Showing papers in "Physical Geography in 1993"
TL;DR: In this paper, a more accurate ten-year sediment budget for Nahal Yael catchment in the Southern Negev Desert was derived, and the authors concluded that the main source of potential errors in sediment budgets, especially in those involving considerable amounts of bed material, lies not so much in the volumetric before-after comparisons, based on surveying.
Abstract: The method used to derive a crude ten-year sediment budget for Nahal Yael—a small hyper-arid catchment in the Southern Negev Desert—is applied to a later ten-year period, for which a much more accurate sediment budget is available. Results indicate that the budget of the first decade has overestimated the suspended sediment output by a factor of four, and underestimated the bed material output by a factor of two. Evaluated against the background of similar sediment budget studies, it is concluded that the main source of potential errors in sediment budgets, especially in those involving considerable amounts of bed material, lies not so much in the volumetric before-after comparisons, based on surveying. Rather, errors are caused mainly by the inadequate procedures presently available for the estimation of sediment input into, and output from, the studied reach.
76 citations
TL;DR: The distributed sediment budget model as discussed by the authors describes the complex sediment storage fluxes of three basin zones (tributaries, upper main valley and lower main valley) in the Paleozoic Plateau of the Midwest and is therefore useful for purposes of watershed management.
Abstract: The distributed sediment budget model describes the complex sediment storage fluxes of three basin zones—tributaries, upper main valley and lower main valley—in the Paleozoic Plateau of the Midwest and is therefore useful for purposes of watershed management, especially for sediment-yield control. Tributary zones, an important sediment source of the past, are increasingly stable and now are often minor sediment sinks. They require little additional management. The upper main valley is the most problematic zone because high banks of historical sediment are being eroded, increasing downstream sediment yield. A variety of management alternatives are available, but all have some negative consequences. Simply permitting this zone to evolve naturally will eventually reduce both sediment loss and flooding in the reach, but this process will require several decades. Although upland erosion has been curtailed, the lower main valley continues to aggrade, causing backswamp areas to increase and local groundwater to ...
71 citations
TL;DR: In this paper, the authors estimate pre-and post-colonial sediment production, transport, and storage in the lower Neuse River basin on the North Carolina Coastal Plain, and show that sediment loads have risen dramatically following colonial-era land clearing.
Abstract: Several lines of evidence are used to estimate pre-and post-colonial sediment production, transport, and storage in the lower Neuse River basin on the North Carolina Coastal Plain. Soil profile truncation indicates upland erosion rates of >9.5t/ha/yr during the post-European period, while pre-colonial rates were negligible. Comparisons of sediment yields between streams in forested and agricultural basins suggest that stream sediment loads have risen dramatically following colonial-era land clearing. Pedological indicators of sediment sources in contemporary and pre-Holocene alluvial soils show a change in dominant sediment source from an important upper-basin Piedmont contribution to a situation where Piedmont sediment is overwhelmed by Coastal Plain sources. Finally, most of the increased sediment input to the lower Neuse River and its tributaries has apparently been stored as alluvium. This is indicated by limited siltation of the Neuse estuary and limited pedogenic development on floodplains and strea...
64 citations
TL;DR: In this paper, the role of downstream conveyance losses associated with channel and floodplain storage in the suspended sediment budget of the 6850 km2 basin of the River Severn above Upton on Severn was investigated.
Abstract: The sediment budget concept offers a valuable tool for interpreting the processes of erosion and sediment yield operating in a drainage basin. However, it is often difficult to assemble the information necessary to establish a reliable sediment budget. Fallout radionuclides offer considerable potential for this purpose. This contribution describes how measurements of the fate of Chernobyl-derived 134Cs have been used to investigate the role of downstream conveyance losses associated with channel and floodplain storage in the suspended sediment budget of the 6850 km2 basin of the River Severn above Upton on Severn. The results relate to a 3-year period, 1986–1989, and indicate that conveyance losses associated with floodplain and channel storage respectively accounted for 23% and 2% of the total suspended sediment load passing through the main channel system. [Key words: sediment budget, floodplain storage, channel storage, suspended sediment, radionuclides, cesium-134, Chernobyl.]
53 citations
TL;DR: In this paper, a model based on vertical clay distribution and textural differentiation is introduced to account for the major factors that lead to differentiation of soil series in the study area, and the model is unstable and potentially chaotic and predicts that even where all other soil-forming factors are similar, the diversity and spatial vari...
