Evaluation and comparison of different methods for determining the contribution of climatic factors and direct human interventions in reducing watershed discharge

Planning for reducing climate changes impacts and human interventions on river discharge relies on determining the extent to which factor has contributed to the observed changes. However, the diversity of approaches and methods proposed for assessing the impact of human and climatic factors, coupled with limitations in data and time, necessitate the careful selection of suitable methods. This study aims to address these challenges by providing a reliable framework to reduce uncertainty and select appropriate methods for quantifying the contribution of human and climatic factors to runoff changes using available information. To achieve this goal, a comparative analysis of different approaches and methods was conducted in three stages: trend determination, assessment of homogeneity and breakpoints of the meteorological and hydrological watershed, and quantification of the contribution of climatic and human factors, followed by validation against real evidence. Subsequently, these methods were employed to evaluate the contribution of climatic and human factors in the Boukan watershed, enabling a quantitative comparison of the results. The findings revealed an upward trend in temperature, a downward trend in precipitation and runoff, and significant changes in annual runoff in 1997. The results obtained from various methods exhibited a range of variations, attributing human factors to 35% to 85% of the reduction in runoff, while climatic factors accounted for 15% to 64%. In general, the box plot analysis indicated that human factors contributed approximately 57% on average, whereas climatic factors contributed around an average of 47%. Additionally, the examination of land use changes, resource utilization, and consumption patterns further supported the notion of human factors playing a more substantial role in the regional runoff reduction. Based on the available evidence, the double-mass curve methods, the water balance model, and the SWAT are identified as the most suitable approaches for this watershed, displaying a better fit to reality. Therefore, given the wide range of results, adopting multiple methods with different methodologies becomes crucial to reduce uncertainty. In this context, the proposed framework can serve as a valuable guide for selecting appropriate methods and decision-making processes.