ALBERT

Description: The landscape dynamics (1927–2003) of one reach at the Middle Ebro River (NE Spain) was examined using aerial pictures and GIS techniques. Moreover, changes in the natural flow regime and anthropic activities within the river-floodplain system were investigated. Our results indicate that hydrological and landscape patterns have been dramatically changed during the last century as a consequence of human alteration of the fluvial dynamics within the studied reach, as well as the overall basin. The magnitude and variability of river discharge events have decreased, especially since 1981, and flood protection structures have disrupted the river floodplain connectivity. As a result, the succesional pathways of riparian ecotopes have been heavily modified because natural rejuvenation no longer takes place, resulting in decreased landscape diversity. It is apparent from these data that floodplain restoration must be incorporated as a significant factor into river management plans if a more natural functioning wants to be retrieved. The ecotope structure and dynamics of the 1927–1957 should be adopted as the guiding image, whereas hydrologic and landscape (dykes, raised surfaces) patters should be considered. Under the current socio-economic context, the more realistic option seems to create a dynamic river corridor reallocating dykes and lowering floodplain heights. The extent of this river corridor should adapt to the restored flow regime, although periodic economic investments could be an option if the desired self-sustained dynamism is not reached.

Description: In this paper regional (synoptic) and large-scale climate drivers of rainfall are investigated for Victoria, Australia. A non-linear classification methodology known as self-organizing maps (SOM) is used to identify 20 key regional synoptic patterns, which are shown to capture a range of significant synoptic features known to influence the climate of the region. Rainfall distributions are assigned to each of the 20 patterns for nine rainfall stations located across Victoria, resulting in a clear distinction between wet and dry synoptic types at each station. The influence of large-scale climate modes on the frequency and timing of the regional synoptic patterns is also investigated. This analysis revealed that phase changes in the El Niño Southern Oscillation (ENSO), the Southern Annular Mode (SAM) and/or Indian Ocean Dipole (IOD) are associated with a shift in the relative frequency of wet and dry synoptic types. Importantly, these results highlight the potential to utilise the link between the regional synoptic patterns derived in this study and large-scale climate modes to improve rainfall forecasting for Victoria, both in the short- (i.e. seasonal) and long-term (i.e. decadal/multi-decadal scale). In addition, the regional and large-scale climate drivers identified in this study provide a benchmark by which the performance of Global Climate Models (GCMs) may be assessed.

Description: This study presents a new methodology not only to evaluate willingness to pays (WTPs) for the improvement of hydrological vulnerability using a choice experiment (CE) method but also to do a cost-benefit analysis (CBA) of some feasible alternatives combing the derived WTPs with an alternative evaluation index (AEI). The hydrological vulnerability consists of potential streamflow depletion (PSD), and potential water quality deterioration (PWQD) and can be quantified using a multi-criteria decision making technique and pressure-state-response (PSR) framework. PSD and PWQD not only provide survey respondents with sufficient site-specific information to avoid scope sensitivity in a choice experiment but also support the standard of dividing the study watershed into six sub-regions for site-fitted management. Therefore CE was applied to six regions one after the other, in order to determine WTPs for improvements on hydrological vulnerability considering the characteristics which are vulnerability, location, and preferences with regard to management objectives. The AEI was developed to prioritize the feasible alternatives using a continuous water quantity/quality simulation model as well as multi-criteria decision making techniques. All criteria for alternative performance were selected based on a driver-pressures-state-impact-response (DPSIR) framework, and their weights were estimated using an Analytic Hierarchy Process (AHP). In addition, the AEI that reflects on residents' preference with regard to management objectives was proposed in order to incite the stakeholder to participate in the decision making process. Finally, the economic values of each alternative are estimated by a newly developed method which combines the WTPs for improvements on hydrologic vulnerability with the AEI. This social-economic-engineering combined framework can provide the decision makers with more specific information as well as decrease the uncertainty of the CBA.

