Prospect of Possible Changes in the Frequency of Frost Days in Iran Using General Atmospheric Circulation Models

Document Type : Full length article


1 Professor of Climatology, Department of Physical Geography, Faculty of Geography and Environmental Planning, Tabriz University, Tabriz, Iran

2 Assistant Professor of Climatology, Department of Physical Geography, Faculty of Geography and Environmental Planning, Sistan and Baluchistan University, Zahedan, Iran

3 PhD candidate in Climatology, Department of Physical Geography, Faculty of Geography and Environmental Planning, Tabriz University, Tabriz, Iran


Global warming and climate change are one of the most important bioenvironmental challenges in recent decades. Winter ecological processes are important drivers of vegetation and ecosystem functioning in temperate ecosystems. There, winter conditions are subject to the effects of rapid climate change. The potential loss of a longer-lasting snow covers with implications to other plant related climate parameters and overwintering strategies make the temperate zone particularly vulnerable to winter climate change. One of the indices suggested in analysis of climate changes and global warming is the frequency of frost days. Frost is an atmospheric phenomenon affecting agricultural activities in many parts of the Earth. The highest increase in average temperature is occurred in minimum temperature. Modeling and scientific research indicate that global warming and rise in night temperature have reduced the number of frost days in many parts of the globe.
Materials and Methods
The data of this study consisted of two groups of observational data and simulated data. The observational data are the daily minimum temperature values from 44 synoptic stations in various regions of Iran. The stations have the full data of thirty years (1981-2010) received from Iran Meteorological Organization.
The simulated data of the future period are generated using the downscaling output of general circulation models of atmosphere. One of the most famous models is stochastic weather generator, LARS-WG. The model is used to produce values of precipitation, radiation, and maximum and minimum daily temperature at one station under the present and future climate conditions. Among 15 LARS Models, two global climate models were selected; HadCM3 and GFCM21 Models. The data simulated by the two models for the periods 2045-2065 and 2080-2099 were performed and produced under the three emission scenarios AB, A2 and B1.
Results and discussion
The average frequency of frost days in the selected stations in the period 1981-2010 is 62 days per year. The dispersion of the number of frost days in the area is highly different. The range of frost days (0-134) per year in the studied stations is different. The highest frequency of the frost days is associated with Hamadan, Ardabil, Shahrekurd, Zanjan, Uremia and Khoy with a frequency higher than 100 days per year. The most frequent frost days were related to Hamadan with an average of 134 days per year. Four coastal stations of southern Bushehr, Bandar Abbas, Bandar Lengeh and Chah Bahar lack frost and Ahvaz and Abadan and Iranshahr stations with an annual average of less than one day. They have the lowest incidence of frost.
Results have indicated that in the period (2046-2065) under the GFCM21 model and the A1B, A2 and B1 scenarios, the average annual frost days in Iran was 37, 46 and 41 days, respectively. Based on the HADCM3 model and the scenarios, the average annual frost days are 41, 42 and 46 days. In both models, in three scenarios greatest reduction occurred in Hamedan station. In the stations of Khorram Abad, Kermanshah and Shahrekord, Shahrood, Yazd and Fassa a large decrease was seen. In the observation period (1981-2010), five southern coastal stations were free of frost while in this period the stations that have a frequency less than 10 day, will be frost-free.
In the period (2099-2081) based on the GFCM21 model and scenarios A1B, A2, and B1, the annual average number of frost days in Iran is estimated to be 31, 29 and 43 days. Based on the HADCM3 model, the annual average number of frost days is 33, 28 and 38 days.
In this study, we have used weather data from 44 synoptic stations of Iran, during the period 1981-2010. We have also applied the two models of the general circulation of atmosphere, HADCM3 and GFCM21, for the periods 2046-2065 and 2080-2099 under three emission scenarios of A1B, A2 and B1. Using these data and the outputs of the models, we have analyzed the effects of global warming on changes in the frequency of frost days in Iran. Both the models performed with the three scenarios have indicated a reduction in the frequency of frost days in both periods. The slope changes of the frequency of frost days in the period (1981-2099) under these scenarios have revealed the reduction of -5.5, -5.1 and -3.6 days per decade. Overall results showed that in all the stations, the number of frost days have declined in the coming decades. The rate of decline in the mid-northern and mountainous areas has the highest frequency of occurrence of frost more than that of the mid-South and beaches.


Main Subjects

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