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Terms modified by Daily Mean Selected AbstractsEffect of snowpack removal on energy balance, melt and runoff in a small supraglacial catchmentHYDROLOGICAL PROCESSES, Issue 14 2002Ian C. Willis Abstract Modelling melt and runoff from snow- and ice-covered catchments is important for water resource and hazard management and for the scientific study of glacier hydrology, dynamics and hydrochemistry. In this paper, a distributed, physically based model is used to determine the effects of the up-glacier retreat of the snowline on spatial and temporal patterns of melt and water routing across a small (0·11 km2) supraglacial catchment on Haut Glacier d'Arolla, Switzerland. The melt model uses energy-balance theory and accounts for the effects of slope angle, slope aspect and shading on the net radiation fluxes, and the effects of atmospheric stability on the turbulent fluxes. The water routing model uses simplified snow and open-channel hydrology theory and accounts for the delaying effects of vertical and horizontal water flow through snow and across ice. The performance of the melt model is tested against hourly measurements of ablation in the catchment. Calculated and measured ablation rates show a high correlation (r2 = 0·74) but some minor systematic discrepancies in the short term (hours). These probably result from the freezing of surface water at night, the melting of the frozen layer in the morning, and subsurface melting during the afternoon. The performance of the coupled melt/routing model is tested against hourly discharge variations measured in the supraglacial stream at the catchment outlet. Calculated and measured runoff variations show a high correlation (r2 = 0·62). Five periods of anomalously high measured discharge that were not predicted by the model were associated with moulin overflow events. The radiation and turbulent fluxes contribute c. 86% and c. 14% of the total melt energy respectively. These proportions do not change significantly as the surface turns from snow to ice, because increases in the outgoing shortwave radiation flux (owing to lower albedo) happen to be accompanied by decreases in the incoming shortwave radiation flux (owing to lower solar incidence angles) and increases in the turbulent fluxes (owing to higher air temperatures and vapour pressures). Model sensitivity experiments reveal that the net effect of snow pack removal is to increase daily mean discharges by c. 50%, increase daily maximum discharges by >300%, decrease daily minimum discharges by c. 100%, increase daily discharge amplitudes by >1000%, and decrease the lag between peak melt rates and peak discharges from c. 3 h to c. 50 min. These changes have important implications for the development of subglacial drainage systems. Copyright © 2002 John Wiley & Sons, Ltd. [source] Daytime sleepiness during Ramadan intermittent fasting: polysomnographic and quantitative waking EEG studyJOURNAL OF SLEEP RESEARCH, Issue 2 2003Rachida Roky Summary During the lunar month of Ramadan, Muslims abstain from eating, drinking and smoking from sunrise to sunset. We reported previously that Ramadan provokes a shortening in nocturnal total sleep time by 40 min, an increase in sleep latency, and a decrease in slow-wave sleep (SWS) and rapid eye movement (REM) sleep duration during Ramadan. During the same study, the effects of Ramadan intermittent fasting on daytime sleepiness were also investigated in eight healthy young male subjects using a quantitative waking electroencephalograph (EEG) analysis following the multiple sleep latency test (MSLT) procedure. This procedure was combined with subjective alertness and mood ratings and was conducted during four successive experimental sessions: (1) baseline (BL) 15 days before Ramadan, (2) beginning of Ramadan (R11) on the 11th day of Ramadan, (3) end of Ramadan (R25) on the 25th day of Ramadan, (4) recovery 2 weeks after Ramadan (AR). During each session, four 20-min nap opportunities (MSLTs) were given at 10:00, 12:00, 14:00 and 16:00 h and were preceded by rectal temperature readings. Nocturnal sleep was recorded before each daytime session. Subjective daytime alertness did not change in R25 but decreased in R11 at 12:00 h, and subjective mood decreased at 16:00 h, both in R11 and R25. During the MSLT, mean sleep latency decreased by an average of 2 min in R11 (especially at 10:00 and 16:00 h) and 6 min in R25 (especially at 10:00 and 12:00 h) compared with BL. There was an increase in the daily mean of waking EEG absolute power in the theta (5.5,8.5 Hz) frequency band. Significant correlations were found between sleep latency during the MSLT and the waking EEG absolute power of the fast alpha (10.5,12.5 Hz), sigma (11.5,15.5 Hz) and beta (12.5,30 Hz) frequency bands. Sleep latency was also related to rectal temperature. In conclusion, Ramadan diurnal fasting induced an increase in subjective and objective daytime sleepiness associated with changes in diurnal rectal temperature. [source] Hydrologic Modeling of an Extreme Flood in the Guadalupe River in Texas,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2010Hatim O. Sharif Sharif, Hatim O., Almoutaz A. Hassan, Sazzad Bin-Shafique, Hongjie Xie, and Jon Zeitler, 2010. Hydrologic Modeling of an Extreme Flood in the Guadalupe River in Texas. Journal