Estimation Of Wetland Evapotranspiration In The Yellow River Delta Based On Multi-source Remote Sensing

Evaporation is an important part of hydrological cycle and one of the important influencing factors of precipitation and redistribution of energy and radiation.The research on the evolution process of evapotranspiration and its internal mechanism is of great significance for deeply understanding the hydrological cycle process on land surface and correctly understanding the mechanism of land-air interaction.The wetland in the Yellow River Delta is the youngest and most well-preserved estuary wetland in China.It plays an important role in maintaining regional water balance,protecting biodiversity,water storage and flood diversion,adjusting climate,etc.The accurate estimation of surface evaporation of the delta wetland can provide scientific basis for further understanding the wetland water cycle,protecting and restoring wetland ecosystem.In this paper,8 remote sensing images of Landsat-5 and Landsat-8 from summer 2000 to 2020 are selected,and the distribution regularities of evapotranspiration of delta wetland at different spatial scales are systematically analyzed based on SEBAL model.The inversion accuracy of this study is evaluated by comparing the measured evaporation,potential evaporation calculated by P-M model and related research results of predecessors.The correlation between evapotranspiration and surface characteristic parameters(NDVI,surface temperature)and meteorological factors(average air pressure,average air temperature,maximum temperature,minimum temperature,relative humidity,wind speed,sunshine hours)was quantitatively studied,and the main factors influencing evaporation of delta wetland and their contributions were determined.The research results can provide reference basis for elucidating the transfer mechanism of water and heat flux of wetlands in the Yellow River Delta.The main research results are as follows:(1)Eight remote sensing images of Landsat-5 and Landsat-8 of wetland in the Yellow River Delta during the summer of 2000-2020 were used to retrieve the daily and monthly evaporation of wetland based on SEBAL model,and compared with the measured evaporation and potential evaporation.The results show that on a daily scale,the evapotranspiration is the highest in August,the second in July and the smallest in September,with typical daily evaporation averages of 393 mm,3.51 mm and 2.26 mm,respectively.The mean relative deviation between inversion results and measured values is 14.09% and the mean relative deviation from potential evaporation is 33.67%.On monthly scale,the evapotranspiration was the largest in July,the second in August and the smallest in September,with the mean values of 108.35 mm,88.75 mm and 86.69 mm respectively,and the relative deviations between inversion results and measured values were 8.63% and 23.14%respectively.Evapotranspiration;Combining with the research results of relevant scholars,it shows that the evapotranspiration inversion results of this study are basically credible,and the SEBAL model has good applicability to invert the evaporation of estuary wetland.(2)On spatial scale,the evapotranspiration of wetland in the Yellow River Delta in July,August and September is greater in the north than in the south,and the evaporation in each month shows a trend of decreasing from coastal to inland.The maximum evaporation generally occurs on the surface of water body and the minimum evaporation occurs in bare inland areas far from the coast.(3)Linear fitting and Pearson correlation analysis were conducted for NDVI,land surface temperature and daily evapotranspiration.The results showed that there was a good consistency between NDVI,land surface temperature and evapotranspiration,and there was a significant correlation between land surface temperature and evapotranspiration at the level of0.01(both sides).It indicates that evapotranspiration has a good correlation with vegetation index and land surface temperature.The results of meteorological factor analysis show that there is a significant correlation between average air pressure and average temperature at the level of 0.05(both sides)and evapotranspiration,and the correlation coefficients are 0.730 and 0.718,respectively.There is a strong correlation between wind speed and evapotranspiration at the level of 0.01(both sides),and the correlation coefficient reaches0.838.Based on principal component analysis,wind speed,average air temperature and average air pressure are the main factors affecting the evapotranspiration of delta wetland,and their contribution rates are 41.84%,25.1% and 18.78%,respectively.