How to improve the representation of hydrological processes in SWAT for a lowland catchment – temporal analysis of parameter sensitivity and model performance

Model diagnostic analyses help to improve the understanding of hydrological processes and their representation in hydrological models. A detailed temporal analysis detects periods of poor model performance and model components with potential for model improvements, which cannot be found by analysing the whole discharge time series. In this study, we aim to improve the understanding of hydrological processes by investigating the temporal dynamics of parameter sensitivity and of model performance for the Soil and Water Assessment Tool model applied to the Treene lowland catchment in Northern Germany. The temporal analysis shows that the parameter sensitivity varies temporally with high sensitivity for three groundwater parameters (groundwater time delay, baseflow recession constant and aquifer fraction coefficient) and one evaporation parameter (soil evaporation compensation factor). Whereas the soil evaporation compensation factor dominates in baseflow and resaturation periods, groundwater time delay, baseflow recession constant and aquifer fraction coefficient are dominant in the peak and recession phases. The temporal analysis of model performance identifies three clusters with different model performances, which can be related to different phases of the hydrograph. The lowest performance, when comparing six performance measures, is detected for the baseflow cluster. A spatially distributed analysis for six hydrological stations within the Treene catchment shows similar results for all stations. The linkage of periods with poor model performance to the dominant model components in these phases and with the related hydrological processes shows that the groundwater module has the highest potential for improvement. This temporal diagnostic analysis enhances the understanding of the Soil and Water Assessment Tool model and of the dominant hydrological processes in the lowland catchment. Copyright © 2013 John Wiley & Sons, Ltd.     

Nonlinear finite and discrete element simulations of multi-storey masonry walls

Bulletin of Earthquake Engineering - This paper reports the results of different finite and discrete element simulations on a well-known benchmark of an unreinforced plane masonry structure....     

Solute transport scales in an unsaturated stony soil

Solute transport parameters are known to be scale-dependent due mainly to the increasing scale of heterogeneities with transport distance and with the lateral extent of the transport field examined. Based on a transect solute transport experiment, in this paper we studied this scale dependence by distinguishing three different scales with different homogeneity degrees of the porous medium: the observation scale, transport scale and transect scale. The main objective was to extend the approach proposed by van Wesenbeeck and Kachanoski to evaluating the role of textural heterogeneities on the transition from the observation scale to the transport scale. The approach is based on the scale dependence of transport moments estimated from solute concentrations distributions. In our study, these moments were calculated starting from time normalized resident concentrations measured by time domain reflectometry (TDR) probes at three depths in 37 soil sites 1 m apart along a transect during a steady state transport experiment. The Generalized Transfer Function (GTF) was used to describe the evolution of apparent solute spreading along the soil profile at each observation site by analyzing the propagation of the moments of the concentration distributions. Spectral analysis was used to quantify the relationship between the solid phase heterogeneities (namely, texture and stones) and the scale dependence of the solute transport parameters. Coupling the two approaches allowed us to identify two different transport scales (around 4-5 m and 20 m, respectively) mainly induced by the spatial pattern of soil textural properties. The analysis showed that the larger transport scale is mainly determined by the skeleton pattern of variability. Our analysis showed that the organization in hierarchical levels of soil variability may have major effects on the differences between solute transport behavior at transport scale and transect scale, as the transect scale parameters will include information from different scales of heterogeneities.     

An assessment of the potential impact of climate change on flood risk in Mumbai

Managing risks from extreme events will be a crucial component of climate change adaptation. In this study, we demonstrate an approach to assess future risks and quantify the benefits of adaptation options at a city-scale, with application to flood risk in Mumbai. In 2005, Mumbai experienced unprecedented flooding, causing direct economic damages estimated at almost two billion USD and 500 fatalities. Our findings suggest that by the 2080s, in a SRES A2 scenario, an ??upper bound?? climate scenario could see the likelihood of a 2005-like event more than double. We estimate that total losses (direct plus indirect) associated with a 1-in-100 year event could triple compared with current situation (to $690?C$1,890 million USD), due to climate change alone. Continued rapid urbanisation could further increase the risk level. The analysis also demonstrates that adaptation could significantly reduce future losses; for example, estimates suggest that by improving the drainage system in Mumbai, losses associated with a 1-in-100 year flood event today could be reduced by as much as 70%.,We show that assessing the indirect costs of extreme events is an important component of an adaptation assessment, both in ensuring the analysis captures the full economic benefits of adaptation and also identifying options that can help to manage indirect risks of disasters. For example, we show that by extending insurance to 100% penetration, the indirect effects of flooding could be almost halved. We conclude that, while this study explores only the upper-bound climate scenario, the risk-assessment core demonstrated in this study could form an important quantitative tool in developing city-scale adaptation strategies. We provide a discussion of sources of uncertainty and risk-based tools could be linked with decision-making approaches to inform adaptation plans that are robust to climate change.     

