Concept, Application, and Approaches of Watershed Hydrological Resilience Assessment

Today, watersheds are severely affected by natural and man-made stresses, and their ability to recover and adapt to altered conditions depends on the resilience of watersheds. Therefore, due to the importance of this issue and the necessity to explain  management models in  order to promote resilience in the country's watersheds, the present paper aims to analyze the concept, application, and methods of hydrological resilience assessment as one of the resilience dimensions in comprehensive watershed management. Studies in this field are very limited worldwide but have an upward trend. Accordingly, the methods used to evaluate hydrological resilience have so far been limited to the use of simple compilation methods such as determining the arithmetic mean of some important hydrological indicators, using the Budyko curve and the Convex model. Budyko's curve analysis was mostly based on rainfall, evapotranspiration, and runoff production. But the convex model is used by considering the failure thresholds of hydrological indicators and establishing a relation between the process of long-term changes and the failure thresholds of indicators. The indicators used are multitude and have different applications depending on the hydrological conditions of each watershed. Among the most important of them can be the ratio of drought index to runoff, temporal trend and frequency of low and high water flow, change in annual water yield, groundwater level, surface runoff intensity, river enrichment from nutrients, and heavy metals, forest degradation percentage, soil erosion, sediment yield, and saline water levels are all the result of the interaction of other influential environmental factors, such as climatic, ecological, economic, biophysical and social.