bluuebunny/crossref_metadata_2025 huggingface dataset:
Root reinforcement and slope bioengineering stabilization by Spanish Broom (Spartium junceum L.)
Authors: Preti F. , Giadrossich F.
Published: April 2010

Abstract. The present paper deals with the characteristics of the root system of Spanish Broom (Spartium junceum L.), a species that is worth taking into consideration for its capacity for adaptation and resistance to drought. In particular, the aims of the study were 1) to investigate the plant's bio-mechanical aspects and 2) to verify whether root reinforcement and the field rooting ability of stem cuttings enhance its potential for use in slope stabilization and soil bio-engineering techniques, particularly in Mediterranean areas. Single root specimens were sampled and tested for tensile strength, obtaining classical tensile strength-diameter relationships. Analyses were performed on the root systems in order to assess root density distribution. The Root Area Ratio (RAR) was analyzed by taking both direct and indirect measurements, the latter relying on image processing. The data obtained were used to analyze the stability of an artificial slope (landfill) and root reinforcement. The measurement and calculation of mean root number, mean root diameter, RAR, root cohesion and Factor of safety are presented in order to distinguish the effect of plant origin and propagation. Furthermore, tests were performed to assess the possibility of agamic propagation (survival rate of root-ball endowed plants, rooting from stem cuttings). These tests confirmed that agamic propagation is difficult, even though roots were produced from some buried stems, and for practical purposes it has to be ruled out. Our results show that Spanish Broom has good bio-mechanical characteristics with regard to slope stabilization, even in critical pedoclimatic conditions and where inclinations are quite steep, and it is effective on soil depths of up to about 50 cm, in agreement with other studies on Mediterranean species. It is effective in slope stabilization, but less suitable for soil bio-engineering or for triggering natural plant succession.
Comment on "Biotic pump of atmospheric moisture as driver of the hydrological cycle on land" by A. M. Makarieva and V. G. Gorshkov, Hydrol. Earth Syst. Sci., 11, 1013–1033, 2007
Authors: Meesters A. G. C. A. , Dolman A. J. , Bruijnzeel L. A.
Published: April 2010

Abstract. In their paper "Biotic pump of atmospheric moisture as driver of the hydrological cycle on land", Makarieva and Gorshkov (Hydrol. Earth Syst. Sci., 11, 1013–1033, 2007) derive from "previously unstudied" properties of atmospheric water vapor, the existence of a hitherto unknown "evaporative force". From this, a novel physical principle is deduced, according to which low-level air flows from regions with weak, to regions with strong evaporation. As such, natural forests are claimed to "suck in" moist air from the ocean, a process labeled the "biotic pump of atmospheric moisture". This commentary focuses on the physical foundations of the biotic pump theory, which is presented as revolutionary by Makarieva and Gorshkov. It is shown that the "evaporative force" on which the theory is built, is an untenable result of confused and inappropriately used physical principles. The problem of moisture transport and its dependence on vegetation cover considered by Makarieva and Gorshkov is certainly important, but cannot be solved along the lines proposed by them.
Hillslope hydrology under glass: confronting fundamental questions of soil-water-biota co-evolution at Biosphere 2
Authors: Hopp L. , Harman C. , Desilets S. , Graham C. , McDonnell J. , Troch P.
Published: April 2010

Abstract. Recent studies have called for a new unifying hydrological theory at the hillslope and watershed scale, emphasizing the importance of coupled process understanding of the interactions between hydrology, ecology, pedology, geochemistry and geomorphology. The Biosphere 2 Hillslope Experiment aims at exploring how climate, soil and vegetation interact and drive the evolution of the hydrologic hillslope behavior using a set of three large-scale hillslopes (18 m by 33 m each) that will be built in the climate-controlled experimental biome of the Biosphere 2 facility near Tucson, Arizona, USA. By minimizing the initial physical complexity of these hillslopes, the spontaneous formation of flow pathways, soil spatial heterogeneity, surface morphology and vegetation patterns can be observed over time. This paper documents the hydrologic design process for the Biosphere 2 Hillslope Experiment, which was based on design principles agreed upon among the Biosphere 2 science community. Main design principles were that the hillslopes should promote spatiotemporal variability of hydrological states and fluxes, facilitate transient lateral subsurface flow without inducing overland flow and be capable of supporting vegetation. Hydrologic modeling was used to identify a hillslope configuration (geometry, soil texture, soil depth) that meets the design objectives. The recommended design for the hillslopes consists of a zero-order basin shape with a 10 degree overall slope, a uniform soil depth of 1 m and a loamy sand soil texture. The sensitivity of the hydrologic response of this design to different semi-arid climate scenarios was subsequently tested. Modeling results show that the timing of rainfall in relation to the timing of radiation input controls the spatiotemporal variability of moisture within the hillslope and the generation of lateral subsurface flow. The Biosphere 2 Hillslope Experiment will provide an excellent opportunity to test hypotheses, observe emergent patterns and advance the understanding of interactions.
Coupled modeling of hydrologic and geochemical fluxes for prediction of solid phase evolution in the Biosphere 2 hillslope experiment
Authors: Dontsova K. , Steefel C. I. , Desilets S. , Thompson A. , Chorover J.
Published: April 2010

