Impact of Climatic Change on an Arid Watershed: Nahal Yael, Southern Israel

Abstract

The Nahal Yael basin is underlain chiefly by schist, amphibolite, and granite. Thin (generally <1 m thick), grussy colluvium which covered the lower portions of granitic hillslopes in the late Pleistocene has now been stripped completely, causing marked contrasts in outcrop morphologies, even where there is no contrast of fracture density or petrologic characteristics. Formerly mantled slopes are now smooth and crumbly, and lack desert varnish. Previously unmantled slopes are rough and craggy, and varnished but little weathered. Such stripping suggests a change from a semiarid to a drier and/or warmer climate. Slopes underlain by amphibolite responded similarly to the climatic change, but the amphibolite was more deeply weathered, and the colluvium was only partially stripped. The least stripping of colluvium occurred on schist hillslopes, partly because schist outcrops require more rain to generate runoff, and partly because angular blocks of schist require larger flows for transport, compared to other slope lithologies. The stream subsystem responded to the climatically induced changes in the discharge of water and sediment from the hillslopes. Increase in sediment yield caused valley alluviation in the early Holocene, and a decrease in sediment yield later in the Holocene caused entrenchment of the valley fill. More granite and amphibolite gravel-size particles are transported now than when the hillslopes were extensively mantled. Dense networks of trails are not common on Holocene geomorphic surfaces, but are present on remnants of Pleistocene surfaces.

The geomorphic setting of upper paleolithic sites in Wadi el Sheikh, Southern Sinai

“…The synoptic reconstruction is based almost exclusively on physical evidence, evidence that considers erosion or deposition as mutually exclusive, climatically forced events. Alluviation is attributed to humid conditions, and entrenchment to arid ones, while others have recognized in the Negev alluviation during postPleistocene hyperarid conditions and entrenchment during more humid phases of the Holocene (Bull and Schick, 1979).…”

Climatic control on palaeohydrology and cyclical sediment distribution in the Plio-Quaternary deposits of the Guadix Basin (Betic Cordillera, Spain)

“…As a result, a generally drier climate can be inferred for the ITS sediments in comparison with the AS ones. The deposition of alluvial fans under arid conditions is widely recorded in the literature (Bull and Schick, 1979;Wells et al, 1987;Harvey and Wells, 1994, among others) and is exemplified in Southern Spain by the Quaternary alluvial fans studied by Viseras et al (2003).…”

Geomorphology and tectonics at the intersection of Silurian and Death Valleys, Southern California - 2005 Guidebook Pacific Cell Friends of the Pleistocene

“…Deposition of Qydf4 sediment commenced during or immediately following the regional pluvial highstand at the end of the last glacial maximum . During the transition from a wetter to drier climate near the beginning of the Holocene, the landscape may have adjusted to changing vegetation, rainfall/runoff patterns, and colluvial cover by eroding hillslopes and aggrading fans (e.g., Bull & Schick, 1979). A shift to a drier climate, causing a decrease in the overall canopy cover, can increase both the intensity and amount of precipitation reaching the ground.…”