Assessing the hydrological impacts of climate change at the local scale: Dynamical coupling of a regional climate model to a hydrological model

Transcription

1 Assessing the hydrological impacts of climate change at the local scale: Dynamical coupling of a regional climate model to a hydrological model Martin Drews 1, Søren H. Rasmussen 1, Jens Hesselbjerg Christensen 1, Michael B. Butts 2, Karsten H. Jensen 3, and Jens Christian Refsgaard 4 1 Danish Climate Centre, Danish Meteorological Institute 2 DHI 3 Department of Geography and Geology, University of Copenhagen 4 Geological Survey of Denmark and Greenland 1

2 Overview Motivation Hydrological modelling and climate change Dynamical coupling of a RCM to a hydrological model Conclusions 2

3 Mean global precipitation changes From IPCC WG1-AR4 (2007): Relative changes in precipitation (in percent) for the period vs

4 Key climate change impacts on hydrological systems Increased/reduced availability of freshwater (e.g. precipitation) Extreme precipitation Draughts Evapotranspiration Examples of hydrogical impacts of climate change: Water availability (irrigation, hydropower, etc.) Changes in groundwater head Changes in surface water, e.g. river runoff Increased risk of floods Transport of pollutants 4

5 Example: Groundwater head Courtesy of: Geological Survey of Denmark and Greenland; Roosmalen et al. 5

6 Example: Mean annual discharge Courtesy of: Geological Survey of Denmark and Greenland; Roosmalen et al. 6

7 Modelling hydrological change Emissions scenario km GCM (or reanalysis) Dynamical downscaling km 100 m 1 km Regional climate model Hydrological model, geology Statistical downscaling, bias correction Bias correction E.g. ground water head, runoff, etc. 7

8 Coupling an RCM to hydrological models Further downscaling is (often) needed Bias correction Different temporal resolution Propagation of uncertainties (!) In traditional hydrological modelling, feedbacks from the surface to the atmosphere are typically neglected! 8

9 Need for bias correction Observed ( ) HIRHAM4 RCM (12 km) 9

10 Normalized precipitation (-) Drizzle problem RCM Observed Precipitation bin (mm/day) 10

11 HYACINTS coupled modelling system MIKE SHE (DHI) Physically based, commercial, hydrological model (SVAT module) HIRHAM5 (DMI) Regional climate model 11

12 Two-way dynamical coupling Air temperature Precipitation Wind speed Relative humidity Global radiation Air pressure HIRHAM5 Latent heat flux Sensible heat flux Surface temperature MIKE SHE 12

13 HIRHAM proxy Model coupling - outline.net / C# Distributed model 13

14 Data out IENGINE HIRHAM proxy Data in Control Model coupling - outline High performance PC LINUX PC LINUX PC (or HPC).NET remote HIRHAM5- OMI* OpenMI front-end (Windows.NET) OpenMI back-end (Linux Mono) Binaries or text Linux Fortran *HIRHAM5 + extensions 14

15 HIRHAM: rotated latitute-longitude, km MIKE SHE: UTM, m Linking model grids MIKE SHE domain is a subset of the HIRHAM domain HIRHAM to MIKE SHE is handled by OpenMI (interpolation) MIKE SHE to HIRHAM is handled by HIRHAM Need for further downscaling, bias correction? 15

16 A simple 1-column test case: FIFE FIFE area, 15 x 15 km 2, Kansas, USA 10 meteorological stations 22 flux stations 32 soil moisture stations MIKE SHE model calculations (2 km grid) Forced by observations Forced by HIRHAM (one-way coupling) Forced by HIRHAM (two-way coupling) HIRHAM calculations From: Søren H. Rasmussen, DMI 16

17 Evapotranspiration [mm/day] Test: Evapotranspiration 12,00 10,00 8,00 6,00 Eva. Obs. 4,00 Eva. HIRHAM alone 2,00 0,

18 Evapotranspiration [mm/day] Test: Evapotranspiration 12,00 10,00 8,00 6,00 Eva. Obs. Eva. MIKE (HIRHAM) 4,00 Eva. HIRHAM alone 2,00 0,

19 Evapotranspiration [mm/day] Test: Evapotranspiration 12,00 10,00 8,00 6,00 4,00 Eva. Obs. Eva. MIKE (HIRHAM) Eva. HIRHAM alone Eva. Coupled 2,00 0,

20 Conclusions One-way RCM-hydrological model coupling Preliminary results are very encouraging added value for hydrological modelling Dynamic RCM-hydrological model coupling Technically quite challenging Different scales Direct coupling has been implemented Need for further downscaling and/or bias correction will be investigated Importance of feedback to the atmosphere will be investigated Thank you for your kind attention 20