Propagation of H and He cosmic ray isotopes in the Galaxy: astrophysical and nuclear uncertainties

Observations of light isotopes in cosmic rays provide valuable information on their origin and propagation in the Galaxy. Using the data collected by the AMS-01 experiment in the range ∼0.2–1.5 GeV nucleon⁻¹, we compare the measurements on ¹ H, ² H, ³ He, and ⁴ He with calculations for interstellar propagation and solar modulation. These data are described well by a diffusive-reacceleration model with parameters that match the B/C ratio data, indicating that He and heavier nuclei such as C–N–O experience similar propagation histories. Close comparisons are made within the astrophysical constraints provided by the B/C ratio data and within the nuclear uncertainties arising from errors in the production cross section data. The astrophysical uncertainties are expected to be dramatically reduced by the data upcoming from AMS-02, so that the nuclear uncertainties will likely represent the most serious limitation on the reliability of the model predictions. On the other hand, we find that secondary-to-secondary ratios such as ² H/³ He, ⁶ Li/⁷ Li or ¹⁰ B/¹¹ B are barely sensitive to the key propagation parameters and can represent a useful diagnostic test for the consistency of the calculations.     

Structural uncertainty assessment in a discharge simulation model

Abstract

A major goal in hydrological modelling is to identify and quantify different sources of uncertainty in the modelling process. This paper analyses the structural uncertainty in a streamflow modelling system by investigating a set of models with increasing model structure complexity. The models are applied to two basins: Kielstau in Germany and XitaoXi in China. The results show that the model structure is an important factor affecting model performance. For the Kielstau basin, influences from drainage and wetland are critical for the local runoff generation, while for the XitaoXi basin accurate distributions of precipitation and evapotranspiration are two of the determining factors for the success of the river flow simulations. The derived model uncertainty bounds exhibit appropriate coverage of observations. Both case studies indicate that simulation uncertainty for the low-flow period contributes more to the overall uncertainty than that for the peak-flow period, although the main hydrological features in these two basins differ greatly.

Citation Zhang, X. Y., Hörmann, G., Gao, J. F. & Fohrer, N. (2011) Structural uncertainty assessment in a discharge simulation model. Hydrol. Sci. J. 56(5), 854–869.     

Effect of Pumice and Sand on the Sustainability of Granular Iron Beds for the Aqueous Removal of CuII,NiII, and ZnII

Current knowledge of the basic principles underlying the design of Fe⁰ beds is weak. The volumetric expansive nature of iron corrosion was identified as the major factor determining the sustainability of Fe⁰ beds. This work attempts to systematically verify developed concepts. Pumice and sand were admixed to 200 g of Fe⁰ in column studies (50:50 volumetric proportion). Reference systems containing 100% of each material have been also investigated. The mean grain size of the used materials (in mm) were 0.28 (sand), 0.30 (pumice), and 0.50 (Fe⁰). The five studied systems were characterized (i) by the time dependent evolution of their hydraulic conductivity (permeability) and (ii) for their efficiency for aqueous removal of Cu^II, Ni^II, and Zn^II (about 0.3 mM of each). Results showed unequivocally that (i) quantitative contaminant removal was coupled to the presence of Fe⁰, (ii) additive admixture lengthened the service life of Fe⁰ beds, and (iii) pumice was the best admixing agent for sustaining permeability while the Fe⁰/sand column was the most efficient for contaminant removal. The evolution of the permeability was well‐fitted by the approach that the inflowing solution contained dissolved O₂. The achieved results are regarded as starting point for a systematic research to optimize/support Fe⁰ filter design.