تاثير تغيير اقليم بر طول مراحل رشد و نياز آبي گندم (Triticum aestivum L.) و جو (Hordeum vulgare L.) (مطالعه موردي: دشت بيرجند)

Effects of climate change on length of growth stages and water requirement of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) (Case study: Birjand plain)

تغييرات آب و هوايي ناشي از تغيير اقليم، در كنار ساير اثرات خود، بر بارندگي و چرخه هاي هيدرولوژيكي اثر خواهد گذاشت و اين تاثير ات بر توليدات كشاورزي كه مستقيماً وابسته به محيط فيزيكي هستند بيشتر خواهد بود. كشاورزي به عنوان يك مصرف كننده عمده آب نياز خواهد داشت تا به منظور حصول پايداري، در كنار ساير چالش ها، نسبت به اين تغييرات تطابق پيدا كند و پيش آگاهي در خصوص تغييرات آتي اقليمي و تاثير آن بر مصرف آب كشاورزي مي تواند در اين زمينه راه گشا باشد. در تحقيق حاضر اثر تغيير اقليم بر نياز آبي گندم (Triticum aestivum L.) و جو (Hordeum vulgare L.) و عملكرد گندم در دوره زماني 2039-2010 ميلادي در منطقه بيرجند مورد بررسي قرار گرفت. پارامترهاي اقليمي دما و بارندگي در دوره زماني 2039-2010 با استفاده از مدل LARS-WG شبيه سازي شدند. تبخير و تعرق پتانسيل و واقعي به روش پنمن مانتيث و بارندگي موثر به روش USDA محاسبه شد و نياز آبي محصول توسط نرم افزار كراپ وات برآورد گرديد. اثر تغيير اقليم بر عملكرد گندم با استفاده از مدل DSSAT مورد ارزيابي قرار گرفت. نتايج نشان داد كه در آينده درجه حرارت هاي كمينه و بيشينه در تمامي ماه‏هاي سال افزايش مي يابند و متوسط بارش ساليانه نيز اندكي بيشتر خواهد بود. با وجود بيشتر شدن تبخير و تعرق گياه مرجع، به دليل كاشت زودتر گندم و جو و كوتاه شدن طول دوره رشد آن‌ها، نياز آبي محصولات در آينده بين 5/19 درصد (گندم) تا 5/22 درصد (جو) كمتر خواهد شد. از سوي ديگر، عملكرد گندم نيز به علت كوتاه تر شدن طول دوره رشد محصول تحت تاثير تغيير اقليم حدود 30 درصد كاهش خواهد يافت.

Introduction The global climate is changing and, despite efforts to reduce greenhouse gas emissions, weather variation is inevitable. Meanwhile, agriculture as a major water consumer will require adaptation to these variations, along with other challenges, to guarantee its persistence and sustainability. Given the arid and semi-arid climate of Iran, water, as a main limiting factor for agricultural production, plays an important role in determining the type of farming activities (Osamu et al., 2005). Crop water requirements and evapotranspiration are the main cause of water consumption in agricultural sector, the both accepted to face a dramatic increase in future under influence of increasing temperatures resulting from climate change (Koocheki et al., 2001). In this regard, the foreknowledge about future changes in climate and its effects on agricultural water use can be helpful for farmers and decision-makers. This study aimed to evaluate the climatic conditions of Birjand plain in the next two decades, and to investigate the effects of climate change on water consumption of wheat and barley as two main crops in this region. Materials and methods In the present survey, the effects of estimated climate change in Birjand plain on water requirement of wheat and barley and wheat yield in the 2010-2039 period were studied. Based on average weather data for the last thirty years from Birjand synoptic stations, climatic parameters of temperature and precipitation for the time period of 2010-2039 were simulated with LARS-WG5 using A1 scenario confirmed by the IPCC. Wind speed and relative humidity also were estimated for the future period. Common planting and harvesting dates were obtained from local farmers and Birjand Agriculture Organization and duration and crop coefficients (Kc) for early, developmental, middle and final crop growth stages in the current period were extracted from FAO Irrigation and Drainage Paper No. 56. For the future period, these dates and growth stages duration were estimated by matching the average daily temperature at the current time with the time of their occurrence in the future. The reference and crop evapotranspiration were calculated based on Penman-Monteith equations and effective rainfall was determined with USDA method. Crop water requirement was also calculated using the CropWat software and effects of climate change on crop yield was evaluated using DSSAT model. The genetic factors were taken from the study of Mansouri (2012) in Birjand. Other required input data (edaphic and crop data) obtained from Agricultural Organization and local farmers. Results and discussion The results showed that the minimum and maximum temperatures of the future years will increase, and there would be an approximately 3.5 percent more annual rainfall in the future decades. The largest temperature increase will occur in cold months, with a maximum rise in temperature of 2 °C in February. Overall, the average maximum temperature for 2010-2039 would be up to 0.6 °C higher than current period in Birjand. These higher temperature will result a significant decrease in the length of crop growth period, so that the time of planting to maturity will be reduced from 240 and 219 days (in current terms) to 227 and 193 days (in the future) for wheat and barley, respectively. Koocheki et al. (2001) has estimated 26 days shorter growing season for wheat in Mashhad due to higher temperatures in future. Despite higher reference evapotranspiration, crop water requirement will drop in the future between 19.5 percent (wheat) to 22.5 percent (barley), due to earlier planting of these crops and their shorter growing period. Indeed, due to the shorter duration of crop growth under climate change condition, the wheat yield will be reduced by about 30 percent. It was also previously estimated that despite an increase in carbon dioxide, wheat yield will be lower between 13 and 28 percent towards year 2050, which depends to location and employed general circulation models. Obviously, the agricultural practices and management should improve to comply with the inevitable climate changes. Increasing tolerance of wheat cultivars grown in this area to higher temperatures, especially during flowering time, can be effective in order to adapt to climate change. Conclusion Climate change is one of the main challenges facing the agricultural sector, especially in arid and semi-arid regions, and simulation of its effects in the future, can be useful for the planning and policy making to ensure food security for the community and welfare for the producers. The models which used in this study have already been successfully used in different studies.Our results showed that the use of these models to predict climate change and its effects on crops water requirements in Birjand plain will be possible with a good accuracy.