| Naoli River Basin is the largest basin in the Sanjiang Plain of Heilongjiang Province,China.Human activities and climate change are the main driving forces affecting the hydrological process of the basin,especially land use change has more influence on the runoff process than natural factors.This study studied the impact of land use change on runoff in Naoli River Basin in Heilongjiang Province under different scenarios in the future.Firstly,the CLUE-S model is used to analyze the characteristics of land use change in the historical period,and different scenarios are set to analyze the land use change in 2030.Then,the distributed hydrological model Wet Spa is selected to rate and verify the runoff in Naoli River Basin,and finally,it is coupled with the CLUE-S model.The influence of land use change under different scenarios in 2030 on runoff from May to September in2030 in the study area was simulated,and the runoff process was analyzed from land use type and total runoff change,runoff depth change under different scenarios,runoff mutation test under different scenarios,and runoff long-term trend change under different scenarios.The main conclusions are as follows:(1)The land use data of Naoli River Basin in 2000,2010 and 2020 were used to analyze the characteristics of land use change in the study area in the past two decades.The results show that the land use structure of Naoli River Basin from 2000 to 2020 is mainly composed of six land types,namely cultivated land,forest,grassland,wetland,water body and artificial surface.The land with the largest area mainly includes cultivated land,forest and grassland.During the past 20 years,the area of cultivated land and grassland decreased to different degrees,while the area of forest,wetland,water body and artificial surface increased.From 2000 to 2020,the forest,wetland,water body and artificial land surface will increase by 0.22%/a,0.11%/a,4.6%/a and 0.69%/a,respectively,while the cultivated land and grassland will decrease by 0.03%/a and 0.86%/a.The L values of comprehensive land use dynamic attitude were 0.24%,0.07%and 0.15%respectively,showing a development trend of"first decreasing and then increasing"in general.From 2000 to 2010,the area of cultivated land,grassland and artificial surface increased,while the area of forest,wetland and water body decreased.The largest area of grassland was 598.43 km~2,while the smallest area of wetland was 32 km~2.From 2010 to 2020,the land area of cultivated land,grassland and water body increased,while the land area of forest,wetland and artificial surface decreased.The converted area was 557.81 km~2 for forest and 46.29 km~2 for water body.In 2000,the fractal dimension D value was ranked as wetland>forest>cultivated land>grassland>water body>artificial land surface.In2010,wetland=forest>cultivated land>grassland>water body>artificial land surface;By 2020,forest>cultivated land>wetland>grassland>water body>artificial land surface;The S value is the opposite of the D value.In general,in 2000,2010 and 2020,the land class with the larger fractal dimension is forest and wetland,while the smaller one is artificial surface land,indicating that forest and wetland land class have the most complex structure and irregular spatial boundary,while artificial surface land is opposite.(2)The CLUE-S model was simulated and verified to be suitable for the simulation of land use change in Naoli River Basin.The Kappa coefficient was 0.894,and the overall accuracy of the simulation was 91.18%,indicating a high accuracy.Under the baseline scenario,the area of cultivated land in 2030 will decrease by 0.32%,the area of artificial land surface will increase by12.91%,the area of forest and wetland will increase,and the area of grassland and water body will decrease.Under the scenario of agricultural development,the area of cultivated land in 2030 will increase by 23.68%compared with 2020,while the area of forest,grassland,wetland and water body will decrease by 50%,50%,40.02%and 29.31%respectively compared with 2020.Under the ecological protection scenario,the area of forest,grassland,wetland and water body in 2030 will increase by 49.94%,50%,30.23%and 20.78%,respectively,compared with that in 2020.In 2030,the ecological land in Naoli River Basin will account for 47.47%of the total area of the study area.The cultivated land decreased from 1,499.61 km~2 in 2020 to 11,531.58 km~2 in 2030,a decrease of22.86 percent.(3)Based on Wet Spa model,DEM,soil type data,spatial distribution parameters extracted from land use data and daily hydrometeorological data from May 1 to September 30,2017--2019were used for parameter calibration,and daily runoff from May 1 to September 30,2020 was used for verification.The results showed that:The daily Nash efficiency coefficient(Nash)of the four hydrological stations is greater than 0.6,and the absolute value of the daily relative deviation(Re)is less than 19%,indicating that the Wet Spa model is applicable in the Naoli River Basin and can be used to simulate future runoff changes.(4)Based on the Clue-S-Wet Spa coupling model,the average daily runoff from May to September in 2030 in Naoli River Basin was simulated.Then,the simulation results were analyzed from land use types and runoff changes as well as runoff depth changes under different scenarios.The results showed that the total runoff under the three scenarios from May to September in 2030was greater than the total runoff from May to September in 2020.The runoff depth is also greater than that from May to September in 2020.Under the agricultural development scenario,the total runoff is the largest,which is 2.848 billion m~3;under the ecological protection scenario,the total runoff is the smallest,which is 2.789 billion m~3;under the baseline scenario,the total runoff is between the two,which is 2.816 billion m~3;the maximum and minimum runoff depth are 123.83mm,respectively.121.30 mm.The increase of cultivated land can promote the increase of runoff,while the increase of forest,grassland and wetland can inhibit the increase of runoff.In the three scenarios,there was no mutation point in the runoff mutation test,which did not reach the significance level test,and the change trend increased or decreased alternately.From the perspective of long-term trend,the three trend analysis methods in the three situations all showed significant increase. |
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