Document Type : Research Paper
Authors
1 PhD Candidate in Irrigation and Drainage Engineering, Faculty of Agricultural Engineering, Isfahan University of Technology, Isfahan, Iran.
2 Professor, Department of Water Engineering, Faculty of Agriculture, Isfahan University of Technology, Isfahan, Iran,
3 Professor, Department of Water Engineering, Faculty of Agriculture, Isfahan University of Technology, Isfahan, Iran.
4 Assistant Professor, Department of Water Resources Study and Research, Water Research Institute, Tehran, Iran.
5 Assistant Professor, Department of Water Engineering, Faculty of Agriculture, Isfahan University of Technology, Isfahan, Iran.
Abstract
Keywords
Main Subjects
Methodology
In this study, Isfahan province is considered a study area. The minimum temperature data of the past period and the outputs of 10 general circulation models were downscaled by LARS-WG for the future period (2051-2022). In addition, the three emission scenarios SSP126, SSP245, and SSP585 of 13 stations in Isfahan province were used. General circulation models are weighted based on the average deviation of the minimum temperature simulated in the base period from the average of the observed data. Finally, for all stations, by combining the weight obtained for each model and the difference of the data of each scenario from its base value, the micro-scaled output data for each station was obtained using the LARS-WG6 model. To extract the frost parameters, preparing the minimum temperature data of the observation and future periods was started by controlling the minimum temperature from the first day of September and the first day when the minimum temperature is equal to the desired threshold; less than this threshold is considered the first fall frost (FFF) and the last day of frost (LSF). The dates are set as Julius days. Then the LF, GSL, and FD are calculated, and the spatial changes of the frost parameters in the future period based on all emission scenarios compared to the past period are plotted by the ARC GIS 10.8.
Results and Discussion
Temporal and spatial distribution of changes in the first fall frost and the last spring frost of the future period compared to the past period
On average, Chadegan (Oct 19) and Khour and Biabanak (Dec 6) had the earliest and the latest date of the first fall frost in the past statistical period. The average of the earliest date of the first fall frost at Chadegan station under the SSP585 emission scenario occurs one day later than the past statistical period, and in Khour and Biabank, the average of the latest date of the first fall frost under the emission scenariosof SSP126, SSP245 and SSP585 occur three, five and six days later than the past statistical period, respectively. Zoning the number of changes in the first fall frost in the future period under different emission scenarios compared to the past statistical period shows that the most increasing change in Khour and Biyabank under the SSP585 scenario occurs six days later, and the most decreasing change is related to Isfahan station under SSP126 scenario that it occurs eight days earlier.
For the last spring frost, Chadegan (Apr 21) and Ardestan (Feb 27) had the earliest and the latest date of the last spring frost in the past statistical period. The average of the latest date of the last spring frost at Chadegan station under the SSP126 emission scenario occurs one day later than the past statistical period. At Ardestan, under the emission scenarios of SSP126, SSP245, and SSP585, it happens five, four, and three days later than the past statistical period, respectively. Zoning shows that changes in the date of the last spring frost in the future statistical period compared to the past statistical period in all three scenarios in Khansar, Natanz, and Ardestan stations are increasing, which means the last spring frost occurs later, and the changes in the Semirom, Daran and Fereydun Shahr are decreasing that means the last spring frosts occur earlier.
Temporal and spatial distribution of changes in the frost length period, number of frost days, and growing season length of the future period compared to the past period
The longest frost length period in the past statistical period was observed in Chadegan with 184 days and the shortest in Khour and Biyabank with 81 days. However, the expression of this period in terms of the number of days does not mean that frost occurs every day. In the future statistical period, under all emission scenarios, the length of the frost length period at Chadegan, Khour, and Biabank will decrease. Moreover, some changes in the length of the frost period under all emission scenarios throughout the province are observed. Zoning shows that, in red areas, most changes in the length of the frost period occur decreasingly, and in blue areas, the most changes occur incrementally.
