Contribution of Climate Variability and Human Intervention on Watershed Regime Based on Van Loon Model

Drought and water scarcity are two key phrases in the water resource management. Drought is a large scale natural disaster and its occurrence is beyond control of water resources managers. On the contrary, water scarcity is a result of increasing and wasteful use of water resources, although it may be controlled via proper management decisions aimed at water conservation. Nowadays, these two phenomena often occur simultaneously and result in water deficiency. In this paper, using a conceptual water balance model in an observational-modelling framework, the effects of drought and water scarcity on watershed runoff are separated. This framework was proposed by Van Loon and Van Lanen (2013), which allows the simulation of the natural hydrological response without the impact of human activities. The framework first calibrates a hydrological model during the period that the watershed is not disturbed by human interventions. Then, by comparing with the period when the watershed is influenced by coupled human and natural factors, separates the effect of these two factors. The results indicated that although between the 1379-1380 to 1390-1391 water years, the monthly precipitation decreased by nearly 12% compared with the long-term period of 1351-1352 to 1378-1379, the ecosystem could receive the minimum environmental water requirements while the major cause of water scarcity was extensive human activities. Moreover, even in studied wet years, a considerable decrease in discharge was detected.