of the American Water Resources Association (JAWRA) 1-11. DOI: 10.1111/j.1752-1688.2010.00459.x Abstract:, Many of the storms creating the greatest rainfall depths in Texas, measured over durations ranging from one minute to 48 hours, have occurred in the Texas Hill Country area. The upstream portion of the Guadalupe River Basin, located in the Texas Hill Country, is susceptible to flooding and rapid runoff due to thin soils, exposed bedrock, and sparse vegetation, in addition to the Balcones Escarpment uplift contributing to precipitation enhancement. In November 2004, a moist air mass from the Gulf of Mexico combined with moist air from the Pacific Ocean resulted in the wettest November in Texas since 1895. Although the peak discharges were not the highest on record, the U.S. Geological Survey (USGS) stream gauge on the Guadalupe River at Gonzales, Texas reported a daily mean discharge of 2,304 m3/s on November 23, 2004 (average discharge is 53 m3/s). In this paper, we examine the meteorological conditions that led to this event and apply a two-dimensional, physically based, distributed-parameter hydrologic model to simulate the response of a portion of the basin during this event. The study results clearly demonstrate the ability of physically based, distributed-parameter simulations, driven by operational radar rainfall products, to adequately model the cumulative effect of two rainfall events and route inflows from three upstream watersheds without the need for significant calibration. [source] MASS LOAD ESTIMATION ERRORS UTILIZING GRAB SAMPLING STRATEGIES IN A KARST WATERSHED,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2003Alex W. Fogle ABSTRACT: Developing a mass load estimation method appropriate for a given stream and constituent is difficult due to inconsistencies in hydrologic and constituent characteristics. The difficulty may be increased in flashy flow conditions such as karst. Many projects undertaken are constrained by budget and manpower and do not have the luxury of sophisticated sampling strategies. The objectives of this study were to: (1) examine two grab sampling strategies with varying sampling intervals and determine the error in mass load estimates, and (2) determine the error that can be expected when a grab sample is collected at a time of day when the diurnal variation is most divergent from the daily mean. Results show grab sampling with continuous flow to be a viable data collection method for estimating mass load in the study watershed. Comparing weekly, biweekly, and monthly grab sampling, monthly sampling produces the best results with this method. However, the time of day the sample is collected is important. Failure to account for diurnal variability when collecting a grab sample may produce unacceptable error in mass load estimates. The best time to collect a sample is when the diurnal cycle is nearest the daily mean. [source] Influences of the vegetation mosaic on riparian and stream environments in a mixed forest-grassland landscape in "Mediterranean" northwestern CaliforniaECOGRAPHY, Issue 4 2005Hartwell H. Welsh We examined differences in riparian and aquatic environments within the three dominant vegetation patch types of the Mattole River watershed, a 789-km2 mixed conifer-deciduous (hardwood) forest and grassland-dominated landscape in northwestern California, USA. Riparian and aquatic environments, and particularly microclimates therein, influence the distributions of many vertebrate species, particularly the physiologically-restricted ectotherms , reptiles and amphibians (herpetofauna), and fishes. In addition to being a significant portion of the native biodiversity of a landscape, the presence and relative numbers of these more tractable small vertebrates can serve as useful metrics of its "ecological health." Our primary objective was to determine the range of available riparian and aquatic microclimatic regimes, and discern how these regimes relate to the dominant vegetations that comprise the landscape mosaic. A second objective, reported in a companion paper, was to examine relationships between available microclimatic regimes and herpetofaunal distributions. Here we examined differences in the composition, structure, and related environmental attributes of the three dominant vegetation types, both adjacent to and within the riparian corridors along 49 tributaries. Using automated dataloggers, we recorded hourly water and air temperatures and relative humidity throughout the summer at a representative subset of streams; providing us with daily means and amplitudes for these variables within riparian environments during the hottest period. Although the three vegetation types that dominate this landscape each had unique structural attributes, the overlap in plant species composition indicates that they represent a seral continuum. None-the-less, we found distinct microclimates in each type. Only riparian within late-seral forests contained summer water temperatures that could support cold-water-adapted species. We evaluated landscape-level variables to determine the best predictors of water temperature as represented by the maximum weekly maximum temperature (MWMT). The best model for predicting MWMT (adj. R2=0.69) consisted of catchment area, aspect, and the proportion of non-forested (grassland) patches. Our