1,721,040 research outputs found
Calibrating hydrological models in the spectral domain: Inference of parameter uncertainty using a Metropolis algorithm
No full textUncertainty Analysis in Environmental Modeling: Towards Improved Evaluation and Diagnostics of Hydrological and Environmental Models (2nd International IAHS-PUB Workshop 15th-18th July 2007 in Bertinoro, Italy)
No full textOn the calibration of hydrological models in ungauged basins: A framework for integrating hard and soft hydrological information
No full textThis paper presents a calibration framework based on the generalized likelihood uncertainty estimation (GLUE) that can be used to condition hydrological model parameter distributions in scarcely gauged river basins, where data is uncertain, intermittent or nonconcomitant. At the heart of this framework is the conditioning of the model parameters such as to reproduce key signatures of the observed data within some limits of acceptability. These signatures are either based on hard or on soft information. Hard information signatures are defined as signatures for which the limits of acceptability may be objectively derived from the distribution of long series of observed values, and which effectively constrain the model parameters. Soft signatures are less effective in parameter conditioning or their limits of acceptability cannot be objectively derived. During random parameter sampling, parameter sets are accepted as equally likely if they meet all the hard limits of acceptability. This results in an intermediate parameter distribution, which can be used to reduce the sampling limits. Then, the soft information may be introduced in a second constraining step to reach a final parameter distribution. The modeler can use the final results as a guideline for a further search for information, possibly from new observations yet to collect. In an application of the framework to the Luangwa catchment in Zambia, three information signatures are retrieved from a data set of old discharge time series and used to condition the parameters of a daily conceptual rainfall-runoff model. We performed two independent calibration experiments with two significantly different satellite rainfall estimates as model input. The results show consistent parameter distributions and considerable reduction of the prior parameter space and corresponding output realizations. These results illustrate the potential of the proposed calibration framework for predictions in scarcely gauged catchments
SEHR-ECHO v1.0: A spatially explicit hydrologic response model for ecohydrologic applications
Full text linkThis paper presents the Spatially Explicit Hydrologic Response (SEHR) model developed at the Laboratory of Ecohydrology of the Ecole Polytechnique Fédérale de Lausanne for the simulation of hydrological processes at the catchment scale. The key concept of the model is the formulation of water transport by geomorphologic travel time distributions through gravity-driven transitions among geomorphic states: the mobilization of water (and possibly dissolved solutes) is simulated at the subcatchment scale and the resulting responses are convolved with the travel paths distribution within the river network to obtain the hydrologic response at the catchment outlet. The model thus breaks down the complexity of the hydrologic response into an explicit geomorphological combination of dominant spatial patterns of precipitation input and of hydrologic process controls. Nonstationarity and nonlinearity effects are tackled through soil moisture dynamics in the active soil layer. We present here the basic model set-up for precipitation-runoff simulation and a detailed discussion of its parameter estimation and of its performance for the Dischma River (Switzerland), a snow-dominated catchment with a small glacier cover
How skillful are satellite and reanalysis precipitation products at reproducing hydrological processes in semi-arid catchments?
No full textReanalysis and satellite-based precipitation products have undergone an unprecedented and increasing availability, which has triggered numerous hydrological modelling studies using them as input. In this context, a key open question concerns the ability of these products to reproduce plausible patterns of hydrological processes. This work assesses the skill of 10 satellite-based precipitation products (TAMSAT, CHIRPS, ARC, RFE, MSWEP, GSMAP, PERSIANN-CDR, CMORPH-CRT, TRMM3B42, TRMM3B42-RT), and of 7 reanalysis precipitation products (JRA55, EWEMBI, WFDEI-GPCC, WFDEI-CRU, MERRA2, PGF, ERA5) if used as forcing data in hydrological modelling, and there subsequent ability to reproduce the temporal and spatial dynamics of several hydrological flux and state variables (i.e. streamflow, evaporation, soil moisture and terrestrial water storage). In total, 102 combinations are tested using 6 different temperature datasets (JRA55, EWEMBI, WFDEI, MERRA2, PGF, ERA5) for the calculation of potential evaporation. The model outputs are evaluated with in-situ streamflow data, soil moisture from ESA CCI, evaporation from GLEAM, land surface temperature from MODIS, and terrestrial water storage from GRACE. The study is carried out in the predominantly semi- arid Volta River basin in West Africa, using the fully distributed mesoscale Hydrologic Model (mHM) over a ten-year period (2003-2012). The results highlight the contrasting performances of the rainfall- temperature product combinations with respect to pattern reproduction of hydrological state and flux variables. The best performing rainfall products are CHIRPS, TAMSAT, ARC, MSWEP and GSMAP for streamflow simulation; ARC, TAMSAT, CHIRPS, TRMMB42, and EWEMBI for evaporation; EWEMBI, TRMM3B42RT, TRMMB42, CMORPH-CRT and ARC for soil moisture; and finally CMORPH-CRT, ERA5, MERRA2, PGF and GSMAP for terrestrial water storage
Hydrological model performance and parameter estimation in the wavelet-domain
Full text linkThis paper proposes a method for rainfall-runoff model calibration and performance analysis in the wavelet-domain by fitting the estimated wavelet-power spectrum (a representation of the time-varying frequency content of a time series) of a simulated discharge series to the one of the corresponding observed time series. As discussed in this paper, calibrating hydrological models so as to reproduce the time-varying frequency content of the observed signal can lead to different results than parameter estimation in the time-domain. Therefore, wavelet-domain parameter estimation has the potential to give new insights into model performance and to reveal model structural deficiencies. We apply the proposed method to synthetic case studies and a real-world discharge modeling case study and discuss how model diagnosis can benefit from an analysis in the wavelet-domain. The results show that for the real-world case study of precipitation – runoff modeling for a high alpine catchment, the calibrated discharge simulation captures the dynamics of the observed time series better than the results obtained through calibration in the time-domain. In addition, the wavelet-domain performance assessment of this case study highlights the frequencies that are not well reproduced by the model, which gives specific indications about how to improve the model structure.Civil Engineering and Geoscience
