Influence of Climate Change on Groundwater Resources in Osogbo, Osun State, Nigeria: Fid-Bau Portal

Influence of Climate Change on Groundwater Resources in Osogbo, Osun State, Nigeria

Fadipe, Olusola Olayemi / Kareem, Mutiu Abiodun / Ishola, Kazeem

Groundwater is the world’s primary source of fresh water. However, groundwater resources in the basement complex region, such as Nigeria, have been overstressed due to excessive abstraction, and the rate of groundwater replenishment is declining as a result of climate change. Thus, this study investigated the influence of climate change on groundwater recharge scenarios. Twenty years of data on climatic records were collected from the Nigeria Meteorological Agency of Nigeria (NIMET), Abuja. The data was sorted into annual and average records and were inserted into the empirical formulas to obtain the groundwater recharge, surface runoff, evapotranspiration, and recharge coefficient. The influence of the climatic change on the groundwater variables was investigated using the multiple regression analysis (MANOVA) models of the Paleontological Statistics 4.13 software and a model was developed. The descriptive statistics of the data revealed the highest maximum temperature (33.3 °C) in 2019, minimum temperature (22.5 °C) in 2005, relative humidity (88.63%) in 2008, sunshine (5.85 h) in 2011, wind (4.69 knots) in 2016, Evapotranspiration (1310.28 mm) in 2008 and annual rainfall (1692 mm) in 2010. The lowest climatic variables (max temp (30.8 °C), min temp (20.4 °C), relative humidity (69.63%) sunshine (5.18 h), wind (3.14 knot), annual rainfall (1014.7) and evapotranspiration (1204.14) were reported in 2005, 2020, 2011, 2011, 2001, 2001 and 2012, respectively. The corresponding highest values of groundwater recharge and direct runoff from rainfall are 248.75 mm and 907.39 mm, respectively in 2010 while the highest value of recharge coefficient was 23.92 in 2006. The multivariate multiple regression analysis separated the variables into dependent variables (groundwater recharge, direct runoff, and rainfall coefficient) and independent variables (Min and max temperature, humidity, sunshine, wind, annual rainfall, and evapotranspiration). The Wilks lambda value, P (regression), and F-static are 0.0006994, 6.979E-11, and 16.1, respectively for the overall MANOVA. The tests on independent variables show varying and high Wilki Lambda, P-values, and low F-static; (0.9081, 0.7989, 0.3372 for humidity, 0.701, 0.31,1.361 for sunshine, 0.8603, 0.6647, 0.5414 for wind, 0.8363, 0.5995, 0.6523 for min temp, 0.879, 0.717, 0.459 for max temp, 0.9266, 0.8498, 0.264 for evapotranspiration). The Wilki’s Lambda, P-value, and F-static for annual rainfall is (0.001775, 4.76E-14, 1875. The R² value for Groundwater recharge and direct runoff are 0.99 and 0.91, respectively while that of the recharge coefficient is 0.32. Collectively, there is a significant difference between the groundwater recharge and the climatic factors, and the model developed is significant. However, the individual influence of the climatic variables on groundwater resources is less significant, thus the only climatic factor contributing significantly to the groundwater recharge in the study area is rainfall. The percentage of rainfall contributing to the groundwater recharge is (15.63%) and this is very low for any resource sustainability. The groundwater recharge pattern in the study area has not changed reasonably but rainfall contribution has increased by 1%. Conservative measures and sustainable management practices should be put in place for future management of the resource.