بررسی روند تغییرات پوشش گیاهی تحت تاثیر عنصرهای اقلیمی دمای سطح زمین، تبخیر و تعرق واقعی و بارندگی در استان هرمزگان

تخریب پوشش گیاهی از جمله پارامترهای مهم برای بررسی تغییرات زیست محیطی است. از این‌رو در این مطالعه، با هدف بررسی روند تغییرات پوشش گیاهی (ndvi)، دمای سطح زمین (lst)، تبخیر و تعرق واقعی (et) و بارندگی استان هرمزگان از داده‌های سنجش از دور حاصل ازسنجنده مودیس و داده‌های era5 با روش من-کندال و شیب تخمین‌گرسن در بازه زمانی 2022-2001 استفاده شد. سپس همبستگی بین پوشش گیاهی و دمای سطح خاک، تبخیر و تعرق واقعی و بارندگی در این بازه زمانی محاسبه گردید. بررسی روند تغییرات ماهانه پوشش گیاهی با استفاده از آماره من-کندال نشان داد که پوشش گیاهی در بیش از 80 درصد از مساحت استان افزایشی بوده است، که بررسی شیب تخمین‌گرسن نیز این افزایش را تایید می‌کند. بررسی روند تغییرات دمای سطح زمین، تبخیر و تعرق واقعی و بارندگی نیز نشان داد که روند تغییرات تبخیر تعرق، دمای سطح زمین و بارندگی در اکثر ماه‌ها افزایشی بوده که به ترتیب این افزایش در بیش از 65، 85 و 61 درصد از استان دیده شده است. بررسی رابطه همبستگی بین پوشش گیاهی با شاخص دمای سطح زمین نشان داد که در ماه‌های سرد این رابطه منفی و قوی می‌باشد. بررسی این رابطه بین پوشش گیاهی و تبخیر و تعرق واقعی نیز نشان داد که در اکثر ماه‌ها این رابطه مثبت و در بیش از 53 درصد از سطح استان دیده شده است. همچنین نتایج بررسی رابطه همبستگی بین پوشش گیاهی و بارندگی بیان داشت که این رابطه در اکثر ماه‌های سال مثبت بوده و در بیش از 54 درصد از استان هرمزگان به خوبی مشهود است. با توجه به این نتایج می‌توان بیان داشت که با استفاده از داده‌های سنجش از دور به خوبی می‌توان روابط بین متغیرهای مختلف با تغییرات پوشش گیاهی و روند تغییرات آن‌ها را در طول زمان مورد بررسی قرار داد.

investigating the impact of land surface temperature, evaporation, transpiration, and rainfall on changes in vegetation cover in hormozgan province

extended abstractintroductionin recent decades, land degradation has emerged as a critical global environmental issue that has garnered attention from researchers, planners, and policymakers. it refers to the temporary or permanent decline in land productivity due to physical, chemical, and biological factors impacting agricultural production, ecosystem functions, quality of life, and human livelihood. vegetation and soil degradation, leading to the loss of high-quality vegetation and soil, are considered significant forms of land degradation worldwide. remote sensing data has become valuable and reliable for studying land degradation, particularly in assessing long-term ecosystem function decline. vegetation cover, often measured using the normalized vegetation cover index (ndvi) derived from satellite data, is a crucial parameter for investigating land degradation. studies have explored its relationship with other factors such as land surface temperature (lst), evapotranspiration, and precipitation. this study aims to analyze changes in vegetation trends in hormozgan province and its correlation with evapotranspiration, surface temperature, and rainfall using modis sensor data from 2001 to 2022.methodologyin this study, we used the normalized vegetation index (ndvi) data from the modis sensor (mod13a3) to examine changes in land surface vegetation. the ndvi data was collected monthly with a 1000-meter resolution. additionally, we utilized mod16a2 and mod11a2 products to analyze evaporation, transpiration, and ground surface temperature. these products have spatial resolutions of 500 and 1000 meters and cover 8 days. we downloaded et, ndvi, and lst data from the united states geological survey (usgs) website in hdf format, spanning 2001-2022. furthermore, we used reanalyzed era5 data from the ecmwf database to assess monthly rainfall trends. to prepare the data for analysis, we utilized the geographical longitude and latitude coordinate system and processed it using acgis10.8 and terrset software. i analyzed the changes in vegetation cover, evaporation, transpiration, land surface, and rainfall from 2001 to 2022 using the non-parametric mann-kendall analysis and sen’s slope estimation. initially presented by me and later developed by kendall, this test is based on data ranks in a time series. it is used to determine trends. additionally, i used the slope of the age estimator to assess the accuracy and enhance the process. furthermore, in terrset software, i performed a correlation analysis to examine the relationship between vegetation and soil surface indicators, evaporation, and rainfall. the correlation coefficient ranges between -1 and +1, where a positive value indicates a direct relationship and a negative value indicates an inverse relationship between the two changes.results and discussionthe analysis of spatial and temporal changes in vegetation cover index (ndvi), evapotranspiration (et), land surface temperature (lst), and monthly rainfall from 2001 to 2022 indicates that during winter and early spring, the vegetation cover index, evapotranspiration, and precipitation reach their highest values, while the land surface temperature shows its lowest value during these months. over the 22 years, the average spatial changes in ndvi reveal that the highest vegetation cover is primarily located in the region’s northern, northeastern, and northwestern parts, aligning with the monthly rainfall patterns during this period. the examination of the land surface temperature index (lst) indicates that the highest values are observed in the southern parts of hormozgan province, particularly in the persian gulf and oman sea. the analysis of changes in the z-kendall index of the ndvi (normalized difference vegetation index) showed an increase throughout all the months studied, with the increase observed in over 80% of hormozgan province. the examination of the slope of the monthly estimator confirmed the increase in vegetation cover during these months. similarly, the z-kendall evapotranspiration index analysis indicated an increase in the evapotranspiration index in most months, occurring in over 54% of the region. the slope of the estimator for evaporation and transpiration index also supported these findings. the z-kendall lst (land surface temperature) index exhibited increasing trends in the majority of months over the 21 years, encompassing over 61% of the area. the slope statistics of the age estimator for this index confirmed the monthly increase in the hormozgan province. lastly, based on the z-kendall change, the rainfall index over the 21 years increased in most months, covering more than 76% of the province. the slope statistics of the age estimator of this index also supported the monthly increase. from 2001 to 2022, the monthly correlation between the vegetation cover index and the evapotranspiration index in hormozgan province indicated a strong positive relationship in most months, covering over 80% of the province. additionally, the vegetation cover index and surface temperature correlation showed a predominantly negative relationship, especially during autumn and winter, covering more than 54% of the area. furthermore, the correlation between the vegetation cover index and the rainfall index revealed a positive relationship in over 54% of the province for most months over the 21 years.conclusionthe analysis of monthly vegetation changes in hormozgan province using mann-kendall statistics and the age estimator slope indicates that there has been an increase in vegetation cover in over 80% of the area. the study by eskandari doman et al. in 2019 confirmed that the trend of vegetation changes, as indicated by the ndvi index between 2018 and 2019, showed a significant increase, particularly in the higher classes of the index (exceeding 0.4). furthermore, examining changes in the earth’s surface temperature, evaporation, transpiration, and rainfall revealed that these factors increased in most months, with increases observed in over 65%, 85%, and 61% of the province, respectively. the study also found a correlation between vegetation cover and earth surface temperature, indicating a positive relationship in most areas of the province and both negative and positive correlations between evaporation, transpiration, and rainfall. given the comprehensive nature of this study, it is recommended to conduct similar research and compare the results with those presented here.