Study On Spatio-temporal Change Of Water Reserves Based On GRACE Data On The African Continent

Observing spatio-temporal change of regional water reserves is beneficial to the study of regional water resources and water balance.GRACE gravity satellite has become a new way to invert variation of regional water reserves in the medium and long space scale.In recent years,climate change,desert expansion and economic development have had a great impact on the distribution of water reserves in Africa.However,the signal intensity of water reserves in Africa is not as strong as that of Antarctica,Greenland and Amazon.There are few researches on the change of water reserves in Africa based on GRACE,and the time span and version of the data are insufficient,the scope of the study is not comprehensive enough,and the depth of the research in Where water reserves vary significantly is limited.Distribution of temperature,dryness,topography and vegetation will affect the change of water reserves,the African continent has a vast territory,based on those data,African continent will be divided into 5 geographical zones:northern desert region,North central transition region,Central basin area,Eastern Rift Valley and Southern Plateau region.In this paper,by using the GRACE data and GLDAS data in 2003?2014,the spatial and temporal variations of water storage in each geographic region are retrieved,also,obtaining the monthly variation and the interannual variation of African continent.In order to ensure the correctness of the inversion results,the GLDAS-NOAH data are selected to verify the results,and good correlation between the two data was displayed.The most obvious change in the continent's water reserves during one year was the drought/rainy season in the transition zone of North China,the central basin and the eastern rift valley,the analysis of the inter annual trend of geographical zones shows that the African continent,besides Central basin area,is in a state of continuous loss in 2009?2014.By superposition of the 2009?2014 years of equivalent water height data,the result show that annual loss of water reserves in the N ile basin,Sahel between northern desert area and North central transition region,Cara Harry basin in the northwestern Plateau and Johannesburg-Pretoria area was most obvious.Based on the data of DDI desertification index,precipitation data and luminous data,this paper makes a deep research on the areas with obvious loss,and analyzes the reasons for the change of water reserves.Results show:(1)the area of the Furtwangler glacier and ice sheet in Tanzania is shrinking,and the melting of the ice sheet in Kenya has been largely reduced,leading to a decline in the water level of the equatorial lakes,which in turn leads to a loss of water reserves in the upper of the Nile River Basin.A strong correlation in water storage changes and DDI index of desertification,loss is mainly caused by desertification caused by expansion.In the basin,there is a serious loss of national water reserves,and the problem of water politics still exists,water resources management needs more stronger cooperation among countries in the basin.(2)Combined with the data of GRACE,DDI desertification index and precipitation data,water reserves in the Sahel region and the Kalahari basin which are the world's most severe desertification areas showed successive losses year by year.The desertification control in the African continent is seriously lagging behind.Desertification monitoring area of Shaanxi was one of areas with good effect of desertification control,water storage change in desertification monitoring area of Shaanxi showed desertification control makes the water reserves recover to a certain extent.Research on Desertification Based on GRACE provides a new perspective for desertification monitoring.(3)Luminous data show that Johannesburg-Pretoria region is the continent's highest brightness,the widest range of economic belt.There was a negative correlation between the change of water reserve and the gray value of luminous image,water reserves loss in small margin,and the results show that the correlation between the annual variation of water reserves and the rainfall in the economic zone is weakened,economic development has affected the change of water reserves in the area.