Temporal patterns and controls on runoff magnitude and solution chemistry of urban catchments in the semiarid southwestern United States

Urban expansion and the scarcity of water supplies in arid and semiarid regions have increased the importance of urban runoff to localized water resources. However, urban catchment responses to precipitation are poorly understood in semiarid regions where intense rainfall often results in large runoff events during the short summer monsoon season. To evaluate how urban runoff quantity and quality respond to rainfall magnitude and timing, we collected stream stage data and runoff samples throughout the 2007 and 2008 summer monsoons from four ephemeral drainages in Tucson, Arizona. Antecedent rainfall explained 20% to 30% of discharge (mm) and runoff ratio in the least impervious (22%) catchment but was not statistically related to hydrologic responses at more impervious sites. Regression models indicated that rainfall depth, imperviousness and their combined effect control discharge and runoff ratios (p < 0.01, r² = 0.91 and 0.75, respectively). In contrast, runoff quality did not vary with imperviousness or catchment size. Rainfall depth and duration, time since antecedent rainfall and event and cumulative discharge controlled runoff hydrochemistry and resulted in five specific solute response patterns: (i) strong event and seasonal solute mobilization (solute flush), (ii) event chemostasis and strong seasonal flush, (iii) event chemostasis and weak seasonal flush, (iv) event and seasonal chemostasis and (v) late seasonal flush. Our results indicate that hydrologic responses of semiarid catchments are controlled by rainfall partitioning at the event scale, whereas wetting magnitude, frequency and timing alter solute stores readily available for transport and control temporal runoff quality. Copyright © 2012 John Wiley & Sons, Ltd.     

Climate and economic competitiveness: Florida freezes and the global citrus processing industry

Summary Casual observers of the impacts associated with four recent freezes in Florida's citrus producing areas might be inclined to agree with an assessment by Miami Herald reporters that these freezes had caused the king of citrus to be toppled from its throne, enabling Brazil to take its place. Research on the citrus industry, however, reveals that the impacts of these recent freezes only explain part of the story of the interaction between climate variability and the relationship between the citrus industries of Florida and Brazil. Climate characteristics and their variability have directly as well as indirectly affected the economic competitiveness of citrus producers whose output is in large measure climate-dependent. Climate variability has had direct impacts on Florida's citrus industry by adversely affecting the productivity of citrus groves in some areas, by altering growers' perceptions of freeze probabilities and, occasionally, by suddenly reducing output, thus elevating the price that consumers must pay for that commodity. Indirectly, competition can be affected by climate as a potential producer identifies a weakness in the supply system of an existing industry and seeks to fill the gap.Brazil's involvement in the toppling of King Citrus began not in the early 1980s (as a result of the four freezes in the past six years), but in 1962 as a result of a major freeze in that year, one that sharply increased FCOJ prices by reducing Florida's output. It was then that the climate had an impact on the economic competitiveness of the citrus industry. The records document the steady, almost meteoric, rise in Brazilian FCOJ production and exports. Subsequent freezes only served to abet a process that had been well underway two decades before the recent devastating freezes.As for Florida's ability to continue and perhaps expand its key role in the global citrus economy, the recent freezes do not appear to have fatally damaged that. Rather, those freezes have reawakened Florida's citrus producers to the fact that they are involved in a climate-sensitive industry and have reminded them that the potential for freeze-related problems is never far away. That reawakening has sparked interest in developing hardier citrus varieties, more effective freeze protection methods, and better ways to hedge economically against freeze impacts to the industry.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Use of GIS in Optimizing Timber Thinning Strategies in the Eastern Sierra Nevada*

This paper demonstrates the use of a Geographic Information System (GIS) to develop timber thinning strategies on the Kyburz Planning Area of the Tahoe National Forest in northeastern California. The primary criteria used in an assessment of selective thinning potential were forest health and fire hazard ratings. By eliminating environmentally sensitive, economically unfeasible, or low fire hazard areas from consideration, the use of GIS reduced the area that was considered appropriate for thinning by approximately 58%. GIS offers considerable potential for improving resource management strategies.     

A method for quantitatively analysing dynamic recrystallization in deformed quartzitic rocks

Quantification of the microstructural changes brought about by dynamic recrystallization is essential for the interpretation of deformation mechanism histories and for the understanding of recrystallization as a syn-kinematic process. A method is presented for analysing the degree of dynamic recrystallization and for reconstructing the original grain-size distribution from that measured in the deformed specimen. This is based on size distribution measurements and comparative volume calculations between subsets of grains which contain rutile inclusions and subsets which do not. Application of the method to some quartzites from the Kilmory Bay Syncline, S. W. Highlands, Scotland, demonstrates that up to 25% of the apparent matrix grains are new grains produced by the dynamic recrystallization of porphyroclasts, and that the new grains alone compose more than 12% of the total rock volume. These figures are 2–3 times larger than estimates made by normal petrographic inspection. It is also shown that grain-size distributions alone convey little information about the microstructural changes and that grain-size vs volume fraction graphs are more meaningful.     

