a layer of black soils on the surface. [8] The valley experiences extremes of  hydrometeorological  and  climatic  conditions with the upper catchment having an annual  precipitation  in the range of 1,000 mm (3.3 ft) to 1,850 mm (6.1 ft) and with half or even less than half in its lower regions (650 mm (2.1 ft)–750 mm (2.5 ft)); the