bluuebunny/crossref_metadata_2025 huggingface dataset:
A steady-state saturation model to determine the subsurface travel time (STT) in complex hillslopes
Authors: Sabzevari T. , Talebi A. , Ardakanian R. , Shamsai A.
Published: April 2010

Abstract. The travel time of subsurface flow in complex hillslopes (hillslopes with different plan shape and profile curvature) is an important parameter in predicting the subsurface flow in catchments. This time depends on the hillslopes geometry (plan shape and profile curvature), soil properties and climate conditions. The saturation capacity of hillslopes affect the travel time of subsurface flow. The saturation capacity, and subsurface travel time of compound hillslopes depend on parameters such as soil depth, porosity, soil hydraulic conductivity, plan shape (convergent, parallel or divergent), hillslope length, profile curvature (concave, straight or convex) and recharge rate to the groundwater table. An equation for calculating subsurface travel time for all complex hillslopes was presented. This equation is a function of the saturation zone length (SZL) on the surface. Saturation zone length of the complex hillslopes was calculated numerically by using the hillslope-storage Boussinesq (hsB) model in the steady state conditions, so an analytical equation was presented for calculating the saturation zone length of the straight hillslopes and all plan shapes geometries. Based on our results, the convergent hillslopes become saturated very soon and they showed longer SZL with shorter travel time compared to the parallel and divergent ones. The subsurface average flow rate in convergent hillslopes is much less than the divergent ones in the steady state conditions. Concerning to subsurface travel time, convex hillslopes have more travel time in comparison to straight and concave hillslopes. The convex hillslopes exhibit more average flow rate than concave hillslopes and their saturation capacity is very low. Finally, the effects of recharge rate variations, average bedrock slope and soil depth on saturation zone extension were investigated.
Reading the bed morphology of a mountain stream: a geomorphometric study on high-resolution topographic data
Authors: Trevisani S. , Cavalli M. , Marchi L.
Published: April 2010

Abstract. High-resolution topographic data expand the potential of quantitative analysis of the earth surface, improving the interpretation of geomorphic processes. In particular, the morphologies of the channel beds of mountain streams, which are characterised by strong spatial variability, can be analysed much more effectively with this type of data. In the present study, we analysed the aerial LiDAR topographic data of a headwater stream, the Rio Cordon (watershed area: 5 km2), located in the Dolomites (north-eastern Italy). The morphology of the channel bed of Rio Cordon is characterised by alternating step pools, cascades, and rapids with steps. We analysed the streambed morphology by means of ad hoc developed morphometric indices, capable of highlighting morphological features at a high level of spatial resolution. To perform the analysis and the data interpolation, we carried out a channel-oriented coordinate transformation. In the new coordinate system, the calculation of morphometric indices in directions along and transverse to the flow direction is straightforward. Three geomorphometric indices were developed and applied as follows: a slope index computed along the whole width of the channel bed, directional variograms computed along the flow direction and perpendicular to it, and local anomalies, calculated as the difference between directional variograms at different spatial scales. Directional variograms in the flow direction and local anomalies have proven to be effective at recognising morphologic units, such as steps, pools and clusters of large boulders. At the spatial scale of channel reaches, these indices have demonstrated a satisfactory capability to outline patterns associated with boulder cascades and rapids with steps, whereas they did not clearly differentiate between morphologies with less marked morphological differences, such as step pools and cascades.
Future extreme precipitation assessment in Western Norway – using a linear model approach
Authors: Caroletti G. N. , Barstad I.
Published: April 2010

Abstract. The need for local assessments of precipitation has grown in recent years due to the increase in precipitation extremes and the widespread awareness about findings of the IPCC 2003 Report on climate change. General circulation models, the most commonly used tool for climate predictions, show an increase in precipitation due to an increase in greenhouse gases (Cubash and Meehl, 2001). It is suggested that changes in extreme precipitation are easier to detect and attribute to global warming than changes in mean annual precipitation (Groisman et al., 2005). However, because of their coarse resolution, the global models are not suited to local assessments. Thus, downscaling of data is required. A Linear Model (Smith and Barstad, 2004) is used to dynamically downscale orographic precipitation over Western Norway from twelve General Circulation Model simulations based on the A1B emissions scenario (IPCC, 2003). An assessment of the changes to future Orographic Precipitation (2046–2065 and 2081–2100 time periods) versus the historical control period (1971–2000) is carried out. Results show an increased number of Orographic Precipitation days and an increased Orographic Precipitation intensity. Extreme precipitation events are up to 20% more intense than the 1971–2000 values. Extremes are defined by the exceedence of the 99%-ile threshold in the time slice. Using station-based observations from the control period, the results from downscaling can be used to generate simulated precipitation histograms at selected stations. The Linear Model approach also allows for simulated changes in precipitation to be disaggregated according to their causal source: (a) the role of topography and (b) changes to the amount of moisture delivery to the site. The latter can be additionaly separated into moisture content changes due to: (i) temperature; (ii) wind speed; (iii) stability. An analysis of these results suggests a strong role for warming in increasing the intensity of extreme Orographic Precipitation events in the area.
Validation of SWAT model for stream flow simulation and forecasting in Upper Bernam humid tropical river basin, Malaysia
Authors: Alansi A. W. , Amin M. S. M. , Abdul Halim G. , Shafri H. Z. M. , Aimrun W.
Published: April 2010

