EFFECTS OF RAINFALL AND TEMPERATURE ON COASTAL FLOODING IN VICTORIA ISLAND, LAGOS STATE, NIGERIA

Abstract

Coastal flooding has been and will continue to be a major problem for many coastal cities and settlements in Nigeria. One of the key factors in the design of flood forecasting models for the institution of a robust flood early warning system and towards the amelioration and effect of this flood is a good knowledge of rainfall and temperature trends as well as extremes. This study assessed the effect of rainfall and temperature on coastal flooding in Victoria Island, Lagos state, Nigeria. Data for this study was obtained from both primary and secondary sources. The primary data was from field survey on the causes and effects of flooding in the study area, while the secondary data which includes temperature, rainfall, and actual flood data were collected from the archives of the Nigerian Meteorological Agency (NiMet) and National Emergency Management Agency (NEMA) respectively. Results were presented by the use of mean, departures, regression, and correlation. To determine the annual trend in the meteorological parameters, a statistical Z-test was carried out at the 5% level of significance. An increasing trend in rainfall and temperature was observed though rainfall was not statistically significant. A further test on the rainfall data using a simple regression on the Extreme Daily Rainfall (EDR) with a threshold of 129.1mm revealed that extreme rainfall events have increased at the rate of 0.3mm per decade in the study area. Also, subjecting the actual flood data and extreme daily rainfall to a correlation analysis produced a correlation coefficient (R) of 94% indicating that there is a strong linear relationship between the number of EDR and the number of flood cases. Similarly, the coefficient of determination of 89% existing between the EDR and the flood cases means that 89% of the flood cases can be predicted by changes in EDR. For one-unit increase in EDR, flood increased by 0.34 in the study area between 2012 – 2017ges adequate monitoring. This study encourages adequate monitoring and study of rainfall and temperature characteristics as well as proper record of flood data towards the institution of a robust flood early warning system and to aid research. This will form a strong decision support system to policy makers.