286 research outputs found
Uncertainty, sensitivity analysis and the role of data based mechanistic modeling in hydrology
International audienceIn this paper, we discuss the problem of calibration and uncertainty estimation for hydrologic systems from two points of view: a bottom-up, reductionist approach; and a top-down, data-based mechanistic (DBM) approach. The two approaches are applied to the modelling of the River Hodder catchment in North-West England. The bottom-up approach is developed using the TOPMODEL, whose structure is evaluated by global sensitivity analysis (GSA) in order to specify the most sensitive and important parameters; and the subsequent exercises in calibration and validation are carried out in the light of this sensitivity analysis. GSA helps to improve the calibration of hydrological models, making their properties more transparent and highlighting mis-specification problems. The DBM model provides a quick and efficient analysis of the rainfall-flow data, revealing important characteristics of the catchment-scale response, such as the nature of the effective rainfall nonlinearity and the partitioning of the effective rainfall into different flow pathways. TOPMODEL calibration takes more time and it explains the flow data a little less well than the DBM model. The main differences in the modelling results are in the nature of the models and the flow decomposition they suggest. The "quick'' (63%) and "slow'' (37%) components of the decomposed flow identified in the DBM model show a clear partitioning of the flow, with the quick component apparently accounting for the effects of surface and near surface processes; and the slow component arising from the displacement of groundwater into the river channel (base flow). On the other hand, the two output flow components in TOPMODEL have a different physical interpretation, with a single flow component (95%) accounting for both slow (subsurface) and fast (surface) dynamics, while the other, very small component (5%) is interpreted as an instantaneous surface runoff generated by rainfall falling on areas of saturated soil. The results of the exercise show that the two modelling methodologies have good synergy; combining well to produce a complete modelling approach that has the kinds of checks-and-balances required in practical data-based modelling of rainfall-flow systems. Such a combined approach also produces models that are suitable for different kinds of application. As such, the DBM model can provides an immediate vehicle for flow and flood forecasting; while TOPMODEL, suitably calibrated (and perhaps modified) in the light of the DBM and GSA results, immediately provides a simulation model with a variety of potential applications, in areas such as catchment management and planning
Fuzzy set approach to calibrating distributed flood inundation models using remote sensing observations
The paper presents a methodology for the estimation of uncertainty of inundation extent, which takes account of the uncertainty in the observed spatially distributed information and implements a fuzzy evaluation methodology. The Generalised Likelihood Uncertainty Estimation (GLUE) technique and the 2-D LISFLOOD-FP model were applied to derive the set of uncertain inundation realisations and resulting flood inundation maps. Conditioning of the inundation maps on fuzzified Synthetic Aperture Radar (SAR) images results in much more realistic inundation risk maps which can better depict the variable pattern of inundation extent than previously used methods. It has been shown that the evaluation methodology compares well to traditional approaches and can produce flood hazard maps that reflect the uncertainties in model evaluation
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Switching off? Challenges in engaging students in energy efficiency. Findings from an EU wide energy saving project
The success of projects encouraging pro-environmental behaviour change amongst students in university accommodation has been well documented but typically focuses on small-scale interventions â whether geographically or temporally. This paper presents findings from an EU funded international competition, which discusses insights on a scale previously unseen. SAVES is an inter-dormitory energy-saving competition that is being run in five countries and has reached over 50,000 students over the last two years specifically, over 480 dormitories at 17 Universities. Building on the successful UK âStudent Switch Offâ (SSO) competition run by the National Union of Students, SAVES provides engagement with students, enabling, empowering and motivating them to save energy â focusing specifically on the last stage of the âAwareness, Interest, Desire, Actionâ framework. Smart meter data is used to run real-time energy challenges through an energy dashboard that informs students how much energy they are using, and encourage peer-to-peer learning and international cooperation through a virtual twinning scheme. This paper presents findings on the effectiveness of Student Switch Off competition, as it has been implemented in Europe. A mixed methods approach (pre- and post- intervention surveys, focus groups and analysis of energy meter data) was taken to evaluate the level of energy savings and quantifiable behaviour change delivered in students across participating dormitories and countries. Reflections and recommendations are offered towards the role of student-led competitions and energy dashboards as a method for communicating data to students
Geo-neutrinos: A systematic approach to uncertainties and correlations
Geo-neutrinos emitted by heat-producing elements (U, Th and K) represent a
unique probe of the Earth interior. The characterization of their fluxes is
subject, however, to rather large and highly correlated uncertainties. The
geochemical covariance of the U, Th and K abundances in various Earth
reservoirs induces positive correlations among the associated geo-neutrino
fluxes, and between these and the radiogenic heat. Mass-balance constraints in
the Bulk Silicate Earth (BSE) tend instead to anti-correlate the radiogenic
element abundances in complementary reservoirs. Experimental geo-neutrino
observables may be further (anti)correlated by instrumental effects. In this
context, we propose a systematic approach to covariance matrices, based on the
fact that all the relevant geo-neutrino observables and constraints can be
expressed as linear functions of the U, Th and K abundances in the Earth's
reservoirs (with relatively well-known coefficients). We briefly discuss here
the construction of a tentative "geo-neutrino source model" (GNSM) for the U,