Abstract. The study was to evaluate SWAT model for flow simulation and forecasting in the Upper Bernam humid tropical river basin, which is the main source of irrigation water supply for a rice granary. Land use in the study area has rapidly changed from the year of 1984 until today. The study was conducted using 27 years of records (1981–2007). Calibration was performed for the period of 1981 through 2004 while, the period of 2005 through 2007 for the validation of both simulation and forecasting of flow. During calibration, the annual and monthly results were 0.82, 0.65, 0.81 and 0.62 for R2 and ENS, respectively and 0.99, 0.93, 0.98 and 0.92, respectively during validation. As for forecasting validation, were 0.88, 0.78, 0.86 and 0.74 for R2 and ENS, respectively. In general model shows good performance in flow simulating as well as forecasting. Five scenarios were performed to identify the individual effect of mixed land use change on stream flow. The scenarios results demonstrate, land use changes are responsible for an increase in the annual flow depth between 8% to 39% while 16% to 59% during high flow months and decreases between 3% to 32% during low flow months. Flow forecasting for the year 2020 using 30 forecasting cycles which found to be the optimal for the study area was performed. The results show decrease by 50% below the monthly irrigation water demand during low flow months, which emphasize the need to include structured best management practices (BMPs) such as ponds to the study area future land development plan to mitigate the future changes in land use on flow quantity. This study showed that SWAT was able to simulate and forecast flow in humid tropical condition successfully and can be used to study the effects of future land use changes on flow.
Groundwater response to leakage of surface water through a thick vadose zone in the middle reaches area of Heihe River Basin, in China
Authors: Wang X.-S. , Ma M.-G. , Li X. , Zhao J. , Dong P. , Zhou J.
Published: April 2010

Abstract. The behavior of groundwater response to leakage of surface water in the middle reaches area of Heihe River Basin is significantly influenced by a thick vadose zone. The variation of groundwater level is a result of two recharge events corresponding to leakage of Heihe River and irrigation water with different delay time. A nonlinear leakage model is developed to calculate the monthly leakage of Heihe River in considering changes of streamflow, river stage and agricultural water utilization. Numerical modeling of variable saturated flow is carried out to investigate the general behaviors of leakage-recharge conversion through a thick vadose zone. It is found that the variable recharge can be approximated by simple reservoir models for both leakage under a river and leakage under an irrigation district but with different delay-time and recession coefficient. A triple-reservoir model of relationship between surface water, vadose zone and groundwater is developed. It reproduces the in situ water table movement during 1989–2006 with variable streamflow of Heihe River and agricultural water utilization. The model is applied to interpret groundwater dynamics during 2007–2008 that observed in the Watershed Airborne Telemetry Experimental Research (WATER).
Snow cover data derived from MODIS for water balance applications
Authors: Gafurov A. , Bárdossy A.
Published: April 2010

Abstract. Snow cover information is of central importance for the estimation of water storage in cold mountainous regions. It is difficult to assess distributed snow cover information in a catchment in order to estimate possible water resources. It is especially a challenge to obtain snow cover information for high mountainous areas. Usually, snow depth is measured at meteorological stations, and it is relatively difficult to extrapolate this spatially or temporally since it highly depends on available energy and topography. The snow coverage of a catchment gives detailed information about the catchment's potential source for water. Many regions lack meteorological stations that measure snow, and usually no stations are available at high elevations. Satellite information is a very valuable source for obtaining several environmental parameters. One of the advantages is that the data is mostly provided in a spatially distributed format. This study uses satellite data to estimate snow coverage on high mountainous areas. Moderate-resolution Imaging Spectroradiometer (MODIS) snow cover data is used in the Kokcha Catchment located in the north-eastern part of Afghanistan. The main disadvantage of MODIS data that restricts its direct use in environmental applications is cloud coverage. This is why this study is focused on eliminating cloud covered cells and estimating cell information under cloud covered cells using six logical, spatial and temporal approaches. The results give total cloud removal and mapping of snow cover for the study areas.
Hydrological effects of the temporal variability of the multiscaling of snowfall on the Canadian prairies
Authors: Shook K. R. , Pomeroy J. W.
Published: April 2010

