Rainfall characteristics and occurrence of floods in Gombe Metropolis, Nigeria

Abstract

Gombe metropolis has been experiencing urban flooding particular in the last two decades. The flood disasters of 2004, 2012 and 2014 in the metropolis were alarming. This paper is aimed at analyzing the rainfall characteristics of Gombe metropolis in order to examine the implications on the occurrence of flooding in the metropolis. Linear trend line equation was used to determine the nature of the rainfall trend. The rainfall series was also sub-divided into 10-year non-overlapping sub-periods in order to identify decadal trends. Rainfall Anomaly Index (RAI) was used to determine years of dryness and wetness. The calculated seasonality index showed that most rain is in July, August and September. The result of the linear trend lines revealed that the increase in the annual rainfall yield is predominantly as a result of an increased in August rainfall. The 5-year running means revealed that rainfall has been increasing from the 2000s to the end of the study period. Findings also showed that the last two sub-periods, 1995-2004 and 2005-2014, depict an increasing rainfall pattern which may be responsible for the floods of 20^th August, 2004, 25^th and 30^th July, 2012 and 5^th September, 2014 that ravaged Gombe metropolis. It is recommended that designing of drainage infrastructures by engineers should take into account the increasing nature of rainfall in the area; government should lay emphasis on policies that steer development away from high risk areas; and there is need to enlighten the general public on the environmental causes of floods.

Keywords: Decadal trends, Disaster, Flooding, Linear trends, Metropolis, Wet and dry years