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.
Fatemrh Dargahian; Somayeh Heidarnejad; Samaneh Razavizadeh
Volume 28, Issue 3 , October 2021, , Pages 564-577
Abstract
Today, global warming and climate change are considered to be the greatest challenge of human life that has overshadowed other environmental challenges. In this study, it has been attempted to detect climate change phenomena in Yazd by monitoring the trend of heat wave changes and its relation to temperature ...
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Today, global warming and climate change are considered to be the greatest challenge of human life that has overshadowed other environmental challenges. In this study, it has been attempted to detect climate change phenomena in Yazd by monitoring the trend of heat wave changes and its relation to temperature anomaly. For this purpose, daily temperature data for the time period (1960– 2017) were used. Finally, the characteristics of heat waves such as the number of occurrences of heat waves, frequency of days with heat waves, heat wave continuity, magnitude and intensity of heat waves and average heat wave (hottest day of heat wave) using ClimPACT software in programming environment R 2.10 were calculated. Heat waves are the result of incremental temperature changes. Therefore, temperature anomaly of Yazd station was extracted and compared with the temperature anomaly of the Land's surface. The relationship between heat wave indices and temperature anomalies was investigated. The results showed that the highest number of heat wave events occurred in 2010 and 2016. The number of days associated with the hot wave has increased significantly, with 47 and 42 days in 2010 and 2016, respectively. An increasing trend in the continuity and intensity of heat waves was also observed. The longest continuation for 2013 was estimated to be 13 days. The findings also show that in the last two decades the magnitude of the heat wave has reached more than 31 ° C. Investigation of the relationship between all indices related to heat wave and Yazd temperature anomaly showed good correlation and coefficient of explanation of temperature anomaly and frequency of days with heat wave was higher than other indices and its R2 was approximately 0.6108. In general, the results indicate the intensification, continuity and intensity of heat waves in Yazd city, which can indicate the occurrence of climate change, especially in the last two decades in this region of the country as a representative of the arid regions. Due to the increasing temperature in the coming years on the frequency, intensity and continuity of these waves will increase, knowing how heat waves are processed can help managers and planners make risk management decisions about energy efficiency.