基于SEBAL模型的赤峰市植被修复下林草蒸散耗水特征

水是制约干旱半干旱地区实现可持续发展的关键因素，维持降水与蒸散发的平衡是开展植被修复工程时需要着重考量的因素.利用陆面地表平衡算法（Surface Energy Balance Algorithm for Land，SEBAL）模型反演了2000年、2008年、2016年赤峰市全域及森林与草地生态系统的实际蒸散发，通过参考蒸散比不变法与日气象数据将反演结果扩展至日尺度，累加得到月际与生长季尺度的实际蒸散发；结合降水变化，分析植被修复工程开展后赤峰市实际蒸散发的时空变化特征与水分盈亏状况.结果表明:①2000年、2008年、2016年赤峰市生长季的实际蒸散量分别为440.86、452.76、474.34 mm，呈增加趋势，蒸散发高值区（>400 mm）由北向南扩增.②2016年生长季森林分布区的耗水量比2000年增加了27.69×108 t，水分亏缺量增加了8.03×108 t，表明过度造林会使森林生态系统遭受严重的干旱胁迫.③一个生长季内，草地生态系统蒸散量的增幅远低于森林生态系统，1 m2草地生态系统的耗水量比森林生态系统少0.18 t.研究显示，在降水量低于300 mm的区域，草地生态系统面临较轻的干旱，且部分区域可以实现水分平衡.为了维持区域水资源存量，建议赤峰市在今后的植被修复工作中，对于降水量低于300 mm的区域以草本修复为主. 

Characteristics of Actual Evapotranspiration and Water Consumption of Forest and Grassland Ecosystems under Vegetation Restoration Projects Based on the SEBAL Model in Chifeng City, China

Water is the key restricting factor for sustainable development in arid and semiarid regions. It is imperative to maintain the balance between precipitation and evapotranspiration when carrying out vegetation restoration projects in arid and semiarid regions. The actual evapotranspiration values of Chifeng City in 2000, 2008 and 2016, as well as those of the forest and grassland ecosystems were estimated by the Surface Energy Balance Algorithm for Land (SEBAL) model. The constant reference evaporative fraction and daily meteorological data were used to extend the results to a daily scale and accumulate the above daily results to obtain the actual evapotranspiration on monthly and growing season scales. In combination with precipitation changes, the temporal and spatial variation characteristics of actual evapotranspiration and regional water profit and loss during the vegetation restoration projects were calculated. The results showed that:(1) The actual evapotranspiration in the growing season of Chifeng City was 440.86, 452.76 and 474.34 mm in 2000, 2008, and 2016, respectively, reflecting an upward trend. The high-value region (>400 mm) gradually shifted from north to south. (2) In 2016, the water consumption in the forest area during the growing season was 27.69×10⁸ t greater than that in the same area in 2000. In the context that regional precipitation continuously increased, the water deficit in 2016 was 0.80×10⁸ t greater than that in 2000, which indicated that large-scale afforestation exacerbated drought stress in the forest ecosystem. (3) Within one growing season, the growth rate of actual evapotranspiration in the grassland ecosystem was much lower than that in the forest ecosystem, and the former consumed less water than the latter by 0.18 t per square metre. The results showed that in the area with rainfall less than 300 mm, the grassland ecosystem suffered from less drought, and some areas can even achieve water balance. Therefore, to reduce aridity, it is suggested that in future vegetation restoration projects, areas with precipitation below 300 mm should be restored mainly by herbaceous plants.