Abstract. Daily historical snowfall data were analysed with the objective of determining the stability of their variability at short temporal scales. The data are weakly multifractal over periods shorter than one month, which controls their scaling properties and which can be used to statistically downscale monthly data to shorter-duration values. Although the daily snowfall values appear to be stationary, their multifractality, as indexed by the universal multifractal parameters shows much temporal variability, with most sites showing statistically-significant trends. Through use of a physically-based model of cold regions hydrology, it is demonstrated that the variability of the multiscaling parameters of snowfall can affect the timing and quantity of snow accumulation and melt in catchments where the snowpacks are subject to wind redistribution, and so trends in scaling based on multifractal characteristics should be taken into account when downscaling climate model scenario outputs.
Evidence for enhanced infiltration of ion load during snowmelt
Authors: Lilbæk G. , Pomeroy J. W.
Published: April 2010

Abstract. Meltwater ion concentration and infiltration rate into frozen soil both decline rapidly as snowmelt progresses. Their temporal association is highly non-linear and a covariance term must be added in order to use time-averaged values of snowmelt ion concentration and infiltration rate to calculate chemical infiltration. The covariance is labelled enhanced infiltration and represents the additional ion load that infiltrates due to the timing of high meltwater concentration and infiltration rate. Previous assessment of the impact of enhanced infiltration has been theoretical; thus, experiments were carried out to examine whether enhanced infiltration can be recognized in controlled laboratory settings and to what extent its magnitude varies with soil moisture. Three experiments were carried out: dry soil conditions, unsaturated soil conditions, and saturated soil conditions. Chloride solution was added to the surface of frozen soil columns; the concentration decreased exponentially over time to simulate snow meltwater. Infiltration excess water was collected and its chloride concentration and volume determined. Ion load infiltrating the frozen soil was specified by mass conservation. Results showed that infiltrating ion load increased with decreasing soil moisture as expected; however, the impact of enhanced infiltration increased considerably with increasing soil moisture. Enhanced infiltration caused 2.5 times more ion load to infiltrate during saturated conditions than that estimated using time-averaged ion concentrations and infiltration rates alone. For unsaturated conditions, enhanced infiltration was reduced to 1.45 and for dry soils to 1.3. Reduction in infiltration excess ion load due to enhanced infiltration increased slightly (2–5%) over time, being greatest for the dry soil (45%) and least for the saturated soil (6%). The importance of timing between high ion concentrations and high infiltration rates was best illustrated in the unsaturated experiment, which showed large inter-column variation in enhanced ion infiltration due to variation in this temporal covariance.
Groundwater flow and storage within an alpine meadow-talus complex
Authors: McClymont A. F. , Hayashi M. , Bentley L. R. , Muir D. , Kruschell E.
Published: April 2010

Abstract. The different types of geological deposits and rock formations found in alpine watersheds play key roles in regulating the rate and timing of runoff to mountain rivers. Talus and alpine meadows are dominant features in these areas, but scant data exist for their capacity to store and transmit groundwater. To gain further understanding of these processes, we have undertaken a combined geophysical and hydrological study of a small (2100 m2) alpine meadow and surrounding talus within the Lake O'Hara watershed in the Canadian Rockies. Several intersecting ground-penetrating radar (GPR) and electrical resistivity tomography (ERT) profiles and a seismic refraction profile were acquired to map the thickness of the talus and to image the topography of the bedrock basin that lies under the meadow. From analysis of the GPR and seismic profiles, we estimate that the talus deposits are relatively thin (<6 m). Combined interpretations from the GPR and ERT data show that the fine-grained sediment, that the meadow basin is comprised of, has a total volume of ca. 3300 m3 and has a maximum thickness of ca. 4 m. Annual snow surveys and stream gauging reveal that the total input volume of snowmelt and rainfall to the meadow basin is several times larger than its groundwater storage capacity, giving rise to low total-dissolved species concentrations (14–21 mg/L) within the meadow groundwater. Observations from four piezometers established on the meadow show that the water table fluctuates rapidly in response to spring snowmelt and precipitation events but otherwise maintains a relatively stable depth of 0.3–0.4 m below the meadow surface during summer months. A slug test performed on one of the piezometers indicated that the saturated hydraulic conductivity of the shallow meadow sediments is 2.5×10−7 m/s. We suggest that a bedrock saddle imaged underneath the southern end of the meadow forms a natural constriction to subsurface flow out of the basin and helps to maintain the stable water-table depth.
Spatial variability in floodplain sedimentation: the use of generalized linear mixed-effects models
Authors: Cabezas A. , Angulo-Martínez M. , Gonzalez-Sanchís M. , Jimenez J. J. , Comín F. A.
Published: April 2010

