bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the representative elementary area (REA) concept and its utility for distributed rainfall‐runoff modelling
Authors: Blöschl G. , Grayson R. B. , Sivapalan M. 
Published: February 2007

AbstractSince the paper of Wood et al. (1988), the idea of a representative elementary area (REA) has captured the imagination of catchment modellers. It promises a spatial scale over which the process representations can remain simple and at which distributed catchment behaviour can be represented without the apparently undefinable complexity of local heterogeneity. This paper further investigates the REA concept and reassesses its utility for distributed parameter rainfall‐runoff modelling. The analysis follows Wood et al. (1988) in using the same topography and the same method of generating parameter values. However, a dynamic model of catchment response is used, allowing the effects of flow routing to be investigated. Also, a ‘nested catchments approach’ is adopted which better enables the detection of a minimum in variability between large‐ and small‐scale processes. This is a prerequisite of the existence of an REA.Results indicate that, for an impervious catchment and spatially invariant precipitation, the size of the REA depends on storm duration. A ‘characteristic velocity’ is defined as the ratio of a characteristic length scale (the size of the REA) to a characteristic time‐scale (storm duration). This ‘characteristic velocity’ appears to remain relatively constant for different storm durations. Spatially variable precipitation is shown to dominate when compared with the effects of infiltration and flow routing. In this instance, the size of the REA is strongly controlled by the correlation length of precipitation. For large correlation lengths of precipitation, a separation of scales in runoff is evident due to small‐scale soil and topographic variability and large‐scale precipitation patterns. In general, both the existence and the size of an REA will be specific to a particular catchment and a particular application. However, it is suggested that a separation of scales (and therefore the existence of an REA), while being an advantage, is not a prerequisite for obtaining simple representations of local heterogeneity.
Physical interpretations of regional variations in the scaling exponents of flood quantiles
Authors: Gupta Vijay K. , Dawdy David R. 
Published: February 2007

AbstractThe concepts of simple scaling and multiscaling provide a new theoretical framework for the study of spatial or regional flood frequency relations and their underlying physical generating mechanisms. In particular, the scaling exponents in the power law relationship between flood quantiles and drainage areas contain a ‘basic signature of invariance’ regarding the spatial variability of floods, and therefore suggest different hypotheses regarding their physical generating mechanisms. If regional floods obey simple scaling, then the slopes do not vary with return periods. On the other hand, if regional floods obey multiscaling, then the slopes vary with return periods in a systematic manner. This premise is expanded here by investigating the empirical variations in the scaling exponents in three states of the USA: New York, New Mexico and Utah. Distinct variations are observed in the exponents among several regions within each state. These variations provide clear empirical evidence for the presence of both simple scaling and multiscaling in regional floods. They suggest that snowmelt‐generated floods exhibit simple scaling, whereas rainfall‐generated floods exhibit multiscaling. Results from a simple rainfall‐runoff experiment, along with the current research on the spatial scaling structure of mesoscale rainfall, are used to give additional support to these physical hypotheses underlying two different scaling structures observed in floods. In addition, the rainfall‐runoff experiment suggests that the behaviour of the flood exponents in small basins is determined by basin response rather than precipitation input. This finding supports the existence of a critical drainage area, as has been reported for the Appalachia flood data in the USA, such that the spatial variability in floods in basins larger than the critical size is determined by the precipitation input, and in basins smaller than the critical size is determined by the basin response.
Delineating hydrological response units by geographical information system analyses for regional hydrological modelling using PRMS/MMS in the drainage basin of the River Bröl, Germany
Authors: Flügel Wolfgang‐Albert 
Published: February 2007

AbstractA modified concept of hydrological response units (HRUs) for regional modelling of river basins using the PRMS/MMS model is presented. The HRUs are delineated by geographical information system (GIS) analysis from physiographic basin properties such as topography, soils, geology, rainfall and land use using a thorough hydrological systems analysis. The HRUs, once classified by GIS analysis, preserve the three‐dimensional heterogeneity of the drainage basin. The River Bröl basin (A = 216 km2), Rheinisches Schiefergebirge, Germany was selected to apply the concept. In total, 23 HRUs were delineated and tested with the PRMS/MMS model using a 20‐year hydrometeorological daily database. The hydrological systems analysis revealed that interflow is the dominant flow process through the basin's slopes and the major contribution to groundwater recharge and river runoff. This was accounted for by parameterizing the HRUs in the model control file to drain their surplus water not used for satisfying the demand of evapotranspiration to a common conceptual subsurface storage. This storage was simulated by interflow drainage to the groundwater aquifer in the valley floor, which in turn drained to the channel network. The PRMS/MMS model simulated the observed daily discharge very well and the fit was described by a daily correlation coefficient of r = 0.91. The NASIM and HSPF models using different means to represent the basin's physiographic heterogeneity were applied to the Bröl basin as well, but did not achieve this correlation. The HRU concept was found to be a reliable method for regional hydrological basin modelling and allows spatial up‐ and downscaling. Future research on this concept will focus on incorporating the variable precipitation distribution into the classification of HRUs and on the hydrodynamic routing of the modelled discharge. Additionally, satellite imagery must be used for classifying land use in macroscale drainage basins.
Estimation of subgrid scale kinematic wave parameters for hillslopes
Authors: Willgoose Garry , Kuczera George 
Published: February 2007

