Assessment of Water Footprint in Upper Ogun River Basin, Southwest Nigeria

Abstract

The Upper Ogun River Basin in southwest Nigeria is a pure agrarian zone, with the majority of food cro[ps produced being sold off to the  lower basin (particularly Lagos). Thus, this study is necessary to provide information on basic water accounting indices needed to attain  improved water resources management and planning beyond the traditional approach through a well-defined sustainable plan. In order  to quantify the amount of water resources available in this area, a hydrological modeling approach was applied. The SWAT (Soil and  Water Assessment Tool) model which is a physically based model that can represent real life situations, was used to model the water  footprint (green and blue water) and estimate variation of hydrological response units (HRUs) within the basin for a period of 30 years  (1990 – 2019). The model also simulated and the average daily and annual water balance in the hydrological storage phases and  predicted excess water yield with an average runoff curve number (CN) of 81.26mm. The basin showed a high rate of sediments yields  indicating its vulnerability to erosion due to the various modifications of the Land surfaces especially due to agricultural practices. The  water balance ratios for stream flow/precipitation are 0.39, base flow is 0.31, surface runoff is 0.69, percolation is 0.16, deep recharge is  0.01 while evapotranspiration is 0.56 (all units in mm). A 30 days of water stress, 1 day of Temperature stress, 25 days of Nitrogen stress  and 2 days of Phosphorus stress, annually was predicted.