Abstract. Sediment, Total Organic Carbon (TOC) and total nitrogen (TN) accumulation during one overbank flood (1.15 y) were examined at one reach of the Middle Ebro River (NE Spain) for elucidating spatial patterns. To achieve this goal, four areas with different geomorphological features and located within the study reach were examined by using artificial grass mats. Within each area, 1 m2 study plots consisting on three pseudo-replicates were placed in a semi-regular grid oriented perpendicular to the main channel. TOC, TN and Particle-Size composition of deposited sediments were examined and accumulation rates estimated. Generalized linear mixed-effects models were used to analyze sedimentation patterns in order to handle clustered sampling units, specific-site effects and spatial self-correlation between observations. Our results confirm the importance of channel-floodplain morphology and site micro-topography in explaining sediment, TOC and TN deposition patterns, although the importance of another factors as vegetation morphology should be included in further studies to explain small scale variability. Generalized linear mixed-effect models provide a good framework to deal with the high spatial heterogeneity of this phenomenon at different spatial scales, and should be further investigated in order to explore its validity when examining the importance of factors such as flood magnitude or suspended sediment solid concentration.
Uncertainties in climate change projections and regional downscaling: implications for water resources management
Authors: Buytaert W. , Vuille M. , Dewulf A. , Urrutia R. , Karmalkar A. , Célleri R.
Published: April 2010

Abstract. Climate change is expected to have a large impact on water resources worldwide. A major problem in assessing the potential impact of a changing climate on these resources is the difference in spatial scale between available climate change projections and water resources management. Regional climate models (RCMs) are often used for the spatial disaggregation of the outputs of global circulation models. However, RCMs are time-intensive to run and typically only a small number of model runs is available for a certain region of interest. This paper investigates the value of the improved representation of local climate processes by a regional climate model for water resources management in the tropical Andes of Ecuador. This region has a complex hydrology and its water resources are under pressure. Compared to the IPCC AR4 model ensemble, the regional climate model PRECIS does indeed capture local gradients better than global models, but locally the model is prone to large discrepancies between observed and modelled precipitation. It is concluded that a further increase in resolution is necessary to represent local gradients properly. Furthermore, to assess the uncertainty in downscaling, an ensemble of regional climate models should be implemented. Finally, translating the climate variables to streamflow using a hydrological model constitutes a smaller but not negligible source of uncertainty.
Projected impacts of climate change on groundwater and stormflow in a humid, tropical catchment in the Ugandan Upper Nile Basin
Authors: Kingston D. G. , Taylor R. G.
Published: April 2010

Abstract. The changing availability of freshwater resources is likely to be one of the most important consequences of projected 21st century climate change for both human and natural systems. However, substantial uncertainty remains regarding the precise impacts of climate change on water resources, due in part to uncertainty in GCM projections of climate change. Here we explore the potential impacts of climate change on water resources in a humid, tropical catchment (the River Mitano) in the Upper Nile Basin of Uganda. Uncertainty associated with GCM structure and climate sensitivity is explored, as well as from parameter specification within hydrological models. This is achieved by running pattern-scaled GCM output through a semi-distributed hydrological model (developed using SWAT) of the catchment. Importantly, use of pattern-scaled GCM output allows investigation of specific thresholds of global climate change including the purported 2 °C threshold of "dangerous" climate change. In-depth analysis of results based on HadCM3 climate scenarios shows that annual river discharge first increases, then declines with rising global mean air temperature. A coincidental shift from a bimodal to unimodal discharge regime also results from a projected reduction in baseflow (groundwater discharge). Both of these changes occur after a 4 °C rise in global mean air temperature. These results are, however, highly GCM dependent in both the magnitude and direction of change. This dependence stems primarily from projected differences in GCM scenario precipitation rather than temperature. GCM-related uncertainty is far greater than that associated with climate sensitivity or hydrological model parameterisation.
A geophysical analysis of hydro-geomorphic controls within a headwater wetland in a granitic landscape, through ERI and IP
Authors: Riddell E. S. , Lorentz S. A. , Kotze D. C.
Published: April 2010

Abstract. Wetlands are undergoing considerable degradation in South Africa. As interventions are often technical and costly, there is a requirement to develop conceptual process models for these wetland systems so that rehabilitation attempts will be successful. This paper presents an approach using the geophysical methods of Electrical Resistivity Imaging (ERI) and Induced Polarization (IP) to delineate sub-surface hydro-geomorphic controls that maintain equilibrium disconnectivity of wetland-catchment processes, which through gully erosion are increasing the catchments connectivity through loss of water and sediment. The findings presented here give insight into the geomorphic processes that maintain the wetland in an un-degraded state, this allows for the development of a conceptual model outlining the wetland forming processes. The analysis suggests that sub-surface clay-plugs, within an otherwise sandy substrate are created by illuviation of clays from the surrounding hillslopes particularly at zones of valley confinement.
Hydrochemical analysis of stream water in a tropical, mountainous headwater catchment in northern Thailand
Authors: Hugenschmidt C. , Ingwersen J. , Sangchan W. , Sukvanachaikul Y. , Uhlenbrook S. , Streck T.
Published: April 2010

