An Analysis of Rainfall Characteristics for Flood Risk Assessment in the Delimi River Catchment, Jos Plateau State

Rainfall characteristics are analyzed for a forty-year record (1977-2016) in the Delimi Catchment. Results showedan average rainfallamount of 1353.21mm/yr. Significant rainfall months are March to October (8 months), with peaks in July thentrailed closely in June. July 2012 had the highest depth rainfall with 680.1mm and July 2002 recorded the least with 132.5mm. A count of daily rainfall ?24.00mm showed June, July, August, and September with high counts;with July having the highest records of 171 occurrences. Standard Precipitation Index (SPI) analysis and the Probability of Exceedance (Px) analysis carried out revealeda steady but upward trend in SPI values from 1977 to 2016meaning an increase in wetness over the years (-1.83 in 1977 to a + 1.69 in 2016). And Px calculations from three methods (Hazen, Welbul, and California) showed that eight different years 1978, 1981, 1991, 1994, 1996, 2012, 2014, and 2015 had less than 20% probability (having weather conditions called humid). With a corresponding return period (recurrence interval) Tx of between 5 to 40 years.This indicates years of excess or extreme rainfall and probable floods. Thereby allowing for a better understanding of the influences of rainfall characteristics on catchment runoffs and flooding's.