AbstractThe kinematic wave approximation is commonly used in the new generation of so‐called physically based, distributed rainfall‐runoff models. However, although the kinematic wave approximation is commonly accepted for channel and experimental flows, its applicability to actual hillslopes remains unvalidated. Because it is not possible to measure, nor model, all of the details of the flow on any realistic surface, we use subgrid approximations to provide an effective parameterization of the processes that occur on scales smaller than those that can be modelled. This paper explores different effective parameterizations, the data required to identify the correct parameterization, and the implications of not being able to identify all of the parameters on the scale dependence of flood hydrology. Data from small‐scale plot experiments (100 m2) and large‐scale catchments (1 km2) are used to explore these issues. It has been found that infiltration parameters can be adequately calibrated from small‐scale plots. However, it is more difficult to calibrate the kinematic wave parameters using small‐scale data alone. The conveyance properties of the hillslope cross‐sections are parameterized by two kinematic wave parameters, cr and em, to yield the discharge Q = cr A S0.5 with S being the slope and Acs the cross‐sectional area. It is shown that these two parameters are highly correlated, particularly when inferred from small‐scale data. The surface roughness, amount of rilling and undulations of the surface all influence the kinematic wave parameters. The runoff response at large scales is very sensitive to changes in cr and em, yet is not readily apparent in small‐scale data. Unfortunately, using small‐scale data cr and em cannot be estimated with acceptable precision to reliably extrapolate to larger scales. The significance of this behaviour is demonstrated and some possible solution strategies are discussed.
Linking parameters across scales: Subgrid parameterizations and scale dependent hydrological models
Authors: Beven Keith 
Published: February 2007

AbstractIt is argued that the aggregation approach towards macroscale hydrological modelling, in which it is assumed that a model applicable at small scales can be applied at larger scales using ‘effective’ parameter values, is an inadequate approach to the scale problem. It is also unlikely that any general scaling theory can be developed due to the dependence of hydrological systems on historical and geological perturbations. Thus a disaggregation approach to developing scale‐dependent models is advocated in which a representation of the distribution of hydrological responses is used to reflect hydrological heterogeneity. An appropriate form of distribution may vary with both scale and environment. Such an approach is dependent on the data available to define and calibrate the chosen subgrid parameterization. A parameterization based on a minimum patch representation is suggested and the problems of identification at the larger scale discussed.
Towards a catchment‐scale model of subsurface runoff generation based on synthesis of small‐scale process‐based modelling and field studies
Authors: Kubota Jumpei , Sivapalan Murugesu 
Published: February 2007

AbstractMethodologies for developing a macro‐scale model of subsurface stormflow generation on a steep forested catchment in Japan are addressed. Field studies on this catchment have indicated that subsurface flow, consisting mainly of ‘old’ water displaced by ‘new’ rain water, dominates the storm response. Detailed field measurements on the catchment allowed simple, catchment‐scale relationships to be developed between the volume of saturated groundwater, on the one hand, and discharge, and surface and subsurface saturated areas, on the other. Attempts are made to find linkages between these empirical relationships and physically‐based descriptions of hydrological processes operating at smaller scales. A distributed model based on the saturated‐unsaturated groundwater flow on steep catchments was developed and tested with field data collected on this catchment. Derivation of catchment‐scale relationships can be carried out by a straightforward integration of the distributed model output. An alternative disaggregation‐aggregation approach is presented, whereby the catchment is divided into a number of hillslope flow strips. By applying the distributed model on each flow strip, under steady‐state conditions, it is possible to infer the spatial variability of groundwater volume in the various flow strips. This variability is related to a measure of hillslope topography and geometry. Knowing the catchment topography and geometry for any catchment, it is then possible to derive useful catchment‐scale relationships which are applicable under quasi‐steady‐state conditions. Hydrological relationships derived in this manner are compared with corresponding empirical relationships. The methodologies presented are effective for understanding the linkages between catchment scale response and small‐scale flow processes.
Scale issues in boundary‐layer meteorology: Surface energy balances in heterogeneous terrain
Authors: Raupach M. R. , Finnigan J. J. 
Published: February 2007

