Historical changes in drought characteristics and their impact on vegetation cover over Madagascar

Abstract

Drought has become one of the most devastating natural hazards in recent decades, causing severe vegetation degradation. This study aims to analyze the spatiotemporal characteristics of drought (duration, frequency, severity, intensity) over Madagascar during 1981-2022. In addition, it evaluates the relationship between the Standardized Precipitation Index (SPI) and the Normalized Difference Vegetation Index (NDVI) during 2000-2022, representing the impact of drought on vegetation over the studied area. Drought assessment was conducted on SPI-3, SPI-6, and SPI-12 timescales, accompanied by seasonal and annual analyses, while the NDVI-SPI relationship was examined through the analysis of vegetation changes based on specific selected SPI time periods and the correlation analysis. The findings reveal that drought events have become more consecutive during the most recent past (2017 to 2022) and have intensified over the southern part of the country. Links between drought occurrences and vegetation changes have been confirmed: monthly vegetation losses are severe and noticeable when prominent negative SPI values occur simultaneously across SPI-3, SPI-6, and SPI-12 over a region, and the impact of drought on seasonal and annual vegetation is detected when prominent negative SPI values occur from seasonal and annual SPI analyses over a region. The correlation between the NDVI anomaly and the SPI emphasizes the NDVI-SPI relationship found with statistical significance, especially over southern Madagascar. These findings are crucial for complementing other climatic factors that influence Madagascar's vegetation besides drought.