Mohammad Khosroshahi; Zahra Saeedifar; Khosro Shahbazi; Samira Zandifar; Sakineh Lotfinasabasl; Azadeh Gohardoust; Fatemeh Dargahian; Maryam Naeemi; Tahereh Ensafi Moghadam; Leila Kashi Zenouzi; Zohreh Ebrahimi Khosefi; Morteza Khodagholi
Volume 30, Issue 4 , February 2024, , Pages 521-541
Abstract
Background and objectivesWind erosion and dust phenomenon are considered as one of the important processes of land degradation and a serious challenge in Iran. This phenomenon occurs due to the interaction between weather and terrestrial processes. The purpose of this research is to investigate and analyze ...
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Background and objectivesWind erosion and dust phenomenon are considered as one of the important processes of land degradation and a serious challenge in Iran. This phenomenon occurs due to the interaction between weather and terrestrial processes. The purpose of this research is to investigate and analyze the trend of temporal and spatial changes in the number of dusty days in Iran and to investigate the role of climate in its spread. MethodologyIn this research, after receiving hourly and daily statistics of dust events (through 148 synoptic and climatology stations) and parameters of precipitation, evaporation, temperature as key climatic elements (from 171 stations) in 22 provinces located in arid and semi-arid regions of Iran, The spread of dust was investigated and the correlation between climate and dust was determined. After calculating the number of dust days in Iran, the information was called in the GIS environment and a map of the spatial changes of the parameter of the number of dust days in the three decades of 1987-1996, 1997-2006, 2007-2016 was prepared. In the following, the spatial analysis of this parameter and its expansion over three decades were investigated. Next, the climate parameter that had the highest correlation with the number of dusty days was selected and after preparing a map of its spatial changes in the GIS software environment, the spatial compatibility of the desired parameter with the expansion of the number of dusty days was investigated. In the next step, after performing the homogeneity test on the dust occurrences, the partial square regression model was used to determine the contribution of the three mentioned climatic elements as independent variables and the number of dust days as a dependent variable. ResultsThe results showed that the number of dusty days and the area of its occurrence have increased in Iran, so that in the last decade under study (2007-2016) compared to the previous two decades, the dustiest event occurred in Iran. This increase has been more intense especially in the western and southwestern regions of the country, which were also affected by extra-local dust events. These dust events have spread to the central regions of the country with greater frequency. The homogeneity test in many provinces showed a common change point (year 2007-2008) in the number of dusty days, which could be related to the beginning of severe droughts and climate changes from this year in Iran. The study of climatic parameters (temperature, precipitation and evaporation) on changes in the number of dust days in Iran showed that during recent years, temperature had the highest significant correlation level (0.58) with the occurrence of dust. The temperature gradient map in the last decade (2007-2016) compared to the previous decade (1997-2006) also showed the increasing trend of temperature, especially in the western and southwestern regions as well as the southeastern regions of Iran. Modeling the effect of climatic parameters of temperature, precipitation and evaporation on the parameter of the number of dusty days showed that the contribution of the studied climatic parameters to the occurrence of dusty days is about 33% and other effects can be related to things such as human factors or soil characteristics, type of vegetation, solar radiation, etc. ConclusionIn general, the results of examining the trend of changes in the number of dust days and climatic indicators for nearly 3 decades indicate a significant increase in the number of dust days in most parts of Iran and the conditions for this increase have been provided and if the trend of changing these indicators in the coming years is according to the current trend, the risk of environmental problems in the country can be expected to increase.
Sakineh Lotfinasabasl; Fatemeh Dargahian; Azadeh Gohardoost; Asad Hatam Baharvand; Samaneh Razavizadeh
Volume 30, Issue 2 , September 2023, , Pages 335-354
Abstract
Background and ObjectiveOver the past decade, the Zagros region, specifically its Zagros oak trees, has experienced significant impacts from droughts and climate change. Climate change has resulted in heightened desertification and oak forest decline. This study examines and analyzes meteorological droughts ...
