Climate change impact assessment on agricultural crop virtual water under RCPs Scenarios in Khouzestan province

Agricultural sector has a vital role in the national economy and food production in Iran, so that about 27 percent of the country's gross domestic product and 22 percent of the workforce are related to this sector. Due to special climatic condition of Iran and poor temporal and spatial distribution of rainfall, irrigated farming is the main form in food production. Despite, somehow, the same dry and irrigated cultivation in the country, the highest production is obtained through irrigation, so that during the last 5 years almost always close to 90 percent of total Iran agricultural production has been by irrigated cultivation. In order to meet the food needs until the year 1410, based on approximate 2600 kcal/day, more than 150 billion cubic meters of annual water will be required that is not available in water cart of Iran. In a globalizing world, where problems increase with the effect of warming and climate changes, it is thought that a decrease in usable freshwater bodies will pose a serious problem. Allan presented the term virtual water for the first time. In the last decade, this concept was paid attention by most researchers of water industry. The term virtual water content (VWC) connects water, food, and trade together and is the opposite of water efficiency. This study intends to investigate climate change impacts on the virtual water content of agricultural crop in Khouzestan province in future periods. The strategic products and production whose data is available such as wheat, barley, rice, corn and sugar cane were selected for this study. Potential evapotranspiration of these products were used during the cultivation periods. The average crop production of each city was taken from ministry of Agricultural affairs and each crop virtual water content was calculated. Wheat and barley are planted both in irrigated and rainfed lands in Khouzestan. The cultivation of rice, maize, and sugar cane are just in irrigated form. The virtual water for each crop was calculated separately. In order to investigate climate change impact on VWC, the CanESM2 atmospheric general circulation model (GCM) data under two RCP scenarios (IPCC-AR5) were used. In order to downscale CanESM2 model data, SDSM analysis software was used. The data used in this study include precipitation, minimum and maximum temperature, daily average temperature, and daily evaporation. To determine the feasibility of future periods meteorological data production of SDSM model, calibration and verification were performed for the base periods. Minimum and maximum temperature and precipitation estimated by SDSM method using CanESM2 data in three future periods: 2030s, 2060s and 2090s and compared with historical data. Results showed that temperature on average increased in all selected scenarios, this increase is higher in the case of RCP8.5 compared to RCP4.5, as precipitation will reduce in 2060s and 2090s. Highest increase of average temperature in Khouzestan is about 4.6° C in 2090s under RCP8.5 and decrease in temperature in 2030s is about 1° C under RCP4.5. The maximum and minimum temperature variation compared to the monitoring period under two RCP scenarios from June to November have increasing trends in 2060s. Precipitation under RCP8.5 for most months on average is declining and the sharpest decline occurs in November, while most months are associated with increased precipitation under RCP4.5. The minimum and maximum temperatures will decrease and increase, respectively, in most months of the year in 2090s, and precipitation has a sharp decrease compared to the observed period under RCP8.5, and a decrease will occur in January, February, and December, although precipitation will increase from August to October. Crop virtual water under RCP4.5 compared to baseline is always less than that of RCP8.5 scenario. Wheat, barley and sugar cane VWC increase compared to RCP4.5. There is 22.5% difference for wheat VWC between two RCP scenarios in 2030s compared to baseline period. For barley, there is 17.5% difference between the two RCP scenarios in 2090s compared to baseline period. For rice, there is 18.2% difference between the two RCP scenarios in 2090s compared to baseline period.