Randriatsara et al. (2025) Historical changes in drought characteristics and their impact on vegetation cover over Madagascar

Identification

• Journal: Natural hazards and earth system sciences
• Year: 2025
• Date: 2025-09-01
• Authors: Herijaona Hani‐Roge Hundilida Randriatsara, Eva Holtanová, Rizwan Karim, Hassen Babaousmail, Mirindra Finaritra Tanteliniaina Rabezanahary, Kokou Romaric Posset, Donnata Alupot, Brian Ayugi
• DOI: 10.5194/nhess-25-2939-2025

Research Groups

• Department of Atmospheric Physics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
• Key Laboratory of Meteorological Disaster, Ministry of Education (KLME)/Joint International Research Laboratory of Climate and Environment Change (ILCEC)/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing, University of Information Science and Technology, Nanjing, China
• School of Atmospheric Science and Remote Sensing, Wuxi University, Wuxi, China
• Climate Change Department, Pan African University Institute for Water and Energy Sciences (Including Climate Change), Tlemcen, Algeria
• Uganda National Meteorological Authority, Kampala, Uganda
• East Africa Hub, Wyss Academy for Nature at the University of Bern, Nanyuki, Kenya

Short Summary

This study analyzes historical drought characteristics (1981–2022) and their impact on vegetation cover (2000–2022) across Madagascar using the Standardized Precipitation Index (SPI) and Normalized Difference Vegetation Index (NDVI). It finds that drought events have intensified and become more consecutive, particularly in southern Madagascar, leading to severe vegetation losses.

Objective

• To analyze the spatiotemporal characteristics (duration, frequency, severity, intensity) of drought over Madagascar from 1981 to 2022.
• To evaluate the relationship between the Standardized Precipitation Index (SPI) and the Normalized Difference Vegetation Index (NDVI) to assess the impact of drought on vegetation cover over Madagascar from 2000 to 2022.

Study Configuration

• Spatial Scale: Madagascar, covering approximately 592 040 km2, divided into three regions (southern, western, eastern).
• Temporal Scale:
  • Drought characteristics analysis: 1981–2022 (42 years).
  • Drought impact on vegetation analysis: 2000–2022 (23 years).

Methodology and Data

• Models used:
  • Standardized Precipitation Index (SPI) for drought assessment (SPI-3, SPI-6, SPI-12, seasonal, and annual timescales).
  • Normalized Difference Vegetation Index (NDVI) for vegetation cover assessment.
  • Pearson and Spearman correlation coefficients for statistical relationship analysis.
• Data sources:
  • Precipitation: Ensemble mean of Climate Hazards Group InfraRed Precipitation with Station data version 2.0 (CHIRPS v2.0) and ECMWF Reanalysis v5 (ERA5).
  • Vegetation: Terra's Moderate Resolution Imaging Spectroradiometer (MODIS) MOD13C2 version 6.1 monthly vegetation index.

Main Results

• Drought events have become more consecutive and intensified over Madagascar, particularly in the southern part, during the most recent period (2017–2022).
• Drought characteristics (duration, frequency, severity) are generally higher in the eastern and southern regions, with SPI-12 showing the longest duration (over 10 months) and highest severity (over 155) in the southern region.
• Severe and noticeable monthly vegetation losses occur when prominent negative SPI values are simultaneously detected across SPI-3, SPI-6, and SPI-12 over a region.
• The impact of drought on seasonal and annual vegetation is detectable through seasonal and annual NDVI anomalies when prominent negative SPI values occur from seasonal and annual SPI analyses.
• A statistically significant positive correlation (correlation coefficients 0.12 to 0.21) exists between NDVI anomaly and SPI, being strongest over southern Madagascar, indicating a connection between precipitation deficits and vegetation changes.
• The southern region (R1) experienced a considerable and statistically significant decline in annual mean NDVI from 0.44 to 0.35 by the end of the study period (2000-2022), with the most severe decline observed in January and February.

Contributions

• Provides the first comprehensive assessment of historical drought characteristics (duration, frequency, severity, intensity) and their impact on vegetation cover over Madagascar using SPI and NDVI.
• Offers a detailed spatiotemporal analysis of drought characteristics across multiple timescales (3, 6, 12 months, seasonal, annual) for Madagascar.
• Quantifies the relationship between precipitation deficits and vegetation response, highlighting regional vulnerabilities, especially in southern Madagascar.
• Complements existing literature by providing in-depth analysis for Madagascar, addressing the IPCC's reported lack of sufficient evidence for drought changes in the region.

Funding

• Ministry of Education, Youth and Sports (MEYS, MŠMT in Czech) through OP Johannes Amos Comenius (OP JAC), natural and anthropogenic georisks (grant no. CZ.02.01.01/00/22_008/0004605).

Citation

@article{Randriatsara2025Historical,
  author = {Randriatsara, Herijaona Hani‐Roge Hundilida and Holtanová, Eva and Karim, Rizwan and Babaousmail, Hassen and Rabezanahary, Mirindra Finaritra Tanteliniaina and Posset, Kokou Romaric and Alupot, Donnata and Ayugi, Brian},
  title = {Historical changes in drought characteristics and their impact on vegetation cover over Madagascar},
  journal = {Natural hazards and earth system sciences},
  year = {2025},
  doi = {10.5194/nhess-25-2939-2025},
  url = {https://doi.org/10.5194/nhess-25-2939-2025}
}