Interannual MODIS NDVI Dynamics of the Grazing Areas Under Variable Precipitation in Northern Sahel

ABSTRACT

The Sahel region of sub-Saharan Africa has suffered from a severe rainfall decline since the mid-1960s. This study aims to assess the applicability of satellite-based observations in quantifying the dynamics of MODIS NDVI in the central-south of the Republic of Niger. MODIS NDVI (MOD13Q1.061) data from 2000 to 2023 and CHIRPS precipitation data from 1981 to 2023 were used to assess vegetation changes. We applied the Mann–Kendall (MK) and Sen's slope tests to evaluate long-term trends and their magnitude and used Linear Mixed-Effects (LME) models to assess interannual NDVI variability. Pearson correlation analysis was also conducted to examine the relationship between NDVI and precipitation. Results indicate that (1) there was a positive and significant increase in the precipitation time series from 1981 to 2023, with a p-value equal to 0.01 and a Z-value equal to 2.34. A rupture period in the rainfall time series located between 2001 and 2002 was discovered. The analysis of the vegetation trend based on the MK test and Sen's slope estimator showed a positive Z-value of 2.10, which is greater than 1.98 and a β > 0 value, indicating a significant positive trend in vegetation density (Z = 2.10, p = 0.04). Pearson correlation (2) A moderate, positive and significant correlation (r = 0.4, p = 0.05) between NDVI and rainfall was established. These findings align with previous studies across the Sahel. The use of remote sensing provides key insights into vegetation trends and supports sustainable rangeland management strategies under climate variability in a semi-arid environment.