Michael M. Benedetti

Future changes in snowmelt-driven runoff timing over the western US

We use a high-resolution nested climate model to investigate future changes in snowmelt-driven runoff (SDR) over the western US. Comparison of modeled and observed daily runoff data reveals that the regional model captures the present-day timing and trends of SDR. Results from an A2 scenario simulation indicate that increases in seasonal temperature of approximately 3 degrees to 5 degrees C resulting from increasing greenhouse gas concentrations could cause SDR to occur as much as two months earlier than present. These large changes result from an amplified snow-albedo feedback driven by the topographic complexity of the region, which is more accurately resolved in a high-resolution nested climate model. Earlier SDR could affect water storage in reservoirs and hydroelectric generation, with serious consequences for land use, agriculture, and water management in the American West.

Controls on overbank deposition in the Upper Mississippi River

Abstract Floodplains contain valuable stratigraphic records of past floods, but these records do not always represent flood magnitudes in a straightforward manner. The depositional record generally reflects the magnitude, frequency, and duration of floods, but is also subject to storm-scale hysteresis effects, flood sequencing effects, and decade-scale trends in sediment load. Many of these effects are evident in the recent stratigraphic record of overbank floods along the Upper Mississippi River (UMR), where the floodplain has been aggrading for several thousand years. On low-lying floodplain surfaces in Iowa and Wisconsin, 137Cs profiles suggest average vertical accretion rates of about 10 mm/year since 1954. These rates are slightly less than rates that prevailed earlier in the 20th Century, when agricultural land disturbance was at a maximum, but they are still an order of magnitude greater than long-term average rates for the Holocene. As a result of soil conservation practices, accretion rates have decreased in recent decades despite an increase in the frequency of large floods. The stratigraphic record of the Upper Mississippi River floodplain is dominated by spring snowmelt events, because they are twice as frequent as rainfall floods, last almost twice as long, and are sometimes associated with very high sediment concentrations. The availability of sediment during floods is also influenced by a strong hysteresis effect. Peak sediment concentrations generally precede the peak discharges by 1–4 weeks, and concentrations are usually low ( The great flood of 1993 on the Mississippi River focused attention on the geomorphic effectiveness and stratigraphic signature of large floods. At McGregor, where the peak discharge had a recurrence interval of ∼14 years, the flood was most notable for its long duration (168 days above 1600 m3s−1), high sediment concentrations (three episodes >180 mg/l), and large suspended load (1.71 Mt). The flood of 2001, despite its greater magnitude (recurrence interval ∼70 years), was associated with relatively low sediment concentrations (

Paleolithic Landscapes and Seascapes of the West Coast of Portugal

The antiquity of coastal adaptations has gained renewed attention in the last several years as archaeologists have recognized that coasts have long been important foci of human settlement (Bailey 2004; Bailey and Milner 2003; Erlandson and Fitzpatrick 2006; Fa 2008; Price 1995; Sauer 1962; Westley and Dix 2006).

Portable art and personal ornaments from Txina-Txina: a new Later Stone Age site in the Limpopo River Valley, southern Mozambique

This paper reports on preliminary fieldwork at the Later Stone Age site of Txina-Txina in Mozambique. Excavation yielded a long stratigraphic sequence, a large lithic assemblage, a unique decorated gastropod shell fragment and two ostrich eggshell beads—the first of their type recovered from a Stone Age context in Mozambique.