南水北调对我国北方局地气候影响的一个理论分析

A Theoretical Analysis on the Effect of Water Transportation from South to North China on the Local Climate in the Northern Part of China

从简单的一维气柱能量平衡模式研究在我国北方土壤中增加水份含量后引起的局地气候变化 ,应用气柱中的辐射、降水、水汽和内 ,位能辐合间的平衡 ,可以推导出降水、温度、地表反射率各变化量之间的关系 ,而地表反射率的变化又与地表水份含量有关 ;而从地表能量平衡方程也可得到降水、温度、地表水份含量各变化量之间的关系 ,从上述这些关系最终可以得到地表水分变化对降水变化和温度变化的影响 .结果表明降水和温度变化与植被复盖度有关 .在我国西北地区 ,当土壤水增加 1/15 ,随植被复盖度的从大到小 ,年降水可增加原年降水量的 1/30～ 1/11,在华北地区 ,当土壤水增加 1/2 0 ,随植被复盖度的从大到小 ,年降水可增加原年降水量的 1/80～ 1/35 .而年平均温度减少约在 0 .1℃的量级 ,在线性理论范围内 ,降水量的增加与温度的降低均与土壤水的增加量成正比 .

The local climate variation induced by the increase of water in the soil in the northern part of China is investigated by use of an one_dimensional energy equilibrium model in an air column. In the model, on the basis of the equilibrium among radiation, precipitation and convergences of the moisture, internal and potential energies of air in the air column, we can get the relation among the perturbed quantities of precipitation, temperature and the albedo of the ground. The albedo of the ground depends on the moisture in the soil. Meanwhile, from the energy equilibrium equation at ground surface, we can also derive the relation among the perturbed quantities of precipitation, temperature and the water content in the soil. Then finally we can obtain the effects of the variations of the water content in the soil on the variations of precipitation and temperature. From the computation of the above relations, we may canclude that when the soil moisture is increased by the transportation of water from south to north in China, the albedo of the ground will decrease and then the precipitation will increase while the temperature will decrease in the northern part of China. The results show that the variations of precipitation and temperature are connected with vegetation cover. In the northwest China, the annual rainfall amount may increase by 1/30～1/11 compared with the original amount with different vegetation cover when water in the soil increases by 1/15; while in the north China, annual rainfall amount may increase by 1/80～1/35 depending on the vegetation cover when the soil water increases by 1/20. The order of the magnitude for the decrease of annual mean temperature is about 0.1 ℃. Both the increase of rainfall and the decrease of temperature are proportional to the increase of the soil water content in the scope of the linear model of this paper. The energy equilibrium model is more appropriate in the northwestern part of China.