Title
Benefits and drawbacks of using data assimilation for hydrological modelling in karstic regions:
recent work on the Lez basin - 11:15
Speaker
V. Borrell Estupina
Session
Hw15S2 - Testing simulation and forecasting models in non-stationary conditions
Author(s)
Coustau, M. 1; Harader, E. 2; Borrell Estupina, V. 3; Ricci, S. 2; Bouvier, C. 4; Thual, O. 5; Piacentini, A.
2 - 1 HSM, UMR5569 CNRS IRD UM1 UM2, Montpellier, France, France; 2 CERFACS-CNRS, URA1875,
France; 3 University Montpellier II - HydroSciences Montpellier UMR5569, France; 4 IRD HydroSciences Montpellier UMR5569, France; 5 INPT CNRS IMFT, France
Abstract number
Hw15S2.04
Abstract
The present study focuses on the 114 km2 Lez catchment near the Montpellier agglomeration in
Southern France. This region is subject to violent rainfall that may lead to devastating flash floods. An
event-based, distributed, parsimonious rainfall-runoff model is used to simulate discharges at the
catchment outlet. Model efficiency is limited by uncertainties in the rainfall spatial variability and the
initial catchment wetness state. Rainfall measured by weather radar are used to force the model in
order to better represent spatial variability. Because of seasonal variations in the quality of radar
data, radar rainfall were only used during the fall, when spatial variations in rainfall are the greatest.
In winter, radar rainfall are of poor quality due to the weak vertical extension of the clouds and the
low altitude of the 0°C isotherm; during this period, the model is forced by rain gauge
measurements. By using different rainfall products based on the season considered, we are able to
adapt the hydrological model to temporal variations in data quality. Bias in radar rainfall and
uncertainties in the assessment of the catchment initial wetness state are also reduced using a data
assimilation technique: the Best Linear Unbiased Estimator (BLUE) algorithm. This algorithm was
used to assimilate discharges observed at the catchment outlet to correct either radar rainfall or
errors in the initial condition of the model. In most cases, correcting either radar rainfall or the model
initial condition leads to an improvement in peak discharge simulations. Nevertheless, in some cases,
the assimilation method is limited by the capacity of the model to correctly reproduce the rising limb
of the hydrograph. To draw more general conclusions, the hydrological model and the data
assimilation technique have been transferred to the French national service for flood forecasting
(SCHAPI) in order to be tested on a larger number of sample catchments.