Integration of Spectral Indices and the SPEI for Spatiotemporal Detection of Invisble Drought in the Said Sadiq Region Using Geographic Information Systems (GIS)

Abstract

This study aims to monitor and analyze hidden drought in the Said Sadiq region of northeastern Iraq during the period 1981–2024 by integrating the Standardized Precipitation Evapotranspiration Index (SPEI) with satellite-derived spectral indices (NDVI, NDWI, VCI). Hidden drought refers to conditions not evident in traditional rainfall data but manifested through vegetation degradation or soil moisture decline. The SPEI was calculated based on the water balance (P - PET) using the Penman-Monteith equation, while spectral indices were analyzed both spatially and temporally using Geographic Information Systems (GIS). Results revealed significant temporal fluctuations in SPEI, with severe drought events particularly evident in years such as 1999 and 2021. Spectral analysis showed vegetation and moisture degradation in areas not classified as drought years by climate indices alone. Moreover, the Local Indicators of Spatial Association (LISA) analysis was employed to identify spatial clustering patterns of hidden drought. The Low-Low category, indicating persistent dry hotspots, represented 2.09% of the area. The final hidden drought map revealed that approximately 5.29% of the region suffers from environmentally degraded zones that are not reflected in climatic drought records. These findings highlight the importance of combining spectral and climatic indicators with spatial pattern analysis to enhance early warning systems and support drought adaptation planning in semi-arid environments.