University of Twente Student Theses
Effects of spatial variability of rainfall on runoff and soil erosion: A case study in Ribeira Seca catchment, Santiago Island, Cape Verde
Hailemariam, Kebede Bilisa (2013) Effects of spatial variability of rainfall on runoff and soil erosion: A case study in Ribeira Seca catchment, Santiago Island, Cape Verde.
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| Abstract: | Soil erosion is a land surface degradation process caused by water and wind, and aggravated by human activities. Runoff is one of the main causes of soil erosion. The impact of soil erosion is more serious in developing countries and in arid to semi-arid environments around the world. Many studies have been conducted to model runoff and soil erosion in particular study areas around the world to understand the diverse effects of soil erosion and runoff on economic and social activities. Policy makers and planning agencies at various levels need quantitative evaluation of the extent and magnitude of soil erosion and runoff problems to develop conservation measures to guard the landscape and prevent soil erosion. Rainfall-runoff modeling helps in providing the opportunity to understand the hydrological response of a watershed. Rainfall measured either by rain gauges or estimated by satellite is the main inputs of runoff and soil erosion modeling. Event based models are able to evaluate the effect of single events on runoff and soil erosion. Limburg Soil erosion Model (LISEM), a newly developed hydrological and soil erosion model is one of the main physically based event model. Rainfall from satellite, which takes in to account the spatial variability of rainfall hasn’t been yet used as an input to LISEM model to simulate runoff and soil erosion processes. This study is conducted in medium sized (71.5 km2) Ribeira Seca catchment, Santiago Island, Cape Verde. The main objectives of the study are: (i) to compare the Meteosat Second Generation Multi-sensor Precipitation Estimate ( MSGMPE) estimated rainfall to ground (rain gauge and disdrometer) measured rainfall and (ii) to examine the effects of spatial variability of rainfall on runoff and soil erosion. The results obtained from the 15 minutes based temporal resolution comparisons of the rainfall depth estimated by MSGMPE and measured by disdrometer at a single location in the catchment reveal poor correlation. A maximum correlation with coefficient of determination R2 equals 0.35 is obtained. However, correlation is improved as the 15 minutes rainfalls are aggregated to daily rain depth and compared. Daily based monthly and yearly comparisons of rain depth from MSGMPE to ground measurements resulted in up to R2 equals 0.9 and 0.6, respectively. 2009 was the year with poor correlation; whereas, 2010 was the year with the best correlation obtained between ground and satellite based rainfall measurements. OpenLISEM v1.56 is applied to Ribeira Seca catchment with homogeneous and spatially variable rainfall to simulate runoff and soil erosion. Since, the total rainfall that is derived from the MSGMPE over the entire catchment was lower that derived from disdrometer for the selected rainfall event, a ratio correction factor was used. Despite the same amount of rainfall over the entire catchment from both sources, the total discharge and erosion results were different. However, the spatial patterns of infiltration, runoff and erosion from both rainfall inputs were found to be similar and appear to follow the soil properties. The discharge to rainfall ratio from MPE rainfall input was 41%; whereas, that from homogeneous rainfall input was 26 %. This is attributed to either the low intensity or spatial variability of rainfall from MSGMPE, which makes the water to infiltrate as compared to the disdrometer rainfall. The sediment delivery ratio obtained from the homogenous rainfall input at the main outlet of the catchment (17.1 %) was about three-fold higher than the spatially variable MSGMPE derived rainfall input, which is 6.02 %. Key words: Ribeira Seca, LISEM, MSGMPE, disdrometer, rainfall events, runoff, soil erosion. |
| Item Type: | Essay (Master) |
| Faculty: | ITC: Faculty of Geo-information Science and Earth Observation |
| Programme: | Geoinformation Science and Earth Observation MSc (75014) |
| Link to this item: | https://purl.utwente.nl/essays/93734 |
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