Abstract: Nonlinear dynamical systems (NDS) models of soil systems suggest that soil evolution may be potentially chaotic, and thus sensitive to initial conditions and to small perturbations. Chaos implies that the diversity of the soil cover should increase over time. This hypothesis was tested by comparing the diversity of soil types on either side of the Suffolk Scarp on the lower coastal plain of North Carolina. While parent material and other soil-forming factors at the two sites are similar, the Pamlico Terrace east of the scarp is late Pleistocene and the Talbot Terrace west of the scarp is middle to late Pleistocene and at least twice as old. A soil system model based on vertical clay distribution and textural differentiation is introduced to account for the major factors that lead to differentiation of soil series in the study area. The model is unstable and potentially chaotic and, like more general models, predicts that even where all other soil-forming factors are similar, the diversity and spatial vari...
44 citations
TL;DR: In this paper, the authors examined temporal trends in the spatial variability of soil color, cementation, horizon thickness and development with time and found that soil development increased with time, but spatial variability in degree of development also increased.
Abstract: Twenty-four soil pedons on each of four sandy lake terraces in northwestern lower Michigan that ranged in age from 3000 to 11,000 years BP were studied to assess trends in soil morphological variability with time. After verifying the general uniformity of parent materials within and between the four surfaces, we examined temporal trends in the spatial variability of soil color, cementation, horizon thickness and development. E horizons attained high color values (lightness) by 3000 years and changed little after that time, whereas B horizons continued to get darker with time. Cementation within B horizons increased in strength and amount with time, as did B horizon thickness. Soils ≥4000 years old had deeper eluvial zones but much greater variabilities in the thickness of that zone than did younger soils. Soil development increased with time, but spatial variability in degree of development also increased with time. These patterns are best explained by invoking spatially random soil mixing upon a surface ...
44 citations
TL;DR: The sediment and solute budget of the Lillooet River basin in British Columbia (3,150 km2) has been investigated in this article, and the role and status of the components of the sediment budget are examined.
Abstract: The sediment and solute budget of the Lillooet River basin in British Columbia (3,150 km2) is developed to exemplify a methodology that has the potential to unify geomorphological research. Sediment and solute transport processes in Holocene time are identified and quantified. The budget is demonstrated to be severely unbalanced. Historical events and transient response to those events are implicated. A minimum of four time scales of integration—geological, Pleistocene, Holocene and contemporary—are proposed, and the role and status of the components of the sediment budget are examined. Storage sites and solute sinks, linkages among sediment and solute transport processes, the role of biotic factors, weathering, stratigraphic evidence, and the hydrologic balance are individually reviewed. Spatial scale considerations provide a way of interpreting and aggregating the above complex factors. In general, there appears to be no spatial scale at which sediment and solute supply from the slopes is in balance wit...
38 citations
TL;DR: In this article, a measure of blowing dust amounts on a regional scale is derived from meteorological data for Lubbock, Texas, based on visibility records and wind speeds during blowing dust events.
Abstract: Blowing dust is commonly studied in terms of climatic conditions that affect the amount of erosion A new measure of blowing dust amounts on a regional scale is derived from meteorological data for Lubbock, Texas, based on visibility records and wind speeds during blowing dust events Regression analysis suggests that the fraction of time of potential erosion (based on wind speed) and the Palmer Drought Severity Index (an index of regional soil moisture) are poor predictors of blowing dust amounts Changing agricultural management techniques may account for much of the variability of blowing dust in the region [Key words: blowing dust, drought, wind erosion, Southern High Plains]
35 citations
TL;DR: A radiocarbon age of 12,960 ± 350 yr B.P. from sediments immediately proximal to the northwestern part of the Inner Port Huron moraine in Michigan's Southern Peninsula was reported in this article.
Abstract: Until now, radiocarbon age estimates of the Port Huron moraine in Michigan have been based largely on 14C dates from beyond the state. This study reports a radiocarbon age of 12,960 ± 350 yr B.P. from sediments immediately proximal to the northwestern part of the Inner Port Huron moraine in Michigan's Southern Peninsula. Geologic relationships indicate that this section of the moraine predates the age estimate. Stratigraphic and morphologic relationships of sediments of ancestral Great Lakes phases related to the Port Huron morainic system, 14C ages from sediments of those lake phases, and a 14C age from wood buried by till of the Wyoming moraine (a morphostratigraphic equivalent of the Port Huron moraine), have collectively supported the interpretation that the morainic system was formed between 13,500 and 12,700 yr B.P. Our radiocarbon age estimate, the first from sediments immediately proximal to the Port Huron system in Michigan, is compatible with this interpretation. Furthermore, because the Port Hu...
