The Effects of Climate Change on Water Resources in the West: Introduction and Overview

The results of an experimental `end to end' assessment of the effects of climate change on water resources in the western United States are described. The assessment focuses on the potential effects of climate change over the first half of the 21st century on the Columbia, Sacramento/San Joaquin, and Colorado river basins. The paper describes the methodology used for the assessment, and it summarizes the principal findings of the study. The strengths and weaknesses of this study are discussed, and suggestions are made for improving future climate change assessments.     

Genetic relationship of rift-stage crustal structure, terrane accretion, and foreland tectonics along the southern Appalachian-Ouachita orogen

Abrupt along-strike variations in tectonostratigraphic composition, internal structural style, and detachment level in the southern Appalachian and Ouachita foreland thrust belts are defined at a large-scale bend in strike and a truncation of Ouachita structures by the frontal Appalachian thrust fault. The along-strike variations correspond to differences in the pre-orogenic rifted Laurentian margin, in the history and nature of terrane accretion, and in the response of the foreland to these differences. Within the Ouachita embayment of the Laurentian margin, diachronous arc-continent collision migrated northwestward along a rift-stage transform margin from the Black Warrior foreland basin on the southeast in Late Mississippian time to a short-wavelength, high-amplitude foreland basin (Arkoma basin) on the northwest in front of the Ouachita thrust-belt salient in Early-Middle Pennsylvanian time. Off-shelf, deep-water strata of both passive-margin and synorogenic facies comprise an accretionary prism and subduction complex, and the Ouachita allochthon consists of mud-dominated thrust sheets that are internally disharmonic and folded. The allochthon of off-shelf strata was thrust over the passive-margin carbonate shelf, which remains in the Ouachita footwall. Along the southeast side of the Alabama promontory of the Laurentian margin, passive-margin shelf carbonates are imbricated in the Appalachian thrust belt, which is characterized by internally coherent thrust sheets and high-amplitude frontal ramps. The palinspastic extent of shelf-carbonate rocks corresponds to the extent of structurally shallow basement rocks on the upper-plate rift-stage margin of the Alabama promontory of Laurentian crust. Terranes accreted to the Laurentian margin during the Taconic and Acadian orogenies were driven over the shallow basement by continent-continent collision of Laurentia with Africa (Gondwana). Emplacement of the thrust-translated terranes tectonically stripped and replaced the shelf carbonate. The frontal thrust fault of the Appalachian thrust belt truncates the southeastern end of the slightly older frontal Ouachita thrust belt, as well as the southeastern part of the greater Black Warrior basin in the Ouachita foreland. Shallow basement beneath the Appalachian thrust belt extends cratonward beneath the low-amplitude Appalachian foreland basin.     

Wildlife management and land reform in southeastern Zimbabwe: a compatible pairing or a contradiction in terms?

This paper examines the melding of two discourses in southeastern Zimbabwe: land reform and wildlife management. The former seeks to redistribute large, ‘under-utilized’ landholdings to smallholders whilst the latter needs extensive land holdings to be viable. These two discourses are rooted in very different models of development. The land reform exercise emphasizes direct redistribution, equity and land for crops; whilst the wildlife management discourse tends to stress maximizing foreign exchange earnings, encouraging public-private partnerships and trickle down. Yet there has been a recent flurry of interest in the development of ‘wildlife models’ for land reform which would combine the two. This paper investigates whether the competing discourses about land for smallholders and wildlife-based land reform are compatible or can be successfully reconciled. It traces the ways they have come together in Zimbabwe’s southeast lowveld and examines the ‘science’ and politics underlying their melding. Finally it explores the potential implications for rural people’s livelihoods of this development. It concludes that land reform and wildlife management can be reconciled, but probably not in a particularly equitable way: it is more likely to provide an opening for an equitable land reform agenda to be usurped by local and non-local elites with wildlife interests.     

