Mapping precipitation-corrected NDVI trends across Namibia.

Area of Science:

• Ecology
• Remote Sensing
• Environmental Science

Background:

• Savannas are vital ecosystems providing essential services.
• Understanding savanna vegetation dynamics and their drivers is crucial for conservation and management.
• Previous studies noted widespread greening in southern Africa, but its causes remain unclear.

Purpose of the Study:

• To identify vegetation trends in southern African savannas independent of rainfall variations.
• To investigate the drivers and ground-level manifestations of observed vegetation changes.
• To differentiate between rainfall-driven greening and other forms of vegetation change.

Main Methods:

• Utilized Normalized Difference Vegetation Index (NDVI) time-series data from MODIS.
• Applied linear regression to remove precipitation effects from NDVI data, creating a residual time-series.
• Analyzed trends in relation to biomes and used high-resolution imagery for ground-truthing.

Main Results:

• Positive vegetation trends, not driven by rainfall, were observed across 23.25% of the study area, encompassing all biomes.
• Negative trends, indicative of vegetation clearing and deforestation, were found in 3.23% of the area, primarily in humid regions.
• Qualitative analysis suggested greening trends may relate to reduced woody species richness and a shift towards drought-tolerant shrubs.

Conclusions:

• Observed greening trends are likely due to indirect drivers, such as changes in vegetation composition rather than direct rainfall increases.
• Deforestation is a significant driver of vegetation loss in more humid areas.
• This study highlights the complexity of savanna dynamics and the need for nuanced monitoring approaches.