29 citations
TL;DR: In this article, a model requiring only five parameters is developed by combining the principles of order statistics and traditional flow-frequency analyses and is applied to flow-duration curves for rivers in the province of British Columbia, Canada.
Abstract: The estimation of flow quantiles and the regionalization of hydrologic characteristics are two major foci of current hydrologic research. A flow-duration curve represents the annual flow-frequency characteristics of rivers by depicting the cumulative frequencies for average ranked flows in a river. Generally the process requires the empirical estimation of the mean flow at each of 365 ranks. A model requiring only five parameters is developed by combining the principles of order statistics and traditional flow-frequency analyses and is applied to flow-duration curves for rivers in the province of British Columbia, Canada. Results from the model may be interpreted both statistically and physically and allow the identification of hydrologically similar regions. Streamflows in British Columbia are generated from a number of distinct physical processes operating in highly diverse environments. The mixture of the streamflow-generating processes requires that the statistical model be capable of encompassing the...
27 citations
TL;DR: The incorporation of some dead micro-colonials into developing rock coatings is therefore unlikely to lead to anomalously high calcium levels for cation ratio dating as discussed by the authors, with amounts present in dead organisms being relatively low.
Abstract: Microcolonial fungi are found on rock coatings at various sites throughout the arid regions of Australia. Fungi tend to concentrate in depressions, although it is uncertain whether they contribute to enlargement of microhollows. As determined by SEM-EDAX, the chemical characteristics of microcolonial fungi are variable but do not reflect those of the surfaces on which they are found. Most fungi contain calcium, sulfur, chlorine and sometimes phosphorus, but not manganese, in quantities greater than those of adjacent rock coatings. Major sources for accumulated elements may be rainfall or dust. Some elements, especially calcium, are apparently concentrated temporarily in microcolonial fungi, with amounts present in dead organisms being relatively low. The incorporation of some dead microcolonial fungi into developing rock coatings is therefore unlikely to lead to anomalously high calcium levels for cation ratio dating. As rock coatings contain trace or undetectable amounts of some other elements concentrat...
TL;DR: In this paper, a post-settlement erosion on the North Carolina Coastal Plain was estimated at the regional scale based on soil-profile truncation of a representative upland soil (Norfolk series).
Abstract: The Atlantic Coastal Plain of the United States has long been considered to have negligible soil erosion owing to low relief and permeable soils. Several recent studies point to a need for reassessment. Post-settlement erosion on the North Carolina Coastal Plain was estimated at the regional scale based on soil-profile truncation of a representative upland soil (Norfolk series). Apparent post-settlement soil-profile truncation ranges from 2.5 to 30 cm (mean 14.5 cm), implying a minimum regional average rate of 0.55 mm/yr since the region was settled in the 1700s. This amounts to a conservative estimated average rate of 9.3 t/ha/yr, a rate of the same general magnitude as estimated erosion rates in the North Carolina Piedmont, long recognized as a problem erosion area. Results imply accelerated water erosion despite the low slopes and permeable soils, and suggest the possibility of significant eolian erosion in the region. This rapid erosion in an area noted for its geological stability is a testament to t...
TL;DR: In this article, the authors show that degradation in the upstream reach produced a number of inset terraces, while the production of sediment in the degrading reach simultaneously caused further aggradation downstream.
Abstract: Terrace remnants are commonly used to reconstruct longitudinal profiles of rivers and floodplains, and to establish temporal correlations of events in fluvial systems. In most cases, it is assumed that the terrace remnants represent time-equivalent surfaces. Our observations of terrace formation in flume experiments and in a degrading braided river, Ash Creek, Arizona, suggest that this assumption is not always valid. Degradation resulted from a reduction in upstream sediment delivery to braided channels. In both the flume and Ash Creek, degradation in the upstream reach produced a number of inset terraces, while the production of sediment in the degrading reach simultaneously caused further aggradation downstream. Thus, stratigraphically lower surfaces in the upstream reaches are temporally equivalent to higher surfaces in downstream reaches. The downstream progression of the wave of incision produced more terraces upstream than downstream, and terrace surfaces could not be correlated on the basis of rel...
