The limited role of localized convective storms in runoff production in the western Negev Desert

Abstract

High-scale floods in the Negev Desert are usually linked to rains originating from the Red Sea Trough (RST), characterized by high-intensity rainspells. While the effect of the RST storms was assessed in the southern, central and eastern parts of the Negev, almost no information exists as to their possible impact in the western parts of the Negev.Rain characteristics and its role in runoff production were studied during the years 1989–1994 in the Nizzana research site in the western Negev Desert. Only 7 out of 49 rainstorms (≥1mm) originated from the RST, and only two of these seven storms produced runoff. While the RST-induced runoff accounted for only 3.9% of the total runoff in Nizzana, it accounted for 83.5–100% of the total runoff of four major ephemeral streams in the eastern part of the Negev. It is suggested that the limited role of the RST in the western Negev and its major role in flood formation in the eastern Negev may contribute to stream capture of formerly westward flowing streams eastward into the Dead Sea. A positive feedback mechanism is thus suggested. Whereas the topography may enhance atmospheric instability and hence high convective rainstorms, the resultant floods may enhance rift widening which in turn will foster atmospheric instability.