Abstract. Land use in the vulnerable mountainous parts of the Mae Sa watershed, northern Thailand, has been changed from subsistence agriculture to market-driven production within the past decades. This change is reflected in an increased application of agrochemicals on agricultural areas to secure yields and control pests. Our study site is a steep and fast-responding headwater catchment (77 km2), which transfers agrochemicals that might get lost from soils to waters quickly to the lowlands posing the risk of environmental contamination. This work describes the study, which has been carried out in a subcatchment (7 km2) of the Mae Sa watershed to identify runoff generation processes and contributing flow paths to encircle potential flow paths of pesticides leaching from soil to surface water. We observed three events during the rainy seasons in 2007 and 2008, which were analysed on major ions and EC at high temporal resolution. Based on the samples a two-component hydrograph separation was carried out for three events. For two out of the three events a three-component hydrograph separation was performed to identify the contributions of baseflow, interflow and surface runoff. Baseflow remained the dominant flow fraction, but interflow outshined surface runoff in its amount. Interflow could be observed at the hillslope seeping from the soil in 2007, but not in 2008. We suggest, that interflow highly depends on a constant input of rainfall and requires a certain minimum amount of rainfall per season to be triggered and sustained. Former studies found that pesticides mainly get lost by interflow in this area. Hence, we can point out that pesticide leaching risk is particularly high after a certain amount of rainfall. Critical conditions are therefore mainly present, when the soil layers are close to saturation but not, when these layers are generated or degenerated.
The benefits of gravimeter observations for modelling water storage changes at the field scale
Authors: Creutzfeldt B. , Güntner A. , Vorogushyn S. , Merz B.
Published: April 2010

Abstract. Water storage is the fundamental state variable of hydrological systems. However, comprehensive data on total water storage changes (WSC) are practically inaccessible by hydrological measurement techniques at the field or catchment scale, and hydrological models are highly uncertain in representing the storage term due to the lack of adequate validation or calibration data. In this study, we assess the benefit of temporal gravimeter measurements for modelling WSC at the field scale. A simple conceptual hydrological model is calibrated and evaluated against records of a superconducting gravimeter, soil moisture and groundwater time series. The model is validated against independently estimated WSC data. Using gravimeter data as a calibration constraint improves the model results substantially in terms of predictive capability and variation of the behavioural model runs. Thanks to their capacity to integrate over different storage components and a larger area, gravimeters provide generalised information on total WSC that is useful to constrain the overall status of the hydrological system in a model. The general problem of specifying the internal model structure or individual parameter sets can, however, not be solved with gravimeters alone.
Stream depletion rate with horizontal or slanted wells in confined aquifers near a stream
Authors:   Pei Rong Tsou,   Zheng Yi Feng,   Hund Der Yeh,   Ching Sheng Huang
Published: April 2010

Abstract. The stream depletion rate (SDR) associated with pumping from vertical wells located in an aquifer is commonly estimated, where a large drawdown near the well may, however, be produced. In this paper, the solution is first developed for describing the groundwater flow associated with a point source in a confined aquifer near a stream. Based on the principle of superposition, analytical solutions for horizontal and slanted wells are then developed by integrating the point source solution along the well axis. The solutions can be simplified to quasi-steady solutions by neglecting the exponential terms to describe the late-time drawdown, which can provide useful information in designing horizontal well location and length. The direction of the well axis can be determined from the best SDR subject to the drawdown constraint. It is found that hydraulic conductivity in the direction perpendicular to the stream plays a crucial role in influencing the time required for reaching quasi-steady SDR. In addition, the effects of the well length as well as the distance between the well and stream on the SDR are also examined.
An approach to identify urban groundwater recharge
Authors: Vázquez-Suñé E. , Carrera J. , Tubau I. , Sánchez-Vila X. , Soler A.
Published: April 2010

Abstract. Evaluating the proportion in which waters from different origins are mixed in a given water sample is relevant for many hydrogeological problems, such as quantifying total recharge, assessing groundwater pollution risks, or managing water resources. Our work is motivated by urban hydrogeology, where waters with different chemical signature can be identified (losses from water supply and sewage networks, infiltration from surface runoff and other water bodies, lateral aquifers inflows, ...). The relative contribution of different sources to total recharge can be quantified by means of solute mass balances, but application is hindered by the large number of potential origins. Hence, the need to incorporate data from a large number of conservative species, the uncertainty in sources concentrations and measurement errors. We present a methodology to compute mixing ratios and end-members composition, which consists of (i) Identification of potential recharge sources, (ii) Selection of tracers, (iii) Characterization of the hydrochemical composition of potential recharge sources and mixed water samples, and (iv) Computation of mixing ratios and reevaluation of end-members. The analysis performed in a data set from samples of the Barcelona city aquifers suggests that the main contributors to total recharge are the water supply network losses (22%), the sewage network losses (30%), rainfall, concentrated in the non-urbanized areas (17%), from runoff infiltration (20%), and the Besòs River (11%). Regarding species, halogens (chloride, fluoride and bromide), sulfate, total nitrogen, and stable isotopes (18O2H, and 34S) behaved quite conservatively. Boron, residual alkalinity, EDTA and Zn did not. Yet, including these species in the computations did not affect significantly the proportion estimations.
Modeling relationship between runoff and soil properties in dry-farming lands, NW Iran
Authors: Vaezi A. R. , Bahrami H. A. , Sadeghi S. H. R. , Mahdian M. H.
Published: April 2010

