The use of remote sensing to quantify wetland loss in the Choke Mountain range, Upper Blue Nile basin, Ethiopia

E Teferi,J Wenninger,S Uhlenbrook,W Bewket,B Simane

doi:10.5194/hess-14-2415-2010

Abstract

Abstract. Wetlands provide multiple ecosystem services such as storing and regulating water flows and water quality, providing unique habitats to flora and fauna, and regulating micro-climatic conditions. Conversion of wetlands for agricultural use is a widespread practice in Ethiopia, particularly in the southwestern part where wetlands cover large areas. Although there are many studies on land cover and land use changes in this region, comprehensive studies on wetlands are still missing. Hence, extent and rate of wetland loss at regional scales is unknown. The objective of this paper is to quantify wetland dynamics and estimate wetland loss in the Choke Mountain range (area covering 17 443 km2) in the Upper Blue Nile basin, a key headwater region of the river Nile. Therefore, satellite remote sensing imagery of the period 1986–2005 were considered. To create images of surface reflectance that are radiometrically consistent, a combination of cross-calibration and atmospheric correction (Vogelman-DOS3) methods was used. A hybrid supervised/unsupervised classification approach was used to classify the images. Overall accuracies of 94.1% and 93.5% and Kappa Coefficients of 0.908 and 0.913 for the 1986 and 2005 imageries, respectively were obtained. The results showed that 607 km2 of seasonal wetland with low moisture and 22.4 km2 of open water are lost in the study area during the period 1986 to 2005. The current situation in the wetlands of Choke Mountain is characterized by further degradation which calls for wetland conservation and rehabilitation efforts through incorporating wetlands into watershed management plans.

Highlights

It is well documented that wetlands play critical roles in the hydrological system (e.g. Ehrenfeld, 2000; Tiner, 2003)
The study demonstrated the use of remote sensing techniques to delineate headwater wetlands from non-wetlands and determine the dynamics over large areas of Choke Mountains with the overall accuracy of 94.1% and 93.5% and Kappa Coefficient of 0.908 and 0.913 for the 1986 and 2005 imageries, respectively
Ground-based wetland surveying for large area, especially for small wetlands is a very time consuming and ineffective process

Summary

Introduction

It is well documented that wetlands play critical roles in the hydrological system (e.g. Ehrenfeld, 2000; Tiner, 2003). It is well documented that wetlands play critical roles in the hydrological system Ehrenfeld, 2000; Tiner, 2003). Moderating the impact of extreme rainfall events and providing base flow during dry periods is one of the key functions of wetlands. Wetlands can moderate flow dynamics and mitigate flooding. They play a regulating role on the water quality by capturing sediment and capturing and converting pollutants. Wetland functions are important in areas with high rainfall variability as they help to sustain smaller discharges during the dry season and, improve the availability of water. Wetland conservation has a vital role to play in alleviating water problems at different scales Wetland conservation has a vital role to play in alleviating water problems at different scales (e.g. Koeln, 1992; Jensen et al, 1993; Reimold, 1994)

Objectives

Methods

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Conclusion