bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of vertical resolution and map scale of digital elevation models on geomorphological parameters used in hydrology
Authors: Gyasi‐Agyei Yeboah , Willgoose Garry , De Troch Francois P. 
Published: February 2007

AbstractThe advent of digital elevation models (DEMs) has made it possible to objectively extract, calculate and store geomorphological parameters for hydrological modelling at several scales. For a grid‐based DEM, the threshold area used to extract the channel network is analogous to the scale of the map produced. In addition to the map scale, the effects of the vertical resolution of the DEM on some frequently used geomorphological parameters in hydrology are examined using high‐resolution DEMs of two natural and two artificial catchments. The vertical resolution was varied between 1 cm and 1 m, the most common vertical resolution of DEMs. At a fixed map scale, the mean absolute percentage error in the geomorphological parameters caused by a decrease in vertical resolution is within the range 0–5% for the medium‐sized catchments and 0–10% for the small catchments studied. Although it is true that a change in vertical resolution may cause a change in the individual pixel slope, area and topographic index (area/slope), particularly in low relief terrain, their cumulative distributions do not show any significant change with the vertical resolution. The shape of the normalized width function is not very sensitive to the vertical resolution and the map scale. For small catchments order change may occur at different map scales for the different vertical resolution DEMs of the same catchment, causing a significant change in order‐related parameters such as Horton ratios. It is suggested that the vertical resolution of the DEM of a catchment be considered satisfactory for most hydrological applications if the ratio of the average drop per pixel and vertical resolution is greater than unity. This ratio criterion could be used to define the minimum pixel area for reliable channel network definition for any given vertical resolution. The minimum pixel area places a lower bound on the horizontal resolution with which a channel network can be extracted from a DEM. These results could potentially be used to assess the adequacy for hydrological purposes of existing and proposed digital elevation databases.
Predicting catchment‐scale soil moisture status with limited field measurements
Authors: Kalma J. D. , Bates B. C. , Woods R. A. 
Published: February 2007

AbstractA catchment‐wide soil moisture index based on spatially distributed point measurements of soil moisture is used to describe the temporal trend in regional soil moisture status in a 26 km2 catchment in south‐eastern Australia. The temporal variation in runoff, evaporation and soil moisture storage is simulated with a modification of the lumped SFB water balance model of Boughton (1984), which assumes a fixed bucket size, and with the variable infiltration capacity (VIC) model of Wood et al. (1992), which assumes a variable bucket representation. Comparison of simulated catchment soil moisture storage and the soil moisture index based on measurements indicates that both models can make useful predictions of soil moisture status at the catchment scale, with the VIC model performing slightly better than the SFB model. It is also shown that the quasi‐distributed VIC model can predict the relative wetness at individual locations, given their relative frequency of occurrence, thus allowing the disaggregation of catchment‐scale storage values to point‐scale soil moisture values.
Application of the meta‐channel concept: Construction of the meta‐channel hydraulic geometry for a natural catchment
Authors: Snell John , Sivapalan Murugesu 
Published: February 2007

AbstractThis is the second in a series of three papers about the meta‐channel concept which illustrates the derivation of the principles behind the concept, the construction of the hydraulic geometry and the application of the concept to flood routing, respectively. It was shown in the first of these that a channel network in a catchment can be conceptualized into a single ‘effective channel’ representation: a meta‐channel. This study uses this conceptualization to show how such a meta‐channel can be constructed. The techniques derived are applied to one catchment in New Zealand. We derive hydraulic geometries expressed as functions of flow distance throughout this catchment based on the Leopold and Maddock power laws. This derivation uses classical published values for hydraulic geometry coefficients and exponents, regional parameterization of the index flood relationship for New Zealand as a whole, together with local knowledge regarding the order of magnitude of the channel roughness. Conservation principles derived from the continuity and mechanical energy balance equations are used to construct the hydraulic geometry of the meta‐channel of this catchment. A meta‐channel long profile is established and compared against the mainstream long profile. The effectiveness of the Leopold and Maddock power law assumptions is tested by comparing the derived hydraulic geometry against available field cross‐sectional data for the gauging site at the outlet of the catchment.
Scaling theory to extrapolate individual tree water use to stand water use
Authors: Hatton Thomas J. , Wu Hsin‐I 
Published: February 2007