Abstract. A reactive transport geochemical modeling study was conducted to help predict the mineral transformations occurring over a ten year time-scale that are expected to impact soil hydraulic properties in the Biosphere 2 (B2) synthetic hillslope experiment. The modeling sought to predict the rate and extent of weathering of a granular basalt (selected for hillslope construction) as a function of climatic drivers, and to assess the feedback effects of such weathering processes on the hydraulic properties of the hillslope. Flow vectors were imported from HYDRUS into a reactive transport code, CrunchFlow2007, which was then used to model mineral weathering coupled to reactive solute transport. Associated particle size evolution was translated into changes in saturated hydraulic conductivity using Rosetta software. We found that flow characteristics, including velocity and saturation, strongly influenced the predicted extent of incongruent mineral weathering and neo-phase precipitation on the hillslope. Results were also highly sensitive to specific surface areas of the soil media, consistent with surface reaction controls on dissolution. Effects of fluid flow on weathering resulted in significant differences in the prediction of soil particle size distributions, which should feedback to alter hillslope hydraulic conductivities.
Copula based multisite model for daily precipitation simulation
Authors: Bárdossy A. , Pegram G.
Published: April 2010

Abstract. From the point of view of multisite stochastic daily rainfall modelling, there are two new ideas introduced in this paper. The first is the use of asymmetrical copulas to model the spatial interdependence structure of the rainfall amounts together with the rainfall occurrences in one relationship. The second is in the evaluation of the (necessary but often ignored) clustering behaviour of the simulated rainfall; this evaluation is performed by calculating the entropy of the observations at all the acute angled triangles that can be formed from the sequences at the gauge sites, as a function of their mutual separation distance. It turns out that the model captures the qualities desired and offers a fresh approach to a relatively mature problem in hydrometeorology.
Influence of thermodynamic soil and vegetation parameterizations on the simulation of soil temperature states and surface fluxes by the Noah LSm over a Tibetan plateau site
Authors: van der Velde R. , Su Z. , Ek M. , Rodell M. , Ma Y.
Published: April 2010

Abstract. In this paper, we investigate the ability of the Noah Land Surface model (LSm) to simulate temperature states in the soil profile and surface fluxes measured during a 7-day dry period at a micrometeorological station on the Tibetan Plateau. Adjustments in soil and vegetation parameterizations required to ameliorate the Noah simulation on these two aspects are presented, which include: (1) Differentiating the soil thermal properties of top- and subsoils, (2) Investigation of the different numerical soil discretizations and (3) Calibration of the parameters utilized to describe the transpiration dynamics of the Plateau vegetation. Through the adjustments in the parameterization of the soil thermal properties (STP) simulation of the soil heat transfer is improved, which results in a reduction of Root Mean Squared Differences (RMSD's) by 14%, 18% and 49% between measured and simulated skin, 5-cm and 25-cm soil temperatures, respectively. Further, decreasing the minimum stomatal resistance (Rc, min) and the optimum temperature for transpiration (Topt) of the vegetation parameterization reduces RMSD's between measured and simulated energy balance components by 30%, 20% and 5% for the sensible, latent and soil heat flux, respectively.
Discharge simulations performed with a hydrological model using bias corrected regional climate model input
Authors: van Pelt S. C. , Kabat P. , ter Maat H. W. , van den Hurk B. J. J. M. , Weerts A. H.
Published: April 2010

Abstract. Studies have demonstrated that precipitation on Northern Hemisphere mid-latitudes has increased in the last decades and that it is likely that this trend will continue. This will have an influence on discharge of the river Meuse. The use of bias correction methods is important when the effect of precipitation change on river discharge is studied. The objective of this paper is to investigate the effect of using two different bias correction methods on output from a Regional Climate Model (RCM) simulation. In this study a Regional Atmospheric Climate Model (RACMO2) run is used, forced by ECHAM-5 under the condition of the SRES-A1B emission scenario, with a 25 km horizontal resolution. The RACMO2 runs contain a systematic precipitation bias on which two bias correction methods are applied. The first method corrects for the wet day fraction and wet day average (WD bias correction) and the second method corrects for the mean and coefficient of variance (MV bias correction). The WD bias correction initially corrects well for the average, but it appears that too many successive precipitation days were removed with this correction. The second method performed less well on average bias correction, but the temporal precipitation pattern was better. Subsequently, the discharge was calculated by using RACMO2 output as forcing to the HBV-96 hydrological model. A large difference was found between the simulated discharge of the uncorrected RACMO2 run, the WD bias corrected run and the MV bias corrected run. These results show the importance of an appropriate bias correction.
Global-scale analysis of river flow alterations due to water withdrawals and reservoirs
Authors: Döll P. , Fiedler K. , Zhang J.
Published: April 2010

