0.1℃-0.3 ℃ 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.