AbstractExtrapolation of measurements of water use by individual trees to that for a stand of trees is a critical step in linking plant physiology and hydrology. Limitations in sampling resources and variation in tree sizes within a stand necessitate the use of some scaling relationship. Further, to scale tree water use in space as well as time, the relationship must reflect the changing availabilities of energy and water supply. It is argued here that tree leaf area is the most appropriate covariate of water use to achieve this aim. However, empirical results show that the relationship is not always linear. A theory is developed, based on the concepts of hydrological equilibrium (sensu Nemani and Running, 1989) and ecological field theory (Walker et al., 1989) which accounts for (occasional) non‐linear behaviour of the flux/ leaf area relationship in evergreen trees. A key feature of this theory is the notion of a non‐linear, quasi‐equilibrium reflecting plant water stress. An equation is derived from these concepts and a standard, explicit treatment of tree water use (Landsberg and McMurtrie, 1984), which is used to characterise this relationship. This equation has the form Q = aIA + bΨsAf. The theory is tested against field data and published reports on Eucalyptus tree water use.
Estimation of terrestrial water and energy balances over heterogeneous catchments
Authors: Silberstein R. P. , Sivapalan M. 
Published: February 2007

AbstractModelling experiments have been undertaken to address the effects of land surface heterogeneity on the energy and water fluxes at catchment scales. The simulation results indicate that in the presence of strong contrasts (i.e. patchiness) in the land surface characteristics (for example, soil moisture, leaf area index or vegetation type) significant inter‐patch advection can result. For example, small areas with high levels of soil moisture surrounded by drier areas have a disproportionately high latent heat flux. The sensible heat flux showed a complementary suppression. The response to changes in leaf area index, however, was found to be much more complex. At constant soil moisture levels, it was found that under some conditions the latent heat flux of patches of high leaf area index increased as its proportion of the surface increased as a result of the increase in net radiation and roughness. There was also an increase in sensible heat flux. This effect was also found on surfaces with low moisture levels and strong contrasts in surface vegetation. Although these results do depend on the initial boundary layer and terrestrial conditions, a consequence of this is that significant biases can be generated in modelling catchment output if the heterogeneity effects are not fully accounted for. The model simulations demonstrate that the fluxes from a ‘homogenized’ surface with catchment‐average land surface properties (e.g. soil moisture) can be significantly higher than that for a heterogeneous surface with explicitly modelled inter‐patch interactions. These results have particular implications for nested catchment models where the responses of individual subcatchments are as important as that of the total catchment. They are also significant in efforts towards developing lumped land surface parameterizations for use in atmospheric models such as general circulation models.
Meteorlogical impact of replacing native perennial vegetation with annual agricultural species
Authors: Xinmei Huang , Lyons T. J. , Smith R. C. G. 
Published: February 2007

AbstractFollowing the clearing of native perennial vegetation for agriculture based on winter growing annual species, the surface characteristics of south‐western Australia have been significantly altered. Analysis of the annual variation of these characteristics based on satellite data and a one‐dimensional boundary layer model suggests that convective mixing over the cleared land is no longer able to reach the lifting condensation level for a significant period of the year. This implies a decrease in convective cloud formation and a reduction in the convective enhancement of rainfall.
Scaling of land‐atmosphere interactions: An atmospheric modelling perspective
Authors: Avissar Roni 
Published: February 2007

AbstractInvestigations of the impact of the ground surface on energy and mass fluxes in the atmosphere as well as on the dynamic response of the atmosphere at different scales are reviewed to emphasize the requirements for hydrological schemes for atmospheric models. Based on these investigations, a discussion on the scaling of the most important land processes and characteristics, from an atmospheric modelling perspective, is provided. It appears that because of the strong, non‐linear response of the atmosphere to the spatial variability of land‐surface characteristics, the scaling of hydrological processes and parameters is not linear. This implies that appropriate hydrological schemes for atmospheric models need to provide higher statistical moments and characteristic length scales of the spatial distribution of water availability for evapotranspiration.
Simulating heterogeneous vegetation in climate models. Identifying when secondary vegetation becomes important
Authors: Pitman A. J. 
Published: February 2007

AbstractTo parameterize the land surface in global climate models (GCMs) data must be provided at a variety of resolutions. In GCMs, high‐resolution data must be aggregated to the coarser resolution of the GCM. The method used for parameter aggregation can lead to the simulation of very different land surface climatologies. It is shown that the most important transition from a simulation of homogeneous tundra to one of homogeneous coniferous forest is the initial increase in forest. The differences between the simulation of tundra and the simulation of tundra with two‐ninths coniferous forest are considerable. This suggests that the land surface is sensitive to the aggregated parameters in non‐linear ways. It suggests that more care is needed in data aggregation, and that improved algorithms for data aggregation must be developed, because these data sets represent the foundations on which advanced land surface parameterizations are built. Finally, it shows that the influence of relatively small amounts of secondary vegetation should be represented in GCMs.
Estimating macropore and matrix flow using the hydrograph separation procedure in an experimental forest plot
Authors: Návar José , Turton Donald J. , Miller Edwin L. 
Published: February 2007

