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University of Twente (2012)

The power of rain : rainfall variability and erosion in Cape Verde.

Sánchez-Moreno, J.F.

Titre : The power of rain : rainfall variability and erosion in Cape Verde.

Auteur : Sánchez-Moreno, J.F.

Etablissement de soutenance : University of Twente

Grade : Doctor University of Twente 2012

Résumé partiel
Pressure over land for agriculture and rainfall variations caused by weather and climate variability and by climate change, are increasing soil erosion processes and resulting in desertification. Tropical semi-arid countries, with occurrence of extreme rainfall events in short time intervals are more susceptible to flash floods and erosion, that are aggravated if the relief effect is added to the equation. The majority of the semi-arid areas of the world are in developing countries, where pressure over land is even higher and where measures against erosion are still inadequate due to financial limitations. Data availability poses a challenge for the understanding of rainfall and erosion processes in many semi-arid developing countries. Cape Verde, off the west coast of Africa, is a semi-arid country conformed by a group of islands located in the tropical zone, subject to a short rainy season with extreme inter annual variation, and where data is scarce. In Cape Verde, poor agricultural practices along with few arable land and extreme events are intensifying erosion processes leading to desertification.Parameterization of rainfall in Santiago Island, the largest of Cape Verde, showed that elevation can be used as main predictor for monthly and seasonal rainfall. A few days only with extreme high and intense rainfall events can control the rainfall patterns of the month and the season. On the other hand, extreme weather events act more independently of orography. For drought studies and agricultural purposes, rainfall variability can be studied in terms of elevation, however erosion models are better studied in terms of single events. In Cape Verde, rain gauges are not always operative and observations are not all of the same reliability, which makes adequate rainfall parameterization difficult. As ground rainfall measurements are not always available, estimates from satellite were considered for Cape Verde, particularly from readily available data such as the Tropical Rainfall Meteorological Mission (TRMM) and the Multi Precipitation Estimate from MeteoSat 2nd generation. Comparison with ground data measurements showed that the products from these sensors underestimate the amount of rainfall. A newly derived estimate based on cloud top temperature of precipitable clouds correlated better with high temporal resolution ground data measured by an optical disdrometer, and provided a more acceptable fit and rainfall depths within the ranges measured on the ground. The estimate could be calculated for 15 minutes intervals, which makes it usable as input for erosion studies based on single events.


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