Zonation and Estimation of the Trend of the Thermal Unit of Growing Season due to Temperature Changes, Iran

Document Type : Full length article


1 Assistant Professor of Climatology, Meybod University, Yazd, Iran

2 MSc in Climatology, Yazd University, Yazd, Iran


One of the challenges in the 21st century is the issue of climate fluctuations. The increased average global temperature and its pursuing changes are part of the climatic changes that have been addressed in all ecological theories. In addition to this global increase in the air temperature, many of the phenomenological, meteorological and satellite-based studies have reported a surge in the length of the growing season caused by the augmented temperature in northern areas during the twentieth century. Any crop for its germination and growth requires a minimal temperature below which the growth process is impeded or stopped. This temperature is specific for each plant variety. One of the critical effects of this phenomenon (global warming) is a change in the degree-days of plants. A plant growth is a variable of the temperature. The growing degree day index and its availability for a crop plays a vital role in the process of the growth and enhanced productivity of inputs, including cultivation date and greater yield. Thus, the growing degree-days vary relative to the temperature fluctuations. Investigating the effects of temperature in different time periods on the growth and development of organisms, especially plants, is of paramount importance.  
The objective of this paper is to investigate whether there are specific trends in the number of heat units during the growing season using temperature indices to determine indicators, capacities and limitations of the agricultural climate in planting varieties with different adaptation styles.
Materials and methods
In this paper, daily temperature data (minimum, maximum and average) reported by 31 Iranian synoptic meteorological stations over a 25-year common statistical period were used to estimate the trend of heat units during the growing season for 1985-1986 and 2009-2010 periods.
To calculate heat units, the length of growth season was initially extracted for temperature thresholds of 5 °C and 10 °C using Julian coding (January 21st with code 1 and January 20th with code 365) and then heat units of the length of growth season were calculated by subtracting average day temperature from base temperature. Maps of heat units have been prepared in GIS. The statistical defects have also been reconstructed using autocorrelation method, and the randomization of the data has been tested by the Mann-Kendall test. The series that had specific changes or trends at the confidence level of α=0.05 were identified. Then, using Mann-Kendall test, it was determined how and when these trends were started and variations in heat units were estimated.  
Results and discussion
To calculate the base heat units at 5 °C, the start and end dates of 5 °C and the length of growing season have been first extracted and then based on the length of growing season, the number of heat units during each season has been calculated for the stations. The average length of the growing season at a temperature of 5 °C is varied in different stations ranging from 147 days at Shahrekord station to 365 days at Bandar Abbas and Bushehr stations. The heat units during the growing season also varied from 2218 to 4174 degree-days at stations under study, with the lowest number belonging to Shahr-e-Kord Station and the highest to Gorgan Station. The length of growing season at 10 °C was variable from 67 days at Shahrekord Station to 348 days at Bandar Abbas Station. The number of heat units during the growing season for this base was 861 degree-days for Shahrekord station and 5664 degree-days of the Bandar Abbas station. The results of the Mann-Kendall test indicated that the average heat units in most stations under study over the past 25 years followed a specific trend throughout the growing season. That is, for a temperature threshold of 5 °C, changes in most stations had an increasing trend, with the exception Sanandaj and Shahrekord stations, which pursued a negative or decreasing trend. For a temperature threshold of 10 °C, most stations displayed a positive and incremental trend, except for Abadan and Ahwaz stations that had a negative and declining trend.  The results of Mann-Kendall's graphic test on heat unit data with a temperature threshold of 5° C revealed that changes in all stations followed an incremental trend, except for Abadan and Bandar Abbas stations that had a dramatic and decreasing trend. Among the series of heat units at 10 °C, unlike Abadan, Ahwaz and Bam stations, which have a dramatic and declining trend, the rest of the stations followed an incremental trend.
The analysis of the change trends of heat units during the growing season for temperature thresholds of 5 °C and 10 °C indicated that most of these changes were dramatic except few of them following a progressive and steady trend. For a 5 °C temperature threshold, the changes in all stations had an incremental trend with the exception of Bandar Abbas station, which demonstrated a sudden and declining change. Considering the temperature threshold of 10 °C for the analysis of heat unit series, it was observed that Abadan and Ahwaz stations had a sudden and decreasing trend whereas other stations such as Gorgan, Arak, Zahedan, Ramsar, Mashhad, Qom, Sanandaj, Anzali and Tehran followed a steady and incremental trend.  Among the series of heat units for 10 °C, unlike the Bam station, which displayed a sudden declining trend, the stations of Urmia, Bushehr, Birjand, Khoy and Sabzevar followed a sudden incremental event.  The results of the research exhibited more significant changes in the series of heat units at a threshold of 10 °C in comparison with heat units at a threshold of 5 °C. At the base temperature of 5 °C, the number of heat units for the length of growing season is increased from south to north and from west to east, and at the base temperature of 10 °C, it revealed an increasing trend from south to north and from west to east of the country. According to the results, it can be suggested that in the areas where the length of the growing season declines, given that farmers struggle with low yields and crops that are not grown adequately, farmers would be better off cultivating crops with the low growth period or early plants to provide the heat energy needed by the plant during the growing season.


