پديد آورندگان :
محمدي، الهام نويسنده دانشگاه علم و صنعت ايران , , يزدان پناه، حجت ا... نويسنده استاديار اقليمشناسي، دانشگاه اصفهان ,
كليدواژه :
مدل اقليمي , تاريخ كاشت , گندم , طول دوره رشد , تغيير اقليم
چكيده لاتين :
Introduction
Climate change, generally, affect all economic sectors. But agriculture is the most sensitive and vulnerable sector, because agricultural products are highly associated with climatic resources. According to scientific evidences, climate change in the future, especially the combined effects of rising temperature and CO2 concentrations in the atmosphere and increase in the likelihood of some natural events, may have significant impacts on agricultural products. This paper is aimed to explore the trend of climatic parameters in the past and future, and their outcomes on the sowing date and length of the growing season for rainfed wheat in the Kermanshah region.
Methodology
The synoptic station of Sararood, Kermanshah, has geographical position at 47 degrees and 20 minutes western with elevation of 1351.6 meters above sea level. Simulation of climate parameters i.e., maximum and minimum temperatures and rainfall in coming decades was carried out using the results from the output of CCSM4 model under the scenario RCP4.5.
The outputs of the above mentioned model is low. Thus, to produce the climatic data of temperature in the study area, these outputs were statistically small-scaled in the period 2013-2039 and consequently the simulated data were used for next stages.
In order to study the impact of climate change on the displacement of sowing date and change in the length of growth period in the future, to estimate sowing date of rainfed wheat, initial rainfall dates were extracted from the synoptic station of Sararood. Then, according to the definition that the sowing date can be considered when the total rainfall by early October reaches to five mm, if 15 days after that should not be dry, sowing date for both past and future climates was determined. In regard to the correlation between growth stage in wheat and the temperature factor, the length of growth period of wheat using the index GDD (growth degree day) was calculated. But the remarkable point here is that due to the lack of data on the growth period before 1988, this year was considered as the length of growth period for base period.
Results and Discussion
Changes in temperature and rainfall in the past
Results of Kendall and senʹs Estimator slope indicated that changes in rainfall have been decreased in most of the months of the year. This trend was significant (P < 0.01) in March and annually; and temperature variables has significantly increased in most of the months of the year. Thus, it can be concluded that the temperature of the region has been influenced by the factors in the past that has increased the temperature.
The results of climate change on the study area in the period of 2013-2039, in which climate behavior of base period is compared with the future period, indicated that average maximum temperature was lesser than average minimum and maximum temperatures, with the except for the years 2013 and 2022, and minimum temperature with the except for the years 2015 and 2018. The rainfall during the years under study in the future was more than that of the average long-term in the base period.
Appropriate time for sowing date of wheat in the present and future conditions
To study the changes of initiation times of sowing in the future periods, we compared the long-term average of initiation date of wheat sowing based on distance from the source (first of October) of base climate with the initiation of sowing date of wheat based on future years. The results indicated, on average, that sowing date of wheat in the past climate was started from the second decade of December, while sowing date in future climate will be started from third decade of October. Furthermore, temperature in future climate will be more than past climate, thus the only reason for this, could be the start of earlier rainfall, in future years. Based on these, on average, rainfall in the past climate was started from the second decade of October and will be started in future climate from the second decade of December.
Changes of growth period length
To investigate the changes in length of growth period of wheat for the future periods, the mean of growth period length in base climate was compared with the growth period length in future years. The results indicated that mean of growth period length in past climate was 209 days, while in future climate was 184 days. Thus, it can be concluded that mean of growth period length of wheat in future climate will be 25 days shorter. The reason of decrease in growth period length can be due to increasing of temperature in future climate, where the mean temperature in the future climate will be 15.8 oC and in past climate 14.5o C.
Conclusion
The results indicated that in Kermanshah region, rainfall of past periods has a decreasing trend, while temperature has an increasing trend in most months of year, especially in cold months. In the future period, the temperature in all months of year will be increased from 1.7 to 2.5 C ? until the end of 2039. Appropriate sowing dates for wheat will also be the second decade of December for the past period, whereas for the future period it will be the third decade of October and later. Displacement of rainfall in the future period toward early cool-season has caused that sowing dates of wheat to start earlier in future climate compared with that of the past. Comparison of growth period length in the future and past periods indicated that in spite of initiation of sowing date of wheat in the past period later than future period, the length of growth period of wheat in the future climate will be shorter than 25 days relative to past climate. This can be resulted from increasing temperature in future periods relative to past.
