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A. Amengual and V. Homar

Universitat de les Illes Balears. Reunión PREDIMED 2014A 5-6 Junio. Hydrometeorological ensemble forecasts for the 28 September 2012 (IOP8) extreme flash-flood in Murcia, Spain. A. Amengual and V. Homar. Grup de Meteorologia, Departament de Física,

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A. Amengual and V. Homar

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  1. Universitat de les Illes Balears Reunión PREDIMED 2014A 5-6 Junio Hydrometeorological ensemble forecasts for the 28 September 2012 (IOP8) extreme flash-flood in Murcia, Spain A. Amengual andV. Homar Grup de Meteorologia, Departament de Física, Universitat de les Illes Balears, Palma, Mallorca, Spain e-mail: arnau.amengual@uib.es

  2. The Guadalentín flash-flood event • Hydrological and meteorological tools • Probabilistic versus deterministic QPFs • Probabilistic versus deterministic QDFs • Conclusions and further remarks Hydrometeorological ensemble forecasts for the 28 September 2012 (IOP8) extreme flash-flood in Murcia, Spain

  3. Entrance of a deep upper- • level closed trough • Generation of a surface • mesoscale cyclone • Advection of warm and • moist air toward Almería and Murcia from the Mediterranean • Convergence zone between • easterly advection and • westerly low-level flow • + • orographic enhancement • quasi-stationary mesoscale convective system 1. The Guadalentín flash-flood event: synoptic situation H500+T500+PV250 T850+SLP 27 September 2012 12 UTC 28 September 2012 12 UTC

  4. 1. The Guadalentín flash-flood event: observations • Torrential precipitation took place on 27, 28 and 29 September 2012 • Daily precipitation amounts: 214 mm in Andalucía, 240 mm in Murcia and 230 mm in Valencia • The Guadalentín catchment is a medium size basin with an area of 3343 km2and a length close to 121 km • Accumulated rainfall in 8 h up to 214 mm inside the basin • Peak discharges: • 616.3 m3s-1 in Lorca • 1081.2 m3s-1in Paretón de Totana

  5. 1. The Guadalentín flash-flood event • 10 casualties. Material losses estimated at about 120 M€

  6. 2. Hydrological and meteorological tools • WRF model set-up • Initial and boundary conditions: ECMWF forecasts (update 6h, 0.3º; 62 vertical levels) • One domain: 4 km and 28 vertical eta-levels • Schemes: Microphysics ─ WSM6; Long-wave radiation ─ RRTM ; Short wave radiation ─ Dudhia; surface model ─ NOAH; time-step ─ 30 s • The experiments consider a 48 hperiod simulation (27/09/2012 - 29/09/2012 00 UTC) • HEC-HMS model set-up • Loss rate: Soil Conservation Service Curve Number (SCS-CN) model • Transform: SCS Unit Hydrograph model • Flow routing:Muskingummethod • Reservoirs: elevation-storage-outflow relationship + initial elevation of the water level • The experiments consider a 72 hperiod simulation (27/09/2012-01/10/2012 00 UTC)

  7. 2. Hydrological and meteorological tools

  8. Guadalentín NSE EV (%) EP (%) rain-gauges 0.91 -5.7 -2.6 control 0.12 -88.4 -89.9 3. Probabilistic versus deterministic QPFs Flow observations only available for this study case: perfect-model assumption. Optimal estimation of the initial conditions and dynamical formulation after calibration. Difficulties to correctly forecast precise location and timing of convectively-driven rainfall system affecting a medium size basin

  9. 3. Probabilistic versus control QPFs • Mesoscale EPS (WRF) • Diversity source only from IC/BC (dynamical downscaling) • Obtained from ECMWF-EPS forecast (Global Singular Vectors) • 50 equally-likely members • Studyof the spatial and temporal uncertainties of QPFs into a medium-sized catchment

  10. 3. Probabilistic versus control QPFs • WRF ensemble comprises 51 elements (control + 50 perturbed) • Important spread on rainfall values • Essential role of atmospheric dynamical forcing (c) Ensemble mean ( in mm, shaded) and standard deviation (in mm, continuous line starting at 10 mm interval) (d) Probability-matched ensemble mean

  11. 4. Probabilistic versus deterministic QDFs • Elements of the HEPS are considered equally-like • Cumulative distribution functions (CDFs) of driven runoff peak flows

  12. 4. Probabilistic versus deterministic QDFs • Elements of the HEPS are considered equally-like • Cumulative distribution functions (CDFs) of driven runoff peak flows

  13. 5. Conclusions and further remarks • WRF control simulation is deficient for the Guadalentín event: maximum precipitation amounts are obtained quite far away from the basin • EPS reduce biases obtained for the control forecast • For civil protection purposes, a hypothetical first warning for a peak flow exceeding • Qp (T = 25 yrs) would have produced a probability of exceedenceof 0.4 and 0.3 at Lorca and Paretón. This fact points out the benefits of a HEPS versus a deterministic prediction system • The performance of the hydrometeorological simulations strongly depends on the initial conditions of the databases and on the case under study • References: • Amengual et al. (2014): Hydrometeorological ensemble forecasts for the 28 September 2012 (IOP8) extreme flash-flood in Murcia,Spain. Quart. J. R. Meteorol. Soc [submitted]

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