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Background and ObjectiveOver the past decade, the Zagros region, specifically its Zagros oak trees, has experienced significant impacts from droughts and climate change. Climate change has resulted in heightened desertification and oak forest decline. This study examines and analyzes meteorological droughts and their correlation with climate change. This is a prominent contributing factor to oak tree decline in Ilam Province. The focus is on study sites in the northern and southern Serabaleh regions, where oak decline has been observed. MethodologyFor this study, comprehensive data on daily precipitation and minimum and maximum temperature were obtained from the synoptic station in Ilam, covering the period from its establishment until 2019. The Standardized Precipitation Evapotranspiration Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) were developed to assess meteorological drought and identify wetter and drier years. The SPI measures the deviation of precipitation from the mean value and normalizes it by the standard deviation. In contrast, the SPEI considers the discrepancy between precipitation and evapotranspiration. These indices were calculated on various time scales, including 3, 6, 12-month, and annual periods, and drought status was analyzed based on their respective classifications. To examine the role of climate change and identify influential precipitation and temperature patterns in drought occurrence, a set of four precipitation indices and eight temperature indices were calculated using ClimPACT software. These indices, developed by climate change experts, capture changes in mean or extreme weather conditions. The analysis also included wind speed. The relationship between drought indices and climate change was assessed through regression analysis and the Pearson correlation coefficient. Moreover, the study employed the Mann-Kendall and Pettitt Test to identify change points or significant abrupt changes in the time series. These tests were conducted at 5% significance and 95% confidence levels. ResultsThe study findings indicate a decreasing trend in the highest consecutive 5-day rainfall since 1995. In addition, there are insignificant reductions in the annual sum of wet days and the highest rainfall events of one or two days since 1998. This decrease in rainfall has been accompanied by increased maximum air temperatures since 1998, with a significant intensification observed from 2007 to 2015. Additionally, there has been a slight increase in minimum temperatures since 2002 and a significant wind speed since 1996. These factors have contributed to increased evaporation since 1998 and the occurrence of droughts on different time scales, ranging from six and twelve months since 1998 to three months since 2003. Global warming has influenced droughts. Three-month droughts have resulted in milder six- and twelve-month droughts, but more severe three-month droughts in oak decline, primarily due to significant changes in maximum temperatures since 2007. The occurrence of these droughts has been associated with an increase in the percentage of days with temperatures above the average since 2007, leading to more severe droughts from 2007 to 2015, with the peak in 2008 coinciding with the highest level of oak decline during the study period and under the influence of climate change phenomena. ConclusionThe SPEI drought index indicates a higher frequency and longer duration of droughts during the study periods, albeit with less severity than the SPI index. This suggests that the rising temperatures during cold months, in addition to dry months, have played a role in influencing the drought conditions. The results demonstrate that drought and climate change are the primary influential factors contributing to oak tree dryness in the forests of Ilam Province. Considering the decreasing precipitation trend and increasing temperature trend observed in the studied region, the occurrence of climate and environmental hazards, such as heatwaves, droughts, and floods, may further increase.
Fatemeh Dargahian; Sakineh Lotfinasabasl; Samaneh Razavizadeh
Volume 26, Issue 4 , December 2019, , Pages 868-886
Abstract
Despite the large extent of the areas affected by 120-day Sistan winds, Zabul region with specific topographic location has the highest and the most severe storms in the east of the country. In order to identify and analyze the dust pattern of the Zabul region and to distinguish it from other parts which ...
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Despite the large extent of the areas affected by 120-day Sistan winds, Zabul region with specific topographic location has the highest and the most severe storms in the east of the country. In order to identify and analyze the dust pattern of the Zabul region and to distinguish it from other parts which are affected by the famous 120-day winds of Sistan, environmental databases; dust codes, and NCEP / NCAR database with a spatial resolution of 2.5× 2.5 degree and latitude longitude of sea level pressure data corresponding to the peak days of dust during the period from 1987-2016 were used. In order to extract atmospheric patterns of dust events on sea level pressure data, cluster analysis was performed in MATLAB software. Finally, four patterns were extracted and for each pattern one day which has the most correlated with other days was selected as the representative day of that pattern. Out of four patterns the dominant pattern with the most frequent occurrence was selected, and July 13-16, 2016 was considered as the representative day for this dominant pattern. For this purpose, the synoptic maps of ground pressure, temperature, equatorial and jet flow in the lower layer of the atmosphere, wind field, and direction of the flow at ground level and the synoptic half instability of the air were plotted.
Results indicated that the Zabul area has the greatest potential for the production of dust due to the gradient of high pressure changes and also the presence of small-grained sediments of the rivers as well as wetlands and the locating in western margin of the low-pressure zone which has the thermal nature and the interaction of the low pressure with the high pressure which is called Turkmenistan high-pressure, Hindu Kush, northeast of Iran and north of Caspian sea. This low pressure in the lower layer of the atmosphere through the dust suction and counter-clockwise movement by passing on the sources of dust in the Zabul area prevented from the penetration to lower latitudes by the impact of the 120-day winds of Sistan and caused to further transportation of sand and dust particles to Afghanistan. Therefore, in regard to situation of Zabul in ratio to this low pressure, which is peaked in July, and distinguishes it from other areas affected by 120-day winds, special arrangements should be taken into account to reduce the intensity of dust storms.