Abstract. The process of transformation of rainfall into runoff over a catchment is very complex and exhibits both temporal and spatial variability. However, in a semi-arid area this variability is mainly controlled by the physical and chemical properties of the soil surface. Developing an accurate and easily-used model that can appropriately determine the runoff generation value is of strong demand. In this study a simple, an empirically based model developed to explore effect of soil properties on runoff generation. Thirty six dry-farming lands under follow conditions in a semi-arid agricultural zone in Hashtroud, NW Iran were considered to installation of runoff plots. Runoff volume was measured at down part of standard plots under natural rainfall events from March 2005 to March 2007. Results indicated that soils were mainly clay loam having 36.7% sand, 31.6% silt and 32.0% clay, and calcareous with about 13% lime. During a 2-year period, 41 natural rainfall events produced surface runoff at the plots. Runoff was negatively (R2=0.61, p<0.001) affected by soil permeability. Runoff also significantly correlated with sand, coarse sand, silt, organic matter, lime, and aggregate stability, while its relationship with very fine sand, clay, gravel and potassium was not significant. Regression analysis showed that runoff was considerably (p<0.001, R2=0.64) related to coarse sand, organic matter and lime. Lime like to coarse sand and organic matter positively correlated with soil permeability and consequently decreased runoff. This result revealed that, lime is one of the most important factors controlling runoff in soils of the semi-arid regions.
A novel algorithm with heuristic information for extracting drainage networks from raster DEMs
Authors: Yang W. , Hou K. , Yu F. , Liu Z. , Sun T.
Published: April 2010

Abstract. Extracting drainage networks from raster DEMs is a necessary requirement in almost all hydrological and environmental analyses and determining surface water flow direction is a fundamental problem. In a raster environment, surface water flow direction of each cell can be directed to the neighboring cell with the steepest downslope drop (The basic D8, deterministic eight-neighbour method), which is inadequate for routing flow over pits and flats. Several improved algorithms are proposed to find the outlet of pits and flats, which typically use entirely different procedures for processing pits and flats. Being different from others, this paper presents a new method to route flow through the pits and flats by searching for the outlet using the heuristic information to compensate inadequate searching information of other methods. Heuristic information can reveal the general trend of the DEM and help the proposed algorithm find the outlet of pits and flats accurately. Furthermore, the proposed algorithm can handle pits and flats effectively in one procedure. This new algorithm is implemented in Pascal and experiments are carried out on actual DEM data. It can be seen from the comparison of the drainage networks generated by the proposed algorithm and ArcGIS 9.2, the proposed algorithm with heuristic information can get a closer match result with existing river networks and avoid the generation of the unrealistic parallel drainage lines, unreal drainage lines and spurious terrain features.
Responses of snowmelt runoff to climatic change in an inland river basin, Northwestern China, over the past 50a
Authors: Wang J. , Li H.-Y. , Hao X.-H.
Published: April 2010

Abstract. The spatial and temporal variations of snowcover distribution, and snowmelt runoffs are considered as sensitive indicators for climatic change. The purpose of this paper is to analyze and forecast the responses of snowmelt runoff to climate change. The upstream of Heihe River Basin in Northwestern China was chose as the representative catchments, and the observation data of the meteorological and hydrological stations were utilized to analyze the status and the regularity for the climatic change from 1956 to 2008. Moderate Resolution Imaging Spectroradiometer (MODIS) data were used to develop an optimized technology for snow mapping in the mountainous region. Snowmelt Runoff Model (SRM) was chose to simulate snowmelt runoff and scenario forecast the change trend of snowmelt runoff in catchment scale for the mountainous region in Northwestern China. The results show that climatic warming was apparent in the upstream of Heihe River Basin in the past 50a. Annual average air temperature of three different weather stations located in the basin has increased 2.1 °C, 2.6 °C and 2.9 °C, respectively. The snowmelt runoff has increased obviously from 1970 to present. With different warming climate scenarios, the results by SRM simulating showed that the first occurred time of snowmelt runoff shift ahead and discharge become larger as responses of snowmelt runoff to air temperature increasing, and the influence of temperature rising on average discharge of the whole snow season is not obvious. On the other hand, simulated discharge showed a marked increase trend with the increase of precipitation. And, the simulated results show that the increase of precipitation almost has no influence on the occurring time of snowmelt runoff.
Roles of spatially varying vegetation on surface fluxes within a small mountainous catchment
Authors: Flerchinger G. N. , Marks D. , Reba M. L. , Yu Q. , Seyfried M. S.
Published: April 2010

