Assessment of rainfall variability, rainwater harvesting potential and storage requirements in Odeda Local Government Area of Ogun State in South-western Nigeria

Rainfall variability with periodicity of 5–6 years has been demonstrated for our study area and may be attributed to tropical and extra-tropical factors which operate during different months, seasons and years. Rainfall variability in terms of coefficient of variation ranges from 24 to 39% and 26 to 41% for the seasons and months. The mean increase of 1.63 mm/year and 1.37 mm/year experienced in the dry season months (November–April) and the wet season months (May–October), respectively, is insignificant from a water management perspective. Hoeffding’s D statistics revealed prevalence of non-monotonic trend in all the months and seasons. Recommended minimum and maximum storage capacity requirements for a six-member household to maximize rainwater harvesting are 1 and 6 m3, respectively. The rainwater harvesting potential for the area of study ranges between 18.16 and 27.45 m3 and 15.23 and 30.40 m3 based on the maximum error estimate and coefficient of variation methods. Domestic rainwater harvesting has the potential to meet 27.51–54.91% of non-potable household water demand as well as 78.34–156.38% of household potable water demand for a six-member household. It is highly encouraged as a supplementary water source especially in rural and peri-urban areas to reduce their vulnerability to acute shortage of water infrastructure.