Abstract. Global-scale information on natural river flows and anthropogenic river flow alterations is required to identify areas where aqueous ecosystems are expected to be strongly degraded. Such information can support the identification of environmental flow guidelines and a sustainable water management that balances the water demands of humans and ecosystems. This study presents the first global assessment of the anthropogenic alteration of river flow regimes by water withdrawals and dams, focusing in particular on the change of flow variability. Six ecologically relevant flow indicators were quantified using an improved version of the global water model WaterGAP. WaterGAP simulated, with a spatial resolution of 0.5 degree, river discharge as affected by human water withdrawals and dams, as well as naturalized discharge without this type of human interference. Mainly due to irrigation, long-term average river discharge and statistical low flow Q90 (monthly river discharge that is exceeded in 9 out of 10 months) have decreased by more than 10% on one sixth and one quarter of the global land area (excluding Antarctica and Greenland), respectively. Q90 has increased significantly on only 5% of the land area, downstream of reservoirs. Due to both water withdrawals and dams, seasonal flow amplitude has decreased significantly on one sixth of the land area, while interannual variability has increased on one quarter of the land area mainly due to irrigation. It has decreased on only 8% of the land area, in areas with little consumptive water use that are downstream of dams. Areas most affected by anthropogenic river flow alterations are the western and central USA, Mexico, the western coast of South America, the Mediterranean rim, Southern Africa, the semi-arid and arid countries of the Near East and Western Asia, Pakistan and India, Northern China and the Australian Murray-Darling Basin, as well as some Arctic rivers. Due to a large number of uncertainties related e.g. to the estimation of water use and reservoir operation rules, the analysis is expected to provide only first estimates of river flow alterations that should be refined in the future.
The contribution of groundwater discharge to the overall water budget of Boreal lakes in Alberta/Canada estimated from a radon mass balance
Authors: Schmidt A. , Gibson J. J. , Santos I. R. , Schubert M. , Tattrie K.
Published: April 2010

Abstract. Radon-222, a naturally-occurring radioisotope with a half-life of 3.8 days, was used to estimate groundwater discharge to small lakes in wetland-rich basins in the vicinity of Fort McMurray, Alberta, a region under significant water development pressures including both oil sands mining and in situ extraction. A program of field investigations was carried out in March and July 2008 using a Durridge RAD-7® and RAD Aqua® to measure radon-222 activity distributions in dissolved gas in the water column of two lakes as a tracer of groundwater discharge in the timeframe of 4 half-lives (15 days). Radon activity concentrations in lakes was found to range from 0.5 to 72 Bq/m3, compared to radon activity concentrations in groundwaters, measured using a RAD H2O, in the range of 2000–8000 Bq/m3. Radon mass balance, used in comparison with stable isotope mass balance, suggested that the two lakes under investigation had quite different proportions of annual groundwater inflow, one being close to 0.5% of annual inflow and the other about 14%, with lower values in the former attributed to a larger drainage area/lake area ratio which promotes greater surface connectivity. Interannual variability in groundwater proportions is expected despite constancy of groundwater discharge rates due to observed variability in annual surface runoff. Combination of stable isotope and radon mass balance approaches provides information on flowpath partitioning that is useful for evaluating surface-groundwater connectivity and acid sensitivity of individual water bodies of interest in the Alberta Oil Sands Region.
Modeling nutrient in-stream processes at the watershed scale using Nutrient Spiralling metrics
Authors: Marcé R. , Armengol J.
Published: April 2010

Abstract. One of the fundamental problems of using large-scale biogeochemical models is the uncertainty involved in aggregating the components of fine-scale deterministic models in watershed applications, and in extrapolating the results of field-scale measurements to larger spatial scales. Although spatial or temporal lumping may reduce the problem, information obtained during fine-scale research may not apply to lumped categories. Thus, the use of knowledge gained through fine-scale studies to predict coarse-scale phenomena is not straightforward. In this study, we used the nutrient uptake metrics defined in the Nutrient Spiralling concept to formulate the equations governing total phosphorus in-stream fate in a watershed-scale biogeochemical model. The rationale of this approach relies on the fact that the working unit for the nutrient in-stream processes of most watershed-scale models is the reach, the same unit used in field research based on the Nutrient Spiralling concept. Automatic calibration of the model using data from the study watershed confirmed that the Nutrient Spiralling formulation is a convenient simplification of the biogeochemical transformations involved in total phosphorus in-stream fate. Following calibration, the model was used as a heuristic tool in two ways. First, we compared the Nutrient Spiralling metrics obtained during calibration with results obtained during field-based research in the study watershed. The simulated and measured metrics were similar, suggesting that information collected at the reach scale during research based on the Nutrient Spiralling concept can be directly incorporated into models, without the problems associated with upscaling results from fine-scale studies. Second, we used results from our model to examine some patterns observed in several reports on Nutrient Spiralling metrics measured in impaired streams. Although these two exercises involve circular reasoning and, consequently, cannot validate any hypothesis, this is a powerful example of how models can work as heuristic tools to compare hypotheses and stimulate research in ecology.
The water footprint of Indonesian provinces related to the consumption of crop products
Authors: Bulsink F. , Hoekstra A. Y. , Booij M. J.
Published: April 2010

