Effect of Inter-annual Rainfall Variability on Precipitation Effectiveness in Nasarawa State, Nigeria

The study investigated inter-annual rainfall variability effect on precipitation effectiveness in Nasarawa State. Tropical Rainfall Monitoring Mission (TRMM) remote sensing rainfall data was used for the study. The daily rainfall record from 1998-2015 was collected for the study. Onset, Cessation and Length of Growing season are the only precipitation effectiveness indices examined. The pentad method of calculating onset, cessation and length of rainy season was adopted for the study across the entire Local Government Areas of the state. The summary of the findings show that, the averages of Onset dates, Cessation Dates and Length of rainy season dates across the state are not uniform. Rainfall starts early in the Southern zone of the state on 12th April, followed by Western zone 6th May then the Northern zone 12th May. The cessation dates of rainfall are almost the same in all zones with the North and South having cessation dates at 16th October while the West has its cessation date as 18th October. This finding reveals that the dates of cessation are more reliable and predictable than onset dates. Onset date that run between April and May in the state is good because it has not moved far from the expected pattern.