Abstract
Accelerated soil erosion is one of the most important detrimental factors affecting the quality of the watershed health. Due to different environmental pressures and drivers, the effort is needed for ecological health and resilience assessment in regards to erosion changeability. However, this important subject has not been adequately studied yet. Towards this, in the present research, an innovative approach was developed for conceptualizing the watershed health dynamics in viewpoint of soil erosion. A risk-based study was conducted to quantitatively characterize the spatiotemporal variability of erosion-based health in an industrialized watershed i.e., the Shazand Watershed using the conceptual reliability, resilience and vulnerability (RelResVul) framework for four node years of 1986, 1998, 2008 and 2014. To this end, the soil erosion was estimated at monthly scale in 24 sub-watersheds by applying the Revised Universal Soil Loss Equation (RUSLE). The RelResVul indicators were then computed according to the threshold defined for the study watershed. A geometric mean was used to combine the three risk indicators and the erosion-based watershed health index was ultimately calculated for each study sub-watershed. Additionally, the change detection analysis was conducted over the years of 1986 to 2014. According to the results of erosion-based the RelResVul indices, very healthy, healthy, moderately healthy, unhealthy and very un-healthy conditions in the Shazand Watershed were respectively distributed over some 67, 25, zero, zero and eight percent for 1986; 50, 13, eight, zero and 29 % for 1998; 71, eight, 83, zero, zero and eight percent for 2008 and finally 71, zero, 17, zero and 12 % for 2014. The results of change detection revealed an oscillating trend of erosion-based watershed health index during the whole study period (1986 -2014). So that, during periods of 1986-1998, 1986-2008 and 1986-2014, the watershed health decreased at tune of 23, 13 and six percent, respectively. Whilst, the watershed health improved during study periods of 1998-2008 (13 %), 2008-2014 (eight percent) and 1998-2014 (22 %). The results also identified ‘hot spots’ of the most important index of land degradation and ‘bright spots’ of land improvement in the Shazand Watershed.The proposed approach would provide a sustainable framework supporting decision makers to comprehend health-related soil erosion targets according to the integrated watershed management plans.
Highlights
The extent of land degradation in Iran has been recognized as a pressing challenge for the country economy
It is reported that the soil and water degradation and fertilizers application annually costs the country around than USD12.8 billion about four percent of the total gross domestic product (GDP) (Emadodin et al 2012)
Soil erosion as the most important indicator of land degradation affect the quality of watershed ecosystems
Summary
The extent of land degradation in Iran has been recognized as a pressing challenge for the country economy. The RelResVul indicators can be characterized by means of daily, monthly or annual datasets of different determinant factors This framework simultaneously measures the pressure, state and response of the watershed against to external stressors (Chanda et al 2014; Hazbavi et al 2018b and c; Sadeghi et al 2019). The risk assessment of watershed in the context of health is a topic of great interest to many researches seeking to promote sustainable practices In this regards, the reliability (Rel), resilience (Res) and vulnerability (Vul) framework (RelResVul) got more attention due to considering the risk-based indicators to mathematically quantify the potential for an entire watershed to fail, the probability of a failed watershed recovering, and the consequences of a watershed lapsing into a failed status (Ahn and Kim 2017; Hazbavi et al 2018a). The present study has been formulated for better understanding of land degradation situation in the study watershed in time and space hopefully leading to a correct and cost-effective management in the future
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