Spatio-temporal Variations in Mean Heavy Rainfall Days over the Guinea Savanna Ecological Zone of Nigeria

Abstract

Variations in weather parameters are phenomena confirmed by many studies. Various derived rainfall parameters are variable in nature. One of such derived rainfall parameters is heavy rainfall. Rainfall that is 50 mm/day (24 hours) has been considered in this study as heavy. The objectives of the study were to assess the spatio-temporal variations in mean heavy rainfall days and also to determine the pattern of mean heavy rainfall days over the Guinea Savanna Ecological Zone of Nigeria (GSEZN). Purposive sampling was used to select nine (9) major meteorological stations within the zone. These data points which were later divided into flanks (northern, southern, eastern and western) include Makurdi, Lokoja, Jos, Ibi, Abuja, Minna, Ilorin, Lafia and Kaduna. Daily rainfall (mm) data from these points were collected and used for this research. The data spanned from 1981-2015 (35 years) and were split into seven (7) episodes of five (5) years each. Statistical mean and geostatistical analyst built in arctoolbox of ArcGIS were adopted for analysis. Results showed both inter and intra spatio-temporal variations and pattern in mean heavy rainfall days. Northern part had zero (0) high mean heavy rainfall days which are the least, while southern part had eleven (11) which is the highest. Northern and eastern parts had seven (7) moderate mean heavy rainfall days each, west had six (6) which is the least and south had eleven (11) which is the highest. Northern part had fourteen (14) low mean heavy rainfall days which is the highest, east had two (2), south had one (1) and west had zero (0) which is the least. Over the study area, mean high and low heavy rainfall days are four (4) each, while moderate is eight (8). Episode 1 (1981-1985) had the least mean heavy rainfall days of 14, while the 4th episode (19962000) had the highest of 19. The overall long-term mean heavy rainfall days is 7 and there is positive trend in mean heavy rainfall days in recent time. The major implication of this study is annual flooding in the study area. The recommendation of this study focused mainly on frequent heavy rainfall forecast.