Th, and K abundances in the main Earth reservoirs, based on selected
geophysical and geochemical data and models (when available), on plausible
hypotheses (when possible), and admittedly on arbitrary assumptions (when
unavoidable). We use then the GNSM to make predictions about several
experiments ("forward approach"), and to show how future data can constrain - a
posteriori - the error matrix of the model itself ("backward approach"). The
method may provide a useful statistical framework for evaluating the impact and
the global consistency of prospective geo-neutrino measurements and Earth
models.Comment: 17 pages, including 4 figures. To appear on "Earth, Moon, and
Planets," Special Issue on "Neutrino Geophysics," Proceedings of Neutrino
Science 2005 (Honolulu, Hawaii, Dec. 2005
Tracing very high energy neutrinos from cosmological distances in ice
Astrophysical sources of ultrahigh energy neutrinos yield tau neutrino fluxes
due to neutrino oscillations. We study in detail the contribution of tau
neutrinos with energies above PeV relative to the contribution of the other
flavors. We consider several different initial neutrino fluxes and include tau
neutrino regeneration in transit through the Earth and energy loss of charged
leptons. We discuss signals of tau neutrinos in detectors such as IceCube, RICE
and ANITA.Comment: 27 pages, 19 figure
Statistical physics of earthquakes: Comparison of distribution exponents for source area and potential energy and the dynamic emergence of log-periodic energy quanta
Elastic isotropy of hcp-Fe under Earth core conditions
Our first-principles calculations show that both the compressional and shear
waves of hcp-Fe become elastically isotropic under the high temperatures of
Earth inner core conditions, with the variation in sound velocities along
different angles from the c axis within 1%. We computed the thermoelasticity at
high pressures and temperatures from quasiharmonic linear response
linear-muffin-tin-orbital calculations in the generalized-gradient
approximation. The calculated anisotropic shape and magnitude in hcp-Fe at
ambient temperature agree well with previous first-principles predictions, and
the anisotropic effects show strong temperature dependences. This implies that
other mechanisms, rather than the preferential alignment of the hcp-Fe crystal
along the Earth rotation axis, account for the seismic P-wave travel time
anomalies. Either the inner core is not hcp iron, and/or the seismologically
observed anisotropy is caused by inhomogeneity, i.e. multiple phases.Comment: 16 pages, 3 figure
CP violating neutrino oscillation and uncertainties in Earth matter density
We propose a statistical formulation to estimate possible errors in long
baseline neutrino oscillation experiments caused by uncertainties in the Earth
matter density. A quantitative investigation of the effect is made on the CP
asymmetry in future neutrino factory experiments.Comment: Latex, 10 pages, 5 figure
New approach to detect seismic surface waves in 1Hz-sampled GPS time series
Recently, co-seismic seismic source characterization based on GPS measurements has been completed in near- and far-field with remarkable results. However, the accuracy of the ground displacement measurement inferred from GPS phase residuals is still depending of the distribution of satellites in the sky. We test here a method, based on the double difference (DD) computations of Line of Sight (LOS), that allows detecting 3D co-seismic ground shaking. The DD method is a quasi-analytically free of most of intrinsic errors affecting GPS measurements. The seismic waves presented in this study produced DD amplitudes 4 and 7 times stronger than the background noise. The method is benchmarked using the GEONET GPS stations recording the Hokkaido Earthquake (2003 September 25th, Mw = 8.3)
The European 2015 drought from a hydrological perspective
In 2015 large parts of Europe were affected by drought. In this paper, we analyze the hydrological footprint (dynamic development over space and time) of the drought of 2015 in terms of both severity (magnitude) and spatial extent and compare it to the extreme drought of 2003. Analyses are based on a range of low flow and hydrological drought indices derived for about 800 streamflow records across Europe, collected in a community effort based on a common protocol. We compare the hydrological footprints of both events with the meteorological footprints, in order to learn from similarities and differences of both perspectives and to draw conclusions for drought management. The region affected by hydrological drought in 2015 differed somewhat from the drought of 2003, with its center located more towards eastern Europe. In terms of low flow magnitude, a region surrounding the Czech Republic was the most affected, with summer low flows that exhibited return intervals of 100 years and more. In terms of deficit volumes, the geographical center of the event was in southern Germany, where the drought lasted a particularly long time. A detailed spatial and temporal assessment of the 2015 event showed that the particular behavior in these regions was partly a result of diverging wetness preconditions in the studied catchments. Extreme droughts emerged where preconditions were particularly dry. In regions with wet preconditions, low flow events developed later and tended to be less severe. For both the 2003 and 2015 events, the onset of the hydrological drought was well correlated with the lowest flow recorded during the event (low flow magnitude), pointing towards a potential for early warning of the severity of streamflow drought. Time series of monthly drought indices (both streamflow- and climate-based indices) showed that meteorological and hydrological events developed differently in space and time, both in terms of extent and severity (magnitude). These results emphasize that drought is a hazard which leaves different footprints on the various components of the water cycle at different spatial and temporal scales. The difference in the dynamic development of meteorological and hydrological drought also implies that impacts on various water-use sectors and river ecology cannot be informed by climate indices alone. Thus, an assessment of drought impacts on water resources requires hydrological data in addition to drought indices based solely on climate data. The transboundary scale of the event also suggests that additional efforts need to be undertaken to make timely pan-European hydrological assessments more operational in the future
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