Impact Study Of Ecological Diversion Of The Yellow River On Ecological Pattern And Evapotranspiration In The Northern Edge Of Hobq Desert

Due to the lack of water resources,the ecological environment in the northern edge of the Hobq Desert is harsh,and the region is also facing the threat of flood disasters during the Yellow River transit flood season.In order to alleviate the flood control situation and improve the regional ecological environment,relevant departments have explored and implemented the Yellow River ecological diversion project since 2014.Since the implementation of the project,the environment has been significantly improved and the vegetation coverage has been continuously enhanced,but the evolution process of the ecological pattern of the underlying surface has changed,and the hydrological cycle has been affected.Meanwhile,due to the absence of the normal water diversion mechanism,the ecological environment has been restored repeatedly,and the water diversion project has not produced lasting effects in some areas.Therefore,in order to ensure the sustainable restoration of the regional ecological environment and realize the efficient utilization of water resources,it is necessary to carry out the study on the impact of the Yellow River ecological diversion on the ecological pattern and evapotranspiration in the northern Hobq Desert.In this paper,visual interpretation was used to study the changes of ecological patterns before water diversion(2013),at the beginning of water diversion(2016)and after continuous water diversion(2020).Based on METRIC remote sensing model and Dlton algorithm,quantitative characterization and spatial and temporal distribution of evapotranspiration in vegetation growing season were studied to clarify the mechanism of regional hydrological cycle process change.In order to explore the driving mechanism of evapotranspiration under dynamic difference of water diversion conditions,correlation analysis and residual analysis were used to analyze the driving mechanism of evapotranspiration and evaluate its contribution rate to evapotranspiration.The main research results are as follows:1.The ecological diversion project of the Yellow River interferes with the evolution of the ecological pattern of the underlying surface and improves the surface ecological environment significantly.The interpretation results of land use types show that:From 2013to 2020,the area of sandy land decreased from 65.95km~2 to 14.4km~2.From 2013 to 2016and from 2016 to 2020,the conversion rate of sandy land to other land use types was 33%and 75%,respectively.The lake also grew from zero to 24.96 km~2.In addition,ecological water diversion made the vegetation coverage of underlying surface deepen continuously,and the vegetation growth trend changed for the better,and the minimum normalized vegetation index increased from 0.43 to 0.59.2.The estimated results based on METRIC model and Dlton algorithm are in good agreement with the measured data,and the relative errors of estimated land and water evaporation values are 10.55%and 9.12%,respectively.The research results of surface characteristic parameters show that the surface albedo,surface temperature and surface roughness of water area are relatively low after water diversion,but higher in other areas.At the same time,according to the quantitative characterization and spatial and temporal distribution of evapotranspiration,evapotranspiration showed an upward trend after water diversion,and evapotranspiration was 0.73mm/d,1.08mm/d and 2.47mm/d in 2013,2016and 2020,respectively.In terms of spatial distribution,areas with large values of evapotranspiration are concentrated in water areas,wetlands and adjacent areas.3.The driving mechanism of evapotranspiration changes before and after water diversion.According to the analysis results,meteorological factors are positively correlated with evapotranspiration,but their contribution rate to evapotranspiration is weakened.Ecological water diversion plays a role in promoting evapotranspiration and the area of evapotranspiration expands year by year.Residual analysis results show that the area of evapotranspiration increased from 38.43km~2 to 77.42km~2 from 2016 to 2020.According to the evaluation results of contribution rate:,the contribution rate evaluation results show that from 2016 to 2020,the contribution rate of meteorological factors decreases from 57%to28%,and the contribution rate of water diversion projects increases from 43%to 72%,and ecological water diversion is the main factor to expand evapotranspiration.