Modeling And Analysis Of The Hydrological Processes In Wusuli River Under Changing Environment

Under the changing environment,the water cycle system of the river basin is undergoing significant changes,which brings serious challenges to regional water resources security.The Wusuli River basin is located in the northeast of China and is an important tributary of the Heilongjiang River basin.Because the snowmelt process in cold regions has an important impact on the hydrological process,the hydrological changes in these basins will be more obvious under the changing environment.Based on ERA5-Land data and CMIP6 data,this study analyzes the trend,mutation and periodic characteristics of the historical data of annual precipitation,annual average temperature and annual potential evapotranspiration in Heilongjiang Basin.The snow melting model is added to the existing HH hydrological model,and the HH distributed hydrological model is built in Wusuli River to simulate the change process of flow,actual evapotranspiration,and snow melting in the basin.It revealed the water cycle evolution process of the Wusuli River basin under the changing environment.Based the 3 future scenatios of SSP12.6,SSP2-4.5 and SSP5-8.5,the flow,actual evapotranspiration and snowmelt in the basin are simulated and the change rules are analyzed.The main achievements are as follows:(1)Mann-Kendall method and Morlet wavelet analysis method are used to analyze the evolution law of meteorological elements in Heilongjiang river basin.From 1950 to 2021,the mean annual precipitation was 796.57 mm,the mean annual temperature was 1.57℃,and the mean annual potential evapotranspiration was 913.02 mm.The precipitation in the historical period has no significant trend,while the temperature and potential evapotranspiration have a significant upward trend.The spatial distribution shows that the precipitation of Heilongjiang river basin is low in the west and high in the east.The spatial distribution of temperature is low in the north and high in the south.The spatial distribution characteristics of potential evapotranspiration are low in the north and high in the south,and that in the central region is between the two.In the future,the annual precipitation,annual temperature and annual potential evaporation will increase most significantly under the SSP5-8.5 scenario,and will increase in the three scenarios from 2081 to 2100.Under SSP1-2.6,SSP2-4.5 and SSP5-8.5 scenarios,the annual precipitation growth rates are 0.72mm/a,1.21mm/a and 1.97mm/a,respectively,the annual average temperature growth rates are 0.012℃/10a,0.035℃/10a and 0.079℃/10a,respectively,and the annual potential evapotranspiration growth rates are 0.29mm/a,0.75mm/a and 1.67mm/a,respectively.(2)The HH model of the Wusuli river basin was constructed after adding the snow-melting module to the original HH model.The NSE coefficient and mean absolute percentage error(MAPE)are used to evaluate the simulated result and ε-NSGAII optimization algorithm is used to optimize the parameters.The model was used to calibrate and validate the model parameters.The results show that the HH hydrological model with the snow-melting module is effective in simulating the daily runoff during the calibration period of 2011-2015 and validation period of 2016-2021,and the simulated values of 11 hydrological station for the validation are close to the measured values.The actual monthly evapotranspiration of typical watersheds does not vary much with the time.The maximum monthly potential evapotranspiration for all watersheds occur in June-August,with relatively stable fluctuations.Snowmelt increased with the snowfall increase during 2011-2021,and the changes of snowmelt and actual evapotranspiration were similar.The changes of daily snowmelt were not significant,and the daily snowmelt is in the range of 1～5mm.(3)Under the three scenarios of SSP1-2.6,SSP2-4.5 and SSP5-8.5,the meteorological data are downscaling to daily value series,and HH hydrological model is used to simulate the monthly runoff process,monthly evapotranspiration process and monthly snow melting process of each typical hydrological station.The runoff in the future period will significantly increase,and the actual evapotranspiration will increase in the future period,which is positively correlated with temperature.There will be a significant increase in snowmelt.Compared with historical periods,under the three scenarios of SSP1-2.6,SSP2-4.5,and SSP5-8.5,the runoff increased by 10.6%,12.6%,and 16.7%respectively,while the actual evapotranspiration increased by 14.5%,17.5%,and 20.9%,and the snowmelt increased by 5.7%,6.4%,and 8.4%respectively.Under the three scenarios of SSP1-2.6,SSP2-4.5,and SSP5-8.5,the runoff of the Wusuli River Basin shows no significant increase trend in the next 75 years.The actual evapotranspiration shows a significant upward trend in all three scenarios.There is a significant upward trend in snowmelt under three scenarios.Among the three scenarios,the SSP5-8.5 scenario has the highest long-term average annual runoff,while the SSP1-2.6 scenario has the lowest recent average annual runoff;The SSP5-8.5 scenario has the highest long-term actual evapotranspiration,while the SSP1-2.6 scenario has the lowest recent actual evapotranspiration;The SSP5-8.5 scenario has the highest long-term snowmelt,while the SSP2-4.5 scenario has the lowest recent snowmelt.