The highest number of frost days is related to Chadegan with 149 days, and the lowest is related to Khour and Biyabank with 25 days. In the future statistical period, the number of frost days at all stations will decrease under all emission scenarios. Zoning shows that Changes in the number of frost days in all selected provincial stations are decreasing.
The most extended growing season length is related to Khour and Biyabank with 146 days, and the lowest is related to Chadegan with 91 days. In the future statistical period, under all emission scenarios, the longest growing season length is associated with Khour and Biabank, and the shortest is related to Chadegan, but the changes in the growing season length are increasing in all stations. Zoning shows that the most changes in the growing season length are related to Chadegan, which increases under the emission scenarios of SSP126, SSP245, and SSP585 for 17, 18, and 21 days, respectively.
The effect of frost changes on the yield of agricultural products in the future
Spring does not start at the same time in different stations of the province, and the growth of some early flowering trees, such as almonds and apricots, starts earlier than the spring season, so it is essential to pay attention to the growth stages of plants that coincide with these frosts. Suppose the date of occurrence of the last spring frost in different stations in the future statistical period under all 3 diffusion scenarios coincides with the critical stages of plant growth (flowering stage). In that case, there is a possibility that spring frosts and agricultural yields will be reduced. Due to changes in the date of the first fall frost and the last spring frost, the length of the growing season varies at different stations; therefore, choosing the proper planting time and cultivars resistant to cold and frost is essential in the production efficiency of agricultural products.
Conclusion
Every year, early fall and late spring frost, due to the coincidence with the critical stages of plant life, reduces agricultural product yield. In the past statistical period, the average date of occurrence of the first fall frost is related to Chadegan, Daran, Fereydunshahr, and Shahreza, and the average of the last spring frost in Khour and Biabank, and Ardestan occur earlier than other stations. In the future statistical period, the date of occurrence of the first fall frost and the last spring frost under all emission scenarios are the same as in the past statistical period. In addition, increasing and decreasing changes were observed in the date of the first fall frost and the last spring frost in the future statistical period compared to the past. The average of the earliest date of the first fall frost at Chadegan station under the SSP585 emission scenario occurs one day later than the past statistical period, and in Khour and Biabank, the average of the latest date of the first fall frost under the emission scenarios of SSP126, SSP245 and SSP585 occur three, five and six days later than the past statistical period, respectively. The average of the latest date of the last spring frost at Chadegan station under the SSP126 emission scenario occurs one day later than the past statistical period. Moreover, in Ardestan, under the emission scenarios of SSP126, SSP245 and SSP585 occur five, four, and three days later than in the past statistical period, respectively. By knowing the date of the last spring frost, it is possible to determine the planting date of many crops, and planting time should be chosen so that the critical stages of plant growth are not exposed to spring frost. Also, changes in frost length period, number of frost days, and growing season length were observed in the future statistical period compared to the past statistical period throughout the Isfahan province. The most prolonged frost length period in the past statistical period was observed in Chadegan with 184 days and the shortest in Khour and Biyabank with 81 days. The highest number of frost days is related to Chadegan with 149 days, and the lowest is related to Khour and Biyabank with 25 days. In the future statistical period, the number of frost days at all stations will decrease under all emission scenarios. The longest growing season is related to Khour and Biyabank with 146 days, and the lowest is related to Chadegan with 91 days. In the future statistical period, under all emission scenarios, the longest growing season length is associated with Khour and Biabank, and the shortest is related to Chadegan, but the changes in the growing season length are increasing in all stations. The most changes in the growing season length are related to Chadegan, which increases under the emission scenarios of SSP126, SSP245, and SSP585 for 17, 18, and 21 days, respectively.
Acknowledgment
The author gratefully thanks the Isfahan University of Technology and the Iran Meteorological Organization for providing the necessary facilities and data for this study.
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