Study On Spatiotemporal Variation Of Green Water Resources In Kubuqi Desert

Kubuqi Desert,located in the north of Ordos,is an ecologically fragile area in the Yellow River region and plays an irreplaceable role in maintaining the stability and security of the ecological environment in North China.With the rapid economic development in our country,water shortage in northern area is becoming increasingly serious.As a typical semiarid and arid area,the lack of water resource in the Kubuqi Desert will further aggravate the deterioration of regional ecological environment.Therefore,on the basis of the succession of land use pattern,it is one of the key issues in the regional ecological environment to carry out a systematic and in-depth study of the green water resource change law in the Kubuqi Desert,which has important practical significance in the current situation of the rapid development of desert ecological research and environmental restoration.Taking Kubuqi Desert as the study area,this paper analyzed the spatial distribution of land use and its area changes from 1995 to 2021.SEBAL model and TVDI model were used to estimate evapotranspiration and soil water content in the growing season from 2016 to2021,and the applicability of the model was evaluated.The relevant results matched well.The main research results obtained in this paper are as follows:(1)The evapotranspiration of the Kubuqi Desert was retrieved by SEBAL model,and the simulated values were close to the measured values.The low value area of NDVI and Rn in the study area was in the west,and the high value area was in the east,which showed a trend of first increasing and then decreasing from April to October.The model can simulate ET well,and the implementation is good.The ET arrangement of different land types is as follows: sandy land < construction land < grassland < shrub < artificial vegetation < water body.(2)The data of Landsat8 from 2016 to 2021 were collected and sorted,and the Ts-NDVI feature space was established based on the temperature vegetation drought index method.The soil moisture in the study area was obtained.The analysis showed that the distribution of soil moisture in the east was higher than that in the west,and the soil moisture decreased slowly.During the rainy season,the soil moisture is significantly higher,which is consistent with the local climate change.For 0-10 cm soil depth,the average accuracy of soil moisture obtained by inversion is 76.09%,and for 10-30 cm soil depth,the average accuracy is 74.03%.The inversion accuracy of each soil layer is high,which can effectively estimate soil moisture content.(3)The image data of 6 periods from 1995 to 2021 were selected,and the supervised classification and visual interpretation methods were used to classify the land types of the Kubuqi Desert.According to the area transfer matrix,the desert decreased from 7510.67km2 to 4022.81 km2,and the grassland decreased from 1030.88 km2 during the study period.The area of shrub,artificial vegetation and cultivated land all showed an increasing trend,indicating that the ecology of Kubuqi desert was gradually improved and desertification was effectively improved.(4)The green water flow and green water reserves from 1995 to 2021 were estimated by inversion of evapotranspiration and soil water content.The M-K method was used to analyze the interannual variation of green water resources,and the analysis showed that the green water resources decreased from 1997 to 2008,increased from 2008 to 2012,and significantly increased from 2013.The average annual green water resources in the study area are 401.23 mm,about 0.82×1010m3,in which green water flow(evapotranspiration)accounts for 93.54%,and green water reserves account for 6.46%.In 2021,the green water resources are mainly distributed in July and August,and the green water resources in two months account for 47.79% of the whole year.On this basis,based on the land classification from 2000 to 2021,the spatial distribution of green water resources was systematically analyzed,showing that the distribution was more in the east and less in the west.The land type with the largest contribution was grassland,which was mainly distributed in the central region.