65 research outputs found
How crucial is it to account for the antecedent moisture conditions in flood forecasting? Comparison of event-based and continuous approaches on 178 catchments
This paper compares event-based and continuous hydrological modelling approaches for real-time forecasting of river flows. Both approaches are compared using a lumped hydrologic model (whose structure includes a soil moisture accounting (SMA) store and a routing store) on a data set of 178 French catchments. The main focus of this study was to investigate the actual impact of soil moisture initial conditions on the performance of flood forecasting models and the possible compensations with updating techniques. The rainfall-runoff model assimilation technique we used does not impact the SMA component of the model but only its routing part. Tests were made by running the SMA store continuously or on event basis, everything else being equal. The results show that the continuous approach remains the reference to ensure good forecasting performances. We show, however, that the possibility to assimilate the last observed flow considerably reduces the differences in performance. Last, we present a robust alternative to initialize the SMA store where continuous approaches are impossible because of data availability problems
Technical Note: On the puzzling similarity of two water balance formulas â TurcâMezentsev vs. TixerontâFu
This Technical Note documents and analyzes the puzzling similarity of two widely used water balance formulas:
TurcâMezentsev and TixerontâFu. It details their history and their
hydrological and mathematical properties, and discusses the mathematical
reasoning behind their slight differences. Apart from the difference in their
partial differential expressions, both formulas share the same hydrological
properties, and it seems impossible to recommend one over the other as more
âhydrologically foundedâ: hydrologists should feel free to choose the one
they feel more comfortable with.</p
Inundation mapping based on reach-scale effective geometry
The production of spatially accurate representations of potential inundation
is often limited by the lack of available data as well as model complexity.
We present in this paper a new approach for rapid inundation mapping, MHYST,
which is well adapted for data-scarce areas; it combines hydraulic geometry
concepts for channels and DEM data for floodplains. Its originality lies in
the fact that it does not work at the cross section scale but computes
effective geometrical properties to describe the reach scale. Combining
reach-scale geometrical properties with 1-D steady-state flow equations,
MHYST computes a topographically coherent relation between the height above
nearest drainage and streamflow. This relation can then be used on a past
or future event to produce inundation maps. The MHYST approach is tested here
on an extreme flood event that occurred in France in MayâJune 2016. The
results indicate that it has a tendency to slightly underestimate inundation
extents, although efficiency criteria values are clearly encouraging. The
spatial distribution of model performance is discussed and it shows that the
model can perform very well on most reaches, but has difficulties modelling
the more complex, urbanised reaches. MHYST should not be seen as a rival to
detailed inundation studies, but as a first approximation able to rapidly
provide inundation maps in data-scarce areas.</p
On the lack of robustness of hydrologic models regarding water balance simulation: a diagnostic approach applied to three models of increasing complexity on 20 mountainous catchments
This paper investigates the robustness of rainfallârunoff models when their
parameters are transferred in time. More specifically, we propose an approach
to diagnose their ability to simulate water balance on periods with different hydroclimatic
characteristics. The testing procedure consists in a series of parameter
calibrations over 10 yr periods and the systematic analysis of mean flow volume
errors on long records. This procedure was applied to three conceptual models
of increasing structural complexity over 20 mountainous catchments in southern France.
The results showed that robustness problems are common. Errors on 10 yr mean
flow volume were significant for all calibration periods and model structures.
