Use of Meteorological Forecast Data and Products as Input into Hydrological Models Jožef Roškar, Enviromental Agency of the Republic of Slovenia Branka Ivančan-Picek, Meteorological and Hydrological Service of Croatia Regional Workshop on Hydrological Forecasting and Real Time Data Management 11 – 13 May 2009, Park Hotel, Dubrovnik, Croatia

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Hydrological Model Input = Precipitation (Air temperature, Evapotranspiration etc.) Input = Precipitation (Air temperature, Evapotranspiration etc.) Matematical description of complex hydrological system including characteristics of the watershed, evapotranspiration, infiltration etc. Matematical description of complex hydrological system including characteristics of the watershed, evapotranspiration, infiltration etc. Output = Discharge (Soil Moisture, etc.) Output = Discharge (Soil Moisture, etc.)

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Hydrological Model (deterministic, conceptual, distributed, lump, etc) Hydrological Model (deterministic, conceptual, distributed, lump, etc) Observed or estimated rainfall Observed or estimated rainfall Forecasted rainfall Forecasted rainfall Simulated discharge Forecasted discharge T = 0 State variables T = 0 Simulation Forecast Hydrological Forecasting System

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Quantitative precipitation point precipitation measurements radar measurements rainfall estimation based on satellite imagery point precipitation measurements radar measurements rainfall estimation based on satellite imagery Numerical Weather Prediction Models Global: ECMWF, DWD, Arpege, NCEP/GFS,etc. LAM: Aladin, NMM, WRF-ARW, etc. Quantitative Precipitation Forecast Values in equidistant discrete grid Quantitative Precipitation Forecast Values in equidistant discrete grid Mean Areal Precipitation Thiessen Polygons, Inverse Distance Weighting Spline, Radar Maps, Cold Cloud Duration,etc.

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Rainfall Estimation – Example from Nile Forecast Centre IR/T ~ CCD ~ R Method useful only in areas with predominant convective raifall

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Accumulated rainfall 29 March UTC – 30 March UTC estimated by Radar and observed rainfall at some stations (figures) Example of by radar estimated rainfall

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Accumulated rainfall 29 March UTC – 30 March UTC estimated by NMM over Slovenia, model run start at 29 March 00 UTC and observed rainfall at some stations (figures) LAM - Example

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Regression models are used in some NMHS’s using observed precipitation at some stations. Some of them cooperate with JRC in the EFAS (European Flood Alert System) project, designed for simulation of rainfall- runoff processes in large catchments (Danube, Drava, Sava). Facts Majority of present countries doesn’t use hydrological conceptual or dynamic modells for a real time hydrological forecast.

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 To overcome the existent deficiencies and to improve the flood warning capabilities in the Sava Basin the “Sava Project” - Development and Upgrading of Hydrometeorological Information and Forecasting System for the Sava River Basin [Albania, Bosnia and Herzegovina, Croatia, Montenegro, Slovenia and Serbia] developed Facts There is relatively scarce network of real-time rainfall stations for flash-flood warning

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Numerical Weather Prediction Models - NWP Weather Observing System Weather Observing System Data Analysis Data Asimilation Initialization Data Analysis Data Asimilation Initialization Integration Atmospheric Physics Surface Physics Surface Processes Numerical Methods Simulated Fields Postprocessing Vizualization Postprocessing Vizualization

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Numerical Weather Prediction Models - NWP Simulated/ Predicted Athmospheric Variables/Fields Initial and Boundary Conditions (data archive) Integration Numerical resolving of mathematical equations describing development of athmospheric variables in time Air Pressure Wind Temperature Humidity Cloudiness Precipitation Evaporation Soil Moisture

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Real continous space is in a model presented in equidistant discrete grid form Space resolution defines the smallest structures seen by a NWP: Low resolution (~200 km) – simulation of basic structures (planetary waves, big frontal systems) – used for climate modeling and studies of global mechanisems; Medium resolution ( km) – simulation of sinoptic and mesoscale systems – used for general weather forecast; High resolution (< 10 km) – simulation of local systems (wind, fog, tunderstorms, etc.) Regardless the resolution, there are Global models covering entire globe and Limited Area Models simulating weather over choosed smaller area Numerical Weather Prediction Models - NWP

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Very important over montainous areas Relief presentation depends on horizontal resolution Example: slope and precipitation: Wind Numerical Weather Prediction Models - NWP This is why majority of NWP models underestimate precipitation

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Numerical Weather Prediction Models - NWP To run a LAM, access to global archives of weather patterns is needed Data in regular grid, internally consistent, without errors (+) Not directly related to actual situation “on ground” (-)

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 DATA SOURCE: European Centre for Middle-range Weather Forecasts (ECMWF) Available data sets: 1.Operational data set; 2.ERA-Interim - Daily re-analyses of weather patterns for last 20 years (1989 – 2008) 3.ERA-40 - Daily re-analyses of weather patterns for time period (1957 – 2001) Numerical Weather Prediction Models - NWP