Abstract. Understanding the role of ecosystems in modulating energy, water and carbon fluxes is critical to quantifying the variability in energy, carbon, and water balances across landscapes. This study compares and contrasts the seasonal surface fluxes of sensible heat, latent heat and carbon fluxes measured over different vegetation in a rangeland mountainous environment within the Reynolds Creek Experimental Watershed. Eddy covariance systems were used to measure surface fluxes over low sagebrush (Artemesia arbuscula), aspen (Populus tremuloides) and the understory of grasses and forbs beneath the aspen canopy. Peak leaf area index of the sagebrush, aspen, and aspen understory was 0.77, 1.35, and 1.20, respectively. The sagebrush and aspen canopies were subject to similar meteorological forces, while the understory of the aspen was sheltered from the wind. Estimated cumulative evapotranspiratation from the sagebrush, aspen understory, and aspen trees were 399 mm, 205 mm and 318 mm. A simple water balance of the catchment indicated that of the 700 mm of areal average precipitation, 442 mm was lost to evapotranspiration, and 254 mm of streamflow was measured from the catchment; water balance closure for the catchment was within 7 mm. Fluxes of latent heat and carbon for all sites were minimal through the winter. Growing season fluxes of latent heat and carbon were consistently higher above the aspen canopy than from the other sites. While growing season carbon fluxes were very similar for the sagebrush and aspen understory, latent heat fluxes for the sagebrush were consistently higher. Higher evapotranspiration from the sagebrush was likely because it is more exposed to the wind. Sensible heat flux from the aspen tended to be slightly less than the sagebrush site during the growing season when the leaves were actively transpiring, but exceeded that from the sagebrush in May, September and October when the net radiation was offset by evaporative cooling. Results from this study illustrate the influence of vegetation on the spatial variability of surface fluxes across mountainous rangeland landscapes.
Modelling soil moisture at SMOS scale by use of a SVAT model over the Valencia Anchor Station
Authors: Juglea S. , Kerr Y. , Mialon A. , Wigneron J.-P. , Lopez-Baeza E. , Cano A. , Albitar A. , Millan-Scheiding C. , Carmen Antolin M. , Delwart S.
Published: April 2010

Abstract. The main goal of the SMOS (Soil Moisture and Ocean Salinity) mission is to deliver global fields of surface soil moisture and sea surface salinity using L-band (1.4 GHz) radiometry. Within the context of the preparation for this mission over land, the Valencia Anchor Station experimental site, in Spain, was chosen to be one of the main test sites in Europe for the SMOS Calibration/Validation (Cal/Val) activities. Ground and meteorological measurements over the area are used as the input of a Soil-Vegetation-Atmosphere-Transfer (SVAT) model, SURFEX (Externalized Surface)-module ISBA (Interactions between Soil-Biosphere-Atmosphere) so as to simulate the surface soil moisture. The calibration as well as the validation of the ISBA model was made using in situ soil moisture measurements. It is shown that a good consistency was reached when point comparisons between simulated and in situ soil moisture measurements were made. In order to obtain an accurate soil moisture mapping over the Valencia Anchor Station (50×50 km2 area), a spatialization method has been applied. To validate the approach, a comparison with remote sensing data from the Advanced Microwave Scanning Radiometer on Earth observing System (AMSR-E) and from the European Remote Sensing Satellites (ERS-Scat) was performed. Despite the fact that AMSR-E surface soil moisture product is not reproducing accurately the absolute values, it provides trustworthy information on surface soil moisture temporal variability. However, during the vegetation growing season the signal is perturbed. By using the polarization ratio a better agreement is obtained. ERS-Scat soil moisture products were also used to be compared with the simulated spatialized soil moisture. The seasonal variations were well reproduced. However, the lack of soil moisture data over the area (45 observations for one year) was a limit into completely understanding the soil moisture variability.
Shallow soil moisture – ground thaw interactions and controls – Part 2: Influences of water and energy fluxes
Authors: Guan X. J. , Spence C. , Westbrook C. J.
Published: April 2010