TL;DR: In this paper, the authors examined the yearly onset of the spring green wave and associated phenomena from 1908 to 1987 using phenological models, and analyzed regional dynamics and recent changes in the major agricultural regions of eastern North America.
Abstract: This study is part of a program to examine spring plant-climate interactions in the major agricultural regions of eastern North America. The project's objectives were to: (1) document the yearly onset of the spring green wave and associated phenomena from 1908 to 1987 using phenological models, and (2) analyze regional dynamics and recent changes. Examining past variations in the green wave provides a context within which present and future variations can be assessed. Spring index dates, last -2.2°C (28°F) frost dates, and the difference between these two dates (termed the damage index) were generated for selected United States Daily Historical Climatology Network (HCN) stations between 1908 and 1987. The results show considerable geographic and temporal variations over the study period, and suggest that the threat of late spring frost damage may have decreased slightly from about 1960 to 1987. In future research, an improved version of the spring index (and associated surface phenological data) will be c...
TL;DR: The effects of climatic variability on the time distribution of runoff and the timing and magnitude of maximum flow events during the winter-spring season of December-April were examined through statistical analysis of hydrologic and climatic data for thirteen river basins in Vermont, New Hampshire, and Massachusetts as discussed by the authors.
Abstract: The effects of climatic variability on the time distribution of runoff and the timing and magnitude of maximum-flow events during the winter-spring season of December-April were examined through statistical analysis of hydrologic and climatic data for thirteen river basins in Vermont, New Hampshire, and Massachusetts. Within each basin, higher temperatures and lower snowfall result in a more uniform distribution of flow throughout the season. This relationship is also observed across the region's average spatial temperature gradient. In the extreme south of the region, runoff is uniformly distributed throughout the season, while in the extreme north, runoff is more concentrated in the latter part of the season. On average, maximum flows occur earlier in basins with higher average temperature—approximately 5.4 days earlier for each 1° C—but only within basins in the extreme north of the region is there a significant relationship between temperature and the time of occurrence of the maximum daily flow. Maxi...
TL;DR: In this paper, six experimentally derived formulae that predict the conditions for alternate bar formation and equilibrium bar dimensions are assessed using field data using an artificially straightened section of the Embarras River located approximately 16 km south of Champaign, Illinois.
Abstract: Six experimentally derived formulae that predict the conditions for alternate bar formation and equilibrium bar dimensions are assessed using field data. The study site is an artificially straightened section of the Embarras River located approximately 16 km south of Champaign, Illinois. Data were collected on channel form, gradient, alternate bar dimensions, bar sediment size, and flow conditions over a two-year study period. Experimental flume studies suggest that alternate bars form in wide, straight, shallow streams, have wavelengths between 4 and 15 channel widths, and have heights that are roughly equal to the average depth of flow. Bar formation under unsteady flow conditions can be predicted accurately by the experimentally derived steady-flow formulae, but these formulae fail to predict bar dimensions sucessfully. These results suggest that the process of bar formation in artificially straightened, sand-bedded natural streams may occur outside the range of flow conditions predicted by existing em...
TL;DR: In this paper, soil moisture was measured over a four-month period at 31 sample points on a 1 ha clear-cut site on southern Vancouver Island, and the data were used to determine spatial and temporal variations in soil moisture, and to infer the most likely mechanism(s) of soil-water movement vertically through the soil profiles and laterally across the site.
Abstract: Soil moisture was measured over a four-month period at 31 sample points on a 1 ha clear-cut site on southern Vancouver Island. At each sample point measurements were collected at 10-cm intervals to the base of the soil profile. The data were used to determine spatial and temporal variations in soil moisture, and to infer the most likely mechanism(s) of soil-water movement vertically through the soil profiles and laterally across the site. All soils showed an increase in moisture content through the monitoring period. There was no strong tendency for moisture content to increase downslope along the topographic gradient. All soils exhibited an increase in soil moisture at depths of 20–30 cm, followed by a decline. This zone of increased soil moisture was correlated with the main root zone, and not with any textural contrasts. Topographic and textural influences on moisture movement through the soil matrix appear to be of minor importance. Moisture appears to follow paths dictated by root systems, which do n...
TL;DR: Paleochannel evidence from both Adrian and Mason valleys, hydrological modeling, and Pleistocene shoreline evidence in the Walker Lake Basin indicate that the Adrian Valley is a Holocene abandoned channel of the Walker River as discussed by the authors.
