Toward an integrated watershed zoning framework based on the spatio-temporal variability of land-cover and climate: Application in the Volta river basin

Authors: Sohoulande, Clement

Submitted to: Environmental Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2018
Publication Date: 12/13/2018
Citation: Sohoulande Djebou, D.C. 2018. Toward an integrated watershed zoning framework based on the spatio-temporal variability of land-cover and climate: Application in the Volta river basin. Environmental Development. 28:55-66. https://doi.org/10.1016/j.envdev.2018.09.006.
DOI: https://doi.org/10.1016/j.envdev.2018.09.006

Interpretive Summary: A new procedure is proposed for watershed zoning studies. The procedure is developed using statistical methods that group objects in such a way that objects in the same group (called a cluster) are similar to each other than to those in other groups. The procedure can be used to subdivide a large watershed into homogeneous regions based on climate and vegetation cover for regional water management purposes. A case study is presented to illustrate an application and evaluate the relevance of the zoning procedure. The procedure was applied to the Volta river basin which is a watershed shared by six countries in West Africa. The procedure subdivided the Volta basin into five homogeneous zones (clusters), each zone showing specific climate and vegetation characteristics. The outcome of this case study is that significant contrasts in water resources availability were found among the identified zones for their potential use in agriculture. This case study demonstrated that the new proposed procedure for watershed regionalization is coherent and can be used as a tool for water resource management for large scale watersheds cases.

Technical Abstract: This article details a watershed regionalization approach which uses the concept of entropy in combination with the k-means clusters analysis. The regionalization approach aims to subdivide a watershed into relatively uniform zones based on the spatial variability of the local climate and land-covers. A case study is presented to illustrate the approach and outline the environmental implications of the outcomes. Especially, the study reports an application in the Volta river basin which is a transnational watershed, shared by six different countries in West Africa. Over years, the transboundary status of the Volta watershed seems to have exacerbated its environmental challenges, because the environmental policies in the six countries do not necessarily complement. Subsequently, it is desirable to envision unified scientific tools to support the management platform of the Volta basin. To date, the literature on the Volta has virtually neglected this aspect. Hence, this case study is timely as it intends to create a unified zoning system for the Volta river basin. In the study, formulations of entropy theory and k-means clustering were jointly applied to 16-years gridded time-series of monthly leaf area index, precipitation, and temperature across the Volta basin. Based on a clustering optimization criterion, a total of five zones were identified then the related land-cover and climatic patterns were comparatively analyzed. Significant environmental contrasts were diagnosed then specificities were pinpointed for each zone. A comparison of the new zones with an existing macro-scale ecoregion shows similarities which sustain the capacity of the regionalization approach to capturing meaningful biophysical signals. Hence, the zoning technique may be valued for further applications in environmental management.