Investigation of the effect of climate change on net irrigation-requirement of main crops of Hamadan-Bahar plain using LARS-WG5 downscaling model

Climate change and its impacts on water recourses is known as one of the most important challenges which human would be faced with it in the future century. Although different studies are performed to consider the effects of climate change on the metrological and hydrological variables using climatic scenarios and General Circulation Models, but its effects on agricultural sectors such as water requirement are less investigated. The main objective of this study is to asses the effect of climate change on the net irrigation requirement changes of main crops in Hamadan-Bahar plain (winter wheat, barley, potato, sugar beet, maize (grain), maize (grass), peas and onion) in three next decades according to different scenarios using LARS-WG5 model compared with baseline period.
In this study daily metrological variables including precipitation, minimum and maximum temperature and relative humidity were collected from the Islamic Republic of Iran Meteorological Organization for 1981-2010. For main purpose, first of all, the capability of LARS-WG5 model was investigated and verified to simulate meteorological variables including minimum and maximum temperature, solar radiation and precipitation at Hamadan synoptic station in the baseline period (1981-2010). In the next step, meteorological variable values were stimulated by HadCM3 model based on A1B, A2 and B1 emission scenarios in the period of 2011-2040. Finally, the net irrigation requirement values of main crops were estimated for baseline and three future decades.
Based on the simulated results of LARS-WG5 model, the average values of air temperature and precipitation will increase by 0.77, 0.88 and 0.78 oC and 2.1, 5.9 and 10.2% for A1B, A2 and B1 scenarios, respectively.The results showed that average monthly precipitation will increase in October, December and February for three scenarios and decrease in March, April and May for A2 and B1 scenarios. Also, the total amount of net irrigation requirement of examined crops will increase between 2.6 to 28.2 mm for three future decades compared with baseline period. According to A2 scenario, the net irrigation requirements of wheat and barley have the lowest values of increasing change and sugar beet and potato have the highest increasing changes.
According to the A2 as a plausible scenario, the total net irrigation requirement of sugar beet, wheat, barley, potato, maize (grain), maize (grass), peas and onion in 30 next years will increase 267, 75, 57, 275, 250, 153, 145 and 224 cubic meters per hectares, respectively compared with baseline period. In general, considering increasing changes of the net irrigation requirements of different examined crops, the selection of appropriate cropping patterns consistent with climate change is required.