Abstract. National water use accounts are generally limited to statistics on water withdrawals in the different sectors of economy. They are restricted to "blue water accounts" related to production, thus excluding (a) "green" and "grey water accounts", (b) accounts of internal and international virtual water flows and (c) water accounts related to consumption. This paper shows how national water-use accounts can be extended through an example for Indonesia. The study quantifies interprovincial virtual water flows related to trade in crop products and assesses the green, blue and grey water footprint related to the consumption of crop products per Indonesian province. The study shows that the average water footprint in Indonesia insofar related to consumption of crop products is 1131 m3/cap/yr, but provincial water footprints vary between 859 and 1895 m3/cap/yr. Java, the most water-scarce island, has a net virtual water import and the most significant external water footprint. This large external water footprint is releasing the water scarcity on this island. There are two alternative routes to reduce the overall water footprint of Indonesia. On the one hand, it may be reduced by promoting wise crop trade between provinces – i.e. trade from places with high to places with low water efficiency. On the other hand, the water footprint can be reduced by improving water efficiency in those places that currently have relatively low efficiency, which equalises production efficiencies and thus reduces the need for imports and enhances the opportunities for exports. In any case, trade will remain necessary to supply food to the most densely populated areas where water scarcity is highest (Java).
Geodynamical processes in the channel connecting the two lobes of the Large Aral Sea
Authors: Roget E. , Zavialov P. , Khan V. , Muñiz M. A.
Published: April 2010

Abstract. Reasons for the existence of the channel connecting the two lobes of the present Large Aral Sea are discussed. In situ measurements show that differences between the measured depths and those contained in the available digital bathymetry of the lake are considerably different at the channel (7.5±0.9 m, at nine measurement stations along it) and at the northern part of the eastern lobe (1.6±0.3 m, at six stations from the western to the eastern shore). Differences in the misfits observed in the two zones are discussed and thought to be a consequence of the variation of the transversal area of the channel as it enters the eastern lobe, which would affect the flow velocity and thus the strength of the erosion process at the bottom. Field data together with satellite images have been used to modify an original digital bathymetry of the lake and have been implemented into a 3-D hydrodynamical model. A numerical simulation shows that a wind of 12 m/s blowing from the east (112°) generates velocities of up to 45 cm/s in the channel, allowing denser water from the eastern lobe (salinity: 132 g/kg) to flow about 38 km towards the fresher western lobe (salinity: 98 g/kg) in one day. The effect of the inflow on the vertical structure of the western lobe is also illustrated. All in all, the Aral Sea is presented as an example where geomorphologic and geophysical processes, along with hydrological and atmospheric processes, must be taken into account for short-term predictions.
Analysis of surface soil moisture patterns in agricultural landscapes using empirical orthogonal functions
Authors: Korres W. , Koyama C. N. , Fiener P. , Schneider K.
Published: April 2010

Abstract. Soil moisture is one of the fundamental variables in hydrology, meteorology and agriculture. Nevertheless, its spatio-temporal patterns in agriculturally used landscapes affected by multiple natural (rainfall, soil, topography etc.) and agronomic (fertilisation, soil management etc.) factors are often not well known. The aim of this study is to determine the dominant factors governing the spatio-temporal patterns of surface soil moisture in a grassland and an arable land test site within the Rur catchment in Western Germany. Surface soil moisture (0–6 cm) has been measured in an approx. 50×50 m grid at 14 and 17 dates (May 2007 to November 2008) in both test sites. To analyse spatio-temporal patterns of surface soil moisture, an Empirical Orthogonal Function (EOF) analysis was applied and the results were correlated with parameters derived from topography, soil, vegetation and land management to connect the pattern to related factors and processes. For the grassland test site, the analysis results in one significant spatial structure (first EOF), which explains about 57.5% of the spatial variability connected to soil properties and topography. The weight of the first spatial EOF is stronger on wet days. The highest temporal variability can be found in locations with a high percentage of soil organic carbon (SOC). For the arable land test site, the analysis yields two significant spatial structures, the first EOF, explaining 38.4% of the spatial variability, shows a highly significant correlation to soil properties, namely soil texture. The second EOF, explaining 28.3% of the spatial variability, is connected to differences in land management. The soil moisture in the arable land test site varies more during dry and wet periods on locations with low porosity.
Technical Note: Linking soil – and stream-water chemistry based on a riparian flow-concentration integration model
Authors: Seibert J. , Grabs T. , Köhler S. , Laudon H. , Winterdahl M. , Bishop K.
Published: April 2010