Description: Alpine meadow is one of the most widespread grassland types in the permafrost regions of the Qinghai-Tibet Plateau. The transmission of coupled soil water heat is one of the most important processes influencing cyclic variations in the hydrology of frozen soil regions, especially under conditions of changing vegetation cover. The present study assesses the impact of changes in vegetation cover on the coupling of soil water and heat in a permafrost region. Soil moisture (θv), soil temperature (Ts), soil heat content, and differences in θv−Ts coupling were monitored on a seasonal and daily basis under three different densities of vegetation cover (30, 65, and 93%) upon both thawed and frozen soils. Regression analysis of θv vs. Ts plots under different levels of vegetation cover indicates that soil freeze-thaw processes were significantly affected by changes in vegetation cover. With decreasing vegetation cover upon an alpine meadow, the difference between air temperature and ground temperature (ΔTa−s) also decreased. A decrease in vegetation cover also resulted in a decrease in the Ts at which soil froze and an increase in the temperature at which it thawed; this was reflected in a greater response of soil temperature to changes in air temperature (Ta). For ΔTa−s outside the range of −0.1 to 1.0°C, root zone soil-water temperatures showed a significant increase with increasing ΔTa−s; however, the magnitude of this relationship was dampened with increasing vegetation cover. At the time of maximum water content in the thawing season, the soil temperature decreased with increasing vegetation. Changes in vegetation cover also led to variations in θv−Ts coupling. With increasing vegetation cover, the surface heat flux increased, along with the amplitude of its variations. Soil heat storage at 20 cm depth also increased with increasing vegetation cover, and the downward transmitted of heat flux decreased. In addition to providing insulation against soil warming, vegetation in alpine meadows within the permafrost region also slows down the response of permafrost to climatic warming via the greater water-holding capacity of its root zone. Such vegetation may therefore play an important role in conserving water in alpine meadows and maintaining the stability of engineering works constructed within frozen soil of the Qinghai-Tibet Plateau.

Description: For derived flood frequency analysis based on hydrological modelling long continuous precipitation time series with high temporal resolution are needed. Often, the observation network with recording rainfall gauges is poor, so stochastic precipitation synthesis is a good alternative. Here, a hybrid two step procedure is proposed to provide suitable space-time precipitation fields as input for hydrological modelling. First, a univariate alternating renewal model is presented to simulate independent hourly precipitation time series for several locations. In the second step a multi-site resampling procedure is applied on the synthetic point rainfall event series to reproduce the spatial dependence structure of rainfall. The alternating renewal model describes wet spell durations, dry spell durations and wet spell amounts using univariate frequency distributions separately for two seasons. The dependence between wet spell amount and duration is accounted for by 2-copulas. For disaggregation of the wet spells into hourly intensities a predefined profile is used. In the second step resampling is carried out successively on all synthetic event series using simulated annealing with an objective function considering three bivariate spatial rainfall characteristics. In a case study synthetic precipitation is generated for two mesoscale catchments in the Bode river basin of northern Germany and applied for derived flood frequency analysis using the hydrological model HEC-HMS. The results show good performance in reproducing average and extreme rainfall characteristics as well as in reproducing observed flood frequencies. However, they also show that it is important to consider the same rainfall station network for calibration of the hydrological model with observed data as for application using synthetic rainfall data.

Description: The thermal conductivity of porous materials can be related to the electrical conductivity and therefore electrical resistivity tomography can be used to map the thermal conductivity of porous rocks. In this paper, a relationship is developed to connect the thermal conductivity of unsaturated clay-rocks to the thermal conductivity of the different phases of the porous composite, a textural parameter called the thermal formation factor, and the tortuosity of the water phase. The thermal formation factor is related to the electrical formation factor and to the first Archie's first exponent m. The tortuosity of the water phase is related to the second Archie's exponent n and to the relative saturation of the water phase. A very good agreement is obtained between the new model and thermal conductivity measurements of packs of glass beads and cores of the Callovo-Oxfordian argillite at different saturations of the water phase. Anisotropy of the effective thermal conductivity is mainly due to the anisotropy of the thermal conductivity of the solid phase.

Description: We analyzed spatial and temporal dynamics of solute chemistry in a forest watershed impacted by atmospheric deposition in the Adirondack Mountains of New York State, USA. Spatial dynamics of solute chemistry and natural abundance isotopes of nitrate (15N and 18O) were examined in 6 locations and the watershed outlet in 2001 and 2002. Temporal dynamics were examined during 5 discharge periods: winter, snowmelt, spring, summer, and fall, which were based on discharge levels at the outlet. Solute concentrations were statistically significantly different (p≤0.05) among stream sampling locations and discharge periods, with no interaction effects. Groundwater sources located in upper watershed controlled stream chemistry at higher elevations with highest pH, Ca2+, sum of base cations, Si, NO3-, total N, and SO42- and lowest Al concentrations. Two low elevation wetlands had a substantial influence over stream chemistry at those locations contributing lowest NO3-, total N, and highest DOC and DON. Snowmelt exhibited among the lowest pH, sum of base cations, and SO42-, and highest NO3-, total N, DON, and total Al; snowmelt appeared to dilute groundwater, and flush stored soil-derived solutes. Summer discharge, composed mainly of groundwater, exhibited the lowest flow, among the highest Mg2+, Ca2+, and lowest DON, DOC, and total Al concentrations. Isotopic analysis together with patterns of NH4+ versus NO3- dynamics indicated that NO3- was microbial, generated in fall and accumulated in winter in upper watershed soils, and flushed to stream during high discharge events. Highest discharge in snowmelt 2001, a summer drought in 2002, and fall storms following the drought were further evaluated for their specific effects on stream chemistry. Snowmelt 2001 had the lowest pH and highest NO3-, base flow during summer drought had the lowest total Al, and storms in fall 2002 had highest SO42- of all periods, but all other solute concentrations were comparable to other discharge periods in this study. Depending on objectives, watershed outlet alone may sufficiently represent solute dynamics in the watershed, and high-discharge events may sufficiently describe solute fluxes for the watershed.

