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.
Zahedeh Heidarizadi; Majid Ownegh; chooghibiram komaki
Volume 29, Issue 4 , January 2023, , Pages 542-561
Abstract
Drought is an unpleasant climatic phenomenon that directly affects different dimensions of human societies. In order to know and choose the right management decision, it is necessary to design and develop an integrated approach to more effectively control this phenomenon and provide early warnings.In ...
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Drought is an unpleasant climatic phenomenon that directly affects different dimensions of human societies. In order to know and choose the right management decision, it is necessary to design and develop an integrated approach to more effectively control this phenomenon and provide early warnings.In this study, twelve various remotely sensed indices of the Moderate Resolution Imaging Spectroradiometer (MODIS) and digital elevation model (DEM) were used to monitor drought during 2000–2018 growing season. Standardized Precipitation Index (SPI) with time scales of 1 to 12 months was used as reference data. The relations between thirteen indices and SPI with different time scales were modulated using machine learning approach. The random forest technique was used to construct a comprehensive drought monitoring model in Ilam Province. Validation data were provided based on relative soil moisture, Standardized Precipitation Evapotranspiration Index (SPEI), and crop yield data. It was observed that random forest produced good applicability (R2 = 0.88) for SPI prediction. In the next step, the Drought Hazard Index (DHI) was generated based on the probability occurrences of drought using the comprehensive drought model which was made in the previous step. The Drought Vulnerability Index (DVI) was calculated by using 7 socioeconomic indices. Finally, the Drought Risk Index (DRI) was obtained by multiplying DHI and DVI for Ilam province. The result of the DRI map showed that 2 Counties are at very high risk of drought, 4 Counties are at high risk and 4 Counties are at moderate and low risk of drought. Overall, the result of our study provides a comprehensive method for assessment of regional drought. Also based on this model, Counties with high vulnerability can be identified to provide timely management programs to help improve the situation.
Saleh Arekhi; Hasan Fathizad
Volume 21, Issue 3 , December 2014, , Pages 466-481
Abstract
Rapid land-use/land cover changes have taken place in many arid and semi-arid regions of Iran such as west of Iran over the last decades due to demographic pressure, agricultural pressure, government polices and environmental factors such as drought. This study was aimed to investigate the trends of ...
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Rapid land-use/land cover changes have taken place in many arid and semi-arid regions of Iran such as west of Iran over the last decades due to demographic pressure, agricultural pressure, government polices and environmental factors such as drought. This study was aimed to investigate the trends of changes in the landscape, in Doiraj Watershed. In order to provide land cover maps, the satellite images of TM 1985, ETM+2000, ETM+2007 were applied and landscape metrics of class area, largest patch index, number and mean patch size, patch density and edge density were used to quantify landscape patterns. Various class-level landscape pattern metrics were calculated using FRAGTATS, in order to analyze landscape fragmentation. The results of landscape ecology change revealed that in this area during the first period (1985 - 2000), the area of forest lands decreased to 3,415 hectares, while the agricultural lands with 3514 hectares showed an increasing trend. On the other hand, the area of fair rangelands (20,440 hectares) showed a decreasing trend (in both periods) contrary to the area of poor rangelands, indicating the degradation process in the study area. Our results clearly showed that increased number of patches and decreased mean patch area were two important fragmentation indicators and the trend of landscape degradation and fragmentation was increasing. Therefore, the results necessitated paying attention to the quality of land use and cover in the region for decreasing the degradation of natural resources.