Evaluation of Impact of Climate Changes in the Lower Seyhan Irrigation Project Area, Turkey

Abstract

This study quantitatively assesses the impacts of climate change on the irrigated agriculture of the Lower Seyhan Irrigation Project (LSIP) area in Turkey in the 2070s by factoring the projected future climate data into computational simulations of crop growth and the hydrological structure. According to simulation results by models registered to Coupled Model Intercomparison Project Phase 5 (CMIP5) with the representative concentration (RCP) 8.5 scenario, annual temperatures and precipitation around the Mediterranean region in 2081-2100 are, respectively, 4-5 degrees C higher and 10-20% smaller than those in 1986-2005. To assess the effects on these factors at the same time, a grid-based distributed hydrological model - IMPAM (Irrigation Management Performance Assessment Model) - was used. IMPAM, which includes modules for quasi three-dimensional soil-water dynamics, evapo-transpiration, crop-growth, irrigation and seepage, and drainage was developed by the authors for the simulation of the hydrology in irrigated agricultural areas. Three scenarios of adaptation to climate change were employed for the simulations: (a) adaptation without a large amount of investment for water management, (b) increasing the irrigation area, and (c) increasing the net amount of water applied to crops with decreasing water diversion from the river and the introduction of groundwater irrigation for 21,900 ha of orchards. Climate data for the 2070s that was used in this study was derived through RCM (Regional Climate Model) downscaling of the NCEP-reanalysis data and results of two GCMs (MRI-CGCM2 and CCSR/NIES-CGCM) with the "pseudo warming" method. The results revealed that the direct effect of global warming on the hydrology of the LSIP may not be large enough to affect agricultural production. The effect of the sea-level rise might be limited to the range of a few kilometres from the coastline with scarce field crop areas. The reason why the effect of climate change on crop cultivation in the LSIP is not significantly larger than changes in water management is the existing water management, with plentiful water application, including losses. Even the scenarios with large decreases in water diversion from the Seyhan River brought positive effects to hydrological conditions and crop growth through the improvement of over-humidity. The average ratio of actual transpiration to potential transpiration (Ta/Tp ratio), which decreases as water stress on crops increases, varies from 0.81 to 0.89 with combinations of adaptation scenarios and projected climate, while all simulations based on the current management resulted in almost the same Ta/Tp ratio, 0.86. These facts indicate that the effects of changes in water management are much greater than the direct effects of climate change with regard to water balance and agricultural production in the LSIP.