Abstract. The companion paper (Guan et al., 2010) demonstrated variable interactions and correlations between shallow soil moisture and ground thaw in soil filled areas along a wetness spectrum in a subarctic Canadian Precambrian Shield landscape. From wetter to drier, these included a wetland, peatland and soil filled valley. Herein, water and energy fluxes were examined for these same subarctic study sites to discern the key controlling processes on the found patterns. Results showed the key control in variable soil moisture and frost table interactions among the sites was the presence of surface water. At the peatland and wetland sites, accumulated water in depressions and flow paths maintained soil moisture for a longer duration than at the hummock tops. These wet areas were often locations of deepest thaw depth due to the transfer of latent heat accompanying lateral surface runoff. Although the peatland and wetland sites had large inundation extent, modified Péclet numbers indicated the relative influence of external and internal hydrological processes at each site were different. Continuous inflow from an upstream lake into the wetland site caused advective and conductive thermal energies to be of equal importance to conductive ground thaw. The absence of continuous surface flow at the peatland and valley sites led to dominance of conductive thermal energy over advective energy for ground thaw. The results suggest that the modified Péclet number could be a very useful parameter to differentiate landscape components in modeling frost table heterogeneity. The calculated water and energy fluxes, and the modified Péclet number provide quantitative explanations for the shallow soil moisture-ground thaw patterns by linking them with hydrological processes and hillslope storage capacity.
Probabilistic modelling of rainfall induced landslide hazard assessment
Authors: Kawagoe S. , Kazama S. , Sarukkalige P. R.
Published: April 2010

Abstract. To evaluate the frequency and distribution of landslides hazards over Japan, this study uses a probabilistic model based on multiple logistic regression analysis. Study particular concerns several important physical parameters such as hydraulic parameters, geographical parameters and the geological parameters which are considered to be influential in the occurrence of landslides. Sensitivity analysis confirmed that hydrological parameter (hydraulic gradient) is the most influential factor in the occurrence of landslides. Therefore, the hydraulic gradient is used as the main hydraulic parameter; dynamic factor which includes the effect of heavy rainfall and their return period. Using the constructed spatial data-sets, a multiple logistic regression model is applied and landslide susceptibility maps are produced showing the spatial-temporal distribution of landslide hazard susceptibility over Japan. To represent the susceptibility in different temporal scales, extreme precipitation in 5 years, 30 years, and 100 years return periods are used for the evaluation. The results show that the highest landslide hazard susceptibility exists in the mountain ranges on the western side of Japan (Japan Sea side), including the Hida and Kiso, Iide and the Asahi mountainous range, the south side of Chugoku mountainous range, the south side of Kyusu mountainous and the Dewa mountainous range and the Hokuriku region. The developed landslide hazard susceptibility maps in this study will assist authorities, policy makers and decision makers, who are responsible for infrastructural planning and development, as they can identify landslide-susceptible areas and thus decrease landslide damage through proper preparation.
Explicit simulations of stream networks to guide hydrological modelling in ungauged basins
Authors: Stoll S. , Weiler M.
Published: April 2010

Abstract. Rainfall-runoff modelling in ungauged basins is still one of the greatest challenges in recent hydrological research. The lack of discharge data necessitates the establishment of new innovative approaches to guide hydrological modelling in ungauged basins. Besides the transfer of calibrated parameters from similar gauged catchments, the application of distributed data as a hydrological response in addition to discharge seems to be promising. A new approach for model and parameter evaluation based on explicit simulation of the spatial stream network was tested in four different catchments in Germany. In a first step, spatial explicit modelling of stream networks was performed using a simplified version of the process-based model Hill-Vi together with regional climate normals. The simulated networks were compared to mapped stream networks and their degree of spatial agreement was evaluated. Significant differences between good and poor simulations could be distinguished and the corresponding parameter sets relate well with the hydrogeological properties of the catchments. The optimized parameters were subsequently used to simulate daily discharge using an observed time series of precipitation and air temperature. The performance was evaluated against observed discharge and water balance. This approach shows some promising results but also some limitations. Although the model's parsimonious model structure should to be further improved regarding discharge recession and evapotranspiration, the performance was similar to the regionalisation methods. Stream network modelling, which has minimal data requirements, seems to be a reasonable alternative for model development and parameter evaluation in ungauged basins.
Investigation of over-horizon VHF radio signals associated with earthquakes
Authors: Fukumoto Y. , Hayakawa M. , Yasuda H.
Published: April 2010

Abstract. This paper presents the preliminary results on the possible reception of over-horizon VHF radio signals from a FM (frequency modulation) transmitter during abnormal situations (probably in close association with earthquakes). The transmitter is FM Sendai (frequency = 77.1 MHz) and the receiving station is our university (UEC) at Chofu, Tokyo, with the transmitter-receiver distance being about 310 km. We first show a typical example of the reception of over-horizon VHF signals in which we present the amplitude behavior, azimuthal and incident angle estimation, etc. Then, we study the correlation between a signal anomaly and an earthquake and it seems that the over-horizon VHF signals observed are probably associated with earthquakes, observed about 7 to 0 days before an earthquake. The direction finding measurements have indicated that such signals are due to favorable tropospheric (but not ionospheric) conditions attributed to the effects of earthquakes.