Dryland river processes and hazards: examples from the Horn of Africa

In drylands, ephemeral streams flash floods are among the greatest natural hazards. In Africa, water related disasters increased more than four times in the last decades, causing loss of life, damage to property, and promoting the spread of diseases such as malaria, dengue fever, and cholera. Ephemeral streams geomorphologic and hydrologic characteristics are reported from field measurement and observations on a few dry rivers in the Horn of Africa. Channel dynamics, flow hydraulics and sediment transport of dryland rivers are compared to their temperate and humid environment counterparts in order to understand their channel dynamics, hydrology and sediment transport and to improve our strategies for flash flood hazard mitigation. The study points out the need to enlarge our field data to set up rainfall-runoff models specifically designed for ephemeral streams and the relevance of involving developing countries scholars and authorities in this process.