Document Type : Research Paper
Authors
1 Assistant Professor, Soil Conservation and Watershed Management Research Institute (SCWMRI), Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran
2 Associate Professor, Department of Drought and climate change, Soil Conservation and Watershed Management Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran
3 PhD of Climatology, Department of Geography, Fars Province Department of Education, Shiraz, Iran
Abstract
Introduction
One of the most significant impacts of climate change has been the alteration in the average value of meteorological variables, which has led to noticeable changes in the characteristics of meteorological extremes. The warming and ongoing increase in global temperatures primarily exert profound impacts worldwide on human societies, ecosystems, and the environment through the increased occurrence of climatic extremes. Compared to climatic averages, extreme climatic events cause more significant changes in the natural and human environment, and due to their disastrous environmental and socio-economic consequences, they are of great concern to the general public, governments, and academic communities. Based on studies conducted by universities and other research institutions, the most significant consequence of climate change in Iran is the increased occurrence of extreme climatic events, particularly extreme warm temperature events. The increase in extreme events affects various sectors of the environment, socio-economy, agriculture, and others at national, regional, and local levels. The decrease in the number of rainy days and the lengthening of the dry season, along with the increase in extreme warm temperature events and the decrease in extreme cold temperature events, lead to reduced water availability for irrigation and increased crop water demand, this also promotes the spread of pests and diseases in agricultural crops, causes delays in planting and harvesting, results in poor plant growth, reduces cultivation efficiency, alters cropping patterns and crop types, and ultimately leads to a decline in agricultural yields. Therefore, investigating extreme climate events and analyzing their spatio-temporal changes in the past and future of Iran is of great importance for making necessary decisions to confront and mitigate their consequences, which is the primary focus of this research.
Materials and methods
To investigate the spatio-temporal change of extreme temperature events in Iran during the observational period as well as the future periods, daily maximum and minimum temperature data from 123 synoptic stations across the country were used, along with data from the CNRM-CM6-1 model for the period 2020–2060 under two scenarios: the optimistic SSP126 and the pessimistic SSP585. The quantitatively and qualitatively control of the receive data was carried out using the Climpact2 software. To calculate cold and warm extreme temperature indices over different periods, 14 temperature indices recommended by the CCL/CLIVAR expert group were used. The calculation of the indices and their final outputs were performed in the MATLAB software.
Results and discussion
Overall, the calculation of warm extreme temperature indices during the observational period showed that for most stations, the frequency and trend of warm indices—such as warm nights, warm days, the number of summer days, and the number of tropical nights—have exhibited an upward and increasing trend. In contrast, the temporal changes in cold indices showed that for most stations, the trends of cold indicators such as cold days, cold nights, and the number of frost days have generally been decreasing and declining. An analysis of the frequency of the SU25 index as one of the most common extreme warm indices revealed that the highest occurrence of this index was recorded at Konarak (Airport) station with 363 days, while the lowest value occurred at Ardabil station with 21 days. The maximum value of the frost days (FD) index—one of the most common extreme cold indices in the country—was recorded at Sarab station with 179 days, while the lower limit, indicating the absence of frost, was observed at some stations in the southwestern part of the country. An analysis of future temperature indices for the period 2020–2060 indicates that the behavior of extreme cold and warm temperature indices does not depend on the geographical location and topographical conditions of different regions of the country. This is because, according to the outputs of the CNRM-CM6-1 model for the two scenarios, SSP126 and SSP585 during the period 2020–2060, the trend of extreme warm indices in regions with higher-elevation and higher-latitude regions did not differ significantly compared to lower-elevation and lower-latitude. The trend behavior across areas with different geographical characteristics is quite similar, with only minor variations.
Conclusions
In summary, based on the findings of this study and similar research, it can be concluded that warm temperature extremes in Iran have increased in the past and are projected to continue increasing in the future, while cold extreme have decreased, and the rate of these changes varies considerably across different regions of the country. This condition is particularly evident when comparing indices of the lowest minimum and maximum temperatures and the highest minimum and maximum temperatures. This situation indicates a warming climate in Iran, a shift in the climate types of various regions, and a trend toward increased aridity. One of the main reasons for this situation, in addition to local characteristics, is the change in the Earth’s energy balance and the higher rate of warming at the poles compared to the equator, this has altered the Earth's energy equilibrium, ultimately leading to changes in atmospheric conditions and shifts in climate patterns. Therefore, it is necessary for decision-makers at various management levels to adopt appropriate measures to confront or mitigate the potential consequences of rising temperatures and extreme warm events in different regions of Iran.
Keywords
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