Regional climate change scenarios and their impacts on water requirements for wheat production in Iran

We simulate the effect of climate change on water requirements of cold seasonwheat in various climatic zones of Iran. The research considers both observedclimate (temperature and precipitation) changes during recent decades (1960-2009)based on instrumental records and projected future changes to 2100 based on theMAGICC/SCENGEN 5.3 compound model. 20 General Circulation models are usedbased on a single scenario known as P50, which is the average of SRES or emissionscenarios. Results indicate that whilst winter precipitation has marginally increasedacross the country as a whole, a significant decline in mean spring precipitation isrecorded between 1960 and 2009. However, considerable variability in trends ismeasured across various climatic regions of Iran. Mean annual temperature / rainfallchanges in the various climate zones of Iran for the period 1960-2009 follow: +0.1 °C/ decade / +0.43 mm / decade in arid regions, -0.1 °C / decade / -1.7 mm / decade insemi-arid regions, +0.1 °C / decade / -1.33 mm / decade in Mediterranean / semihumidregions and -0.01 °C / decade / -0.04 mm / decade in humid / hyper humidregions. Temperature projections to 2100 indicate an overall temperature rise of ca.4.25 °C relative to that for 1961-1990, with increases projected for all climaticregions of Iran. Despite an overall projected mean precipitation increase of 36% forthe year 2100, relative to that for 1961-1990, these are insufficient to compensate fortemperature increases. Consequently, calculated water deficits during the growingseason (autumn to spring) in Iran’s wheat producing areas are expected to increasefrom 5.2% in 1980 to over 23% by 2050 and 38% by 2100.