Modeling adaptation policies to increase the synergies of the water-climate-agriculture nexus under climate change

The water-climate-agriculture nexus quantifies synergies, trade-offs, advantages and disadvantages that arise between water management, food production, and climate change consequences taking into account the environmental impacts, economic conditions, and population growth. This work evaluates the water-climate-agriculture nexus in the Gharanghu basin, Iran, seeking to achieve sustainable management of its water system. An optimization model solves for water-release adaptive strategies corresponding to five nexus scenarios to cope with reduced water resources under climate change. The scenarios are as follows (Afshar et al., 2006): change in cropping pattern (Asadieh and Afshar, 2019), reduction of areas under cultivation (Asgari et al., 2015), reuse of agricultural wastewater in irrigated land (Ashofteh et al., 2017), combination of scenarios (Afshar et al., 2006) and (Asgari et al., 2015), namely change in cropping pattern and reuse of agricultural wastewater simultaneously, and (Bates et al., 2008) integration of scenarios (Asadieh and Afshar, 2019) and (Asgari et al., 2015) namely, reduction of areas under cultivation and reuse of agricultural wastewater simultaneously. The nexus scenarios are evaluated with the time reliability index (the ratio of the number of months in which water is supplied to the total months of reservoir operation) based on changes in water supply and agricultural water demand. Results show the time reliability index in the climate change interval (monthly time series for the period 2040–2069) without implementing any nexus scenario equals 28%, and it increases with the implementation of the water-climate-agriculture nexus scenarios. The time reliability of the system equals 85% implementing scenario (Bates et al., 2008) (reducing the area under cultivation and reusing agricultural wastewater in irrigated land). The authors' previous research projects that climate change impacts in the study region would be severe. This paper's findings provide water managers and planners with useful strategies for optimal reservoir operation that rely on decreasing water demand and increasing water supply. The approach introduced and applied in this study, which develops modeling adaptation policies to increase the synergies of the water-climate-agriculture nexus, is applicable to other basins.