Contrasting soil temperature and moisture dynamics across urban greenspaces in Accra, Ghana: seasonal patterns and implications for urban cooling in coastal tropical West African cities

Greenspaces are widely endorsed as a nature-based solutions to mitigate urban heat intensity and associated thermal stress in modern cities. However, data on soil thermal and moisture characteristics in rapidly urbanizing regions of West Africa is rare. Here, we investigated the seasonal dynamics of topsoil (0-15 cm) temperature and volumetric moisture content (VWC) across an urbanization gradient in Accra, Ghana. We hypothesized that greenspaces nearer the city center, affected by infrastructure and heightened economic activities, would exhibit higher temperatures and lower VWC than those farther away.

Between April 2023 and June 2024, we installed eight coupled temperature and moisture sensors at five greenspace sites, capturing all seasons within an annual cycle: peak-dry (Dec–Feb), transition-dry (Mar–May), peak-wet (Jun–Aug), and transition-wet (Sep–Nov). We classified three sites within a 20-minute drive of the central business district as inner-greenspaces (IG) and the two beyond as outer-greenspace (OG). Landsat-derived (30 m resolution) mean ± standard error surface temperature was 26±0.7°C for IG and 23.3±0.4°C for OG sites in 2021. Across all seasons, IG soils had consistently higher temperatures, with a marked (p< 0.005) 31±0.01°C versus 29±0.01°C difference during the peak-dry period. VWC was also higher at IG sites, measuring 0.32±0.0009 m³ m^-3 compared to 0.21±0.0009 m³ m^-3 during peak-wet and transition periods. While IG soils reflected the hypothesized temperature rise linked to urbanization, their higher VWC suggests notable water-storage capacity, buffering extreme heat. This was corroborated by the diminished temperature differences in wet periods alongside elevated VWC, underscoring the important role of soil water in enhancing greenspace cooling. Our findings provide baseline data to inform sustainable urban planning in West African cities like Accra, which face rapid urbanization and escalating heat stress. These insights can guide local authorities in implementing targeted interventions to enhance greenspace resilience amid intensifying urban climate challenges.