Abstract: The Lahontan Basin of western Nevada was influenced by geomorphic changes in river channels that produced interbasin diversions of surface drainage. Adrian Valley contains evidence of drainage diversion from the Walker River Basin to the Carson River Basin. Paleochannel evidence from both Adrian and Mason Valley, hydrological modeling, and Pleistocene shoreline evidence in the Walker Lake Basin indicate that: (1) the Adrian Valley is a Holocene abandoned channel of the Walker River, and (2) the valley was formed by lake overflow from the Walker subbasin of Pleistocene Lake Lahontan. A provisional six-stage history of Adrian Valley is presented. [Key words: geomorphology, Quaternary, Pleistocene Lake Lahontan, abandoned river channels, Great Basin.]
TL;DR: In this paper, the structure and composition of woody trees and shrubs along a cutbank forest edge in an Iowa floodplain was quantified and compared to floodplain interior sites, edge sites exhibit higher stem and sapling densities.
Abstract: Actively meandering rivers advance into mature floodplain vegetation, resulting in the continual creation and destruction of cutbank edges across a floodplain with successive channel advancements. To examine specific changes in vegetation initiated by the lateral migration of a river channel, we quantify the structure and composition of woody trees and shrubs along a cutbank forest edge in an Iowa floodplain. When compared to floodplain interior sites, edge sites are more diverse and exhibit higher stem and sapling densities. These patterns are similar to contrasts between edge and interior sites observed in previous studies of upland habitats. Total basal area, however, is statistically equivalent in floodplain edge and interior sites, in contrast to results from studies of stable upland edges. Variability among all measures is greater along the riparian edge. We attribute the relatively small basal area and high variability to disequilibrium conditions caused by cutbank erosional processes along the rip...
TL;DR: In this paper, detailed population data were gathered for 106 1 m2 quadrats on two point bars on the Cedar River, Iowa, in the year following a major establishment event when a brief steady river stage coincided with the dispersal period for common riparian pioneer species (Salix interior, S. nigra, Populus deltoides) during a drought year.
Abstract: Vegetation on point bars must be adapted to changing hydrological and geomorphological conditions. Detailed population data are gathered for 106 1 m2 quadrats on two point bars on the Cedar River, Iowa, in the year following a major establishment event when a brief steady river stage coincided with the dispersal period for common riparian pioneer species (Salix interior, S. nigra, Populus deltoides) during a drought year. Significant differences were found in the location of seedlings and different forms of sprouts on a gradient of elevation. Most seedlings, mostly Salix interior, established in a very narrow range that produced a band along the edge of the river. While density in this band is in part related to sediment texture, it is clear that the densities found (e.g., > 500 m-2) must result from dispersal by water to the strand line. [Key words: establishment, point bar, riparian, Salix, seedling.]
TL;DR: A detailed analysis of weathering-pit distribution on Georgia's Stone Mountain granite dome reveals a complex relationship between pit size and density, compared with slope aspect and angle as mentioned in this paper, and shows a dimensional and density increase toward a southwestern aspect as well as an increase with decreasing slope angle.
Abstract: A detailed analysis of weathering-pit distribution on Georgia's Stone Mountain granite dome reveals a complex relationship between pit size and density, compared with slope aspect and angle. The uniform nature of the lithology provides an ideal natural laboratory for the analysis of weathering pits. Through the random establishment of 32 dome-encircling, ten-by-ten meter study plots within an elevational range from 610 to 650 meters, the distribution, size, aspect, slope and lithology of pit features were mapped, measured, and analyzed. Thematic maps were used in the visual representation of pit distribution and dimension data. Correlation coefficients, ANOVA, and multiple regression analyses were utilized to determine the relationships of these variables. Pits showed a dimensional and density increase toward a southwestern aspect as well as a dimensional and density increase with decreasing slope angle. Greatest pit dimensions were found at approximately the 200° N azimuth. These findings lead the author...
TL;DR: In this article, the authors document the spatial and temporal characteristics of northeast United States tornadoes and the synoptic patterns associated with their development and identify three preferred areas of tornadic development across the northeast region.