AbstractThis paper, part review and part new work, falls into three main sections. The first is a review of scale issues in both hydrology and meteorology, focusing on their origins in the water and energy conservation equations, integrated over control volumes of different scales. Several guidelines for scale translations are identified.The second section reviews the upscaling problem in boundary‐layer meteorology, setting out two ‘flux‐matching’ criteria for upscaling models of land‐air fluxes: the conservation requirement that surface fluxes average linearly and the practical requirement that model form be preserved between scales. By considering the effects of boundary conditions, it is shown that the combination or Penman‐Monteith equation is a model for elemental energy fluxes which leads to physically consistent flux‐matching rules for upscaling surface descriptors (resistances). These rules are tested, along with some other possibilities, and found to perform well.The third section tests the hypothesis that regionally averaged energy balances over land surfaces are insensitive to the scale of heterogeneity, X. Heterogeneity is classified as microscale when X ⩽ UmT*, mesoscale when UmT* ⩽ X ⩽ UmTe, and macroscale when UmTe ⩽ X [where Um is the mean wind speed in the convective boundary layer (CBL) and T* and Te the convective and entrainment time scales, respectively]. A CBL slab model is used to show that regionally averaged energy fluxes are remarkably insensitive to X in both the microscale and macroscale ranges. Other reviewed evidence suggests that the mesoscale range behaves similarly in dry conditions. Questions remain about the consequences of clouds and precipitation for regionally averaged surface energy fluxes.
Estimation of land surface parameters using satellite data
Authors: Xinmei Huang , Lyons T. J. , Smith R. C. G. , Hacker J. M. 
Published: February 2007

AbstractSurface observations and NOAA advanced very high resolution radiometer (AVHRR) satellite data are combined to provide area‐averaged values of albedo, canopy resistance, leaf area index and fractional vegetation cover. Albedo, fractional vegetation cover and leaf area index are derived from the reflectance of the visible and infra‐red NOAA AVHRR channels. Canopy resistance is estimated by closing the surface energy balance equation using the surface infra‐red temperature and the normalized difference vegetation index. These land surface parameters are evaluated against independent measurements and used as input into a numerical model to simulate the energy exchange between the surface and the overlying atmosphere. Simulation results are validated against detailed aircraft observations undertaken in south‐western Australia over both natural and agricultural vegetation.
Evaluation of the effects of general circulation models' subgrid variability and patchiness of rainfall and soil moisture on land surface water balance fluxes
Authors: Sivapalan Murugesu , Woods Ross A. 
Published: February 2007

AbstractMany existing general circulation models (GCMs) use so‐called ‘bucket algorithms’ to represent land‐surface hydrology. Wood et al. (1992) presented a generalization of the simple bucket representation, based on their variable infiltration capacity (VIC) model. The VIC model, in essence, assumes a statistical distribution of bucket sizes within the grid square. In this way, it provides a simple, computationally efficient and yet physically realistic model of land‐surface hydrology. A preliminary attempt is made here, using this simple model, to evaluate the effects of the spatial variability of rainfall intensities and the resulting soil moisture within a hypothetical GCM grid square. Rainfall is assumed to be patchy, with only a fraction of the grid square being wetted by rainfall at any given time. Within the wetted area, however, rainfall is allowed to vary randomly in space. Evaporation during interstorm periods is estimated from the rest of the grid square by a simple non‐linear function of the available soil moisture. The soil moisture is also assumed to be patchy and spatially variable due to the antecedent rainfall that caused it. A number of simplifying assumptions have been made in the model about the redistribution of soil moisture at the end of storm and interstorm periods, and the effects of a vegetation canopy have been ignored. The model is applied, under a variety of conditions, to estimate the biases in the modelled water balance fluxes if the assumed spatial heterogeneity is neglected. The model is also used to simulate the long‐term water balance dynamics under assumed hypothetical storm and inter‐storm climatic inputs, to see how the steady‐state hydrological regime is affected by spatial variability. These simulations are relevant to current efforts towards developing simple parameterizations of land‐surface hydrology that explicitly incorporate subgrid heterogeneity.
Accuracy of kinematic wave and diffusion wave approximations for time‐independent flows
Authors: Singh V. P. , Aravamuthan V. 
Published: February 2007

AbstractErrors in the kinematic wave and diffusion wave approximations for time‐independent (or steady‐state) cases of channel flow were derived for three types of boundary conditions: zero flow at the upstream end, and critical flow depth and zero depth gradient at the downstream end. The diffusion wave approximation was found to be in excellent agreement with the dynamic wave approximation, with errors in the range 1–2% for values of KF (⩾ 7.5), where K is the kinematic wave number and F0 is the Froude number. Even for small values of KF (e.g. KF20 = 0.75), the errors were typically less than 15%. The accuracy of the diffusion wave approximation was greatly influenced by the downstream boundary condition. The error of the kinematic wave approximation was found to be less than 13% in the region 0.1 ⩽ x ⩽ 0.95 for KF = 7.5 and was greater than 30% for smaller values of KF (⩽ 0.75). This error increased with strong downstream boundary control.
Accuracy of kinematic wave and diffusion wave approximations for space‐independent flows on infiltrating surfaces with lateral inflow neglected in the momentum equation
Authors: Singh V. P. 
Published: February 2007