Abstract. The riparian zone, the last few meters of soil through which water flows before entering the stream, has been identified as a first order control on key aspects of stream water chemistry dynamics. We propose that the vertical distribution of lateral water flow across the profile of soil water chemistry in the riparian zone provides a conceptual explanation of how this control functions in catchments where matrix flow predominates. This paper presents a mathematical implementation of this concept as well as the model assumptions. We also present an analytical solution, which provides a physical basis for the commonly used power-law flow-load equation. This approach quantifies the concept of riparian control on stream-water chemistry providing a basis for testing the concept of riparian control. By backward calculation of soil-water-chemistry profiles and comparing those with observed profiles we demonstrate that the simple juxtaposition of water fluxes and soil water chemistry provides a plausible explanation for observed stream-water-chemistry variations of several major stream components such as Total Organic Carbon (TOC), magnesium, calcium and chloride. The "static" implementation of the model structure presented here provides a basis for further development to account for seasonal influences and hydrological hysteresis.
Characteristics and drivers of baseflow response in 183 Australian catchments
Authors: van Dijk A. I. J. M.
Published: April 2010

Abstract. Daily streamflow data for 183 Australian catchments were used to assess the characteristics and main drivers of baseflow and quick flow behaviour, and to find an appropriate balance between simplicity and explanatory performance in modelling. Baseflow separation was performed following the Wittenberg algorithm. A linear reservoir model (one parameter) produced baseflow estimates as good as those obtained using a non-linear reservoir (two parameters) and was therefore considered the more appropriate. The transition from storm flow dominated to baseflow dominated streamflow generally occurred 7 to 10 d after the storm event. The catchments investigated had baseflow half-times of about 12 d, with 80% of stations having half-times between 7 and 34 d. The shortest half-times occurred in the driest catchments and were attributed to intermittent occurrence of fast-draining (possibly perched) groundwater. Median baseflow index (BFI) was 0.45 with considerable variation between stations. Catchment humidity explained 27% of the variation in derived baseflow recession coefficients. Another 53% of variance in recession coefficients as well as in BFI showed spatial correlation lengths of 200 to 300 km, corresponding to terrain factors rather than climate or land use. The remaining 16 to 20% of variance remained unexplained. Most (84%) of the variation between stations in average baseflow could be explained by monthly precipitation in excess of potential evapotranspiration. Most (70%) of the variation in average quick flow could be explained by average rainfall. Another 20% of variation was spatially correlated over spatial scales of 400 km, possibly reflecting a combination of terrain and climate factors; the remaining 10 to 16% remained unexplained.
Factors influencing chloride deposition in a coastal hilly area and application to chloride deposition mapping
Authors: Guan H. , Love A. J. , Simmons C. T. , Kayaalp A. S.
Published: April 2010

Abstract. Chloride is commonly used as an environmental tracer for studying water flow and solute transport in the environment. It is especially useful for estimating groundwater recharge based on the commonly used chloride mass balance (CMB) method. Strong spatial variability in chloride deposition in coastal areas is one difficulty encountered in appropriately applying the CMB approach. Furthermore, intensive vegetation clearance for agriculture, for example during the European settlement in many coastal areas of Australia, may have perturbed catchment chloride balance conditions for appropriate use in CMB applications. In order to deal with these issues, a high resolution chloride deposition map in the coastal region is needed. In this study, we examined geographic, orographic, and atmospheric factors influencing chloride deposition in the Mount Lofty Ranges (MLR), a coastal hilly area of approximately 9000 km2 spatial extent in South Australia, using partial correlation and regression analyses. The results indicate that coastal distance, and terrain aspect and slope are two most significant factors controlling chloride deposition. Coastal distance accounts for 65% spatial variability in chloride deposition, with terrain aspect and slope for 8%. The deposition gradient is about 0.08 gm-2 year-1 km-1 as one progresses inland. The results are incorporated into a published de-trended residual kriging approach (ASOADeK) to produce a 1 km×1 km resolution annual chloride deposition map and a bulk precipitation chloride concentration map. The average uncertainty of the deposition map is about 30% in the western MLR, and over 50% in the eastern MLR. The maps will form a very useful basis for examining catchment chloride balances for use in the CMB application in the study area.
Improving the rainfall rate estimation in the midstream of the Heihe River Basin using rain drop size distribution
Authors: Zhao G. , Chu R. , Li X. , Zhang T. , Shen J. , Wu Z.
Published: April 2010

