Abstract
During the monsoon season, the spatiotemporal variability of rainfall impacts the growth of vegetation in the Sahel. This study evaluates this effect for the Ferlo basin in central northern Senegal. Relationships between rainfall, soil moisture (SM), and vegetation are assessed using remote sensing data (TRMM3B42 and RFE 2.0 for rainfall, ESA-CCI.SM for soil moisture and MODIS Leaf Area Index (LAI)). The principal objective was to analyze the response of vegetation growth to water availability during the rainy season using statistical criteria at the scale of homogeneous vegetation-soil zones. The study covers the period from June to September for the years 2000 to 2010. The surface SM is well correlated with both rainfall products. On ferruginous soils, better correlation of intra-seasonal variations and stronger sensitivity of the vegetation to rainfall are found compared to lithosols soils. LAI responds, on average, two to three weeks after a rainfall anomaly. Moreover, dry spells (negative anomalies) of seven days’ length (three days for SM anomaly) significantly affect vegetation growth (maximum LAI within the season). A strong and significant link is also found between total precipitation and the number of dry spells. These datasets proved to be sufficiently reliable to assess the impacts of rainfall variability on vegetation dynamics.
Highlights
The rainy season in the Sahel occurs from May to October
Satellite data were used to evaluate the impact of intra-seasonal rainfall variations on the natural vegetation growth of a small region in the Sahel (Ferlo, Senegal)
These zones were sufficiently large to allow the use of rainfall, soil moisture (SM) and Leaf Area Index (LAI) satellite products, but small enough to properly depict the spatial heterogeneity of the soil and vegetation cover
Summary
The rainy season in the Sahel occurs from May to October. It is highly variable in time and space, maximum monthly rainfall generally occurs in August [1]. The vegetation cycle closely follows the seasonality in rainfall, with almost all biomass production taking place in the humid summer months [2]. The variability in the length and strength of the rainy season strongly affects food production through both arable agriculture, livestock and grazing. Soil properties are important in driving the vegetation species composition and biomass amount [3]. The regional economy is strongly dependent on the combination of soil characteristics and rainfall
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