Spatial-temporal Variation Of Evapotranspiration Of Naiman Banner And Its Effect On Regional Moisture Balance

The Horqin Sandy Land is the main source of sand in the Beijing-Tianjin-Hebei region of China,and it is a serious desertification area in the north,and the Naiman Banner is located in the Horqin Sandy Land.Therefore,water resources are particularly important in this region.The analysis of the impact of water balance in this region is inseparable from an important part of the hydrological cycle-evapotranspiration.Therefore,it is urgent to clarify the impact of evapotranspiration on the hydrological cycle process and water balance in the region,which is of great significance for understanding the regional energy balance,improving the full utilization of water resources,and strengthening water resources management.In this study,based on MODIS remote sensing data,the SEBAL model was used to invert the daily evapotranspiration in the Naiman banner during the 2000-2019 growing season(May-September),and the Penman-Monteith formula and previous measured data were used to verify the accuracy.The temporal and spatial variation characteristics of evapotranspiration in the study area were analyzed,and the main driving factors and the variation characteristics of evapotranspiration for different land use types were discussed.Combined with evapotranspiration and precipitation in 2000,2005,2010,2015,and 2019,the water gain and loss of different land use types in the study area were obtained.Specifically,the following conclusions are drawn:(1)The results of the inversion of the evapotranspiration amount of the SEBAL model and the Penman-Monteith formula calculated to obtain the potential evapotranspiration amount,the potential evapotranspiration amount multiplied by the crop coefficient result and the previous measured data were compared and verified,and the relative error was less than 21%,and the error was within a reasonable range,indicating that the evapotranspiration inversion results of this study had certain reliability in this region.(2)In the growing season from 2000 to 2019,the annual evapotranspiration in the study area showed a unimodal distribution trend,which first increased and then decreased.The evapotranspiration reached the highest value in July,and the evapotranspiration in May and September was lower.From 2000 to 2019,the average evapotranspiration showed an upward trend,with an increase of 0.72 mm/a.Most of the evapotranspiration above350 mm/a occurred in the past 10 years.The evapotranspiration in the vegetation growing season in 2011 was the highest,reaching 522 mm/a;the evapotranspiration in the vegetation growing season in 2000 was the lowest,at 249.71 mm/a.Its spatial distribution is that the evapotranspiration is higher in the southern and northern regions,and lower in the central region.(3)The evapotranspiration of different land use types in the study area,from large to small,consisted of water,construction land,woodland,cultivated land,grassland,and sandy land.(4)Analysis of the correlation between evapotranspiration and influencing factors in the study area shows that there is a significant negative correlation between evapotranspiration and surface temperature,ground reflectivity,wind speed and atmospheric temperature;There is a significant positive correlation between volume and elevation.In terms of the degree of influence,the acquisition of surface temperature,normalized vegetation index and ground reflectivity is the key to simulating evapotranspiration.(5)The average water deficits in the growing seasons of 2000,2005,2010,2015,and 2019 in the study area were 50,130,104,98,and 155 mm,respectively.The water deficit was severe in the south and milder in the north.The average water deficit of each land use type is in descending order: water area,cultivated land,forest land,construction land,grassland and sandy land.Moreover,the sandy land has a water surplus every year,and the forest land has a large water deficit.Therefore,it is not suitable for large-scale afforestation in this area except under special circumstances,and it is beneficial to maintain a certain proportion of the sandy land.