1 Journal of Nigerian Society of Engineers Technical Transaction, Volume 52, No.1, pp 1-10, Dec., 2021 Empirical Estimation of the Effects of Climate Change on Drainage Sections Abstract Variability in climate change has compromised the design capacity of drains. Proper estimation of climate impacts on runoff is therefore necessary for the designof efficient and effective hydrologic sections. In this study, drainage sections were designed by incorporating climate-induced changes in runoff after quantifying the changes in annual runoff due to climate variability. The variability in each meteorological variable was used to estimate the climate- induced changes in the annual runoff. This approach was applied in some river basins in Southeast Nigeria and the highest change of 1.68 m 3 /s, in annual runoff, was observed in the River Adada in Enugu State, and 0.04 m 3 /sin Otamiri River, Imo State. It was also observed that climate change did not significantly affect the drainage sections in Abakiliki and Umuahia although only the drainage width increased by 0.1% in Awka. There was a very significant change of 7% in the dimensions of the drain located in Adada watershed, Enugu while in the Otamiri river basin, Owerri, 0.2%change in the drainage capacity was estimated.It is evident that this study highlights the need for incorporating the excess climate-induced runoff volumes caused by climate change, in the design of efficient and safe hydrologic structures. Keywords: climate, design, drains, hydrology, meteorology 1. INTRODUCTION limate, which is the regular pattern of weather conditions of a place, is reported to be stable if there is insignificant variation in weather elements over a long period of time (Akamigbo and Ninja, 2011).Olusina and Odumade (2012) defined climate change as the change in the statistical properties of climate when considered over long periods of time, regardless of cause. Climate fluctuations over periods shorter than few decades do not represent climate change. As global temperature increased by 0.6 ± 0.2℃ over 100years (Folland et al., 2001), the concentration of greenhouse gas (GHG) such as CO 2 increased from 282ppm to 365ppm between 1800 to 2000 (Rosegrant et al., 2002), confirming that GHG is responsible for global warming. These gases, which are either volcanic or anthropogenic in origin, absorb terrestrial radiations from the earth and eradiate the heat back to the earth, thereby leading to earth surface temperature increase called global watering (Ozor, 2009) Climate change is a global phenomenon that is experienced in many countries in different forms. According to UCS (2010), rain that should have fallen in different days of a month fell within a day or two causing massive floods in parts of India, Pakistan, USA, UK and Japan in 2014. Climate change also manifests as trends in various meteorological records, particularly temperature (Nwaiwu et al., 2014). In Nigeria, increasing temperatures and decreasing rainfall in the semi-arid region of Sokoto, Kastina, Kano, Nguru and Maiduguri have induced increased evaporation, drought and desertification with consequent drying up of some water bodies like Lake Chad (Ayuba, 2005). Like other parts of the globe, Nigeria is highly vulnerable to the impacts of climate change. Climate change was also reported to have increased the number of dry spells during the rainy season from May to September in some areas of Sudan-Sahelian region of northern Nigeria (Sawa, 2010). In high grounds of Jos, Yelwa and Ilorin, Abiodun et Ibeje, A.O. Department of Civil Engineering, Imo State University, Owerri, Nigeria,engineeribeje@gmail.com C