Main Subjects

ترکی، م.؛ مظفری، غ. ع. (1389)، بررسی روند تغییرات طول فصل رشد در ایران، اندیشه جغرافیایی،54، 4 (8)،: 43-25.
لشنی زند، م.؛ پروانه، ب. و امیدی‏مهر، ف. (1393). نقش مدیریت شهری در تعدیل نوسانات آسایش بیوکلیماتیک شهر خرم‏آباد در شرایط تغییر اقلیم، آمایشمحیط. 7(۲۶): ۱۱۱ـ130.
کاویانی م. ر.؛ عساکره، ح. (1384). بررسی آماری روند بلند مدت بارش سالانه­ی اصفهان، مجله پژوهشی دانشگاه اصفهان (علوم انسانی)، 18(1): 162-143.
کوچکی، ع. و علیزاده، ا. (1375).اصول زراعت در مناطق خشک، چ۹، مشهد: انتشارات آستان قدس.
صداقت‏کردار، ع.‏ا. و رحیم‏زاده، ف. (1386). تغییرات طول دورة رشد گیاهی در نیمة دوم قرن بیستم در کشور، مجلة پژوهش و سازندگی در زراعت و باغبانی، 75: ۱۸۲ـ192.
عزیزی، ق. و روشنی، م. (1387). مطالعة تغییر اقلیم در سواحل جنوبی دریای خزر به روش من- کندال، مجلة پژوهش‏های جغرافیایی، 64: ۱۳ـ28.
علیزاده، ا. (1388). اصول هیدرولوژی کاربردی، چ27، مشهد: انتشارات آستان قدس رضوی.
ماوی، ه.‏ا. (1382).اصول و مبانی هواشناسی کشاورزی، ترجمة غلامعلی مظفری، انتشارات نیک‏پندار.
مظاهری، د. و مجنون حسینی، ن. (1380). مبانی زراعت عمومی، تهران: انتشارات دانشگاه تهران.
مظفری، غ.‏ع.؛ ترکی، م. و مهرشاهی، د. (1393). ارزیابی تغییرات طول دورة رشد ناشی از تغییرات اقلیمی در مناطق شمالی ایران، سومین همایش بین‏المللی تغییر اقلیم و گاهشناسی درختی در اکوسیستم‏های طبیعی، پژوهشکدة اکوسیستم‏های خزری، ساری.
مظفری، غ.غ. و دهقان، ح. (1392). پهنه‏بندی طول فصل رشد گیاهان بر مبنای ویژگی‏های دمایی در ایران، جغرافیا و توسعة ناحیه‏ای، 11(۲۱): ۱۲۱ـ137.
معروف‏نژاد، ع. و قاسمی، ش. (1395). روند تغییرات دما با استفاده از روش من- کندال (مطالعة موردی چهار شهرستان استان چهارمحال و بختیاری)، فصل‏نامة آمایش محیطی، 37: ۱۴۹ـ166.
میرمحمدی میبدی، ع. و ترکش اصفهانی، س. (1383). مدیریت تنش‏های سرما و یخ‏زدگی گیاهان زراعی و باغی، اصفهان: انتشارات جهاد دانشگاهی ( واحد صنعتی اصفهان).
موسوی بایگی، م. و اشرف، ب. (1388). هوا و اقلیمشناسی در کشاورزی، مشهد: انتشارات دانشگاه فردوسی مشهد.
Anandhi, A. (2016). Growing degree days – Ecosystem indicator for changing diurnal temperatures and their impact on corn growth stages in Kansas, Ecological Indicators, 61(2): 149-158. https://doi.org/10.1016/j.ecolind.2015.08.023
Alizadeh, A. (2009). Applied Hydrology, Astan Quds publication, Mashhad.
Azizi, GH. And Roushani, M. (2008). Using Mann-Kendall Test to Recognize of Climate Change in Caspian Sea Southern Coasts, Physical Geography Research Quarterly, 2(0): 13-28.
Baker, D.G.; Sharratt, B.S.; Chiang, H.C.; Zandlo, J.A. and Ruschy, D.L. (1984). Base temperature selection for the prediction of European Corn Borer In star by the growing degree day method, Agriculture and Forest Meteorology, 32: 55-60. https://doi.org/10.1016/0168-1923(84)90028-5
Chmielewski, F-M. and Rötzer, T. (2001). Response of tree phenology to climate change across Europe, Agricultural and Meteorology, 108(2): 101-112. https://doi.org/10.1016/S0168-1923(01)00233-7.
Koocheki, A. and Alizadedh, A. (1996). Principles of agriculture in arid areas, ‏Astan Quds publication. Mashhad.
FAO (1978). Reports of the agro-ecological zones project, World Soil Resources Reports, Rome, Italy, 48: 140-178.
Frich, P.; Alexander, L.V.; Della-Marta, P.; Gleason, B.; Haylock, M.; Klein Tank, A.M. G. and Peterson, T. (2002). Observed coherent changes in climatic extremes during the second half of the twentieth century, Climate Research, 19: 193-212.
