Soil Moisture and Rainfall Interplay for Tropical Ecosystems in The West African Terrain Using Satellite-Based Datasets and Gauge measurements

Abstract The interplay of soil moisture (SM) and rainfall (RR) has practical importance for pluvial flood prevention and prediction, drought monitoring, and weather forecasting for agricultural applications. Recent satellite products have shown complicated SM - RR relationships over varied ecosystems, with a diverse range of positive to negative correlation indices. This study presents an assessment of the SM - RR interplay over contrasting tropical ecosystems across Ghana in the West Africa terrain, using RR gauge measurements and satellite-based root zone SM for 22 Synoptic stations spanning 30 years (1990–2019). Spatiotemporal distributions, percentage changes about onset dates, and statistical strength of correlations are presented and discussed. Findings show that, generally, SM decreases northward by a gradient of 0.01, showing weak to strong correlations of 0.38–0.82 ± 0.10 with RR countrywide, the highest is found for stations in the northern Savannah and Coastal Savannah zones, the weakest for stations in the Forest zone. Meanwhile, based on the RR onset dates, the Coastal zone exhibits the highest percentage change in SM, whereas the Forest, Transition, and Savannah zones exhibit low to slightly negative percentage changes. This has been attributed to SM deficits resulting from the dry Harmattan season before RR onset, strongly suggesting a respective delineation of Coastal and Savannah regions as flood and drought-prone zones. The results are in tandem with global-scale assessments, and present a theoretical framework to develop ecosystem water and pluvial flood management schemes over the sub-region.