ارزیابی روند شاخص‌های حدی دما و بارش در حاشیه کویر مرکزی ایران

The activities of humanity on Earth have significantly changed over the past hundred years. The increase in greenhouse gas concentrations has led to global warming and, as a result, has caused changes in climate indices. Assessing extreme temperature and precipitation values is of great importance in agricultural planning and water resource management policies. In this study, using daily temperature and precipitation data from 18 synoptic stations located on the periphery of the central desert of Iran, 12 extreme indices, including 6 temperature indices and 6 precipitation indices defined by ETCCDMI, were evaluated for the time period from 1991 to 2020.
For trend and magnitude determination of the indices, the Mann-Kendall test and Sen's slope estimator were used. The research results indicate an increasing trend in warm extreme indices and a decreasing trend in cold extreme indices in the study area. The Alborz Mountains factor has some influence on these indices, with the decreasing trend in cold extreme indices being less pronounced in the northern part of the region, which is closer to the Alborz Mountains, compared to the southern part. For instance, the Shahroud station and warm extreme indices in the southern part of the region show a significant increasing trend compared to the north. Furthermore, the diurnal temperature range index in the northern part of the region, which is close to the southern slopes of the Alborz Mountains, exhibits the highest increasing trend, while in the southern part, this index shows a decreasing trend. Regarding the 6 precipitation indices, no significant trend was observed in most of the stations.
Introduction
"Natural variations are one of the characteristics of global climate that occur on both short-term and long-term scales. Most climatologists believe that short-term and long-term climate fluctuations are not random events (3). Human activities have significantly altered the Earth's atmosphere over the past century, with an increase in greenhouse gas concentrations leading to global warming and an increase in extreme events. Extreme events refer to rare events that fall in the upper and lower tails of the statistical distribution in such a way that their occurrence is very unlikely under normal conditions (in terms of time and location)."
Certainly, "In recent years, the phenomenon of climate change has been significantly noticeable, and in-depth studies in this regard have been strongly emphasized by international climate change organizations. It has become a major concern for planners, environmentalists, and climatologists alike.
Iran's geographical location in a desert belt and its possession of one-fourth of its water resources (rainfall and surface water) make the importance of addressing the consequences of climate change more evident than ever. Examining extreme temperature and precipitation values and the extreme events resulting from them holds special significance in policy-making and planning in sectors such as agriculture, water resource management, urban planning, construction, and transportation.
Within Iran's geographical framework, numerous regions are identified as key historical centers of Iranian civilization. One of these regions is the periphery of Iran's central desert, which is considered a significant historical axis of Iranian civilization. Since these regions provide the backdrop for extreme weather events, a detailed examination of extreme climate data in these areas is essential."

Materials and methods
Area of study
For the purpose of achieving the research objectives, long-term daily data of precipitation, minimum and maximum temperatures from 18 synoptic stations (Table 1) within the specified region (the periphery of the central desert) during the statistical period (1991-2020) were utilized. The central desert, also known as the desert pit, is situated in the geographical coordinates of approximately 30.54 to 57.00 degrees east and 30.33 to 30.35 degrees north, in the heart of the Iranian Plateau. The central desert is the widest desert in Iran, bordered to the north by the Central and Eastern Alborz mountain ranges, to the west by the vicinity of Qom and Kashan, to the east by the Peer Hajat and Azbakeh mountains, and to the south by the Khor-Khur - Tabas transportation corridor (see Figure 1)
Research method
To investigate the trends of climate extreme indices, 12 extreme indices, comprising 6 temperature indices and 6 precipitation indices defined by ETCCDMI for the time period (1991-2020), were employed (Tables 2 and 3). These indices are calculated using the RclimDex software within the R programming language environment.
The climate indices are then extracted from daily data. To examine the trend of climate changes, time series of extreme temperature and precipitation indices were subjected to trend analysis. One of the common methods for analyzing the trend of time series data is the Mann-Kendall test and Sen's slope, which were used in this study. The steps for calculating the statistics of these tests are detailed in the study by Nazarpour et al. (1401: 237).
Furthermore, maps depicting the trends of the 12 indices were generated using GIS software

Total resulting
The results of the analysis of temporal changes in the occurrence of warm indices during the period 1991-2020 in the study area indicate that, in general, for most stations, the trends of warm indices such as tropical nights (TR20), hot days (TX90p), and hot nights (TN90p) have been upward. Additionally, the research output shows that the warm extreme indices are somewhat different in the northern and southern parts of the region. Specifically, warm extreme indices in the southern part of the region exhibit a significant increasing trend compared to the northern part. It can be stated that the Alborz Mountains have had an influential role in the northern part of the region, preventing temperature increases compared to the southern part.
On the other hand, the temporal changes in the occurrence of cold indices show that, in general, the trends of cold indices such as cold days and cold nights have been downward for most stations.
A crucial point deduced from the comprehensive examination of the warm and cold extreme indices in the research area is the predominance of warming trends during the selected statistical period. This is one of the main reasons for these conditions, driven by global warming, especially since the late 1990s. Based on the findings obtained from the analysis of the trend of precipitation extreme indices in the study area, the total precipitation in this region, like many other parts of the country, has experienced a decrease, although it does not follow a uniform pattern. In contrast, the extreme precipitation index (specific index not mentioned) for the period 1991-2020 shows an increasing trend in some stations. These conditions may indicate an increase in intense and short-term precipitation events, along with a shortening of the rainy season in the region.
The results from this section align with the findings of studies conducted by Mosavi Baygi et al. (1394) and Jones et al. (2012). Attention and significance to the consequences of increasing extreme precipitation events and the occurrence of events such as floods underscore the need to adopt strategies to address these changes, crisis management, and the enhancement and improvement of infrastructure to deal with this phenomenon as it occurs