separation of the effects of climate variability and human activities on runoff of bakhtegan basin

arid and semi-arid ecosystems are very sensitivity to changes. fluctuations in climate variables and increasing human activities; result in the changes in hydrological processes of these ecosystems, and consequently, their structures degradation. in this study, hydro-climatic data of the bakhtegan basin for the period of 1972–2011, were analyzed to assess effects of climate variability and human activities on hydrology processes of the study area. a combined analysis of statistical tests for trend analysis and change pointe detection indicated that the basin runoff had have a significant decreasing trend over last 40 years. the change point of runoff occurred in 1999, the annual runoff of the study basin divided into two periods. the period of 1972–1999 was used as the base period for calibration and validation, and the period of 2000-2011 as a human-induced period for the model processing. then, the hydrologic sensitivity analysis method was the approach employed to evaluate the effects of climate variability and human activities on runoff. according to the analyses conducted, contribution of climate variability in the runoff reduction of bakhtegan basin was estimated equal to 62.45% and contribution of human activities equal to 37.55%. these results can be very useful as a reference for regional water resources assessment; management and maintaining the integrity of regional ecosystems.