Spatial and Temporal Analysis of Monthly Streamflow Deficit Intensity in Gorganroud Watershed, Iran

Drought is a complex natural phenomenon that can occur in any climate. Hydrologic drought in river flow of arid and semi-arid areas cause serious shortages threatens quality of life and impacts on the economy. Understanding this feature is then essential for the management of water resources. Hydrologic drought in the sense of deficient river flow is defined as the periods that river flow does not meet the needs of planned programs for system management.In the present study changes in the monthly discharge of 14 hydrometric stations throughout the Gorganroud watershed over 30-year period (1980-2010) was studied and the deficit flow was determined based on threshold level method and the results were analyzed. Results showed that periods of severe shortages have happened in very humid and semi-arid climates and downstream of the study area while longer periods (28 months) of low flows occurred in the arid climate. The trend of severity and persistence in the central stations of the watershed was increasing. Also shortages are occurring with greater frequency at the end of the study period and river flow shortage during the years 1998-99, 2007-2008, 2008-2009 and 2009-2010 has occurred in the most stations. So in these years, flow deficit has happened in 50, 85.9, 64.3 and 92.8 percent of the stations, respectively.