Authors: SAM, Fredrick P, ALABI, Omowumi, MD, Tawey, MORRIS, Susannah D, UGBALA, E.N, Nimely, DENNIS R
Abstract: This paper investigated the spatial and temporal dynamic pattern of rainfall over four decades (1981-2024) in Monrovia, Liberia. These rainfall data were used, a combined rainfall data that combines surface observations of the Liberia Meteorological Services (LMS) and the satellite-based Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS) estimates. The presence of variability, anomalies, and extremes has been measured using the Mann-Kendall trend test and Sen’s slope estimator and rainfall indices like the Precipitation Concentration Index PCI), Standardized Precipitation Index (SPI), and Rainfall Anomaly Index (RAI). Analysis showed that there is no statistically significant long-term trend in annual rainfall totals (Mann-Kendall, p > 0.05), but there are significant intra-seasonal changes. Drying patterns as identified in the early rainy season (April-May) with slope of Sen’s values between -2.1 mm/yr and -3.7 mm/yr. Conversely, late rainy season months (August-September) showed an increasing part of rainfall with the slope between 1.456 mm/year and 1.966 mm/year, indicating redistribution in the seasonal rainfall time. Moderate rainfall concentration and non-equal seasonal distribution were characterized by PCI values (12.93 to 16.34). The SPI analysis found repeat drought and extreme wet years (1982, 1994, 2009, 2015, 2020, 2022, and 2024) and extreme wet years (1995, 1996, 2006, 2007, 2008, and 2010). The Aggregate outcome of RAI indicated that a greater proportion of the years were in the negative anomaly as opposed to the wet years; this translates to prevalent dry years with high inter-annual variability. The redistribution and increment of extremes, although resulting in no notable reductions in total rainfalls, make it impossible to reinstate only significant declines in the whole annual rainfalls. Water resources management, agriculture, irrigation, and urban flooding control in Monrovia have very significant implications under such circumstances. The implications of the findings reflect evidence-based knowledge in consonance with Sustainable Development Goals (SDG 6: Clean Water and Sanitation, SDG 11: Sustainable Cities and Communities, and SDG 13: Climate Action), the urgency of which relates to adaptive climate strategies of the urban environment in Monrovia.
DOI: http://doi.org/10.5281/zenodo.20679212
