Nairobi — Mombasa is known all over the world as a city of sun-kissed beaches and luxurious hotels packed with tourists having the time of their lives.

But in just 20 years, this world-renowned tourist haven may become an island of misery in which vast stretches of land are submerged in sea.

Salinity will make the water unfit for human consumption, it is feared, and local agriculture will collapse due to excess salts in the soil.

That is the grim projection of scientists who are now warning that authorities must take urgent steps to save the coastal city from collapsing under the weight of the effects of global warming.

"We are already seeing adverse climate change signals. Some hotels at the South Coast are building sea walls to deal with waves, something we have not seen before," says Dr Samuel Mariga, assistant director in charge of climate change at the Kenya Meteorological Department.

"All our models indicate that temperatures will continue going up and we must put in place adaptation and mitigation measures to deal with the problem."

Dr Mariga's views tally with those presented in a new book focusing on how cities can best cope with effects of changing climactic conditions.

The book, "Adapting Cities to Climate Change", highlights challenges facing Mombasa, Dhaka, Cotonou, Mumbai, Rio de Janeiro, Shanghai and Durban.

It is edited by experts from the London-based International Institute for Environment and Development and was released two weeks ago.

It warns that Mombasa, home to approximately 800,000 people, is especially vulnerable to the effects of rising sea levels due to its low altitude, and high temperature and humidity.

Mombasa is on the coastal plain, only about 45 metres above sea level.

The scientists predict that unless urgent mitigation measures are taken, a sea-level rise of just 0.3 metres will see 17 per cent of Mombasa (4,600 hectares) submerged.

They warn that large areas of the island will be rendered uninhabitable and unsuitable for agriculture due to "salt stress" and predict frequent flooding.