All this devastation, the chronicles record, was brought about by a rat dislodging a stone so large that even 50 men could not move it. An unlikely story perhaps, though it neatly symbolises what must at the time have seemed an incomprehensible process of social and economic decline leading to the final catastrophe. Yemen's mountains rise above 10,000 feet and, unlike its Arabian neighbours, it attracts some 400-700mm of rain a year, enough to grow crops without irrigation in many places. The rain, though, comes in short, violent bursts and the water, if left uncontrolled, simply runs off the land, washes the soil away, or buries it in mountain rubble. The breakdown that is happening today is a gradual, almost imperceptible, process.
Farmers notice it, though.
Until recently the plight of these mountain villages received little attention and virtually no outside help. The scheme, based in the Wadi Zabid catchment area, near Yarim, is unusual in many ways. The UNDP gave it a try. The first meetings with villagers showed a widespread awareness of the causes of the problems, although they had not discussed them collectively until the outsiders arrived. The trouble began, everyone agreed, on the steep escarpments above the terraces.