Spatio-Temporal Analysis of Rainfall Distribution and Concentration in Tolon District, Northern Ghana

Rainfall variability and concentration strongly influence agricultural productivity, water security, and climate resilience in semi-arid environments. This paper examines the spatio-temporal variability of rainfall at Tolon District in Northern Ghana in thirty years of monthly data on rainfall (1994-2024) that is available at the Council of Scientific and Industrial Research - Savanna Agricultural Research Institute. Temporal rainfall patterns were compared with annual totals and 3 year moving average and intra-annual distribution of rainfall was measured using Precipitation Concentration Index (PCI). The data on spatial patterns of rainfall concentration were analysed using GIS-based maps. Statistical analysis was done in Microsoft Excel and spatial analysis and PCI hot spot mapping were done in ArcGIS Pro. Results indicate a highly unstable annual rainfall regime with pronounced interannual oscillations, including rainfall peaks around 1999, 2010, and 2020 and notable deficits in 2005 and 2013, confirming heightened hydroclimatic volatility in the district. The results of PCI indicate that intra-annual rainfall distribution is uniform over the majority of the years ( PCI < 10 in 28 out of 30 years, 93.3%), with only two years showing moderate values (10-15), indicating that the main risk is the change in the total annual rainfall, but not the consistent within-year concentration. Spatial PCI maps, however, reveal a progressive shift and intensification of rainfall concentration from northern and central zones toward the eastern and southeastern parts of the district by 2024, creating emerging hotspots of flood and erosion risk. A weak positive relationship between annual rainfall and PCI (R² = 0.17) indicates that total rainfall and its intra annual distribution are largely decoupled. These findings support targeted adaptation focused on water harvesting, small-scale irrigation, and soil and water conservation in emerging concentration hotspots.