Long-term erosion on granitic roadcuts based on exposed tree roots

Exposed roots were used to estimate soil and bedrock erosion on the cut slopes of a 45-year-old road constructed in granitic soils of the Idaho Batholith. The original roadcut surface was defined by projecting a straight line from the toe of the cut past the end of the exposed root to the intersection of a straight line projected along the surface of the hillslope. A cross-sectioning technique was then used to determine erosion to the present roadcut surface. A total of 41 exposed root sites were used to estimate erosion on a 1350 m-long section of road. Average erosion was 1·0 and 1·1 cm/year for soil and bedrock respectively. Buttressing by tree roots caused lower erosion rates for soil as compared to bedrock. Both soil and bedrock erosion rates showed statistically significant correlations with the gradients of the original cut slope. The bedrock erosion data provide a reasonable estimate of the disintegration rate of exposed granitic bedrock exhibiting the weathering and fracturing properties common to this area. The road is located in a study watershed where long-term sediment yield data are available. Sediment data from adjacent study watersheds with no roads were compared to sediment data from the roaded watershed to estimate the long-term increase in sediment yield caused by the road. The increase amounts to about 2·4 m³/year. This figure, compared to the average annual on-site road erosion, provides an erosion to sediment delivery ratio of less than 10 per cent. Based on study results, road construction and maintenance practices are suggested for helping reduce roadcut erosion.     

Cosmogenic nuclide measurements in southernmost South America and implications for landscape change

We measured in situ ¹⁰Be, ²⁶Al and³⁶Cl on glacial deposits as old as 1.1 Myr in the southernmost part of Patagonia and on northern Tierra del Fuego to understand boulder and moraine and, by inference, landscape changes. Nuclide concentrations indicate that surface boulders have been exposed for far less time than the ages of moraines they sit upon. The moraine ages are themselves constrained by previously obtained ⁴⁰Ar/³⁹Ar ages on interbedded lava flows or U-series and amino acid measurements on related (non-glacial) marine deposits. We suggest that a combination of boulder erosion and their exhumation from the moraine matrix could cause the erratics to have a large age variance and often short exposure histories, despite the fact that some moraine landforms are demonstrably 1 Myr old. We hypothesize that fast or episodic rates of landscape change occurred during glacial times or near the sea during interglacials. Comparison with boulder erosion rates and exhumation histories derived for the middle latitudes of semi-arid Patagonia imply different geomorphic processes operating in southernmost South America. We infer a faster rate of landscape degradation towards the higher latitudes where conditions have been colder and wetter.     

Compaction localization in the Earth and the laboratory: state of the research and research directions

Localized compaction in porous rocks is a recently recognized phenomenon that has been shown to reduce permeability dramatically. Consequently, the phenomenon is relevant to a variety of technologies involving fluid injection or withdrawal. This article summarizes current understanding of localized compaction and impediments to further progress. The article is based on discussions at a small workshop on localized compaction sponsored by the Office of Science, U. S. Department of Energy.     

Temporal Zooming

Spatio-temporal knowledge representation often requires changing from one level of detail or granularity to another so users can carry out a desired task. Meteorological occurrences, geological processes, or population movements, for example, can be examined at different granularities. This includes different spatial perspectives as well as temporal views where phenomena may be examined under real time conditions, or over hourly, daily, weekly, or longer periods. Moving back and forth among granularities is a necessary routine for many domain scientists. Changing to a more detailed view uncovers information that otherwise is unknown. Conversely, moving to a simpler view can improve our understanding of phenomena. Although people routinely abstract information from their environment at different granularities and perform mental shifts that increase or decrease detail, formalization of these alterations for use in information systems has proved difficult. Geographic information systems typically treat changes in granularity from the perspective of changes to the geometric properties of objects through graphic zooming. None of the current approaches to zooming offer support for performing this operation over time. This work focuses on the temporal aspects of changing granularity or temporal zooming . The approach is based on a model of change to identifiable objects. In this paper, temporal zooming involves expanding or collapsing the transitions among identity states of the same object as well as revealing or omitting other objects that are linked through transitions. A set of operations to support refining and coarsening the evolution of objects over time is presented. This work offers a new perspective on zooming important for spatio-temporal query languages and for users of large spatio-temporal databases who require the means to shift back and forth among simpler or summarized views of data and more detailed views.