Analysis And Simulation Of Evaporation And Infiltration Process Based On WAVES Model

Forest ecosystem is an important part of land ecosystem.As the natural environment for human survival,it is closely related to the development of human society.Forest ecosystem contains a variety of ecological service functions,which play an important role in water conservation,soil conservation,air purification,climate regulation and biodiversity protection.In the process of economic and social development,the service function of ecosystem is deteriorating,resource depletion,soil erosion,grassland degradation,greenhouse effect,endangered species and other ecological problems seriously threaten the living environment and green development of human society.An important ecological service function of forest ecosystem is to conserve water resources,which conserves more than 90%of land fresh water resources.In this paper,Hailuogou in Gongga Mountain area on the eastern edge of the Qinghai Tibet Plateau is taken as the research area,and lysimeter is used to observe the evapotranspiration under the forest at two altitudes in the research area,and the one-dimensional hydrological model WAVES is used to simulate the evapotranspiration,and the following conclusions are obtained:(1)In 2019,according to the data of meteorological observation stations,the total rainfall of coniferous forest is 1647.7mm,and that of broad-leaved forest is 1289.6mm.The ET of the two vegetation zones reached the maximum value in July,while the ET of broad-leaved forest and coniferous forest accounted for 16.8%and 11.3%of the annual rainfall respectively.The ET of broad-leaved forest and coniferous forest were 217.5mm/a and 186.5mm/a,respectively,and the leakage at 50cm was 429.6mm/a and 875.0mm/a,respectively;ET decreased along the height gradient,while the leakage increased along the height gradient;in rainy season(from May to October),the ET of broad-leaved forest and coniferous forest accounted for 56.3%and 76.9%of the annual ET,and the leakage of broad-leaved forest and coniferous forest accounted for 84.4%and 91.6%of the annual leakage,respectively;broad-leaved forest and coniferous forest accounted for 84.4%and91.6%of the annual leakage.In May(the beginning of rainy season),the monthly total leakage appears the maximum value,while the rainfall is about July;the coniferous forest leakage occurs in March November,while the broad-leaved forest occurs in May September,which is relatively short;the coniferous forest leakage occurs when the rainfall is more than 5mm/d,and the broad-leaved forest leakage occurs when the rainfall is more than 15mm/d.(2)In the study area,the temperature,surface temperature,relative humidity,net radiation and rainfall all showed an increasing trend,the temperature of broad-leaved forest increased faster,on the contrary,the surface temperature,relative humidity,net radiation and rainfall of coniferous forest increased faster;while the sunshine hours all showed a decreasing trend,the broad-leaved forest decreased faster;for wind speed,broad-leaved forest showed a decreasing trend,coniferous forest showed an increasing trend.The net radiation,sunshine hours and wind speed of the two vegetation zones are approaching,and the rainfall gap is expanding.Under the influence of these factors,ET in the two vegetation zones is increasing trend.Path analysis showed that ET was sensitive to net radiation,air temperature and surface temperature.The wind speed of coniferous forest had the least effect on ET,and the relative humidity of broad-leaved forest had the least effect on ET.(3)In the research process,according to the climate and hydrological changes of coniferous forest and broad-leaved forest in Gongga Mountain,through the construction of the basic database,the vegetation,meteorology,soil and other data are obtained,and the hydrological model of different vegetation zones in Gongga Mountain is successfully established.Through verification,the constructed WAVES model has been simulated and verified,and the simulation effect matches the local actual situation to a large extent.Three evaluation indexes,NSE,RMSE and R~2,are used as model evaluation indexes to evaluate the simulated and measured values.The results show that the simulated and measured values in the regular and validation periods fit well,and the correlation coefficients are all above 0.6.It can be seen that the WAVES model constructed in the two vegetation zones of Gongga Mountain can effectively simulate the hydrological process,so as to evaluate the water resources.(4)It can be seen from the simulation for many years that the annual ET peaks of the two vegetation zones are about 200 mm and 260 mm respectively.The annual average ET values of the two vegetation zones are 180.5mm and 232.7mm respectively,showing a rising trend,which is similar to the measured annual average ET values of 186.5mm and217.5mm.The leakage of coniferous forest is relatively large and fluctuates greatly,between 500-1100mm/a,while that of broad-leaved forest is about 350-600mm/a,which is consistent with the measured situation.The average annual leakage of simulated broad-leaved forest is 457.0mm/a,while that of coniferous forest is 834.2mm/a.The analysis of ET and its simulation in different vegetation zones under different weather shows that the average evapotranspiration under the forest is sunny>cloudy>cloudy>rainy,ET decreases with the decrease of solar radiation,the strongest in sunny days and the weakest in rainy days.The trend of ET calculated by WAVES model is basically consistent with that measured in the two vegetation zones.The results of WAVES model show that the broken line of simulated value is relatively small,while that of measured value is relatively large.WAVES model underestimates the ET of broad-leaved forest in sunny and cloudy days.(5)In different situations,the temperature is the highest,the precipitation is the largest,and the annual average ET is the largest.Through the analysis,the temperature plays a decisive role in the evapotranspiration capacity under the forest,and rainfall is an indispensable driving factor.Through comparative analysis,it is found that under the change of rainfall and temperature,the variation range of evapotranspiration in coniferous forest is larger,and it is more sensitive to these two factors.In the simulation period,the temperature is the lowest and the precipitation is the largest,so the annual average leakage is the largest.The relationship between the change of soil leakage and precipitation is consistent with the response trend of observation.The influence of precipitation on soil leakage is greater than that of temperature,that is to say,precipitation is the leading factor of soil leakage.At the same time,through the comparative analysis of coniferous forest and broad-leaved forest,it is found that the change range of annual average leakage of coniferous forest is larger,and the leakage is more sensitive to rainfall and temperature,while broad-leaved forest is weaker.