『Abstract
　In their seminal paper in 1979, Bull and Schick proposed a conceptual model for the geomorphic response to Pleistocene to Holocene climate change, based on the hyperarid Nahal Yael watershed in the southern negev Desert. In this model, the change from semiarid late Pleistocene to hyperarid early Holocene climates reduced vegetation cover, increased the yiel of sediment from slopes, and accelerated aggradation of terraces and alluvial fans. The model is now over 30 yr oil, and during this time, chronologic, paleoenvironmental, and hydrogeomorphic research has advanced. Here, we reevaluate the model using data acquired in Nahal Yael over the 30 yr since the original model was proposed. Recent studies indicate that the late Pleistocene climate was hyperarid, and a transition from semiarid to hyperarid climates did not occur. The revised chronology reveals a major 35-20 ka episode of accelerated late Pleistocene sediment production on slopes (with lower rates probably already at ca. 50 ka) due to increased frequency of wetting-drying cycles caused by frequent extreme storms and floods between 35 and 27 ka. without lag time, these sediments were transported and aggraded in depositional landscape components (fluvial terraces and alluvial fans). This intensified sediment production and delivery phase is unrelated to the Pleistocene-Holocene transition. The depositional landforms were rapidly incised between 20 and 18 ka. Since and/or soon after this Last Glacial Maximum (LDM) incision, most material leaving the basin originated from sediments stored in depositional landforms and was not produced from bedrock.
　Using these new data, we propose a revision to the Bull and Schick model in this hyperarid environment. Our revision suggests that the model should include the frequent storms and floods responsible for a late Pleistocene pulse of intense weathering due to numerous cycles of wetting and drying on slopes and coeval sediment transport to fluvial terraces and alluvial fans. We also discuss the common use and pitfalls of using the Bull and Schick conceptual model to explain observations in diverse arid environments, usually without sufficient data on basin-specific stratigraphic, chronologic, paleoenvironmental, and paleoclimatic information.』

Introduction
Location, field settings, and current hydroclimatology
　Present-day rainstorms in the southern Negv
Paleoclimate of the southern Negev
Soil horizons and past vegetation cover
　Calcic versus gypsic-salic soil horizons in stable alluvial surfaces
Secondary CaCO3, accumulations in Nahal Yael
　Fluvio-pedogenic units
　Diffusive calcic nodules on slopes
　Isotopic composition of the secondary carbonates
Chronology of talus, terrace, and alluvial-fan deposits
　Talus deposits and ages
　Nahal Yael and Nahal Mekorot terraces
　Nahal Yael alluvial fan
　Animal trails
Sources of sediment to Nahal Yael channel
　Intensified weathering in Nahal Yael
　A pulse of sediment production and delivery
　Changes needed in the conceptual model
　Earlier applications of the model
Temporal scales and causes of pulsed sediment production
Future testing of the model
Conclusions
Acknowledgments
References cited