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Limited Area Model Main Idea: Take data from global archive Choose area and grid points Re-simulate weather patterns from global model to obtain more details on a regional scale Numerical Weather Prediction Models - NWP

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 (Non)Predictability Physical Laws  Co-existence of various scales  Interaction of all variables  Exchange of energy among various scales Chaos Numerical Weather Prediction Models - NWP

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Numerical Weather Prediction Models - NWP Lorentz butterfly

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Numerical Weather Prediction Models - NWP (Non)Predictability Physical Laws  Co-existence of various scales  Interaction of all variables  Exchange of energy among various scales Discretization of continous space Limited computing power Incomplete knowledge of initial state

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Numerical Weather Prediction Models - NWP Uncertainty Taking into account (Non)Predictability, we have to consider that by the model simulated parameters and fields are not directly related to actual parameters, in particular to the situation “on ground”. How to reduce uncertainty of the NWP products? 1.to choose the model and setup it in the way that the output best fits the observations (might be difficult for precipitation!); 2.to calibrate the hydrological model with the model simulated precipitation (problem of distribution in space); 3.to use multi-model or assembley prediction (extended streamflow prediction);

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 LAM – Example: Flood in Železniki on 18 September 2007 WRF-ARW, Horizontal resolution app. 1 km Acc. Precipitation ,06-06

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 LAM – Example: Flood in Železniki on 18 September 2007

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 LAM – Example: Flood in Železniki on 18 September 2007

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 LAM – Example: Flood in Železniki on 18 September 2007

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 LAM – Example: Flood in Železniki on 18 September 2007

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Application of NWP for flood and drought monitoring Simulation using operational data from ECMWF Usual process in operational weather forecasting Does it have any potential for flood and drought monitoring?

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 In addition to short middle and/or long term forecasting the model could be used as an analytical tool. Goal: To re-compute re- analyses data over limited area in dense grid to obtain “model climatology”for flood and drought situations interpretation. ECMWF ERA – Interim Limited Model Integration Area Limited Area Model NNM (NCEP) Application of NWP for flood and drought monitoring

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Application of NWP for flood/drought monitoring Limited Area NMM (NCEP) Non-Hydrostatic Meso-scale Model Area: 461 x 289 x 92 = points ( points “on ground”) Top Level: 2 hPa (~ 60 km) Horizontal resolution: 8.5 km Vertical levels: 91 Integration Time: 36 h Time Step: 30 sec. No. days in re-analyse: 7305

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Application of NWP for flood and drought monitoring Horizontal Resolution – Grid density

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 OUTPUT: Simulated and averaged variables (air and soil) – daily aggregates Application of NWP for flood and drought monitoring

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Application of NWP for flood and drought monitoring FLOOD/DROUGHT RELATED VARIABLES Soil moisture? Water balance? Temperature? Evapotranspiration? FLOOD/DROUGHT RELATED TIME SCALE Not daily! Decade? FLOOD/DROUGHT RELATED INTERPRETATION Not absolute values, deviation from normals, percentils …

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Application of NWP for flood and drought monitoring STATISTICS: Model climatology based on ERA – Interim (1989 – 2008) re-analyses

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 STATISTICS: Model climatology based on ERA – Interim (1989 – 2008) re-analyses Application of NWP for flood and drought monitoring

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 STATISTICS: Model climatology based on ERA – Interim (1989 – 2008) re-analyses Application of NWP for flood and drought monitoring

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Application of NWP for flood and drought monitoring STATISTICS: Historical 40 % Percentile of Soil moisture index of upper 10 cm layer averaged over 10 days

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Application of NWP for flood and drought monitoring POSSIBLE PRODUCT: Anomaly of mean 10 days mean temperature, based on re- analyses statistics

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Application of NWP for flood and drought monitoring POSSIBLE PRODUCT: Accumulated Water Balance from 20 February to 30 April 2009 In percentil classes

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Conclusions: With growing computer power and latest generation of atmospheric modells uncertainty of the NWP products gradually reduces; Uncertainty of the simulated precipitation amounts over a limited area is reducing with growing horizontal grid density, but in the same time it increase in term of spatial distribution (important specially for flash flood warning); In spite of NWP outputs uncertainty, use of NWP outputs is the best we can use for the hydrological forecasting; Taking into account the fact that a certain uncertainty of the NWP output used as input into the hydrological model multiplies the uncertainty of hydrological model outputs by more than 1.5, one might consider to calibrate the hydrological model by NWP outputs – use of re-analyses; NWP model climatology based on re-analyses is useful for flood and drought monitoring.

Regional Workshop on HFRTDM, Hotel Park, Dubrovnik, May 2009 Thank you for your attention!