Assessing the impact of AOGCMs uncertainty on the risk of agricultural water demand caused by climate change

A major future challenge and limiting factor for future water resource management and planning is climate change and drought conditions and their impact on agricultural water demand. Many models have targeted climate change predictions for temperature, rainfall, and evapotranspiration and have led to future estimation of water demand for agriculture. However, uncertainty and risk analysis are normally not considered in future water demand estimations. The main objective of this study is to quantify the impact of climate change on agricultural water demand and productivity and better understand the uncertainty and risk involved in using several Atmospheric-Ocean General Circulation Models (AOGCMs) to predict future temperature and water demand. As a case study, the Zayandeh Rud basin, located in the central part of Iran, has been chosen because of its importance for agricultural and food security. The main growing and major crops are wheat, barley, sugar-beet and potato. Future temperatures have been retrieved from the IPCC database, which include AOGCMs climate change data sets. These data sets cover the whole world in a pixel-wise manner. Seven AOGCMs from the IPCC Third Assessment Report, including CCSR NIES, CGCM2, CSIRO MK2, ECHAM4 GFDL R30, HadCM3 and NCAR DOE PCM, with A2 emission scenario have been used to project the future temperatures for the study area for two different time periods (210-2039 and 2070-2099). According to the ranges of temperature resulted from these models, one thousand samples of temperature time series for these two periods are produced for uncertainty and risk analysis of water demand. Preliminary results indicated that there is a significant increase in future temperatures, especially for the second period, ranging from 3-8.1 degrees C, 3.1-8.2 degrees C, 3-6.9 degrees C and 2.3-6.5 degrees C, respectively for the four seasons (spring, summer, autumn, and winter) compared to the base period (1971-2000). As a result, a volume of about 173 and 230 MCM/year will be required to meet the water demands, considering probabilities of 50% and 25% respectively for this period. Also, the responses of each crop to drought/increasing temperature are different; for example, potato is more tolerant for temperature variability. Finally, Considering the uncertainty of these climate models to estimate increasing temperature in future, adaptation strategies are required to mitigate the future impact of increasing future agricultural water demand (especially for the period of 2070-2099).