Investigation the trend of rainfall and runoff using Global Land Data Assimilation System (GLDAS) in the Doosti Dam Basin

Nowadays due to water deficit and crisis, it is necessary to improve water resources management. One of the major steps is an awareness of amount of Rainfall- Runoff in basins.But this effort is face with lack of access toadequatefield datainborderarea. Using remotely sensed data and global land models are good way toovercomethisproblem. The aim of this study is to investigate the trend of rainfall-runoff in the Doosti dam basinwhich is important for decision–makers in Iran.This basin is located between Latitudes of 35-36.5 N and Longitude 59.5-67 W. For this purpose GLDAS data in 7 pixels with 1.5*1.5 degree spatial size located in the study area were used. Then trend of rainfall and runoff changes was investigated using simulation, Pearson correlation coefficient, Man Kendal and the sequence Man Kendal test during 10 years from 2004 to 2013, seasonaland monthly. The resultsofdataanalysisshowed that in theEastand Southeast areas ofbasin,correlation between rainfall and runoffisless thanother area. Also in 95% level of confidence for annual precipitation data only in pixel number 7 and for runoff in pixel numbers 6 and 7 there is negative trends. For seasonal data, just in the spring and in pixel numbers 5 and 7 and for runoff in the winter and summer in pixel number 7 the trend was negative. About seasonal rain data analysis only in pixel 7 and for seasonal runoff in pixels number 6 and 7 the trends were negative. Beside of this it can be consider that using of GLDAS model for study the rainfall-runoff trend analysis in the regions with rare ground data is very useful and economic.