Guan, B.T.; Chung, C.H.; Lin, S.T. and Shen, C. (2009). Quantifying height growth and monthly growing degree day relationship of plantation Taiwan spruce, Forest Ecology and Management, (257): 2270-2276. https://doi.org/10.1016/j.foreco.2009.03.003
Jaagus, J. (2006). Climatic changes in Estonia during the second half of the 20th century in relationship with changes in large-scale atmospheric circulation, Theoretical and Applied Climatology, (83): 77-88. https:/ DOI 10.1007/s00704-005-0161-0
Jeong, S.J.; Ho, C.H.; Gim, H.J. and Brown, M.E. (2011). Phenology shifts at start Vs end of growing season in temperate vegetation over the Northern Hemisphere for the period 1982–2008. GlobalChange Biology, 17(7): 2385-2399. https:// 10.1111/j.1365-2486.2011.02397.x.
Kadioglu, M. and Saylan, L. (2001). Trends of Growing Degree-Days in Turkey, Water, air and soil pollution, 126(1-2): 83-96. https://10.1023/A:1005299619084.
Lashanizand, M.; Parvane, B. and Omidimehr, F. (2014). The role of urban management in moderating fluctuations Khorramabad city bioclimatic comfort on climate change conditions, Quarterly environmental based territorial planning (Amayesh), 7(26): 111-130.
Linderholm, H.W. (2006). Growing season changes in the last century, Agriculture and Forest Meteorology, 137(1-2): 1-14. https://doi.org/10.1016/j.agrformet.2006.03.006.
Mavi, H.S. (2003). Principles of agricultural meteorology, Translated by Gholam Ali Mozaffari, First Edition, Nike Pendar Publications: 496.
Maarofnejad, A. and Ghasami, SH. (2017). Analysis of changes using the method of Mann-Kendall (Case Study of Four townships of Chaharmahal and Bakhtiari Province), Journal Management System, 10(37): 149-166.
Mazaheri, D. and Majnoon Hosseini, N. (2001). Basic principles of agriculture, Tehran University Press, First Edition: 412.
Mirmeybodi, A. and Torkash Esfahani, S. (2004). Management of cold and frost tensions in crops and garden plants, Jihad Daneshgahi Publishing House, Isfahan Industrial Estate.
Mousavi Baygi, M. and Ashraf, B. (2009). Temperature and climatology in the farming, Ferdowsi University Press Mashhad.
Mozafari, G.A.; Torki, M. and Mehrshahi, D. (2014). Assessment of Changes in the Growth Period Caused by Climate Change in Northern Iran, Third International Conference on Climate Change and Dendrochronology in Natural Ecosystems, Caspian Ecosystem Institute, Sarri. https://t.me/Shamsbalapour.
Sharratt, B.S.; Sheaffer, C.C. and Baker, D.G. (1989). Base temperature for the application of the Growing-degree-day Model to field-grown Alfalfa, Field Crop research, 21: 92-102. https://doi.org/10.1016/03784290(89)90045-2.
Sedaghat kerdar, A.A. and Rahimzadeh, F. (2007). Variation of growing season length (GSL) over second half of 20th in Iran, Quarterly Pajouhesh-VA-Sazandegi, 20(2): 182-193.
Torki, M.; Gholamali, M. and Dehghan, H. (2014). The survey of growing season length trend and its zoning in Iran, Journal of Biodiversity and Environmental Sciences (JBES), 5(1): 179-188. http://www.innspub.net
Yuan, J.; Manyu, D.; Chutao, Z. and Dayong, ZH. (2012). Trends in the thermal growing season throughout the Tibetan Plateau during 1960–2009, Agricultural and Forest Meteorology, 166-167: 201-206. https://doi.org/10.1016/j.agrformet.2012.07.013.