Spatio-temporal Change Of Oasis Effect And Its Influencing Factors In Arid Area

The oasis effect plays a significant role in reducing the ineffective loss of water in the arid zone,promoting the self-sustainment of the desert oasis and improving the stability of the oasis.Quantitative study of the spatial and temporal changes of the oasis effect and its influencing factors are of great significance for the full play of the oasis effect and the sustainable development of oasis in the urbanization of arid areas.This paper takes the oasis in the arid oasis,a typical oasis in the Manas River Basin,as the study area,based on the LandsatTM/ETM+/TIRS 8 remote sensing image data,weather stations data and land use data in the hot season(July-September)from 1993 to 2015.Using remote sensing technology,inversion of near-surface temperature by single window method,and establishment of temperature vegetation drought index model(TVDI)to invert near-surface moisture.The temporal and spatial variation characteristics of surface temperature,humidity and oasis cold island effect and wet island effect were quantitatively analyzed by using geostatistics.The key parameters of the oasis effect were quantitatively studied by the projection parameter regression model of genetic algorithm.And analyzing the relationship between the oasis cold island effect and the wet island effect and its relationship with NDVI.The results show:(1)The surface temperature and humidity distribution in the oasis area of the Manas River Basin have obvious low-temperature humid areas and high-temperature drying areas.The difference in surface temperature and humidity distribution between the oasis and the desert areas is obvious,and the conversion between the temperature zones and the humidity zones is frequent,the transfer space is greatly changed.(2)From 1993 to 2015,the cold island effect and wet island effect of the oasis in the Manas River Basin increased year by year.Compared with 1993,the area of cold islands and wet island increased by 25.15% and 26.5% respectively by 2015.The cold island ratio index and the wet island ratio index increased by 0.0895 and 0.0859,respectively.To the direction of cooling and humidification,and the area growth rate was greater than the strength.(3)The size of the oasis effect is the result of multiple factors.The concentration of cultivated land,forest land and wetland has a positive effect on the oasis effect.The contribution coefficients of cold island area ratio,wet island area ratio,cold island ratio index and wet island proportion index have reached 2.02,1.06,0.57;2.07,1.08,0.58;1.30,0.68,0.37;0.17,0.09,0.05;respectively.The area of low coverage grassland,construction land and desert has a negative effect on the cold island effect and wet island effect.The contribution factors of the of cold island area,wet island area,the cold island ratio index and the wet island ratio index reached-0.46,-1.99,-0.70;-0.30,-1.03,-0.45;-3.03,-10.47,-4.61;-3.34,-11.55,-5.09.(4)NDVI has a negative correlation with surface temperature and a positive correlation with surface humidity.That is,the higher the vegetation coverage,the higher the humidity and the lower the temperature;the lower the vegetation coverage,the lower the humidity and the higher the temperature.(5)There is a significant positive correlation between the cold island effect and the wet island effect of the oasis.The cold island area and the wet island area,the cold island ratio index and the wet island ratio index have a synchronous change trend.(6)The spatial and temporal changes of the oasis effect are closely related to the area,expansion direction,intensity and scale development of the oasis.(7)The development of water-saving irrigated agriculture continuously encroached on low-coverage grassland and desert,greatly improved the coverage of surface vegetation,and promoted the cold island effect and wet island effect.The oasis developing effectively improved the vegetation coverage of the desert around the oasis and significantly reduced sand damage.In summary,the formation of oasis effect and the change of time and space are the result of multiple factors,which are closely related to the direction,scale,underlying surface type and layout of oasis,and closely related to the frequency and area of irrigated agriculture.Therefore,the landscape structure should be adjusted,the landscape layout is optimized,the synergy between the landscape and the ecological oasis project construction is strengthened,the degree and area of vegetation,wetland and green space are increased,the concentrated distribution of cement floors such as buildings and squares is reduced,and the area of the irrigation area is reasonably enlarged.Increasing the irrigation frequency is conducive to enhancing the oasis effect and improving the eco-efficiency of the oasis.