Spatial-temporal Evolution Of Water And Soil Vulnerability In Jingdian Irrigation District

The arid regions of Northwest China are rich in land resources,abundant in light conditions,and extremely deficient in natural precipitation.Water resources are the most important influencing factors in promoting the evolution of regional ecosystems and changes in the soil and water environment.The construction of large-scale pumping stations in these arid and semi-arid areas is one of the main ways to solve the desolate land resources and severe shortage of water resources.However,the construction of water-lifting projects in these areas actually injects the most sensitive influencing factor,water,in arid areas,which fundamentally affects the evolution characteristics and laws of the fragility of the soil and water environment in the irrigation areas.The spatiotemporal evolution has had a significant impact,which has fundamentally changed the evolution of regional soil and water environment fragility.Under this strong evaporation in local areas with shallow groundwater burial,salt ions in groundwater and salt in deep soils follow Capillary water migrates to the surface of the soil and participates in the process of modern ecological evolution of the surface,which leads to sudden emergence of soil salinity,such as soil salinization and secondary salinization.From the perspective of green development in irrigation districts,it is necessary to scientifically and reasonably evaluate and predict this long-term and potential evolution trend of water and soil environment vulnerability.So far,people have realized that the evolution of regional soil and water environment vulnerability is determined by the hydrogeological characteristics of the irrigation area,the underlying surface and soil type of the irrigation area,and human activities.However,there is still a lack of quantitative disclosure of the vulnerability of the soil and water environment at the regional scale.In this study,a typical artificial oasis in the arid region of northwest China—Jingtaichuan Gansu Electric Power Irrigation District(hereinafter referred to as "Jingdian Irrigation District")as the research area,was selected from two aspects of natural and man-made factors.Use Landsat imagery remote sensing interpretation and spatial interpolation theory to obtain the quantified value of the spatial distribution of the evaluation indicators;use cloud theory to improve the analytic hierarchy process,calculate the weights of each indicator in the soil and water environment vulnerability assessment system,and use a grid calculator to quantify each indicator's space The spatial distribution maps of soil and water environment fragility in different periods of the irrigation area were obtained at last;the spatial and temporal evolution of soil and water environment fragility in irrigation area was calculated and analyzed using non-linear methods such as entropy-catastrophy theory,and the soil and water environment vulnerability was quantified by the entropy theory Expression,and calculated the point of time when the vulnerability of the soil and water environment in the irrigation district changed abruptly through the catastrophe theory.With the Jingtai county town of the first-stage irrigation area as the center,the characteristics of the soil and water environment vulnerability were analyzed from different distances.The results show that the soil and water environment vulnerability is spatially vulnerable.Continuous gradient.The main findings are as follows:(1)The expansion of cultivated land and the contraction of Gobi,grassland,and dry land in the land use types of Jingdian Irrigation District in 1994,2001,2008 and 2015 formed a sharp contrast.34.13%contracted to 21.35%in 2015,grassland contracted from 24.16%in 1994 to 20.52%in 2015,dry land contracted from 2.94%in 1994 to 2.26%in 2015,and cultivated land expanded from 20.14%in 1994 to 2015.38.89%;the area of saline-alkali land decreased from 5316.5 hm2 in 1994 to 4969.54 hm2 in 2015.(2)The average groundwater burial depth in the irrigation area decreased from 45.9219m in 1994 to 37.7474m in 2015.The average regional reduction was 8.1745m.The overall burial depth showed a decreasing trend from year to year,especially for closed hydrology.The depth of groundwater in geological units changes most drastically;the average groundwater salinity increased from 2.5850 g/L in 1994 to 3.8952 g/L in 2015.It is also in the groundwater of Luyang Town to Caowan Town of the closed hydrogeological unit.The salinity has gradually increased from 2.9 g/L to 4.4 g/L in 1994 to 4.4 g/L to 5.9 g/L in 2015.The salinity of groundwater in open hydrogeological units has gradually increased and oscillated.The soil salinity in the irrigation area showed an increasing trend as a whole.The average soil salinity increased from 0.6817 g/L in 1994 to 1.9685 g/L in 2015,an increase of about 1.2868 g/L.The soil salinity increased with the cultivation period.Shows an upward trend.(3)Through cloud theory improved analytic hierarchy process,it can be obtained that among the ten index factors,the highest weight is the soil salt,and the smallest weight is the slope direction.It shows that the uncertainty of the evaluation results on the same problem is basically consistent with the actual situation.In 1994,the proportion of water and soil environment vulnerability in Jingdian Irrigation District was below 158166.21 hm2,and the proportion of vulnerability above water level 4 was 79985.19 hm2.In 2015,the proportion of soil and water environment vulnerability below water level 2 was 160571.77 hm2,which was above level 4 Vulnerability accounts for 68258.03hm2.Between 1994 and 2015,the vulnerability area below the second level increased,and the vulnerability area above the fourth level decreased,indicating that the vulnerability of the water and soil environment in the irrigation area is generally improving.(4)Using information entropy as a state variable to investigate the fragility of the water and soil environment in Jingdian Irrigation District.The environmental vulnerability of the Computing Institute from 1994 to 2015 highlights the criteria,indicating that the information entropy of the water and soil environment has changed abruptly during this period.Vulnerability appears.Further dividing the interval from 1994 to 2015 and calculating the information entropy of its soil and water environment by using the catastrophe theory showed that the entropy value of the fragility of the soil and water environment in the irrigation area changed suddenly from 2002 to 2004,reflecting the further deterioration of the water and soil environment in the irrigation area during this period.