AbstractThis study was conducted to estimate macropore space, macropore flow and matrix flow in an experimental forest plot in the Ouachita Mountains of Arkansas. Lateral soil water fluxes and soil capillary potentials were observed in the isolated plot during applied rainfall experiments. Rainfalls were applied 17 times during the period 17 July to 10 October 1991. The subsurface hydrograph separation technique was used to estimate macropore space, macropore flux and matrix flux. The boundary between macropore and matrix flow was statistically determined by covariance analysis. The maximum estimated lateral macropore space was approximately 0.006 (cm3 cm−3). The maximum estimated lateral macropore and matrix flow were 0.042 and 0.00066 cm s−1, respectively. This report also emphasizes the need for further research on the hydrograph separation procedure for estimating macropores and macropore flow.
Modelling the growth of cyanobacteria (GrowSCUM)
Authors: Howard A. , Kirkby M. J. , Kneale P. E. , McDonald A. T. 
Published: February 2007

AbstractToxic cyanobacteria have become a common nuisance in freshwater lakes and reservoirs throughout the world, sometimes resulting in the closure of sites with high amenity value. Cyanobacteria are able to regulate their buoyancy state in response to changing photosynthetic rates. Additionally, the cyanobacteria are liable to become entrained within wind‐induced near‐surface turbulent currents, resulting in mixing and mass transport. These movement processes have been modelled. A mathematical function is presented which describes light‐ and nutrient‐limited cyanobacterial growth. The growth model is integrated with a previous movement model (SCUM: simulation of cyanobacterial underwater movement) as movement patterns and wind‐induced lake mixing strongly affect the intensity and duration of light received by the cyanobacteria and thereby determine the photosynthetic potential. Results of the model suggest that cyanobacteria are resistant to periods of lake mixing and continue to increase their biomass, but at a depressed rate. Growth is most rapid under calm conditions. The results agree well with field‐based findings, confirming the validity of the growth function.
On the concept of a representative elementary area in catchment runoff
Authors: Fan Ying , Bras Rafael L. 
Published: February 2007

AbstractA qualitative discussion is presented on the concept of a representative elementary area (REA) proposed by Wood et al. (1988). Their work represents a systematic effort of looking at spatial variability as functions of scale, and over the past few years has stimulated new thoughts and research findings. However, it is argued here that the REA concept has limited utility in catchment hydrology for the following reasons. Firstly, the method of finding the REA using distributed modelling appears flawed. In estimating local runoff, point‐process models are applied to elements of 30 × 30 m2 or larger, but the effect of this particular upscaling on the calculated REA has not been addressed. This causes the REA to be relative to the resolution of the modelling. Secondly, an REA does not seem to exist in a natural environment because of its relativeness in the presence of multi‐scale heterogeneity and its dependence on individual storm events. Based on the above arguments and following a discussion of the hydrological implications of REA, it is pointed out that the REA does not provide a definite and robust measure of the inherent spatial variability in runoff and that its utility in formulating large‐scale hydrology is not as clear as it was first envisioned.
Hydrological and hydrochemical response of a small canadian shield catchment to late winter rain‐on‐snow events
Authors: Maclean R. A. , English M. C. , Schiff S. L. 
Published: February 2007

