Assessment of changes in hydro-meteorological variables upstream of Helmand Basin during the last century using CRU data and SWAT model

Helmand River basin upstream Kajakai dam (Afghanistan), has a considerable role in its annual water yield. In order to deal with the ever going water conflict between Iran and Afgh nist n, the knowledge bout this b sin’s long term hydro-meteorological conditions can be a useful measure for exploit tion of the b sin’s w te esou ces. It is obvious th t such an evaluation needs long term data that is a serious obstacle in Afghanistan due to the poor hydro-infrastructures. For such region with serious scarcity of data, application of the global databases and rainfall-runoff models can be a good alternative. The CRU database is one of these databases with relevant temporal and spatial resolution, which contains these climate data since 1901. SWAT model is also a well know rainfall-runoff model that has been applied for a few trans-boundary basins. Nevertheless, any application of CRU data and SWAT needs pre-assessments, which construct the main objectives of this research work. For this, the paper compared CRU data with the observed data of 17 meteorological stations in Afghanistan that resulted 313 mm compared to 323 mm as annual precipitation for the study area (the upper Helmand). The next step relates to calibration and validation of SWAT, which were done by a limited observed discharge data (1969 to 1979). Furthermore, the model was run using measured and CRU climate data, which the latter performed better. The results of SWAT for the entire period of CRU data set (1913-2012) revealed that there is heterogeneity between the time series before and after 1940, such that the annual rainfall decreases and annual temperature increases. Same behavior was seen for the time series of discharges and its annual average of discharges decreases from 8.1 BMC to 6.07 BMS for the same period. One of the considerable points of this research work is its methodology that can be applied for other transboundary river basins.