Abstract. During the intensive observation period of the Watershed Allied Telemetry Experimental Research (WATER), a total of 1074 raindrop size distribution were measured by the Parsivel disdrometer, a latest state of the art optical laser instrument. Because of the limited observation data in Qinghai-Tibet Plateau, the modeling behavior was not well-done. We used raindrop size distributions to improve the rain rate estimator of meteorological radar, in order to obtain many accurate rain rate data in this area. We got the relationship between the terminal velocity of the rain drop and the diameter (mm) of a rain drop: v(D)=4.67 D0.53. Then four types of estimators for X-band polarimetric radar are examined. The simulation results show that the classical estimator R(Z) is most sensitive to variations in DSD and the estimator R (KDP, Z, ZDR) is the best estimator for estimating the rain rate. The lowest sensitivity of the rain rate estimator R (KDP, Z, ZDP) to variations in DSD can be explained by the following facts. The difference in the forward-scattering amplitudes at horizontal and vertical polarizations, which contributes KDP, is proportional to the 3rd power of the drop diameter. On the other hand, the exponent of the backscatter cross section, which contributes to Z, is proportional to the 6th power of the drop diameter. Because the rain rate R is proportional to the 3.57th power of the drop diameter, KDP is less sensitive to DSD variations than Z.
Assessing the added value of high-resolution isotope tracer data in rainfall-runoff modelling
Authors: Birkel C. , Dunn S. M. , Tetzlaff D. , Soulsby C.
Published: April 2010

Abstract. A study has been undertaken in a small agricultural catchment in east Scotland with the objective of assessing the value of high-resolution isotope data for integration within hydrological models. Daily samples of precipitation and stream flow, collected over a year, have been analyzed for deuterium content using new laser spectroscopy technology. This study set out to evaluate whether the utility of such high-resolution isotope data outweighs the associated uncertainty, as well as uncertainty in discharge measurements. A multi-criteria approach was used to evaluate the simulation of two independent objective functions – stream flow and stream deuterium – against model and data errors. Particular emphasis was placed on different input and output sampling resolutions. The data indicate that moderate isotopic variability in the stream response between rainfall events, which is not captured using weekly tracer data, has little influence on model performance. In contrast, the input resolution of precipitation deuterium concentrations, which were much more variable, proved to be crucial. A low-parameterized Catchment Isotope Model (CIM) was developed and adequately reflects flow dynamics and deuterium peaks, but a simple assumption of ''good-mixing'' in the isotope module is not able to fully reproduce the daily stream deuterium dynamic. Multi-criteria evaluation, however, significantly constrained acceptable behavioural parameter sets and therefore reduced the model's degree of freedom. This approach has provided further assessment of the value of tracers in hydrological modelling, demonstrating their usefulness in terms of model conceptualization, development and calibration, which outweighs the additional parameter and measurement uncertainty.
Flood trends and variability in the Mekong river
Authors: Delgado J. M. , Apel H. , Merz B.
Published: April 2010

Abstract. Annual maximum discharge is analyzed in the Mekong river in Southeast Asia with regard to average flood trends and variability during the 20th century. Data from four gauging stations downstream of Vientiane, Laos, were used, covering two distinct hydrological regions within the Mekong basin. These time series span through over 70 years and are the longest daily discharge time series available in the region. The methods used, Mann Kendal test (MK), ordinary least squares with resampling (OLS) and non-stationary general extreme value function (NSGEV), are first tested in a Monte Carlo experiment, in order to evaluate their detection power in presence of changing variance in the time series. The time series are generated using the general extreme value function with linearly varying scale and location parameter. NSGEV outperforms MK and OLS, both because it incurred in less type II errors, but also because it allows for a more complete description of the trends, allowing to separate trends in average and in variability Results from MK, OLS and NSGEV agreed on trends in average flood behaviour. However, the introduction of a time-varying scale parameter in the NSGEV allowed to isolate flood variability from the average flood trend and to have a more complete view of the changes. Overall, results showed an increasing likelihood of extreme floods during the last half of the century, although the probability of an average flood decreased during the same period. The variance, estimated with the wavelet power spectrum as a function of time, allowed to identify a period of enhanced variance in the last quarter of the 20th century, which confirmed the results of the NSGEV. We conclude that the initial absence of detected positive trends in the hydrological time series was a methodological misconception due to over-simplistic models.
The two-layer surface energy balance parameterization scheme (TSEBPS) for estimation of land surface heat fluxes
Authors: Xin X. , Liu Q.
Published: April 2010

Abstract. A Two-layer Surface Energy Balance Parameterization Scheme (TSEBPS) is proposed for the estimation of surface heat fluxes using thermal infrared (TIR) data over sparsely vegetated surfaces. TSEBPS is based on the theory of the classical two-layer energy balance model, as well as a set of new formulations derived from assumption of the energy balance at limiting cases. Two experimental data sets are used to assess the reliabilities of TSEBPS. Based on these case studies, TSEBPS has proven to be capable of estimating heat fluxes at vegetation surfaces with acceptable accuracy. The uncertainties in the estimated heat fluxes are comparable to in-situ measurement uncertainties.
Increase in surface runoff in the central mountains of Mexico: lessons from the past and predictive scenario for the next century
Authors: Gratiot N. , Duvert C. , Collet L. , Vinson D. , Némery J. , Saenz-Romero C.
Published: April 2010