model provides a useful tool for management of cold-water fauna (e.g. salmonids, stream amphibians) throughout California's "Mediterranean" climate zone. [source] Sea-level pressure variability in the Po Plain (1765,2000) from homogenized daily secular recordsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2004Maurizio Maugeri Abstract A homogenized 236 year daily regional sea-level pressure (SLP) record is constructed for the Po Plain (north Italy) by means of six station records: Bologna, Genoa, Lugano, Milan, Padua and Turin. Station records are subjected to a first homogenization in order to reduce all observations to sea level and to 0°C and to correct the bias introduced by calculating daily means using different sets of observation hours. A second homogenization is performed by means of comparison with other Italian and European series. After homogenization, the root-mean square error of the yearly station records is evaluated within 0.2 hPa after 1880, whereas for the periods 1834,1880 and 1765,1833 it is estimated as between 0.2 and 0.3 hPa and as around 0.4 hPa respectively. Trend analysis is applied to the annual and seasonal regional records and concerns both SLP and its day-to-day variability. The results show that neither the SLP nor its day-to-day variability have an evident trend when considering the entire 1765,2000 period. However, if the series is divided roughly in two parts, then significant trends can be highlighted. The annual and seasonal regional SLP records are also compared with corresponding regional temperature series. The results show that, especially in spring and in summer, temperature and SLP are in good agreement. Copyright © 2004 Royal Meteorological Society [source] A world-wide study of high altitude treeline temperaturesJOURNAL OF BIOGEOGRAPHY, Issue 5 2004Christian Körner Abstract Aim, At a coarse scale, the treelines of the world's mountains seem to follow a common isotherm, but the evidence for this has been indirect so far. Here we aim at underpinning this with facts. Location, We present the results of a data-logging campaign at 46 treeline sites between 68° N and 42° S. Methods, We measured root-zone temperatures with an hourly resolution over 1,3 years per site between 1996 and 2003. Results, Disregarding taxon-, landuse- or fire-driven tree limits, high altitude climatic treelines are associated with a seasonal mean ground temperature of 6.7 °C (±0.8 SD; 2.2 K amplitude of means for different climatic zones), a surprisingly narrow range. Temperatures are higher (7,8 °C) in the temperate and Mediterranean zone treelines, and are lower in equatorial treelines (5,6 °C) and in the subarctic and boreal zone (6,7 °C). While air temperatures are higher than soil temperatures in warm periods, and are lower than soil temperatures in cold periods, daily means of air and soil temperature are almost the same at 6,7 °C, a physics driven coincidence with the global mean temperature at treeline. The length of the growing season, thermal extremes or thermal sums have no predictive value for treeline altitude on a global scale. Some Mediterranean (Fagus spp.) and temperate South Hemisphere treelines (Nothofagus spp.) and the native treeline in Hawaii (Metrosideros) are located at substantially higher isotherms and represent genus-specific boundaries rather than boundaries of the life-form tree. In seasonal climates, ground temperatures in winter (absolute minima) reflect local snow pack and seem uncritical. Main conclusions, The data support the hypothesis of a common thermal threshold for forest growth at high elevation, but also reflect a moderate region and substantial taxonomic influence. [source] Harbour seal movements and haul-out patterns: implications for monitoring and managementAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2009Louise Cunningham Abstract 1.Compliance with conservation legislation requires knowledge on the behaviour, abundance and distribution of protected species. Seal life history is characterized by a combination of marine foraging and a requirement to haul out on a solid substrate for reproduction and moulting. Thus understanding the use of haul out sites, where seals are counted, as well as their at-sea movements is crucial for designing effective monitoring and management plans. 2.This study used satellite transmitters deployed on 24 harbour seals in western Scotland to examine movements and haul-out patterns. 3.The proportion of time harbour seals spent hauled out (daily means of between 11 and 27%) varied spatially, temporally and according to sex. The mean haul-out duration was 5,h, with a maximum of over 24,h. 4.Patterns of movement were observed at two geographical scales; while some seals travelled over 100,km, 50% of trips were within 25,km of a haul-out site. These patterns are important for the identification of a marine component to designated protected areas for the species. 5.On average seals returned to the haul-out sites they last used during 40% of trips, indicating a degree of site fidelity, though there was wide variation between different haul-out sites (range 0% to >75%). 6.Low fidelity haul-out sites could form a network of land-based protected areas, while high fidelity sites might form appropriate management units. Copyright © 2008 John Wiley & Sons, Ltd. [source] | |||||||||||||