Determination and optimization of agricultural water use at basin scale by hydrological model based water footprint method

Over the past century, global and regional water stress problems have increased. Significant causes of this problem include factors such as global warming, climate change, and population growth. Additionally, the agricultural sector, which consumes more than 80% of global water allocation, stands out as the most critical reason for the increasing water scarcity. Consequently, in recent years, researchers have focused on studies to reduce water consumption in agriculture. Specifically, the water footprint (WF) concept, developed in the early 21st century, enables a detailed examination of the impacts of agricultural production on water resources and the analysis of strategies to reduce water consumption. The Ceyhan Basin, located at the intersection of three different climate zones in Turkey, is a significant agricultural region with high climate and crop diversity. Therefore, agricultural water use in the basin is quite high. The primary aim of this study is to conduct detailed WF analyses of agricultural products grown in the Ceyhan Basin based on a hydrological model and to propose measures to reduce agricultural water use by optimizing the current crop pattern. In this context, the present study was conducted in three main stages. In the first stage, the basin's hydrological model was created using the SWAT model with climate data from 2011-2021. In the second stage, agricultural management practices were processed into the SWAT model, and the blue, green, and grey WF amounts of the examined products were determined and mapped. In the final stage, a multi-objective optimization method was used to optimize the crop pattern in the basin based on blue and total WF parameters. This study differs fundamentally from other research in the literature in three main ways: i) while WF studies in the literature have mainly been carried out using empirical methods, the present study achieved high spatial and temporal resolution results through hydrological model-based WF analyses, allowing for clear mapping of crop pattern recommendations; ii) previous studies typically focused on crop-centric adjustments, whereas this study conducted water management-focused crop pattern optimization; iii) the blue WF, the most critical component in the WF concept, was weighted in the objective function, creating optimal crop pattern maps under various scenarios to find the best solution for the basin. According to the main findings of this study, the current general trend shows an increase in the blue WF towards the northern part of the basin and an increase in the green WF towards the southern part. On the other hand, with crop pattern optimization, a potential reduction of 23.4% (614 million m³) in the total WF and a 47.9% (464 million m³) decrease in the blue WF was demonstrated. Accordingly, it was found that by optimizing the crop pattern in the Ceyhan Basin alone, an additional 480,000 tons of wheat could be produced without changing human intervention on water resources, and approximately 5.6 million people could be supplied with enough freshwater annually. The solution proposals offered by this study to reduce water consumption in agricultural production are expected to contribute to water management studies in Turkey, and future research evaluating parameters such as the region's irrigation infrastructure and farmer habits, along with economic analyses, is anticipated to increase the applicability of crop pattern recommendations.