| Evapotranspiration is a key link in the process of land surface hydrology,which directly affects the water and heat transfer in the soil-vegetation-atmosphere system.For vegetation,97-99%of water is lost in the form of evapotranspiration.Therefore,accurate estimation of regional scale evapotranspiration has important guiding significance for in-depth understanding of the hydrological cycle process,quantitative research on ecological water demand and rational allocation of water resources.In this paper,the Weihe Watershed with scarce water resources and serious water pollution was selected as the research area.MODIS data,ASTER GDEM data,surface meteorological data and vegetation,soil and other multi-source data were collected and processed.The SEBS model was used to invert the daily evapotranspiration in the seven periods of the vegetation growth season(April-October)in the Weihe Watershed in 2018,analyze the temporal and spatial distribution characteristics of evapotranspiration in sub-basins and different vegetation types,and explore the applicability of SEBS model in the Weihe Watershed.On this basis,this paper uses the evapotranspiration method to calculate the ecological water demand of different vegetation types in the Weihe Watershed,and analyzes its dynamic change characteristics.The main conclusions drawn in this article are as follows:(1)The estimation results of the key parameters of the SEBS model show that:the ordinary Kriging interpolation method combined with DEM correction has the smallest spatial distribution error of air temperature,which is more suitable for the study area;air temperature and specific humidity have a strong correlation,and the time change law of the two is basically Consistent;during the vegetation growing season,the average surface albedo is between 0.08-0.23,and the overall change is similar to the"U"type distribution.The surface albedo is the lowest in July and August,and the highest in April and October;the surface temperature is affected by the season and the underlying In terms of time,the surface temperature is the highest in June-August and the lowest in April and October.In terms of space,the surface temperature of bare land and construction land is higher than that of vegetation.(2)The spatial and temporal distribution characteristics of evapotranspiration in the vegetation growing season in the study area are as follows:in time,the evapotranspiration showed a single-peak distribution trend,and the evapotranspiration was the largest during the period of vigorous vegetation growth(June-August),which reached the peak in August and the maximum evapotranspiration It is 8.43 mm,with the lowest evapotranspiration in April and a maximum drop of 3.70 mm;spatially,the spatial distribution of evapotranspiration is significantly different.The average daily evapotranspiration of each sub-basin is:middle reaches of the Weihe River(3.68 mm)>Beiluo Watershed 3.58mm)>Lower Weihe River(3.04mm)>Upper Weihe River(3.01mm)>Jinghe Watershed(2.91mm),the evapotranspiration intensity ranking of each vegetation type is:Coniferous forest(4.20mm)>Broadleaf forest(4.17mm)>Shrub(4.00mm)>Meadow(3.86mm)>Grass from(3.80mm)>Cultivated Vegetation(2.90mm)>Grassland(2.45mm).(3)The cross-validation of evapotranspiration in seven different periods during the vegetation growing season and the MOD16 data verified by the Global Flux Tower found that the RMSE between the inversion results of the SEBS model and the MOD16 data is about 0.5,and R~2is greater than 0.85.It shows that using the SEBS model to invert evapotranspiration in the Weihe Watershed has certain reliability.(4)Vegetation ecological water demand in the Weihe Watershed is closely related to vegetation type,distribution area and evapotranspiration.In terms of time,the change of total ecological water demand is the same as that of evapotranspiration,showing a single-peak distribution trend.In summer,the vegetation transpiration and evaporation accelerates,and the total ecological water demand is high.It reached a peak in August and the largest total ecological water demand The value is 609198×10~4m~3;spatially,the ecological water demand of each vegetation type is ranked from high to low:Cultivated vegetation(1697692×10~4m~3)>Broadleaf forest(528422×10~4m~3)>Grassland(245598×10~4m~3)>Shrub(228470×10~4m~3)>Coniferous forest(151660×10~4m~3)>Grass from(109721×10~4m~3)>Meadow(50168×10~4m~3). |
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