Inclusion of potential vorticity uncertainties into a hydrometeorological forecasting chain: application to a medium size basin of Mediterranean Spain

Abstract

Abstract. The improvement of the short-and mid-range numerical runoff forecasts over the flood-prone Spanish Mediterranean area is a challenging issue. This work analyses four intense precipitation events which produced floods of different magnitude over the Llobregat river basin, a medium size catchment located in Catalonia, north-eastern Spain. One of them was a devasting flash flood -known as the "Montserrat" event -which produced 5 fatalities and material losses estimated at about 65 million euros. The characterization of the Llobregat basin's hydrological response to these floods is first assessed by using rain-gauge data and the Hydrologic Engineering Center's Hydrological Modeling System (HEC-HMS) runoff model. In second place, the non-hydrostatic fifth-generation Pennsylvania State University/NCAR mesoscale model (MM5) is nested within the ECMWF large-scale forecast fields in a set of 54 h period simulations to provide quantitative precipitation forecasts (QPFs) for each hydrometeorological episode. The hydrological model is forced with these QPFs to evaluate the reliability of the resulting discharge forecasts, while an ensemble prediction system (EPS) based on perturbed atmospheric initial and boundary conditions has been designed to test the value of a probabilistic strategy versus the previous deterministic approach. Specifically, a Potential Vorticity (PV) Inversion technique has been used to perturb the MM5 model initial and boundary states (i.e. ECMWF forecast fields). For that purpose, a PV error climatology has been previously derived in order to introduce realistic PV perturbations in the EPS. Results show the benefits of using a probabilistic approach in those cases where the deterministic QPF presents significant deficiencies over the Llobregat river basin in terms of the rainfall amounts, timing and loCorrespondence to: A. Amengual (arnau.amengual@uib.es) calization. These deficiences in precipitation fields have a major impact on flood forecasts. Our ensemble strategy has been found useful to reduce the biases at different hydrometric sections along the watershed. Therefore, in an operational context, the devised methodology could be useful to expand the lead times associated with the prediction of similar future floods, helping to alleviate their possible hazardous consequences.

Long‐term effects of climatic–hydrological drivers on macroinvertebrate richness and composition in two Mediterranean streams

“…For example, Amengual et al . () found that two of the most catastrophic extreme floods during the last 50 years in the Llobregat catchment occurred in November 1996 and December 1997. In contrast, in 2005, Spain, Portugal and France experienced an extreme drought with the lowest annual precipitation recorded since 1947.…”

“…The extreme flood and drought periods observed in our study also correspond with what is known for the region: floods were more common at the beginning of the series and droughts more common at the end. For example, Amengual et al (2009) found that two of the most catastrophic extreme floods during the last 50 years in the Llobregat catchment occurred in November 1996 and December 1997. In contrast, in 2005, Spain, Portugal and France experienced an extreme drought with the lowest annual precipitation recorded since 1947.…”

A Retrospective Streamflow Ensemble Forecast for an Extreme Hydrologic Event: a Case Study of Hurricane Irene and on the Hudson River basin

“…Recent studies show the promise of adopting streamflow ensemble forecast techniques due to advantages over deterministic forecasts (Habets et al, 2004;Younis et al, 2008;Boucher et al, 2011;Schellekens et al, 2011;Verkade and Werner, 2011;Alfieri et al, 2013) as well as a way of accounting for uncertainties in hydrological forecasting (Chen and Yu, 2007;Demeritt et al, 2007;Davolio et al, 2008;Pappenberger et al, 2008;Reggiani and Weerts, 2008;Cloke and Pappenberger, 2009;Bao et al, 2011;Bogner and Pappenberger, 2011;Cuo et al, 2011;Schellekens et al, 2011;Alfieri et al, 2012;Amengual et al, 2015). Other advantages include the ability to distinguish between an extreme event forecast that is more or less likely to occur within the model's forecast horizon (Buizza, 2008;Golding, 2009) and better decision making with respect to operational hydrological concerns (Ramos et al, 2007;McCollor and Stull, 2008;Boucher et al, 2012).…”

Mesoscale Numerical Study of Quasi-Stationary Convective System over Jeddah in November 2009

“…Some examples of international efforts in this field are [2,[5][6][7][8]. [5] presented a forecasting approach of the potential for flash flood producing storms using the notion of basic ingredients.…”