Abstract
The Dabus Wetland complex in the highlands of Ethiopia is within the headwaters of the Nile Basin and is home to significant ecological communities and rare or endangered species. Its many interrelated wetland types undergo seasonal and longer-term changes due to weather and climate variations as well as anthropogenic land use such as grazing and burning. Mapping and monitoring of these wetlands has not been previously undertaken due primarily to their relative isolation and lack of resources. This study investigated the potential of remote sensing based classification for mapping the primary vegetation groups in the Dabus Wetlands using a combination of dry and wet season data, including optical (Landsat spectral bands and derived vegetation and wetness indices), radar (ALOS PALSAR L-band backscatter), and elevation (SRTM derived DEM and other terrain metrics) as inputs to the non-parametric Random Forest (RF) classifier. Eight wetland types and three terrestrial/upland classes were mapped using field samples of observed plant community composition and structure groupings as reference information. Various tests to compare results using different RF input parameters and data types were conducted. A combination of multispectral optical, radar and topographic variables provided the best overall classification accuracy, 94.4% and 92.9% for the dry and wet season, respectively. Spectral and topographic data (radar data excluded) performed nearly as well, while accuracies using only radar and topographic data were 82–89%. Relatively homogeneous classes such as Papyrus Swamps, Forested Wetland, and Wet Meadow yielded the highest accuracies while spatially complex classes such as Emergent Marsh were more difficult to accurately classify. The methods and results presented in this paper can serve as a basis for development of long-term mapping and monitoring of these and other non-forested wetlands in Ethiopia and other similar environmental settings.
Highlights
Wetlands are among the most biologically productive ecosystems in the world
The Dabus wetlands can be divided into three main reaches/regions distributed along the stream elevation gradient, i.e., the upper/headwater, middle, and lower region (Figure 4)
The latter was rarely encountered during the field surveys but, in the classifications, its spatial distribution was closely associated with Papyrus Swamp
Summary
Wetlands are among the most biologically productive ecosystems in the world. Their rich biodiversity contributes to sustaining ecosystem functions and services [1] and in regulating and storing water. Wetlands contribute significantly to carbon sequestration as much of the permanently flooded swamps in tropical Africa are dominated by papyrus sedge (Cyperus papyrus) [3], which has productivity comparable to that of forest [4]. Knowledge about the significance of the Dabus wetlands was lacking, despite the fact that they include large papyrus swamps supporting a rich biodiversity [10,11], while farmers and pastoralists benefit from their provision of water during the dry season
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