Abstract. The hydrological response of a medium scale mountainous watershed (Mexico) is analysed over half a century. The hydrograph separation highlights an increasing surface runoff contribution since the early 1970's. This increase is attributed to land use changes while the meteorological forcing (rains) remains statistically stable over the same period. As a consequence, the intensity of annual extreme floods has tripled up over the period of survey, increasing flood risks in the region. The paper ends with a climatic projection over the 21st century. The decrease of precipitation and the increase of temperature should accentuate the trend engaged since the 1970's by reducing groundwater resources and increasing surface-runoff and associated risks.
Frozen soil parameterization in a distributed biosphere hydrological model
Authors: Wang L. , Koike T. , Yang K. , Jin R. , Li H.
Published: April 2010

Abstract. In this study, a frozen soil parameterization has been modified and incorporated into a distributed biosphere hydrological model (WEB-DHM). The WEB-DHM with the frozen scheme was then rigorously evaluated in a small cold area, the Binngou watershed, against the in-situ observations from the WATER (Watershed Allied Telemetry Experimental Research). In the summer 2008, land surface parameters were optimized using the observed surface radiation fluxes and the soil temperature profile at the Dadongshu-Yakou (DY) station in July; and then soil hydraulic parameters were obtained by the calibration of the July soil moisture profile at the DY station and by the calibration of the discharges at the basin outlet in July and August that covers the annual largest flood peak of 2008. The calibrated WEB-DHM with the frozen scheme was then used for a yearlong simulation from 21 November 2007 to 20 November 2008, to check its performance in cold seasons. Results showed that the WEB-DHM with the frozen scheme has given much better performance than the WEB-DHM without the frozen scheme, in the simulations of soil moisture profile at the DY station and the discharges at the basin outlet in the yearlong simulation.
Effect of the spatial distribution of physical aquifer properties on water table depth and stream discharge in a headwater catchment
Authors: Gascuel-Odoux C. , Weiler M. , Molenat J.
Published: April 2010

Abstract. Water table depth and its dynamics is often poorly predicted upslope despite they control both water transit time within the catchment and solute fluxes at the catchment outlet. The paper analyses how relaxing the assumption of lateral homogeneity of physical properties can improve simulations of water table depth and dynamics. Four different spatial models relating of saturated hydraulic conductivity to topography have been tested: a simple linear relationship, a linear relationship with two topographic indexes, two domains with a transitional area. The Hill-Vi model has been modified to test these hypotheses. The studied catchment (Kervidy-Naizin, western France) is underlain by schist crystalline bedrock. A shallow and perennial groundwater highly reactive to rainfall events mainly develops in the weathered saprolite layer. The results indicate that 1) discharge and the water table in the riparian zone are similarly predicted with the four models, 2) distinguishing two domains constitutes the best model and slightly improves prediction of the water table upslope, and 3) including spatial variations in the other parameters such as porosity or rate of hydraulic conductivity decrease with depth does not improve the results. These results underline the necessity of better investigation of upslope areas in hillslope hydrology.
Double diffusion in meromictic lakes of the temperate climate zone
Authors: von Rohden C. , Boehrer B. , Ilmberger J.
Published: April 2010

Abstract. Meromictic lakes are characterized by strong stable density stratification in and below the chemocline, which separates the oxic mixolimnion from the mostly anoxic monimolimnion. Stable density gradients involve slow vertical exchange, especially in the chemocline, where vertical transport can be as low as molecular. Typically, destabilizing temperature gradients establish in the monimolimnion as a consequence of seasonal changing heat fluxes. At the same time, gradients of solutes extending to the lake bottom stabilize the overall stratification. Double diffusive processes may create local instabilities and subsequently cause convective mixing when the destabilization due to heat gradients exceeds the stabilization by solutes (diffusive regime). This configuration can annually occur in the upper part of the monimolimnion, if seasonal temperature changes in the mixolimnion reach the top of the monimolimnion. We present CTD-measurements from two meromictic mining lakes in Germany, which document the seasonal occurrence of convective mixing in discrete horizontal homogeneous layers within the monimolimnion which can be identified by the characteristic step-like structure. In the deeper layers, the steps emerge with a time delay which is determined by the progression of the mixolimnetic temperature changes into the monimolimnion. Interestingly, the chemocline interface is not degraded by these processes. However, double diffusive convection is essential for the redistribution in the inner parts of the monimolimnion at longer time scales, which is crucial for the assessment of the ecologic development of such lakes.
Plot and field scale soil moisture dynamics and subsurface wetness control on runoff generation in a headwater in the Ore Mountains
Authors: Zehe E. , Graeff T. , Morgner M. , Bauer A. , Bronstert A.
Published: April 2010