Abstract: This study documents the spatial and temporal characteristics of northeast United States tornadoes and the synoptic patterns associated with their development. Daily 1200 UTC surface pressure, 500 mb height and 850 mb temperature data are used in a compositing analysis to indicate the general conditions on tornado-producing days during four quasi-seasonal periods. Temporally, two-thirds of all northeast tornadoes occur between the hours of 1800 UTC and 0000 UTC. Annually, greater than 75% occur during the four-month period from May through August. During the period of study (1950 through 1986) the region had an average of 30 tornado occurrences per year. Spatially, three preferred areas of tornadic development are identified across the northeast region. These areas include western and southeastern Pennsylvania and north-central Massachusetts. The general synoptic patterns associated with tornadic events in the northeast United States remain consistent throughout the year. The composite analyses indicate t...
TL;DR: In this article, the influence of climate associated with El Nino/Southern Oscillation (ENSO) events on tree growth in the central Colorado Front Range is investigated through the analysis of two high altitude tree-ring chronologies.
Abstract: The influence of climate associated with El Nino/Southern Oscillation (ENSO) events on tree growth in the central Colorado Front Range is investigated through the analysis of two high altitude tree-ring chronologies. Dendrochronological techniques are used to determine if ENSO-related climatic effects are detectable in tree-ring width patterns in the central Colorado Front Range. The form of the tree-growth response is identified and the variability of the influence of these events on tree growth over time is investigated. Results indicate that tree growth in this area does respond to ENSO events, but the response varies with species and type of event. El Nino-influenced climate tends to result in larger tree rings the year of or year following the event, while La Nina-influenced climate tends to result in smaller rings the year after the event, reflecting spring moisture conditions. Trees have a more consistent response to La Nina events, but El Nino events seem to have a greater effect on extremes in gr...
TL;DR: The largest drift repository in the Great Lakes Area is the Southern Peninsula of Michigan as discussed by the authors, which contains about 35% more drift than the better known Kettle Moraine tract of Wisconsin, which encompasses 50% more area.
Abstract: Michigan's Southern Peninsula is by far the largest drift repository in the Great Lakes Area. Thickness of the glacial sediments averages 85 m and volume, previously unknown, exceeds 9300 km3. The distribution, however, is very uneven, as is the underlying bedrock surface. These variations and known surface characteristics provide a basis for the first qualitative and quantitative identification of distinct drift realms. Even the smallest of the eight realms contains about 35% more drift than the better known Kettle Moraine tract of Wisconsin, which encompasses 50% more area. Comparative analysis within the peninsula shows that Pleistocene glaciation completely transformed the topography to the north, whereas the southern half has palimpsest relationships with subcropping formations. [Key words: drift, drift volume, Michigan, Great Lakes, Pleistocene.]
TL;DR: In this paper, the Upper Fremont Glacier in the Wind River Range of Wyoming was investigated during 1990-1991, and the difference between radio-echo sounding depth and measured drilling depth was about 4 m.
Abstract: Glaciological investigations of the Upper Fremont Glacier in the Wind River Range of Wyoming were conducted during 1990–1991. The glaciological data will provide baseline information for monitoring future changes to the glacier and support ongoing research utilizing glacial-ice-core composition to reconstruct paleoenvironmental records. Ice thickness, determined by radio-echo sounding, ranged from 60 to 172 m in the upper half of the glacier. Radio-echo sounding of ice thickness at one point was confirmed by drilling 159.7 m to bedrock. The difference between radio-echo sounding depth and measured drilling depth was about 4 m. Annual ablation (including snow, firn, and ice) measured for the 1990–1991 period averaged about 0.93 m/a. Densification proceeds rapidly on Upper Fremont Glacier. Measured densities in the near-surface parts of the glacier ranged from 4.4 x 105 g/m3 at the surface to larger than 8.5 x 105 g/m3 at depths exceeding 14 m. Surface ice velocity and direction were monitored from July 199...
TL;DR: In this paper, a numerical model is developed for simulating the nocturnal cooling of the ground and walls in typical urban canyons, which is capable of dealing with homogeneous as well as inhomogeneous (layered) soil and wall substrates.
Abstract: A numerical model is developed for simulating the nocturnal cooling of the ground and walls in typical urban canyons. The model is capable of dealing with homogeneous as well as inhomogeneous (layered) soil and wall substrates. Experiments carried out with the model show that the difference in the thermal properties of urban asphalt and concrete pavements and the rural dry soil substrate could create urban/rural surface temperature differences of up to 4–5K. In narrow cross-section canyons, the influence of geometry on the street microclimate increases and becomes dominant for aspect ratios exceeding 2. The external surfaces of insulated canyon walls cool drastically overnight and therefore induce lower heat island intensities than conventional wall constructions. Some findings of the numerical investigations are corroborated with available nocturnal cooling field observations.
