The Effect of Regional Climate Change on the water requirement of dryland farming Crop in Iran

Agriculture is an essential need and thus an activity of prime importance for human. As such، investigation of impacts of climate change on agriculture gains importance and necessity. One of the effective parameters in the crops productivity is better understanding of irrigation demands of the crops. Global warming via wielding impact on the climate parameters of temperature، precipitation، and evaporation can affect water demand in agricultural sector، and in some cases، challenge the food security of the nation through increasing the water demand and paucity of water resources required to better growth of crops. So، the rationale of the present study include the following: investigation، detection and prognostication f trends of change in temperature and precipitation in the country according to different scenarios of global warming، exploration of agro-climate of the crops، determination of the proper time and place of cultivation and risk and crisis management and food security of the country. The present study aims at the simulation of the impact of global warming on the irrigation demand of the dry cultivation (autumnal) in different regions of Iran. To do the research، data for 92 synoptic and climatic weather stations across the country have been used. To simulate the weather components up to 2100، the MAGICC/SCENGEN 5. 3 has been used in the study. As the purpose of the present study is calculation of irrigation demand، the Terence White method of evaporation-perspiration. Ultimately، the losses and excess of water needed for irrigation for different periods of 1980، 2005، 2025، and 2100 were measured using the method provided by American Soil Conservation System (SCS)، calculating the effective precipitation and then subtracting it from the water demand. Simulations of the temperature trend up to 2100 shows indicates a 4. 25 degrees centigrade rise for Iran compared to that for a long term of 1961 to 1990. Findings are also showing that the increase in water deficit in 2100 will be 152mm compared to that in 1980. It should be noted that in spite of a 36 percent increase in annual precipitation across the country by the year 2100 compared to its mean in the long period of 1961-1990، the increased amount will not suffice the water demand due to the increasing trend in temperature. The conclusion is that water deficit in the dry cultivation period (fall to spring) will rise to 23 percent in 2050 from 5. 2 percent in 1980 and finally it will soar to a 38 percent high in 2100.