Evaluation of effectiveness of the water management strategies with the focus on agricultural water use: A case study on Upper-Sakarya River Basin in Turkey

Water, energy and food nexus is an integrated framework suggests that the security of one resource is inevitably linked to another’s. Water availability assures healthy food production whereas agriculture is the dominant user of global freshwater. Water stress due to population growth, climate change or malpractices threatens food security. Within the scope of water for food governance, the water efficiency of agricultural irrigation has to be improved to aid sustainable water and agricultural management. The study investigates water availability and withdrawals, evaluates water resources management scenarios in the agricultural sector in the Sakarya River Basin, Turkey’s third-largest river basin. Demand-oriented management scenarios propose a variety of technical measures which include improvements in irrigation technology, shifts in the cropping pattern and water-saving irrigation strategies. The effectiveness of scenarios was evaluated using the Water Evaluation and Planning (WEAP) system developed for the upper sub-basin where significant agricultural activities are held with approximately 1 million ha of total effective arable land. WEAP is an integrated water resources system modeling that operates based on the principle of water balance accounting. A climate data set of precipitation, temperature, relative humidity, and wind speed were applied across each sub-basin, partitioned into land-use classes. A one dimensional, two-bucket model for each land-use class transmits water as surface runoff, interflow, percolation, baseflow and evapotranspiration components. The model was calibrated and validated for observed streamflow, reservoir volume, and irrigation water amount. The mean annual precipitation and evapotranspiration in the upper sub-basin are 387 mm/a and 245 mm/a respectively. Agriculture is the dominant user of both surface water and groundwater resources and accounts for the %88 of total water withdrawals in the upper sub-basin. Impacts of agricultural management on irrigation water supply and flow dynamics of streamflow gauges were evaluated upon each measure. When compared to a historic baseline scenario, efficient management measures can save irrigation water up to %10 by shifting crop patterns from sunflower to safflower, %6 by establishing drip irrigation instead of sprinkler, %4 by applying deficient irrigation on cereal cultivated areas. Furthermore, mean streamflow increases by %8 in June where deficient irrigation strategy is practiced on cereals, by %9 in October where cropping pattern is shifted from sunflower to safflower. After a review of various technical measures related to the efficient management of water resources, the study concluded that sustainable agricultural development is possible by adapting conservative agricultural practices that assure water and food security.