A comparison of frameworks for separating the impacts of human activities and climate change on river flow in existing records and different near-future scenarios

Separating the effects of human activities/climate change on lotic ecosystems is one of the important components of environmental management as well as water resources maintenance. A Mann-Kendall analysis of hydro-climatic parameters and vegetation cover (VC), calculated using normalized difference vegetation index (NDVI), during the period 1985-2014 suggested a significant decrease and increase of river flow and temperature at p < 0.01, as well as an insignificant decline and increment of precipitation and VC, respectively within the arid and semi-arid region, that is, Zilbier River basin in north-western Iran. A separation of human activities/climate change effects on the reduction of river flow was carried out using three alternative approaches: a simple eco-hydrological method (coupled water-energy budget (ECH)), elasticity-based analysis (Budyko framework (EBA)), and a process-based watershed model based on the Soil and Water Assessment Tool (SWAT). The efficiency of these approaches was assessed over the periods 1985-1994, 1995-2014, and under five potential near-future human activities/climate change scenarios (S1-S5) by 2030. The results indicated that the climate change impacts on river flow was more severe than those of human activities. Climate change contributed to an average of 83.6% and 77.0% reduction in river flow in the past and the realistic future scenarios (i.e., S4 and S5), respectively, while human activities accounted for 16.4% and 30%. According to our findings, despite the fact that ECH results are more in line with the SWAT model, in case of physical characterization inaccessibility, ECH and EBA (as simple descriptive and quantitative models, respectively) can be used to separate, simulate and project the impacts of human activities and climate changes on river flow.