University of Twente Student Theses


Estimating patterns of potential soil erosion for Eritrea over time and space through remotely sensed rainfall intensity and vegetation indices

Debesay, Habtom Tsegay (2013) Estimating patterns of potential soil erosion for Eritrea over time and space through remotely sensed rainfall intensity and vegetation indices.

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Abstract:Soil in Eritrea is losing productivity because of severe erosion. The numerous small-scale peasants (around 80% of the population) are highly affected their livelihood by this process. Soil erosion assessment can help to make spatial plans for erosion mitigation measures by targeting priority areas. Multi-temporal satellite products can provide important input to such assessments. Given the erratic nature of the erosion processes, it is important that information derived from satellites accounts effectively for the variability of erosion controlling factors. Erosion processes occur on areas with erodible soils and sloping terrain when high-intensity rainfall coincides with limited vegetation cover. Timing of erosion events has implications on the selection of satellite imagery, used to describe spatial patterns of protective vegetation cover. Two of the most dynamic and time-dependent factors for soil erosion estimation are rainfall erosivity and vegetation cover. To estimate when during the year soil erosion risk is highest, coarse-resolution 3-hourly rainfall intensity data from TRMM were combined with 10-daily SPOT VEGETATION NDVI imagery. Monthly and annual erosivity estimates were derived from the 3-hourly rainfall data for the period 1998 to 2012. The NDVI time series were temporally aggregated to monthly data and used as a proxy of green vegetation cover. Combined analysis of both data sources was performed to spatially evaluate the normal seasonal and inter-annual variability of soil erosion risk. This timing of erosion was compared to field evidence obtained from literature for a single location in Eritrea, and six locations in Ethiopia. Integration with other erosion-controlling factors (slope and soil erodibility) was achieved by application of the Universal Soil Loss Equation (USLE), using the FAO soil map of the world and the 90-m SRTM DEM. The USLE was applied on monthly basis, and from that aggregated to annual soil erosion. For most of Eritrea, July and August were identified as the months with highest erosion risk. Moist high lands, and arid highlands showed high potential soil erosion. Parts of the moist low lands and arid low lands have moderate risk. The soil erosion potential is low for the majority of the arid-low lands and coastal areas of the country. Seasonal and inter-annual soil erosion assessment is used to confirm areas that have similar in climatic regime and vegetation development, which assisted to determine whether the high erosion period is always at the same moment. This research did not intend to estimate precisely the amount of soil loss and sediment yield but to provide realistic spatial patterns of soil erosion risk, and an understanding of the temporal variability of soil erosion. This can assist decision makers developing soil and water conservation plans for the country and carry out more detailed analysis for the high potential erosion risk areas.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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