Introduction: Climate change is one of most important environmental issues that can affect agriculture and water resources in an area. Due to importance of climate change on structure of planet and its inhabitants, especially in arid and semi-arid regions, in recent years, as one of most common topics, has been considered by scientific societies and many studies to study effects it is done. Global warming and climate change due to human activities is one of major environmental problems that has attracted the attention of many scientific and political circles in world in last two decades. Climate is considered as most important factor of agricultural production and climate change affects agricultural and livestock production, hydrological balance and other components of agricultural systems. Agricultural sector is affected by both climate change and climate change.

Materials and methods: In present paper, using DAYCENT model, rate of methane, nitrous oxide and nitric oxide emissions is estimated by considering the annual average and precipitation changes of -30, -20, -10, 10 and 20%, and finally amount of global warming potential of citrus orchards and groves of Khuzestan province in these conditions, rainfall changes were calculated. This model was first widely used in 1970s to simulate changes in soil organic matter (SOM), plant productivity, nutrient availability, and other ecosystem parameters in response to changes in land and climate management. Which can be used to simulate plant growth and changes in soil organic matter for most terrestrial ecosystems around world. Increased attention to greenhouse gas analysis led to development of DAYCENT in 1994. DAYCENT model includes a sub-model in plant production phase and a sub-model for step-by-step dynamics of daily scarce gas flow, nutrient circulation, water flow and soil organic matter (SOM). DAYCENT model program is written in FORTRAN and C programming languages and can use a DOS window or a Linux platform. DAYCENT model inputs include observed daily rainfall and maximum and minimum daily temperature; Soil variables include texture, density, thickness, field capacity, wilting point, pH, saturated hydraulics, and EC. This model has been validated using observed data related to crop production, soil organic matter, nutrient circulation and trace gases.

Results and discussion: Based on estimation results of DAYCENT model, highest amount of methane emission modeled at Dezful station, highest rate of oxidation of nitrous and oxidized nitrogen at Abadan station and highest rate of oxidation of nitrous and oxidantric modeled at Dezful station were determined. Also, according to results obtained from the average calculations of global warming potential coefficient of methane, nitrous oxide and nitric oxide in citrus orchards of Dezful 59.150 and in Abadan groves 47.200 tons equivalent to carbon dioxide was obtained. Rainfall changes also showed greatest effect in Dezful station for citrus cultivation and least effect in Abadan station for date cultivation. For gas methane in Dezful station, maximum value of 0.769 tons per hectare per year in precipitation changes was 20% and minimum value of 0.421 tons per year in precipitation changes was -30%. For nitrous oxide in Dezful station, maximum value was 0.201 tons per hectare per year in precipitation changes of 20% and minimum value was 0.004 tons per hectare per year in precipitation changes of -30%. Also for nitric oxide in Dezful station, maximum value of 0.342 tons per hectare per year in precipitation changes was 20% and minimum value of 0.132 tons per hectare per year in precipitation changes was -30%. In general, with decreasing precipitation, progression of all three gases decreases and with increasing precipitation by 10 and 20%, gas flux has an increasing trend. For gas methane at Abadan station, maximum value of 0.638 tons per hectare per year in precipitation changes was 20% and minimum value was 0.304 tons per hectare per year in precipitation changes of -30%. For nitrous oxide in Abadan station, maximum value was 0.278 tons per hectare per year in 20% precipitation changes and minimum value was 0.006 tons per hectare per year in precipitation changes of -30%. Also for nitric oxide gas in Abadan station, maximum value of 0.342 tons per hectare per year in precipitation changes was 20% and minimum value of 0.169 tons per hectare per year in precipitation changes was -30%. In general, with decreasing rainfall, we have a decrease in methane flux. This trend increases with increasing rainfall by 10 and 20%. The flux of nitrous oxide and nitric oxide also decreases with decreasing rainfall and increases very much with increasing it.

Conclusion: The high growth of methane gas in Dezful station is due to type of cultivation. While high flux of nitrous oxide in Abadan station and nitric oxide in Dezful station due to lack of principled use of chemical fertilizers and non-compliance with expert principles in farms has caused high flux of these gases. In two stations, with decreasing precipitation, progress of all three gases decreases, and with increasing precipitation by 10 and 20%, gas flux has an increasing trend. The potential for global warming in Dezful region was greater because more dense cultivation and more fertilizer use was expected. Also in citrus orchards, changes in global warming potential are very high as a result of rainfall changes. In summary, largest share of global warming potential is in evolution of nitric oxide gas. Calculating emission of greenhouse gases and potential for global warming due to agricultural activities can provide necessary warnings to planners and policy makers in agricultural sector and protection of country's environment to take necessary measures for more attention and financial support.