Geospatial Evaluation of Meteorological and Satellite-Derived Vegetation Indicators for Drought Monitoring

Abstract

Drought represents one of the most critical environmental stresses affecting agricultural productivity, water resources, ecosystem stability, and regional socioeconomic development. Selecting an appropriate drought indicator is therefore essential for improving monitoring accuracy and supporting sustainable resource management. This research aimed to determine the most effective meteorological and vegetation-based drought indices for drought characterization in Ordu Province, Türkiye, by integrating geospatial techniques with climatic and satellite observations. Climate variables were obtained from the CHIRPS precipitation archive and the NASA POWER database, while vegetation dynamics were derived from MODIS remote sensing products. Four meteorological drought indices, including the Standardized Precipitation Index (SPI), Reconnaissance Drought Index (RDI), Agricultural Standardized Precipitation Index (aSPI), and Effective Reconnaissance Drought Index (eRDI), were systematically evaluated together with six vegetation indicators, namely NDVI, RDVI, TVI, EVI, SAVI, and OSAVI. Comparative statistical assessment demonstrated that eRDI achieved the strongest agreement with agricultural drought conditions, yielding a correlation coefficient of 0.80, whereas NDVI exhibited the highest correspondence among vegetation indicators with a coefficient of 0.76. Spatial and temporal examination of vegetation responses identified the most pronounced drought conditions during 2000 and 2001, indicating substantial reductions in vegetation vigor throughout the study area. The integrated evaluation confirmed that NDVI provides the most consistent representation of vegetation stress, while eRDI offers the highest reliability for meteorological drought assessment in Ordu Province. The proposed framework establishes a practical basis for drought monitoring and can support future environmental management, agricultural planning, and climate adaptation strategies in humid coastal environments.