Estimation And Spatial-Temporal Distribution Analysis Of Evapotranspiration In Baishan Basin

Evapotranspiration is an important part of hydrological cycle,which reflects the climate,soil,vegetation and other comprehensive hydrological characteristics in the ecosystem.In recent years,the significant change of global climate and increasing human activities have changed the characteristics of the underlying surface,which has affected the evapotranspiration of the basin,and also changed the hydrological conditions and runoff generation mechanisms of the basin.Therefore,accurate estimation of evapotranspiration is of great significance for the study of hydrological cycle and energy flow in the basin,as well as agricultural irrigation and regional water resources planning and management.This paper takes Baishan Basin as the study area.First,Mann-Kendall nonparametric test was used to analyze the hydrological and climatic characteristics and trends from 1958 to 2017 in Baishan Basin.Then,Fu Baopu formula based on hydrothermal coupling was used to estimate the evapotranspiration in Baishan Basin,Gaolichengzi catchment and Hanyangtun catchment.At the same time,the SWAT model of Baishan basin is constructed to calculate the evapotranspiration.The feasibility of different estimation methods in the study area was discussed by comparing the estimated results of SWAT model and Fu baopu formula with the results of multi-year average water balance.Finally,the spatial-temporal variation of evapotranspiration in Baishan Basin were analyzed.This paper can provide reference for the study of hydrological process and the protection and utilization of water resources in Baishan Basin.The main content of this paper are as follows:(1)Trend analysis of hydrometeorological elements in Baishan BasinBased on the hydrological and meteorological data from 1958 to 2017,the Mann-Kendall nonparametric test method was used to analyze the trend of precipitation,temperature and runoff in Baishan Basin.In terms of precipitation,the interannual precipitation showed an insignificant decreasing trend,and the monthly precipitation showed an increasing trend except January,August,September and December.For the temperature,the temperature generally showed a significant upward trend,and the monthly minimum temperature increased significantly.For runoff,the runoff in the study area showed an insignificant downward trend,the runoff in the main flood season(from June to September)showed an insignificantly decreasing trend,and the runoff in spring(from April to May)showed an insignificant increasing trend.(2)Estimation of evapotranspiration in Baishan Basin based on Fu Baopu formulaFu Baopu formula was used to estimate the evapotranspiration of Baishan Basin,Gaolichengzi catchment and Hanyangtun catchment.The results were verified by water balance method.The results showed that the calculation results of Fu Baopu in Baishan Basin and Hanyangtun catchment area meet the estimation requirements,and the calculation effect is relatively poor in the catchment area of Gaolichengzi.The applicability of Fu Baopu formula in the area with greater dryness is better.Overall,Fu Baopu formula can be used to estimate evapotranspiration in Baishan Basin.(3)Evapotranspiration calculation in Baishan Basin based on SWAT modelSWAT model of Baishan Basin was constructed based on physical spatial information data.Baishan Basin was divided into 42 sub-basins and 503 hydrological response units(HRU).The deterministic algorithm program SUFI-02 in SWAT-CUP2019 was used to analyze the sensitivity of 25 parameters,from which 11parameters with the highest sensitivity were selected as the key parameters for calibration.The period from 2005 to 2007 was selected as the preheating period,the period from 2008 to 2014 was selected as the rate period,and the period from 2015 to2017 was selected as the verification period.The results showed that the R~2 of the rate period and the verification period were greater than 0.6,and the NSE were greater than0.5,indicating that the SWAT model was reliable for the runoff simulation of Baishan Basin,and had good applicability in Baishan Basin.The estimation results of water balance were used to test the evapotranspiration calculated by SWAT model,and the results showed that R~2 of both Baishan Basin and typical catchment areas were greater than 0.6 and NSE were greater than 0.5.The calculation effect of evapotranspiration in Baishan Basin is better than that in Gaolichengzi catchment and Hanyangtun catchment.(4)Spatial-temporal distribution analysis of evapotranspiration in Baishan BasinThe evapotranspiration in the study area was calculated based on SWAT model,and the temporal and spatial variation of evapotranspiration was analyzed.Over the time,there was no significant increase in potential evapotranspiration in Baishan Basin,and evapotranspiration in the basin showed an insignificant decreasing trend.Evapotranspiration in Baishan Basin began to increase significantly in March,peaked from July to August,and relatively small from November to March next year.In space,the evapotranspiration in the study area increased from south to north,from 2005 to 2017.In terms of the influence of underlying surface conditions on evapotranspiration,the annual evapotranspiration of different land use types is different.Among them,the water area has the largest evapotranspiration.Then the evapotranspiration of forest land,cultivated land and grassland were in the order.