Assessment of the Effect of land-Use Changes on Streamflow in Helmand Transboundary Basin During 1990 to 2012 Using Remote Sensed Data & SWAT Model

Reduction of Helmand River inflows is one of the main challenges of the water resources of the eastern part of Iran which is more pronounced in the recent years. This research aims to quantify the causes of this problem that accordingly has had direct impacts on dryness of the Hamoun Wetlands as an international Ramsar site. In the first step, the land use changes of Helmand plain in Afghanistan were evaluated in three periods from 1990 to 2011 using remote sensed data. Obviously direct sampling was not possible from the study area and therefore other sources of information including: FAO land use maps, Watershed Atlas of Afghanistan (AIMS), maps of U.S. Geological Survey (USGS), and Google Earth images were applied as the alternative data. It was concluded that the total irrigated area in the region has increased from 103,000 ha in 1990 to 122,000 ha in 2001 and to 167’000 ha in 2011 (62 percent increase). SWAT is run in the next step using the three created land use maps of the region. It was concluded that the average annual discharges of Helmand Basin at Char Burjak station (most downstream station in the Helmand plain) has decreased from 5.1 to 4.28 BMC due to the increase of these irrigated lands.