TL;DR: In this article, a preliminary effort toward developing a sediment budget for the primarily agricultural 3,531 km2 upper and middle drainage basin of the Rio Paute in Andean Ecuador focuses on the geographic locations of potential upland nonpoint sediment sources and compares upland soil erosion estimates based on the Universal Soil Loss Equation (USLE) with others extrapolated from rainfall simulation experiments.
Abstract: This preliminary effort toward developing a sediment budget for the primarily agricultural 3,531 km2 upper and middle drainage basin of the Rio Paute in Andean Ecuador focuses on the geographic locations of potential upland nonpoint sediment sources and compares upland soil erosion estimates based on the Universal Soil Loss Equation (USLE) with others extrapolated from rainfall simulation experiments. Although the USLE-based erosion estimates are consistently higher, spatial patterns of high and low erosion rate classes for the two approaches are relatively similar, differing primarily in urban areas and in peripheral high elevation zones. Relating sediment yield data to the upland erosion rates suggests that 17 to 41 percent of the eroded material leaves the basin annually. [Key words: geomorphology, sediment budget, soil erosion, GIS, Ecuador.]
TL;DR: In this article, the relationship between tropospheric teleconnections and Florida citrus freezes was examined using 70 kPa heights and sea-level pressure data from 1949 to 1987, and the mean RPCA scores were obtained during five-day periods when polar high pressure cells migrated toward the southern United States.
Abstract: The relationship between tropospheric teleconnections and Florida citrus freezes is examined using 70 kPa heights and sea-level pressure data from 1949 to 1987. Rotated principal component analysis (RPCA) is used in determining the main patterns of five-day averaged pressure and height variability. The mean RPCA scores are obtained during five-day periods when polar high pressure cells migrate toward the southern United States. Three upper air teleconnections, including the Pacific/North American pattern, and one sea-level pressure pattern have significantly large mean scores when they are averaged over the time periods when cold outbreaks and citrus freezes occur in the South. Plots of the tracks of all strong anticyclones that move southward over North America during the extreme phases of the teleconnections provide further indication that the highs moving in conjunction with the pronounced ridge/trough configuration of the Pacific/North American pattern are especially likely to reach the southern Unite...
TL;DR: In this paper, the spatial variability in the frequency and duration of hours and days when temperatures were ≥ 32°C (high-heat) was analyzed from 13 first-order National Weather Service stations in the southeastern United States.
Abstract: Forty-one years of data from 13 first-order National Weather Service stations in the southeastern United States were analyzed to determine the spatial variability in the frequency and duration of hours and days when temperatures were ≥32° C (high-heat). Spatial analysis indicated that extreme high temperature characteristics from individual stations should not be combined into a regional or statewide average. For determining high-heat scenarios, May through September (summer) average maximum temperature (Tmax) was found to be a more appropriate indicator of high-heat conditions than the average temperature (Tmean). Comparing conditions in average warm and cool summer seasons indicated that: (1) increases in the frequency and duration of high-heat hours and days from cool to warm summer seasons range from 70 to 997%; (2) the number of high-heat hours per day increases significantly (27 to 118%) from cool to warm summer seasons; (3) increases in Tmax from cool to warm summer seasons are greater than increas...
TL;DR: In this paper, the Tekonsha Moraine is interpreted as a hummocky and pitted (collapsed) outwash plain/kame moraine, and it is shown that the moraine is more common than heretofore recognized.
Abstract: The northwest portion of the Tekonsha Moraine has traditionally been considered to be a product of, and composed of sediments from, the Lake Michigan Lobe. A recent study has also correlated till from the moraine with an exposure (Ganges till) along the shore of Lake Michigan. The results of this paper contradict those interpretations. Multiple lines of evidence—till fabrics, 7-A/10-A peak height ratios of clay minerals, indicator stones, morphology, and elevation relationships—indicate a Saginaw Lobe origin for the till and glaciofluvial sediments. Moreover, aerial photographs reveal the presence of ice-stagnation topography. The moraine is herein reinterpreted as a hummocky and pitted (collapsed) outwash plain/kame moraine. Given that this feature has long been considered a moraine, similar landforms in Michigan and elsewhere may be more common than heretofore recognized. [Key words: glacial geomorphology, Michigan, Quaternary, Tekonsha Moraine.]