Impacts of land use and land cover change on surface runoff, discharge and low flows: Evidence from East Africa

S. Okoth,R.L.B. Nóbrega,A.C. Guzha,S. Jacobs,M.C. Rufino

doi:10.1016/j.ejrh.2017.11.005

Abstract

RegionEast Africa. FocusA review of catchment studies (n=37) conducted in East Africa evaluating the impacts of Land Use and Land Cover Changes (LULCC) on discharge, surface runoff, and low flows. New hydrological insightsForest cover loss is accompanied by increased stream discharges and surface runoff. No significant difference in stream discharge is observed between bamboo and pine plantation catchments, and between cultivated and tea plantation catchments. Trend analyses show that despite forest cover loss, 63% of the watersheds show non-significant changes in annual discharges while 31% show increasing trends. Half of the watersheds show non-significant trends in wet season flows and low flows while 35% reveal decreasing trends in low flows. Modeling studies estimate that forest cover loss increases annual discharges and surface runoff by 16±5.5% and 45±14%, respectively. Peak flows increased by a mean of 10±2.8% while low flows decreased by a mean of 7±5.3%. Increased forest cover decreases annual discharges and surface runoff by 13±1.9% and 25±5%, respectively. Weak correlations between forest cover and runoff (r=0.42, p<0.05), mean discharge (r=0.63, p<0.05) and peak discharge (r=0.67, p<0.05) indicate that forest cover alone is not an accurate predictor of hydrological fluxes in East African catchments. The variability in these results supports the need for long-term field monitoring to better understand catchment responses and to improve the calibration of currently used simulation models.

Highlights

The sustainable management of the earth’s surface including Land Use and Land Cover Changes (LULCC) remains a critical environmental challenge that society must address (Mustard et al, 2004)
Focus: A review of catchment studies (n = 37) conducted in East Africa evaluating the impacts of Land Use and Land Cover Changes (LULCC) on discharge, surface runoff, and low flows
We focus our study on the East Africa region, which includes most of the Nile basin, an important biodiversity hotspot and the Lake Victoria, the world’s largest tropical lake

Summary

Introduction

LULCC are major determinants of global environmental change with potential severe impacts on human livelihoods (Olson et al, 2008). East Africa depends largely on rain-fed agriculture, which makes rural livelihoods and food security highly vulnerable to shifts in water availability. Between 1990 and 2015, East Africa forest cover decreased annually by about 1% while human population increased at an average annual rate of 2% (Fig. 1). The main forest types in East Africa that have undergone this decrease include tropical rain forests, tropical dry forests, tropical shrubs, tropical montane forest, and mangrove forests, while there have been concerted efforts to establish plantation forests. Food production is dependent on water resources and any likely impacts of LULCC on water resources have negative impacts on food production

Objectives

Methods

Results

Discussion

Conclusion