AbstractError equations for the kinematic wave and diffusion wave approximations with lateral inflow neglected in the momentum equation are derived under simplified conditions for space‐independent flows. These equations specify error as a function of time in the flow hydrograph. The kinematic wave, diffusion wave and dynamic wave solutions are parameterized through a dimensionless parameter γ which is dependent on the initial conditions. This parameter reflects the effect of initial flow depth, channel‐bed slope, lateral inflow, infiltration and channel roughness when the initial condition is non‐vanishing; it reflects the effect of bed slope, channel roughness and acceleration due to gravity when the initial condition is vanishing. The error equations are found to be the Riccati equation. The structure of the error equations in the case when the momentum equation neglects lateral inflow is different from that when the lateral inflow is included.
Diurnal variations in streamflow and water quality during the summer dry season
Authors: Kobayashi Daiji , Kodama Yuji , Ishii Yoshiyuki , Tanaka Yumiko , Suzuki Keisuke 
Published: February 2007

AbstractIn a headwater basin covered with boreal forest in northern Japan, the summer dry flow was monitored each summer from 1985 to 1993. Streamflow and specific electrical conductance fluctuated diurnally and these variations were attributed to daytime evapotranspiration. In 1989, the daytime reduction in streamflow and conductance were accompanied by a reduction in the HCO−3 concentration.The low flow hydrograph was separated into two components using HCO−3 and Cl− concentrations in August 1989, assuming low flow to be a mixture of delayed subsurface flow and of quick shallow flow. The slight diurnal variation in the ratio of shallow flow to subsurface flow caused the diurnal variation in conductance by changing the HCO−3 concentration.
Hydrometeorological relationships in a glacierized catchment in the Canadian high arctic
Authors: Wolfe Paul M. , English Michael C. 
Published: February 2007

AbstractRunoff from a small glacierized catchment in the Canadian high Arctic was monitored throughout one melt season. The stream discharge record is one aspect of a larger project involving glacier mass balance, superimposed ice formation and local climate on a glacier in the Sawtooth Range, Ellesmere Island, Northwest Territories, Canada. To better understand the main factors influencing the production of runoff on the glacier during the period of main summer melt, regression analyses were performed relating daily air temperature, shortwave incoming and net radiation, absorptivity and wind speed to daily glacier discharge. Air temperature at the glacier meteorological station on rain‐free days is the element with the greatest correlation with runoff (r2 = 0.57; n = 34). A multiple regression of discharge with air temperature, shortwave incoming radiation, net radiation hours and wind speed achieved the best fit (r2 = 0.84; n = 34). Rain events (> 10mmd−1) can dominate daily discharge when they occur during the period of ice melt, creating more runoff per unit area than can be produced by melt alone, and significantly reduce the accuracy of runoff predictions.
Towards a ligand targeted enzyme prodrug therapy: Single round panning of a β‐lactamase scaffold library on human cancer cells
Authors: Shukla Girja S. , Murray Christopher J. , Estabrook Melodie , Shen Guang‐Ping , Schellenberger Volker , Krag David N. 
Published: February 2007

AbstractA novel β‐lactamase scaffold library in which the target‐binding moiety is built into the enzyme was generated using phage display technology. The binding element is composed of a fully randomized 8 amino acid loop inserted at position between Y34 and K37 on the outer surface of Enterobacter cloacae P99 cephalosporinase (β‐lactamase, E.C. 3.5.2.6) with all library members retaining catalytic activity. The frequency and diversity of amino acids distributions in peptide inserts from library clones were analyzed. The complexity of the randomized loop appears consistent with standards of other types of phage display library systems. The library was panned against SKBR3 human breast cancer cells in 1 round using rolling circle amplification of phage DNA to recover bound phage. Individual β‐lactamase clones, independent of phage, were rapidly assessed for their binding to SKBR3 cells using a simple high throughput screen based on cell‐bound β‐lactamase activity. SKBR3 cell‐binding β‐lactamase enzymes were also shown to bind specifically using an immunochemical method. Selected β‐lactamase clones were further studied for their protein expression, enzyme activity and binding to nontumor cell‐lines. Overall, the approach outlined here offers the opportunity of rapidly selecting targeted β‐lactamase ligands that may have a potential for their use in enzyme prodrug therapy with cephalosporin‐based prodrugs. It is expected that a similar approach will be useful in developing tumor‐targeting molecules of several other enzyme candidates of cancer prodrug therapy. © 2007 Wiley‐Liss, Inc.