16 May 2005

East Africa: How Land Use Planning Can Control Flooding

Nairobi — A day after the recent announcement by Kenya's Agricultural Minister, Kipruto arap Kirwa, that the country is facing imminent famine following a "silent" drought, heavy rains pounded many parts of the country, with some receiving an all-time high of 132mm in a single day.

Days later, some sections of the country and especially the Lake Basin were to experience heavy flooding, which set on course the recurrent phenomenon in which hundreds of Kenyans, seek alternative shelter after their homes become no-go zones.

The flooding, and especially in floodplains of the rivers flowing into Lake Victoria, is a perennial problem. On May 20 last year, floods there killed seven people and displaced more than 4,000 others.

That most parts of Kenya have been receiving quite intensive rainfall - that are spread over a short period - is linked, in a way, to massive destruction of vegetation and particularly forests.

A dense cover of forests, experts say, is crucial for the regulation of rainfall in that it not only enables the supply of substantial amount of moisture though evapotranspiration but also prevents flooding by arresting rain water.

Christian Lambrechts, a Policy and Programme Officer with the United Nations Environmental Programmes's Division of Early Warning and Assessment says that research undertaken by the Biospheric Aspects of Hydrological Cycle (BAHC), one of the core programmes of the globally-famous International Geosphere Biosphere Programme (IGBP), shows that forests contribute substantially to precipitation. "Forests play a critical role as two-thirds of the rainfall come from evapo-transpiration that happens inland while one-third comes from evaporation above the oceans."

Once moisture-laden winds moving from the oceans make it to a forest, the air above the area and its environs is saturated with the moisture leading to precipitation.

In his book, Modelling the Impact of Changes in Land Use, Climate and Reservoir Storage on Flooding in the Nyando Basin, Joseph Sang argues that land use changes contribute immensely to increase in flooding.

His study is based on the 3,587 square-kilometre Nyando Basin, and points out that the construction of four reservoirs along rivers Nyando and Ainabng'etung - as identified by Ministry of Water - would arrest a quarter of the floods.

More importantly though, is the positive impact the adoption of sound agricultural practices in the entire basin would have on the perennial flooding there. In some parts of the basin, as much as 80 per cent of the land is now covered by agricultural activities while forests cover a mere 20 per cent.

In essence, this shows that such efforts as the adoption of agroforestry practices might be more suitable there than attempting to reforest the areas.

However, for the impact to be significant, sound agricultural activities will have to be adopted by all. "Controlling flooding ought to be a collective action involving people living downstream and upstream of the Lake Basin," says Sang.

He cites conservation agriculture as advocated by the World Agroforestry Centre (ICRAF) as a measure that would not only raise yields but also help retain much of the rainwater in the soil.

"Agroforestry can reduce flooding and peak flows of the rivers flowing to Lake Victoria by almost three-quarters," says Sang. Today though, it is a free-for-all situation where downstream farmers not only cultivate right to the banks of the rivers but their counterparts in the upstream operate without any concern over the effects their activities have on the flooding downstream and on the overall sustainability of the entire basin.

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