Various graphical and numerical tools were used to investigate these errors and
unexpectedly strong similarities were found in the temporal evolutions
of these volume errors. We indeed showed that relative changes in simulated
mean flow between 10 yr periods can remain similar, regardless of the calibration
period or the conceptual model used. Surprisingly, using longer records for parameters
optimisation or using a semi-distributed 19-parameter daily model instead of a simple
1-parameter annual formula did not provide significant improvements regarding these
simulation errors on flow volumes. While the actual causes for these robustness problems
can be manifold and are difficult to identify in each case, this work highlights that the
transferability of water balance adjustments made during calibration can be poor,
with potentially huge impacts in the case of studies in non-stationary conditions
Spatial variability of the parameters of a semi-distributed hydrological model
Ideally, semi-distributed hydrologic models should provide better streamflow
simulations than lumped models, along with spatially-relevant water resources
management solutions. However, the spatial distribution of model parameters
raises issues related to the calibration strategy and to the identifiability
of the parameters. To analyse these issues, we propose to base the evaluation
of a semi-distributed model not only on its performance at streamflow gauging
stations, but also on the spatial and temporal pattern of the optimised value
of its parameters. We implemented calibration over 21Â rolling periods and
64Â catchments, and we analysed how well each parameter is identified in time
and space. Performance and parameter identifiability are analysed
comparatively to the calibration of the lumped version of the same model. We
show that the semi-distributed model faces more difficulties to identify
stable optimal parameter sets. The main difficulty lies in the identification
of the parameters responsible for the closure of the water balance (i.e. for
the particular model investigated, the intercatchment groundwater flow
parameter)
EvalHyd v0.1.2: a polyglot tool for the evaluation of deterministic and probabilistic streamflow predictions
The evaluation of streamflow predictions forms an essential part of most hydrological modelling studies published in the literature. The evaluation process typically involves the computation of some evaluation metrics, but it can also involve the preliminary processing of the predictions as well as the subsequent processing of the computed metrics. In order for published hydrological studies to be reproducible, these steps need to be carefully documented by the authors. The availability of a single tool performing all of these tasks would simplify not only the documentation by the authors but also the reproducibility by the readers. However, this requires such a tool to be polyglot (i.e. usable in a variety of programming languages) and openly accessible so that it can be used by everyone in the hydrological community. To this end, we developed a new tool named evalhyd that offers metrics and functionalities for the evaluation of deterministic and probabilistic streamflow predictions. It is open source, and it can be used in Python, in R, in C++, or as a command line tool. This article describes the tool and illustrates its functionalities using Global Flood Awareness System (GloFAS) reforecasts over France as an example data set.</p
Land use change impacts on floods at the catchment scale: Challenges and opportunities for future research
Research gaps in understanding flood changes at the catchment scale caused by changes in forest management, agricultural practices, artificial drainage and terracing are identified. Potential strategies in addressing these gaps are proposed, such as complex systems approaches to link processes across time scales, long-term experiments on physical-chemical-biological process interactions, and a focus on connectivity and patterns across spatial scales. It is suggested that these strategies will stimulate new research that coherently addresses the issues across hydrology, soil and agricultural sciences, forest engineering, forest ecology and geomorphology
Trees, forests and water: Cool insights for a hot world
Forest-driven water and energy cycles are poorly integrated into regional, national, continental and global decision-making on climate change adaptation, mitigation, land use and water management. This constrains humanityâs ability to protect our planetâs climate and life-sustaining functions. The substantial body of research we review reveals that forest, water and energy interactions provide the foundations for carbon storage, for cooling terrestrial surfaces and for distributing water resources. Forests and trees must be recognized as prime regulators within the water, energy and carbon cycles. If these functions are ignored, planners will be unable to assess, adapt to or mitigate the impacts of changing land cover and climate. Our call to action targets a reversal of paradigms, from a carbon-centric model to one that treats the hydrologic and climate-cooling effects of trees and forests as the first order of priority. For reasons of sustainability, carbon storage must remain a secondary, though valuable, by-product. The effects of tree cover on climate at local, regional and continental scales offer benefits that demand wider recognition. The forest- and tree-centered research insights we review and analyze provide a knowledge-base for improving plans, policies and actions. Our understanding of how trees and forests influence water, energy and carbon cycles has important implications, both for the structure of planning, management and governance institutions, as well as for how trees and forests might be used to improve sustainability, adaptation and mitigation efforts
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