The Analysis And Prediction Of The Water-soil Coupling Effect In Shiyang River Basin Under Climate Change

Studies on coupled water and soil elements in inland river basins mostly focus on available water resources and visible land resources in the midstream oasis agricultural area,neglecting the integrated effects of geographic environmental elements and water and land-related elements and the overall correlation and regional differences between the upper,middle and lower reaches of the basin.Especially in the context of climate change,the mismatch of water and land resources in inland river basins in arid zones has intensified,causing a series of ecological and environmental problems.Climate change and human activities affect the regional substratum structure,which in turn affects the hydrological processes of inland river basins and changes the regional pattern of soil and water resources.Therefore,the analysis and prediction of coupled soil and water elements in inland river basins in arid zones are essential for the optimal allocation of soil and water resources and sustainable development.The Shiyang River Basin is one of the inland river basins in China with dense population,high degree of soil and water resources exploitation and severe ecological problems.How to rationally utilize land and water resources and realize the coordinated development of human-water-land-ecology has become the core of the sustainable development of the inland river basin.Therefore,this study establishes a coupled model of water and soil elements in the inland river basin,and applies prediction methods such as MCE-CA-Markov model and SWAT model,combining hydrological,soil,land use,climate and socio-economic data to investigate the characteristics and trends of changes in land use,soil and water resources volume in the Shiyang River basin under the influence of climate change and human activities,assess the coupled water and soil under different scenarios The paper also discusses the optimal allocation and sustainable development of water and land resources in inland river basins in arid regions.The main findings of this paper are as follows:（1）With the period of 20a,the land use changes in the Shiyang River Basin from 1980 to2020 show different characteristics.From 1980 to 2000,the area of transferred land types is little,and the main types of land use conversion are the transfer out of unused land and the transfer in of farmland and grassland.In 2000 to 2020,the area of transferred land use increases,and the main types of conversion are the mutual conversion of farmland and grassland,grassland and unused land,and the transfer of unused land to farmland.From 2020 to 2050,under the natural development scenario,farmland,grassland and built-up land show an overall growth trend,forest land and unused land show a shrinking trend,and water area shows a small increase in 2020-2030,but a decrease in 2020-2050.Under the ecological protection scenario,farmland,forest land,grassland and water area all show an increasing trend,while the built-up land shows an increasing at first and then decrease under the SSP1-2.6,while the unused land has been in an area of decreasing.（2）The soil quality index of Shiyang River Basin decreases from the upper reaches of mountainous to the middle and lower reaches,and the oasis areas are slightly higher than the desert.The soil quality index of the Shiyang River basin in the base period（2010）was distributed between 0.241 and 0.678,and the overall soil quality index was low,with only the alpine mountainous area having higher soil quality index.The soil quality index of each category was ranked from highest to lowest:forest land（0.49）>water area（0.39）>grassland（0.37）>farmland（0.36）>built-up land（0.35）>unused land（0.30）.The soil quality index shows a trend of increase in the 2030 and 2050,and in the NDS（Natural Development Scenario）,the soil quality index increases with higher CO₂ emissions,but in the EPS（Ecological Protection Scenario）,it shows that the soil quality index decreases with higher CO₂emissions.（3）From 1980 to 2014,the blue water quantity in the Shiyang River basin was much smaller than the green water,and both the blue and green water resources in the basin showed fluctuating increase trends.The spatial distribution of blue and green water in the Shiyang River Basin in 1980 and 2000 was characterized,and it was found that blue water depths were higher in the upper mountainous areas,which reached to 300 mm or more,and gradually decreased to less than 10 mm in the middle and lower reaches,while the depths of green water showed a spatial distribution pattern of larger in the mountainous areas than in the western part and then than in the central and eastern parts of the Shiyang River Basin.Simulation and characterization of the blue and green water depths in 2020 and 2050 under different scenarios revealed that the blue and green water depths were all on an increasing trend.From 2000 to 2050,the increment of green water depth under the ecological protection scenario is larger than that of the same climate scenario under the natural development scenario,and it shows the largest increment of SSP5-8.5 scenario and the smallest increment of SSP2-4.5 scenario.（4）The water-land resources coupling index of Shiyang River basin shows a decreasing spatial distribution pattern from the upstream water-conserving area to the middle and downstream water-consuming area,and the water-land resources coupling index is lower than0.1 in most areas,and it is mainly distributed in the water-consuming area.From 1980 to 2000,the water-land resources coupling index of the Shiyang River basin decreased from 0.1105 in1980 to 0.1071 in 2000,with a change of-3.05%.From 2020 to 2050,the average water-land coupling index of the Shiyang River basin and the upstream water connotation area showed an increasing trend,but the average water-land coupling index of the water consumption area shows a decreasing trend.Soil quality index,blue water quantity and elevation are the main determinants of water-land resources coupling in Shiyang River basin,followed by precipitation,temperature and green water quantity.In addition,the interaction between natural and social factors is stronger than the internal interaction of each factor,indicating that natural factors are the main influencing factors of soil-land coupling,while human activities should take into account the interaction with natural factors.