Assessing Impacts of Land Use Changes on the Hydrology of a Lowland Rainforest Catchment in Ghana, West Africa

Michael Aduah,Michele Toucher,Graham Jewitt

doi:10.3390/w10010009

Abstract

Impact assessments of actual and potential land use (LU) changes on hydrology are vital in land use planning, which is a prerequisite for effective water resources management. In this study, impacts of actual, as well as potential, LU changes on the hydrology of the Bonsa catchment (1482 km2), Ghana, West Africa, were assessed using the Agricultural Catchments Research Unit (ACRU) hydrological model. Baseline, current and potential future LU maps for three scenarios, namely, business-as-usual (BAU), economic growth (EG) and economic growth and reforestation (EGR), driven by observed climate between 1990 and 2009, were used for the study. The results indicate that peak and dry season streamflows between 1991 and 2011 have increased by 21% and 37%, respectively, under the current land use in comparison to the baseline due to a decrease in evergreen and secondary forests by 18% and 39%, respectively, and an increase in settlements, mining areas and shrubs/farms by 81%, 310% and 343%, respectively. The potential future LU scenarios suggest that there may be further increases in streamflows, but the historical land use changes between 1991 and 2011 were so substantial that they will continue to impact streamflow changes in any of the future land use scenarios. The study also showed that variability of streamflow changes at the catchment scale was lower than at the subcatchment scale. For the scenarios of potential future LU changes, the BAU shows the highest increases in streamflows, while the EGR shows the least. Policy interventions for effective management of the catchment are recommended.

Highlights

Rapid population growth, rural-urban migration, urbanization, agricultural intensification and extensification, as well as expansion in surface mining, are some of the major causes of land use (LU)changes in West Africa [1,2,3,4]
The temporal changes in streamflows across the selected land use scenarios are described using tables and figures, while maps are used to explore the spatial variability of streamflow responses to the current, as well as future land use (LU) scenarios
The streamflows simulated under the potential future LU change scenarios (BAU, economic growth (EG) and economic growth and reforestation (EGR)) followed the same trend as those for the current (2011) LU, but with higher magnitudes of change, which increased with time

Summary

Introduction

Rural-urban migration, urbanization, agricultural intensification and extensification, as well as expansion in surface mining, are some of the major causes of land use (LU)changes in West Africa [1,2,3,4]. Land use changes modify the partitioning of precipitation between the components of the hydrological cycle, which can impact negatively on the environment and socioeconomic wellbeing of people. To effectively manage water resources in a catchment, the historical and present, as well as the potential future impacts of land use changes need to be assessed [5]. These results are vital in efficient land use planning, which is a prerequisite for effective water resources management. The impacts of land cover/land use changes on hydrology have been assessed over the past several decades, using (i) field-based data-driven statistical methods, based on single catchments or paired

Objectives

Results

Discussion

Conclusion