科尔沁沙地不同土地利用类型对区域水分平衡的影响

The Effects of Land Usage on Water Balance in the Sandy Areas in Horqin of Inner Mongolia

【目的】探索科尔沁沙地不同土地利用类型蒸散量以及水分亏缺量。【方法】以位于科尔沁沙地的奈曼旗为研究对象,利用MODIS数据和气象数据,通过SEBAL模型反演奈曼旗生长季的地表蒸散量。在此基础上分析了各土地利用类型的水分平衡状况。【结果】生长季日均蒸散量最大值出现在7月,为3.74 mm/d,最小值出现在9月,为2.35 mm/d,整体呈南部较高,中部偏低的空间分布格局。蒸散量与地表温度以及地面反射率之间均呈负相关(R^(2)分别为0.94,0.44),与归一化植被指数(NDVI)正相关(R^(2)=0.49)。不同土地利用类型的日蒸散量从大到小为:水域>建设用地>林地>耕地>草地>裸沙地。科尔沁沙地平均水分亏缺量为121 mm,南部林地以及耕地覆盖区水分亏缺量大部分超过100 mm,蒸散过程需要依靠地下水或径流方式来弥补降水不足。林地水分亏缺量达到204.7 mm,需要大量的地下水补充。【结论】该地区除特殊情况下不宜大面积造林。裸沙地的水分盈余量为16.8 mm,表明裸沙地是该地区水源地,对地下水资源有一定的补充作用,因此,在保证裸沙地稳定性的同时,维持一定比例面积的裸沙地对科尔沁沙地生态系统的稳定性是有益的。

【Objective】Water balance in a region is jointly controlled by land usage,precipitation and evapotranspiration.All these are modulated by soil texture.Taking the sandy areas in Horqin of Inner Mongolia as an example,this paper analyzes how land usage affects evapotranspiration and its consequence for water balance.【Method】The analysis was based on MODIS and meteorological data,and the evapotranspiration during crop growth season in Naiman Banner was retrieved by the SEBAL model.Using these data,we calculated the response of water balance to land usage across the region.【Result】The maximum daily evapotranspiration was 3.74 mm/d occurring in July,and the least was 2.35 mm/d occurring in September.Spatially,the evapotranspiration was high in the south and low in the center of the region.It was found that the evapotranspiration was negatively correlated with land surface temperature and reflectance with R^(2)=0.94 and 0.44,respectively,while positively correlated with the normalized vegetation index with R^(2)=0.4.Daily evapotranspiration from different land usage was ranked in the order:land for construction>woodland>cultivated land>grassland>bare soil.On average,the water deficit in the sandy region is 121 mm but varies spatially with land usage.Water deficit in the woodland and the cultivated land in the south was more than 100 mm.In some areas,part of the evapotranspiration emanated from groundwater or runoff;and the water deficit in some woodland could be as high as 204.7 mm.The water surplus in areas with bare soil was 16.8 mm,indicating that regions with bare soil functioned as the water source discharging to groundwater.【Conclusion】Large-scale afforestation in this region is not recommended because of its high demand for water.It is beneficial to keep soil surface in some areas bare to maintain stability of ecological functions in Horqin while in the meantime ensuring its productivity.