Description: It is generally believed that roots have an effect on infiltration. In this study we analysed the influence of tree roots from Norway spruce (Picea abies (L.) Karst), silver fir (Abies alba Miller) and European beech (Fagus sylvatica L.) on preferential infiltration in stagnic soils in the northern pre-Alps in Switzerland. We conducted irrigation experiments (1 m2) and recorded water content variations with time domain reflectrometry (TDR). A rivulet approach was applied to characterise preferential infiltration. Roots were sampled down to a depth of 0.5 to 1 m at the same position where the TDR-probes had been inserted and digitally measured. The basic properties of preferential infiltration, film thickness of mobile water and the contact length between soil and mobile water in the horizontal plane are closely related to fine root densities. An increase in root density resulted in an increase in contact length, but a decrease in film thickness. We modelled water content waves based on fine root densities and identified a range of root densities that lead to a maximum volume flux density and infiltration capacity. These findings provide convincing evidence that tree roots improve soil structure and thus infiltration.

Description: The spatial distribution of groundwater fluxes through a streambed can be highly variable, most often resulting from a heterogeneous distribution of aquifer and streambed permeabilities along the flow pathways. In a previous study, observed temperature profiles in the streambed of a small stream in Germany were used to calibrate the subsurface parameters of a groundwater flow and heat transport model of the stream-aquifer system. Based on the model results, we defined four scenarios to simulate and assess the interplay of aquifer and streambed heterogeneity on the distribution of groundwater fluxes through the streambed: (a) a homogeneous low-K streambed within a heterogeneous aquifer; (b) a heterogeneous streambed within a homogeneous aquifer; (c) a well connected heterogeneous low-K streambed within a heterogeneous aquifer; and (d) a poorly connected heterogeneous low-K streambed within a heterogeneous aquifer. The results showed that the aquifer has a stronger influence on the distribution of groundwater fluxes through the streambed than the streambed itself. However, a homogeneous low-K streambed, a case often implemented in regional-scale groundwater flow models, resulted in a strong homogenization of fluxes, which may have important implications for the estimation of peak mass flows. The simulation results with heterogeneous low-K streambeds, whether or not well connected to the aquifer, were similar to the results of the base case scenario without a separate parameterization of the streambed, despite the lower permeability. We conclude that predictions of water flow and solute transport may significantly benefit from heterogeneous distributions of both aquifer and streambed properties in numerical simulation models.

Description: In order to investigate the effect of land use and land cover changes on hydrological process in northern parts of China, a distributed hydrological model was developed and applied in the Laohahe catchment. The direct evaporation from the intercepted water, potential canopy transpiration and potential soil evaporation were computed using a physically-based two-source potential evapotranspiration model, which would be regarded as input to the distributed hydrological model for the computation of actual evaportranspiration. Runoff generation was based on mixed runoff mechanisms of infiltration excess runoff and saturation excess runoff and the Muskingum-Cunge method was adopted for flow routing. The land cover data were available for 1980, 1989, 1996 and 1999. Daily streamflow measurements were available from 1964 to 2005 and were divided into 4 periods: 1964–1979, 1980–1989, 1990–1999 and 2000–2005, based on the land cover scenarios. The distributed hydrological model was coupled with a two-source potential evaportranspiration model for simulating daily runoff. The result of runoff simulation showed that the saturation excess runoff generation was dominant in the catchment. Model parameters were calibrated using hydrometeorological and land cover data corresponding to the same period. Streamflow simulation was conducted for each period under these four land cover scenarios. The results showed that the change of land use and land cover had a significant influence on evapotranspiration and runoff. The land cover data showed that forest land and water body had decreased from 1980 through 1999 and farm land and grass land had increased. This change caused the vegetation interception evaporation and vegetation transpiration to decrease, whereas the soil evaporation tended to increase. Thus the green water decreased but the blue water increased over the Laohahe catchment. This result was inconsistent with the fact that runoff ratio had a tendency of decrease in the catchment in 2000. It is this reason that water use out of stream channel has been increasing in recent years.