بررسی اثرات تغییر اقلیم بر نیاز آبی و پایداری مصرف آب در بخش کشاورزی دشت یزد- اردکان

Introduction
Water is a scarce resource in the Middle East region and climate change is expected to exacerbate this situation. Developing countries are vulnerable to these changes, primarily due to their limited adaptive capacities in dealing with extreme events. Therefore, investigation of this phenomenon will be very crucial in such areas. In the past decades, water shortage in Yazd province which is located in arid regions of Iran has resulted in transferring the water from Isfahan. But recently, due to increasing in water demand, inadequacy of this project clearly has felt. Evapotranspiration and agricultural water requirements are two crucial issues of this area which affected by climate change. Thus, considering climate change projections and future agricultural water requirements is necessary to determine water stress risks in the study area, Hence, this study aims to answer the following research questions:

Currently, how much irrigation water do we need in the Yazd-Ardakan region?
How does future climate change impact future irrigation requirements?
How does future climate change influence sustainability of the agricultural water consumption?

Materials and Methods
The data used in this analysis represented into two time periods, including (i) present (values for the period 1971–2005), and (ii) future, called year 2070 (values for the period 2021–2070). To evaluate future climate changes, daily climate data from Yazd Synoptic station for 1971-2005 period have been used. Data, including precipitation, maximum and minimum temperatures and sunshine hours. To investigate the climate changes of Yazd-Ardakan plain in the future period of 2021-2070, RCP 4.5 scenario has been used through SDSM 4.2.9 software. The effect of climate change on reference evapotranspiration and agricultural water needs were estimated. Crop evapotranspiration and irrigation requirements for two periods, were estimated following the standard procedure described in the FAO Irrigation and Drainage Paper 56 (UN-FAO, 2007) and CROPWAT software. Two indices considered to evaluate the sustainability of the agricultural water consumption in the study area. These indices including the ratio of evapotranspiration to the precipitation (EPR) and the ratio of maximum agricultural water deficit to the amount of agricultural water need as deficit index (MD). These indices estimated under present and future climatic conditions. To evaluate the amount of water used for main agricultural products, questionnaires were completed in the area.
Results and Discussions
The results of statistical validation of the predicted values, showed no significant differences between historical and predicted values of precipitation, maximum and minimum temperatures and sunshine. Therefore, suitability of LARS-WG model to simulate climatic data of the study area is confirmed. Investigation of the precipitation in the Yazd station showed that in spring season, precipitation will be declining and in autumn will be increasing. In other words, the distribution of precipitation in the future will have significant changes and as winter precipitation decreases the spring precipitation will have increasing trend. Results showed that monthly minimum and maximum temperature will increase in almost all months. Results of estimating agricultural water requirements showed that due to higher temperature, reference evapotranspiration, crop evapotranspiration and irrigation requirements will be increased up to 4% under climate change conditions. The EPR and MD indexes will increase by 24% and 13% respectively. The results revealed the imbalance between agricultural water use and the precipitation in the study area. In the other hand, results of the questionnaires showed that, the water used in irrigated agricultural areas is not in accordance with the requirements of products and therefore leads to water stress and, consequently, yield reduction of products. Therefore, in these conditions, appropriate management strategies and planning should be implemented to ensure the sustainability of water resources inthe Yazd-Ardakan plain.
Conclusion
This work focused on the climate change impact on cultivated area in the Yazd-Ardakan plain considering the possible alterations of crop evapotranspiration and irrigation requirements. According to this study by increasing in maximum temperature in the future, water needs of agricultural section will grow significantly. Therefore, planners and authorities should consider this fact for the future water resources allocation and strategies.