In the Critical Zone: Geography at the U.S. Geological Survey

Geography is again becoming an integral part of the premier natural‐science agency of the federal government. Geographic research emphasizes the surface of the earth, a portion of the earth system that the U.S. Geological Survey (USGS) defines as the “critical zone.” Although geography was part of the USGS from the creation of the agency, in recent years geography in the agency has largely been limited to topographic mapping. Recently, the USGS and an advisory committee of the National Research Council (NRC) reviewed the role of geography at the Survey. The committee's report, along with ongoing decision‐making in the federal government, is likely to reshape geography in the USGS. The newly defined USGS has a regional structure and four disciplines: geology, hydrology, biology, and geography. The NRC report emphasizes the need for the creation of a spatial database called the National Map to replace the existing series of paper topographic maps. The report also outlines the need for geographic research in geographic information science (GIScience), nature‐society connections, and bridging of science to decision‐making. The NRC report has been briefed throughout the USGS, in the federal executive branch, and in Congress. The changing role for geography in the USGS requires change in the agency culture, revised budgetary decisions, and the establishment of a long‐term core agenda for research. Academic geographers will need to prepare a new generation of geographers for participation in the USGS and similar agencies.     

On the variability of the flow along the Meso-American Barrier Reef system: a numerical model study of the influence of the Caribbean current and eddies

A high resolution (3–8 km grid), 3D numerical ocean model of the West Caribbean Sea (WCS) is used to investigate the variability and the forcing of flows near the Meso-American Barrier Reef System (MBRS) which runs along the coasts of Mexico, Belize, Guatemala and Honduras. Mesoscale variations in velocity and temperature along the reef were found in seasonal model simulations and in observations; these variations are associated with meandering of the Caribbean current (CC) and the propagation of Caribbean eddies. Diagnostic calculations and a simple assimilation technique are combined to infer the dynamically adjusted flow associated with particular eddies. The results demonstrate that when a cyclonic eddy (negative sea surface height anomaly (SSHA)) is found near the MBRS the CC shifts offshore, the cyclonic circulation in the Gulf of Honduras (GOH) intensifies, and a strong southward flow results along the reef. However, when an anticyclonic eddy (positive SSHA) is found near the reef, the CC moves onshore and the flow is predominantly westward across the reef. The model results help to explain how drifters are able to propagate in a direction opposite to the mean circulation when eddies cause a reversal of the coastal circulation. The effect of including the Meso-American Lagoon west of the Belize Reef in the model topography was also investigated, to show the importance of having accurate coastal topography in determining the variations of transports across the MBRS. The variations found in transports across the MBRS (on seasonal and mesoscale time scales) may have important consequences for biological activities along the reef such as spawning aggregations; better understanding the nature of these variations will help ongoing efforts in coral reef conservation and maintaining the health of the ecosystem in the region.     

Construction of detrital mineral populations: insights from mixing of U–Pb zircon ages in Himalayan rivers

Fission‐track, U–Pb and Pb–Pb analyses of detrital heavy mineral populations in depositional basins and modern river sediments are widely used to infer the exhumational history of mountain belts. However, relatively few studies address the underlying assumption that detrital mineral populations provide an accurate representation of their entire source region. Implicit in this assumption is the idea that all units have equal potential to contribute heavy minerals in proportion to their exposure area in the source region. In reality, the detrital mineral population may be biased by variable concentrations of minerals in bedrock and differential erosion rates within the source region. This study evaluates the relative importance of these two variables by using mixing of U–Pb zircon ages to trace zircon populations from source units, through the fluvial system, and into the foreland. The first part of the study focuses on the Marsyandi drainage in central Nepal, using tributaries that drain single formations to define the U–Pb age distributions of individual units and using trunk river samples to evaluate the relative contributions from each lithology. Observed mixing proportions are compared with proportions predicted by a simple model incorporating lithologic exposure area and zircon concentration. The relative erosion rates that account for the discrepancy between the observed and predicted mixing proportions are then modelled and compared with independent erosional proxies. The study also compares U–Pb age distributions from four adjacent drainages spanning ～250 km along the Himalayan front using the Kolmogorov–Smirnov statistic and statistical estimates of the proportion of zircon derived from each upstream lithology. Results show that, along this broad swath of rugged mountains, the U–Pb age distributions are remarkably similar, thereby allowing data from more localized sources to be extrapolated along strike.