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

Abstract

【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 R2=0.94 and 0.44, respectively, while positively correlated with the normalized vegetation index with R2=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.

Keywords

• evapotranspiration
• sebal model
• horqin sandy land
• land use
• modis data