AbstractA study was undertaken during the winter of 1990–1991 in a small (3.7 ha) Canadian Shield catchment to examine the hydrological and hydrochemical response during rain‐on‐snow events. The results are presented of two large (37.9 and 34.6 mm) rain‐on‐snow events occurring in early and late March 1991. Peak and total runoff and the groundwater response from the two events are significantly different. Hydrological data indicate that these differences can be attributed to a combination of meteorological (temperature) and physical conditions (antecedent snowpack ripeness, soil moisture and groundwater levels). An immature snowpack (low temperature and density) combined with low antecedent soil moisture conditions significantly reduced the magnitude of the net hydrological input and runoff from the catchment during the early March event, whereas a more mature snowpack and high antecedent soil moisture conditions led to a large runoff event during late March.During both rain‐on‐snow events a significant portion of the pre‐event snowpack chemical load was lost. Based on the maximum snowpack chemical load measured before the events, the two large rain‐on‐snow events and a brief mid‐March warm period during which there were two much smaller rain‐on‐snow events removed 78% of the hydrogen ion and 63% of the sulphate and nitrate load from the snowpack, while only reducing snowpack water equivalence by 7%. A two‐component (rain and snowmelt) isotopic (δ18O SMOW %0) separation of snowmelt lysimeter water during the two events indicated that snowmelt was an important (50 and 65%, respectively) water source available for infiltration and runoff at the snow‐soil interface. Considering the high hydrogen ion loadings to the catchment during these two events (3.3 and 3.0 mequiv.m−2, respectively) streamflow pH was not significantly reduced due to an increase in the discharge of well‐buffered groundwater. A two‐component isotopic hydrograph separation of peak stream discharge during the 2–3 March event indicated that 75% of the total flow was groundwater. In mid‐latitude acid‐sensitive catchments, winter rain‐on‐snow events are an important hydrological occurrence due to their ability to elute much of the chemical load (H+, SO4, NO3) from the snowpack before the onset of spring melt when the maximum annual hydrological input typically occurs.
Accuracy of tretyakov precipitation gauge: Result of wmo intercomparison
Authors: Yang Daqing , Goodison Barry E. , Metcalfe John R. , Golubev Valentin S. , Elomaa Esko , Gunther Thilo , Bates Roy , Pangburn Timothy , Hanson Clayton L. , Emerson Douglas , Copaciu Voilete , Milkovic Janja 
Published: February 2007

AbstractThe Tretyakov non‐recording precipitation gauge has been used historically as the official precipitation measurement instrument in the Russian (formerly the USSR) climatic and hydrological station network and in a number of other European countries. From 1986 to 1993, the accuracy and performance of this gauge were evaluated during the WMO Solid Precipitation Measurement Intercomparison at 11 stations in Canada, the USA, Russia, Germany, Finland, Romania and Croatia. The double fence intercomparison reference (DFIR) was the reference standard used at all the Intercomparison stations in the Intercomparison. The Intercomparison data collected at the different sites are compatible with respect to the catch ratio (measured/DFIR) for the same gauge, when compared using mean wind speed at the height of the gauge orifice during the observation period.The Intercomparison data for the Tretyakov gauge were compiled from measurements made at these WMO intercomparison sites. These data represent a variety of climates, terrains and exposures. The effects of environmental factors, such as wind speed, wind direction, type of precipitation and temperature, on gauge catch ratios were investigated. Wind speed was found to be the most important factor determining the gauge catch and air temperature had a secondary effect when precipitation was classified into snow, mixed and rain. The results of the analysis of gauge catch ratio versus wind speed and temperature on a daily time step are presented for various types of precipitation. Independent checks of the correction equations against the DFIR have been conducted at those Intercomparison stations and a good agreement (difference less than 10%) has been obtained. The use of such adjustment procedures should significantly improve the accuracy and homogeneity of gauge‐measured precipitation data over large regions of the former USSR and central Europe.
Dissolution kinetics, transit times through subglacial hydrological pathways and diurnal variations of solute content of meltwaters draining from an alpine glacier
Authors: Collins David N. 
Published: February 2007

AbstractExperimental results are reported for dissolved solids concentration increase when clear meltwaters from the surface of an Alpine glacier were reacted with suspended sediment derived from the subsole. The experiments, at Findelengletscher, Switzerland, were conducted at temperatures of about 1°C. Rates of reaction, which decrease through time as solute content rises, were slower in meltwaters which had not been allowed to equilibrate with the atmosphere before sediment was added. Diurnal variations in transit times of meltwater from the surface to the glacier portal were derived from injections of rhodamine dye into large moulin‐conduit systems. Experimentally‐determined rates of increase of electrical conductivity were used together with observed transit times in a Lagrangian formulation. This model was used to assess the contributions of rate of reaction and flow‐through velocity to production of observed variations of solute concentration with portal meltwater discharge. The observed diurnal concentrations varied inversely but in phase with portal discharge. Diurnal variations in discharge through such moulin‐conduit systems lead to substantial changes in flow‐through velocity, altering the periods of time available for parcels of meltwater to react with basally‐entrained suspended sediment en route to the portal. Hence, there is considerable variability in the amount of solute acquired by meltwaters in transit. A diurnal pattern of solute concentration variation with discharge is generated by the model, although absolute levels of solute concentration are underestimated. Parcels of meltwaters flowing more slowly, having entered the glacier down small cracks, crevasses and tiny moulins, acquire larger concentrations of solute during longer transit times. These waters, which cumulatively account for a significant proportion of total discharge, mix with those traversing moulin‐conduit systems and presumably raise the overall solute content of the total discharge from Findelengletscher to the measured levels.