تحلیل زمانی و مکانی شاخص ‌های خشکی unep و دومارتن در ایران طی دورۀ 19762020

شاخص خشکی به ‌عنوان نسبت بین تبخیر و تعرق (دما) و بارندگی، بیانگر ویژگی‌های آب‌وهوایی یک منطقه است. پژوهش حاضر با هدف تحلیل زمانی و مکانی شاخص‌های خشکی unep و دومارتن در ایران با داده‌های دمای میانگین (°c)، متوسط رطوبت نسبی (%)، سرعت باد (m/s) و ساعت آفتابی (h) 40 ایستگاه سینوپتیک به بررسی 45 سالۀ طبقه‌بندی اقلیم ایران پرداخت. بارش، دما و تبخیر و تعرق مرجع، پهنه‌بندی و روند تغییرات شاخص‌های خشکی با آزمون من-کندال تحلیل شد. نتایج شاخص unep نشان داد بیش از سه‌چهارم ایستگاه‌‌ها دارای اقلیم بسیار خشک، خشک، نیمه‌خشک و مدیترانه‌ای هستند که ازنظر توزیع مکانی در مناطق جنوب‌ غرب، جنوب، جنوب ‌شرق، مرکز، شمال ‌غرب، غرب، شمال ‌شرق کشور گسترش یافته‌ و ازلحاظ اقلیمی مستعد وقوع پدیدۀ بیابان‌زایی هستند. نتایج شاخص خشکی دومارتن نیز منطبق بر شاخص unep است. براساس نتایج بررسی بارش، دما و تبخیر و تعرق مرجع در مناطق خشک، کاهش میزان بارش، افزایش دما و تبخیر و تعرق مرجع سبب افزایش نیاز آبی گیاهان و کاهش رطوبت خاک شده است. آزمون من-کندال حاکی از روند کاهشی معنا‌دار در سطوح اطمینان 99، 95 و 90% در بیش از نیمی از ایستگاه‌هاست. این امر در شاخص‌های مورد بررسی بیانگر خشکی اقلیم است.

investigating temporal and spatial variations of unep and de martonne aridity indices in iran from 1976 to 2020

introduction: as one of the most threatening natural hazards that has plagued humans for a long time, drought is considered a main natural disaster that affects various aspects of human life (mishra and sin, 2010). on the other hand, while dryness is typically associated with desert lands, little precipitation, and very thin vegetation by laymen, it refers to a kind of permanent climatic feature of a region, showing the insufficient amount of precipitation required for the growth of life in the region (kaviani and alijani, 2010). materials and methods: to analyze the temporal and spatial variations of unep and de martonne aridity indices in iran throughout the study period (1976-2020), this study collected the data of forty synoptic stations in terms of the maximum and minimum temperatures (°c), average relative humidity (%), wind speed (m/s), and sunshine hours (h) using the information published by the iranian meteorological organization. then, different regions of iran were classified in terms of unep and de martonne aridity indices. moreover, to investigate the influence of the factors involved in those indices such as precipitation, temperature, and reference evapotranspiration, the factors were zoned. finally, the trend of changes in dryness indices was analyzed using the mann-kendall test. results: the results of the unep aridity index classification indicated that from among the forty stations investigated in this study, fourteen stations had a very dry climate. moreover, ten stations were found to have been located in dry areas and eight in semi-arid regions. on the other hand, more than three-quarters of the stations with very dry, dry, and semi-arid climates were identified as the most susceptible areas to desertification. on the other hand, the results of the de martonne aridity index analysis confirmed the results found for the analysis of the unep index. as for the spatial distribution of the aforementioned indices, it was found that very dry, dry, semi-dry, and mediterranean classes were located in the southwestern, southern, southeastern, central, northwestern, western, and northeastern regions. the results also revealed that the northern regions, central alborz highlands, and northern coasts had semi-humid, humid, and very humid climates.on the other hand, the results of the investigation of precipitation, temperature, and reference evapotranspiration suggested that in arid regions, the plants’ demand for water was increased and the soil moisture was decreased due to the decrease in precipitation and the increase in temperature and reference evapotranspiration.