| Most of the loess tableland is arid and semi-arid region,where the intensity of human activities is relatively high,and the contradictions among water resources,ecological environment and economic development are prominent in the region.Therefore,it is of great significance to study the hydrological response of typical basins in the loess tableland under changing conditions.This dissertation based on the analysis of the loess tableland area series hydrological situation on the basis of the evolution of distributed hydrological simulation and new water resources system analysis methods,such as water thermal equilibrium hypothesis,explores the hydrological responses and internal mechanisms of typical catchments in the loess tableland under the conditions of human activities and global climate change.Based on the SWAT model of Qishui River Basin,different scenarios were set up to explain the hydrological effects of climate and landuse change.Combined with the theory of hydrothermal coupling balance,the attribution of runoff change was quantitatively analyzed.The main achievements of this dissertation are as follows:(1)Evolution of hydrological situation in loess tablelandLinear fitting method,Mann-Kendall method,Sen's slope estimation method,R/S analysis method,Lorentz curve,inverse distance weight method and temperature vegetation drought index method were used to analyze the evolution of precipitation,temperature and soil water situation in the Loess tableland.According to the variation characteristics of the three factors,it can be seen that there is a positive correlation between precipitation and soil water,and a negative correlation between temperature and soil water in the Loess tableland.On the whole,from 1969 to 2018,precipitation and soil water in the loess tableland decreased,while temperature increased,and the climate became warmer and drier.(2)Response mechanism of runoff under changing environmentA SWAT model for Qishui River Basin was established.Two different climate scenarios S1 and S2 and two different landuse scenarios S3 and S4 were set to analyze the effects of climate and landuse change on runoff in Qishui River Basin.The results show that for scenario S1,after the abrupt change of climate factors,the climate change in scenario S2 reduces the surface runoff by 16.52%.For scenario S3,after watershed management,scenario S4 reduced the surface runoff by 0.11%,and there is a positive correlation between runoff change and precipitation change.Setting up different single landuse scenarios,it is found that the order of runoff under different landuse conditions is as follows: Scenario 1(the rest of the landuse is farmland)> The original 2018 landuse scenario > Scenario 3(the rest of the land is grassland)> Scenario 2(the rest of the land is forestland).The ability of forestland to conserve water is higher than that of grassland.The first choice to control soil and water loss in the loess tableland is to expand the forestland area.Secondly,the grassland area should be expanded and the policy of returning farmland to forest and grassland should be carried out simultaneously.(3)Attribution analysis of runoff change based on theory of coupled hydrothermal The linear fitting method and Pettitt test were used to examine the runoff trend and abrupt change point of Qishui River Basin from 1962 to 2018.The results showed that the runoff trend decreased and the abrupt change occurred in 1985.The Penman-Monteith model was used to calculate the potential evapotranspiration.Based on the coupled hydrothermal balance theory,the results show that: when annual precipitation,annual potential evapotranspiration and underlying surface parameters decrease by 1%,the annual runoff decreases by 3.22%,increases by 2.22% and increases by 2.12%,respectively.The contribution rate of climate change and parameter n change to runoff reduction are 46%,54%,respectively.So parameter n change(human activities)are the key reason for runoff reduction in Qishui River Basin. |
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