Abstract. This study presents an application of an innovative sampling strategy to assess soil moisture dynamics in a headwater of the Weißeritz in the German eastern Ore Mountains. A grassland site and a forested site were instrumented with two Spatial TDR clusters (STDR) that consist of 39 and 32 coated TDR probes of 60 cm length. Distributed time series of vertically averaged soil moisture data from both sites/ensembles were analyzed by statistical and geostatistical methods. Spatial variability and the spatial mean at the forested site were larger than at the grassland site. Furthermore, clustering of TDR probes in combination with long-term monitoring allowed identification of average spatial covariance structures at the small field scale for different wetness states. The correlation length of soil water content as well as the sill to nugget ratio at the grassland site increased with increasing average wetness and but, in contrast, were constant at the forested site. As soil properties at both the forested and grassland sites are extremely variable, this suggests that the correlation structure at the forested site is dominated by the pattern of throughfall and interception. We also found a strong correlation between average soil moisture dynamics and runoff coefficients of rainfall-runoff events observed at gauge Rehefeld, which explains almost as much variability in the runoff coefficients as pre-event discharge. By combining these results with a recession analysis we derived a first conceptual model of the dominant runoff mechanisms operating in this catchment. Finally, long term simulations with a physically based hydrological model were in good/acceptable accordance with the time series of spatial average soil water content observed at the forested site and the grassland site, respectively. Both simulations used a homogeneous soil setup that closely reproduces observed average soil conditions observed at the field sites. This corroborates the proposed sampling strategy of clustering TDR probes in typical functional units is a promising technique to explore the soil moisture control on runoff generation. Long term monitoring of such sites could maybe yield valuable information for flood warning. The sampling strategy helps furthermore to unravel different types of soil moisture variability.
Snow distribution over the Namco lake area of the Tibetan Plateau
Authors: Li M. , Ma Y. , Hu Z. , Ishikawa H. , Oku Y.
Published: April 2010

Abstract. The mesoscale snow distribution over the Namco lake area of the Tibetan Plateau on October 2005 has been investigated in this paper. The control and sensitive experiments were conducted using Weather Research Model (WRF) with three nested grids that included a 1 km finest grid centered on the Namco station. Our simulation ran from 6 October through 10 October 2005, which was concurrent with long term meteorological observations. Evaluation against boundary layer meteorological tower measurements and flux observations showed that the model captured the observed 2 m temperature and 10 m winds reasonably well in the sensitive experiment. The results suggested that output snow depth maximum amounts from two simulated experiments were centered downwind shore of Namco lake. Modified surface parameters for example surface skin temperature on the lake help to increase simulated credibility.
Actual daily evapotranspiration estimated from MERIS and AATSR data over the Chinese Loess Plateau
Authors: Liu R. , Wen J. , Wang X. , Wang L. , Tian H. , Zhang T. T. , Shi X. K. , Zhang J. H. , Lu SH. N.
Published: April 2010

Abstract. The Loess Plateau is located in north of China and has a significant impact on the climate and ecosystem evolvement over the East Asian continent. Based on the land surface energy balance theory, the potential of using Medium Resolution Imaging Spectrometer (onboard sensor of the Environmental Satellite) remote sensing data on 7, 11 and 27 June 2005 is explored. The "split-window" algorithm is used to retrieve surface temperature from the Advanced the Along-Track Scanning Radiometer, another onboard senor of the Environmental Satellite. Then the near surface net radiation, sensible heat flux and soil heat flux are estimated by using the developed algorithm. We introduce a simple algorithm to predict the heat flux partitioning between the soil and vegetation. Combining the sunshine hours, air temperature, sunshine duration and wind speed measured by weather stations, a model for estimating daily ET is proposed. The instantaneous ET is also converted to daily value. Comparison of latent heats flux retrieved by remote sensing data with ground observation from eddy covariance flux system during Loess Plateau land surface process field Experiment, the maximum and minimum error of this approach are 10.96% and 4.80% respectively, the cause of the bias is also explored and discussed.
Recent advances in land surface climate observations on the Tibetan Plateau
Authors: Ma Y. , Wang Y. , Hu Z. , Yang K. , Li M. , Ma W. , Zhong L. , Sun F. , Chen X. , Zhu Z. , Ishikawa H.
Published: April 2010

Abstract. As a unique geological and geographical unit, the Tibetan Plateau dramatically impacts the world's environment and especially controls climatic and environmental changes in China, Asia and even in the Northern Hemisphere. Tibetan Plateau, therefore, provides a field laboratory for studying global change. With support from various agencies in the People's Republic of China, a Tibetan Observation and Research Platform (TORP) is now implementing. Firstly the background of the establishment of the TORP, the establishing and monitoring plan of long-term scale (5–10 years) of the TORP has been introduced. Then the preliminary observational analysis results, such as the characteristics of land surface heat fluxes and CO2 flux partitioning (diurnal variation, inter-monthly variation and vertical variation etc.), the characteristics of atmospheric and soil variables, the structure of the Atmospheric Boundary Layer (ABL) and the turbulent characteristics have also been shown in this paper.