HYDROLOGICAL MODELING IN KABUL RIVER BASIN: A CASE STUDY OF AFGHANISTAN

Abstract

River Basin has been considered as the ideal unit for comprehensive water resource issues. Climate, as well as land use/land cover change, have a direct influence on water resources and hydrological dynamics in a river basin. Climate change impact in a river basin differs from one area to another region, due to hydrologic systems and meteorological scenario. To evaluating the hydrological effects of climate change, several methods have been developed, which are divided into two main groups: time series analysis (statistical methods) and hydrological modeling. The statistical methods have used to analyze the trend of precipitation as well as temperature over the past two decades. One of the most powerful Non-parametric tests is Mann-Kendall (MK)test for Evaluates significant trends and Sen’s slope estimator for finding the true slop in metrological weather series, without determining whether the trend is linear or non-linear. Precipitation and temperature are the two important factors which have more influence and role on climate change as well as hydrology cycle, therefore in this research, the fluctuating trends of rainfall and temperature of the Kabul River Basin, Afghanistan, through 8 different stations are analyzed. The annual and monthly data were used to detect the trends of precipitation, whereas for temperature trend the, maximum and minimum annual data were used. Precipitation data from 2000 to 2018 for eight different metrological stations of the Kabul river basin were analyzed to find the changes in rainfall trend, while for temperature data from the five available weather stations for a period from 2008 to 2018 were used. Precipitation and temperature variation regarding temporal were calculated on the monthly and annual intervals. Mann Kendall and Sen's Slope method are used for the trend analysis, which supports nonparametric statistical analysis. The trend of annual precipitation was calculated over the 18 years for all stations. After trend analysis of precipitation with Mann Kendall Test and Sen's slope, result shown the increasing precipitation trend of 4.88 to 30.42 mm/yr, as well as the minimum temperatures, have increased significantly at a different rate of 0.02 – 0.71 C°/yr. The outcome of the present study may be useful for the water managers to understand the impact of climate change in a sub-basin of Kabul river basin, Afghanistan. After climate change, LULC change has the most effect on a river basin, therefore the impact of LULC change was assessed from 1972, 1979, 1990, 2000, 2008 and 2018 by using the GIS and remote sensing. Kabul river is one of the most famous parts of the Kabul River Basin due to passing through the capital city of Afghanistan. This river adds an aesthetic view to the Kabul city, like the Seine river in Paris. In this research, the impact of land use land cover (LULC) changes on the Kabul river is analyzed by remote sensing and GIS technique. The multi-temporal satellite images are very useful tools for describing as well as exploring the LULC changes. Remote sensing and GIS technology is an easy way to carry out the impacts of LULC change in the study area. Arc GIS 10.4.1 and ERDAS Imagine 2018 are the software, which used to assess the LULC changes during 46 years in Kabul city from 1972 to 2018. Studies on LULC show, change in LULC has a direct effect on water resources. Kabul LULC maps disclose the grass and forest area are decreasing, while the urban and agricultural zones are increasing in the study area. However, drought and civil war are the main reason for deforestation, but LULC change shows the scarcity of water in the study area, which must consider it as a very serious issue. LULC map is an important parameter for hydrological modeling to carry out the impacts of LULC change in a river basin. viii As hydrological models forecast are always unreliable, therefore further studies in water resources are needed to make more effective use of these models. Analyzing and executing of the watershed model to carry out the valid assessment of water resources is essential, individually in Kabul river sub-basin, where the modeling is a challengeable issue due to lack of data. In this research, the Soil and Water Assessment Tool (SWAT) model was used to assess the discharge prediction of the Kabul River sub-basin watershed at Estalif gauge station. The model calibrated with monthly discharge data for 2003 – 2010 and validated for 2010 to 2018. SWAT-CUP which recently has developed with the capacity of providing the decision making for using manual and automated calibration and incorporating sensitivity and uncertainty analysis through (SUFI2) Algorithm, was used for calibration and validation. Impact of climate change on the surface flow as well as LULC change and other different scenarios are evaluating by calibrated SWAT model for further investigation. The sensitive parameter is required to improve the calibration efficiency, therefore in this model the coefficient of determination (R2), Nash Sutcliffe efficiency (NSE) and Present bias (PBIAS) parameters considered as the main parameter.