Abstract Soil water availability during the dry-to-wet season transition drives ecosystem productivity across the semi-arid Sahel. During this period, soil moisture reflects the balance between water supplied by precipitation and atmospheric demand, but how these processes jointly influence the timing of soil moisture accumulation remains unclear. Here, we analyze trends in soil moisture and precipitation during the dry-to-wet season transition from 2003 to 2024 across the semi-arid zone between the Sahara and the humid tropics. We use daily maximum temperature as an index of evaporative demand in a diagnostic soil moisture model to evaluate how precipitation inputs and temperature-driven dry-down each influence soil moisture dynamics. We find that soil moisture onset is systematically delayed relative to precipitation onset across much of the Sahel, and that trends in soil moisture onset and precipitation onset diverge in an east–west pattern. Including daily maximum temperature alongside precipitation in the diagnostic model substantially improves its ability to reproduce onset timing and helps explain the observed divergence between soil moisture and precipitation onset. These results indicate that increased evaporative demand can offset increases in precipitation during the dry-to-wet season transition and delay the emergence of plant-available water. These findings highlight the importance of atmospheric demand alongside precipitation inputs when assessing shifts in soil water availability across the Sahel, with potential implications for rainfed agricultural systems.
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