Spatio-temporal evaluation of MODIS temperature vegetation dryness index in the Middle East

Abstract

Drought, a recurring meteorological event, can potentially cause devastating consequences for human populations, and its attributes vary significantly across diverse geographic areas. Therefore, recognizing drought events is paramount for strategically planning and managing water resource systems. In this study, the Temperature Vegetation Dryness Index (TVDI), derived using Moderate-Resolution Imaging Spectroradiometer (MODIS) data spanning from 2003 to 2022 in the Middle East, was used as the foundation for both trend and spectral analyses. To assess TVDI trends, the Mann-Kendall test and Sen's slope estimator were utilized, and harmonic analysis was conducted for spectral analyses. These methods were applied to a dataset comprising 258,087 pixels within the specified region, covering various time scales, including monthly and seasonal analyses. The monthly analyses indicated significant growth in March and April, with September showing the least significant increase, suggesting stability or decline. Geographically, upward trends were predominant in the northern Middle East, including Turkey, Syria, Iraq, western Iran, and eastern Jordan. Significant downward trends were observed in the southern Middle East during the warmer months. Seasonal assessments showed no significant TVDI trends in winter, but upward trends in the south, west, and northwest were identified during spring. The annual trend map indicates a long-term declining trend in TVDI for most regions within specific latitudes, particularly those below 34 degrees. The results of harmonic analysis revealed the presence of multiple cycles at a 95 % confidence level. Notably, there was a heightened prevalence of significant sinusoidal cycles, especially the 2–3-year cycles. This cycle was widespread in countries such as Iran, Oman, Yemen, and Turkey, as well as in the southern regions of Saudi Arabia and Egypt.