Comparing MODIS snow products Collection 5 with Collection 6 over Italian Central Apennines
No full textRemotely sensed snow-cover information has become a key tool to study temporal and spatial snow-cover patterns and to develop regional snow-cover climatologies. Aqua/Terra MODIS products provide about 20-year daily snow-cover data with 500 m spatial resolution. MODIS Collection 6 represents the most recent release of global snow-cover mapping algorithms and could further increase the high accuracy of previous collections: snow cover is now reported by its NDSI (Normalized Difference Snow Index) values, allowing more flexibility in using the datasets for specific regions than previous releases. We quantified the potential-added value of tuning the NDSI threshold as opposed to a global snow-detection algorithm by developing a 16-year snow-cover climatology for the Central Apennines (Italy) from daily observations in MODIS snow products Collection 5 (C5) and Collection 6 (C6). Seven ground-based stations were used as independent benchmark. Three versions of binary snow-cover maps were generated from the NDSI Snow Cover product (C6), using NDSI-threshold tests for snow detection. The most accurate snow-cover maps show an agreement with available ground data of 88% for Aqua and 89% for Terra MODIS, with an improvement compared to snow-cover maps obtained from C5 Snow Cover Area (SCA) products (yielding 86% for Aqua and 88% for Terra). NDSI thresholds in the range 0.10–0.40 provide an agreement higher than 83% but snow-cover duration, distribution, and spatial extent are sensible to the NDSI threshold: if compared to the optimal NDSI threshold for this region (0.20), the value of 0.40 reduces by 15% the snow-cover extent in all seasons due to increased underestimation. The lowest tested threshold (0.10) estimates at least 10% larger snow-cover fraction in winter and spring but increases commission errors. This high sensitivity to the NDSI threshold makes its choice an essential step for using MODIS C6 snow products in hydrologic or climatologic studies
Towards a conceptualization of the hydrological processes behind changes of young water fraction with elevation: A focus on mountainous alpine catchments
Full text linkThe young water fraction (F-yw*), defined as the fraction of catchment outflow with transit times of less than 2-3 months, is increasingly used in hydrological studies that exploit the potential of isotope tracers. The use of this new metric in catchment intercomparison studies is helpful to understand and conceptualize the relevant processes controlling catchment functioning. Previous studies have shown surprising evidence that mountainous catchments worldwide yield low F-yw*. These low values have been partially explained by isolated hydrological processes, including deep vertical infiltration and long groundwater flow paths. However, a thorough framework illustrating the relevant mechanisms leading to a low F-yw* in mountainous catchments is missing.The main aim of this paper is to give an overview of what drives F-yw* variations according to elevation, thus clarifying why it generally decreases at high elevation. For this purpose, we assembled a data set of 27 study catchments, located in both Switzerland and Italy, for which we calculate F-yw*. We assume that this decrease can be explained by the groundwater storage potential, quantified by the areal extent of Quaternary deposits over a catchment (F-qd), and the low-flow duration (LFD) throughout the period of isotope sampling (PoS). In snow-dominated systems, LFD is strictly related to the snowpack persistence, quantified through the mean fractional snow cover area (F-SCA). The drivers are related to the catchment storage contribution to the stream that we quantify by applying a cutting-edge baseflow separation method to the discharge time series of the study sites and by estimating the mean baseflow fraction (F-bf) over the PoS.Our results suggest that Quaternary deposits could play a role in modulating F-yw* elevation gradients via their capacity to store groundwater, but subsequent confirmation with further, more detailed geological information is necessary. LFD indicates the proportion of PoS in which the stream is sustained and dominated by stored water coming from the catchment storage. Accordingly, our results reveal that the increase of LFD at high elevations, to a large extent driven by the persistence of winter snowpacks and the simultaneous lack of a liquid water input to the catchments, results in lower F-yw*. In our data set, F-bf reveals a strong complementarity with F-yw*, suggesting that the latter could be estimated as F-yw*-1-F-bf for catchments without stable water isotope measurements.As a conclusion, we develop a perceptual model that integrates all the results of our analysis into a framework for how hydrological processes control F-yw* according to elevation. This lays the foundations for an improvement of the theory-driven models
Scale-dependent effects of solar radiation patterns on the snow-dominated hydrologic response
Full text linkSolar radiation is a dominant driver of snowmelt dynamics and streamflow generation in alpine catchments. A better understanding of how solar radiation patterns affect the hydrologic response is needed to assess when calibrated temperature-index models are likely to be spatially transferable for ecohydrological applications. We induce different solar radiation patterns in a Swiss Alpine catchment through virtual rotations of the digital elevation model. Streamflow simulations are performed at different spatial scales through a spatially explicit hydrological model coupled to a physically based snow model. Results highlight that the effects of solar radiation patterns on the hydrologic response are scale dependent, i.e., significant at small scales with predominant aspects and weak at larger scales where aspects become uncorrelated and orientation differences average out. Such scale dependence proves relevant for the spatial transferability of a temperature-index model, whose calibrated degree-day factors are stable to different solar radiation patterns for catchment sizes larger than the aspect correlation scale.CRYOSECH
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