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Status and Needs for Reanalysis: Land-Surface Processes

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Status and Needs for Reanalysis: Land-Surface Processes 1 ECMWF Workshop on Atmospheric Reanalysis Status and needs for reanalysis: Land-Surface Processes Christoph Schär Erich Fischer, Martin Hirschi, Daniel Lüthi, Reinhard Schiemann, Sonia I. Seneviratne Atmospheric and Climate Science, ETH Zürich, Switzerland [email protected] ECMWF, Reading, June 19, 2006 Schär, ETH Zürich 2 Outline Introduction and motivation Large-scale observations of terrestrial water storage variations Sensitivity experiments of the European summer 2003 Role of terrestrial water storage for interannual variability Homogeneity of assimilation products Outlook Schär, ETH Zürich 3 Global Energy Balance Short Wave Long Wave SpaceSpace –100% +22% +8% +10% +60% CO 2 –58% +5% +25% H20 Sensible Latent AtmosphereAtmosphere r g a d l o Heat Heat i +28% a b t a i o l n (Ohmura and Wild) +42% –113% +101% –5% –25% SoilSoil / /Ocean Ocean Global Net radiation R More than 80% of R is converted = net net mean 30% of solar input into ET rather than heating! 2 2 European Summer: Rnet ≈ 120 W/m ET ≈ 3 mm/d ≈ 85 W/m ≈ 70% of Rnet Schär, ETH Zürich 4 Land-Atmosphere Coupling Strength No signal over Europe! Is this confirmed by higher resolution? Schär, ETH Zürich (Koster et al. 2004) 5 Extreme Summers: 2002 … 2003 … 2005 … August 2002, Dresden, D August 2003, Töss, CH August 2005, Brienz, CH Schär, ETH Zürich 6 Swiss Temperature Series 1864-2003 Average of 4 Stations: Zürich, Basel, Berne, Geneva Schär, ETH Zürich (Schär et al. 2004, Nature, 427, 332-336) 7 High-resolution temperature analysis August 1, 2000 August 10, 2003 Aster Satellite (NASA/Japan) NDVI: 5x5 km view NDVI: -0.35 in Central France active NDVI: vegetation -0.00 IR: +20 ºC skin temperature +11 ºC 500 m 500 m 27 ºC 42 ºC 32 ºC 47 ºC Schär, ETH Zürich (Zaitchik et al. 2006) 8 Energy Flux Anomalies, Summer 2003, Europe TOA Net Radiation Surface Net Radiation Sensible Heat Flux Latent Heat Flux Surface Fluxes T2m Anomaly Schär, ETH Zürich (Black et al. , 2004; based on ECMWF data) 9 Soil-moisture threshold effect soil moisture Field Capacity Δ ~ 150 mm Wilting Point threshold latent cooling spring summer fall corresponds to ~45 W/m2 (3 months) Schär, ETH Zürich 10 Key issues What is the role of continental-scale soil-moisture variations for • interannual climate variability? • extreme summers such as the European summer 2003? Is there any evidence of the soil-moisture threshold effect? What is the amplitude of TWS (terrestrial water storage) in terms of • seasonal cycle? • interannual variations? How can we exploit reanalysis data such as ERA-40 for surface hydrology? Are the data homogeneous? Schär, ETH Zürich 11 Outline Introduction and motivation Large-scale observations of terrestrial water storage variations • Water-Balance Approach • GRACE Satellite • Land-surface data assimilation Sensitivity experiments of the European summer 2003 Role of terrestrial water storage for interannual variability Homogeneity of assimilation products Outlook Schär, ETH Zürich 12 Lysimeter (Rietholzbach, CH) Water Content [mm 250 225 200 175 1993 1994 150 1995 1996 1997 125 1998 Mean 100 2.Jan 1.Feb 2.Mär 1.Apr 1.Mai 31.Mai 30.Jun 30.Jul 29.Aug28.Sept28.Okt 27.Nov27.Dez Date • patch-scale soil-moisture data is useful for process studies • but of limited value in terms of the large- scale water balance Schär, ETH Zürich ( Ueli Moser, Achim Gurtz) 13 Water-Balance Approach Terrestrial water balance: S = terrestrial water storage Atmospheric water balance: W = atmospheric water storage Combined water balance: Convergence of the Change in column Runoff vertically integrated storage of water atmospheric water vapour vapour flux From atmospheric From conventional reanalysis data runoff observations (ERA-40) Schär, ETH Zürich (Seneviratne et al. 2004) 14 Case Study: Mississippi River Basin •Study Period: 1987-1996 •Runoff data: USGS •Validation against observations in Illinois (soil moisture, groundwater and snow) 1) Arkansas-Red (~6.105 km2) 2) Missouri (~13.105 km2) 3) Upper Mississippi (~5.105 km2) 4) Ohio-Tennessee (~5.105 km2) 5) Lower Mississippi (~4.105 km2) 6) Illinois (~2.105 km2) Schär, ETH Zürich (Seneviratne et al. 2004, J.Climate, 17, 2039-2057) 15 Validation (1): Monthly Variations Water-balance Excellent agreement in most years Estimates Good representation of extremes Observations (soil moisture+groundwater+snow) drought years flood year Schär, ETH Zürich (Seneviratne et al. 2004) 16 Validation (2): Seasonal Cycle Schär, ETH Zürich (Seneviratne et al. 2004) 17 Validation (3): Correlation corr = 0.84 slope = 0.82 Schär, ETH Zürich (Seneviratne et al. 2004) 18 Application to catchments Systematic application to 37 mid-latitude river basins, with areas between 36,000 and 2,868,000 km2. Validation using soil moisture data (Robock et al. 2000) Data available at http://www.iac.ethz.ch/data/water_balance/ Hirschi, M., S. I. Seneviratne and C. Schär (2006): Journal of Hydrometeorology, 7, 39–60 Schär, ETH Zürich 19 ERA-40 validation with basin-scale water-balance estimates Schär, ETH Zürich (Hirschi et al. 2006) 20 Climate model validation Detailed validation in Central European Domain (1972-1990): • 10 regional climate models PRUDENCE (EU FP5) • 1 global driving model (HadAM3) • ERA-40 Terrestrial water storage variations [mm/d] Water balance (mean +/- 1 σ) Water balance (mean +/- 1 σ) Schär, ETH Zürich (Martin Hirschi, ETH Zurich, work in progress) 21 Model validation with basin-scale estimates Central European Domain (1972-1990) Underestimation of summer precipitation by ERA-40 Schär, ETH Zürich (Martin Hirschi, ETH Zurich, work in progress) 22 Model validation with basin-scale water-balance estimates Central European Domain (1972-1990) Phase error of CRU / ERA-40 almost 1 month Schär, ETH Zürich (Martin Hirschi, ETH Zurich, work in progress) 23 GRACE Mission Distance 220 km Twin satellite Infers low-resolution terrestrial water anomaly from gravity anomaly Quasi-operational since 2002 Schär, ETH Zürich 24 GRACE Observations 2002-2003 Summer Drying Water Storage [cm] 2002 minus 2003 Gravity / Model 6 GRACE 3 0 -3 -6 [cm] 6 Accum. ECMWF Convergence GRACE 3 Superconducting Gravimeters GLDAS 0 GLDAS spatially smoothed -3 -6 Schär, ETH Zürich (Andersen et al. 2004) 25 Comparison Ground Atmospheric water- GRACE LSM data measurements balance assimilation Resolution Point 300-1000 km 1000-2000 km typically 50km measurements (105-106 km2) Main Ground truth Retrospective Global coverage Good results in advantage dataset (1958- regions with good present); large forcing; higher coverage resolution Main Point-scale Depend on quality of Only recent data Results depend limitation measurements; convergence data (since 2002); on quality of limited temporal (radiosonde, satellite low resolution forcing data; and geographical data, drifts) models optimized coverage for regions with validation data Schär, ETH Zürich 26 Outline Introduction and motivation Large-scale observations of terrestrial water storage variations Sensitivity experiments of the European summer 2003 • Global models: ECMWF seasonal forecasting system (Ferranti and Viterbo 2006) • Regional models: RCM driven by ECMWF analysis (Fischer et al. 2006) Role of terrestrial water storage for interannual variability Homogeneity of assimilation products Outlook Schär, ETH Zürich 27 SST versus SM Experiments with ECMWF seasonal forecasting system JJA 2003 surface temperature anomaly effect of prescribed SST effect of reduced soil moisture [K] Schär, ETH Zürich (Ferranti and Viterbo 2006) 28 Sensitivity experiments using an RCM Regional Climate Model (RCM) simulations with prescribed large-scale forcing. Model: CHRM = Climate High-Resolution Model (DWD origin) Lateral boundary conditions: ERA-40 and operational ECMWF analysis Simulations: • CLIM: Control climate, 1958-2001 simulation, driven by ERA-40 • CTL 2003: Control 2003, driven by ECMWF op, continuation of CLIM • Dry and Wet simulations: As CTL 2003, but with modified spring soil moisture on April 1, 2003 Schär, ETH Zürich (Fischer et al. 2006) 29 Validation of surface temperature anomaly JJA 2003 wrt 1970-2000 GISTEMP CHRM Schär, ETH Zürich (Fischer et al. 2006) 30 Terrestrial water storage Simulations Observations (water balance) Interannual variations underestimated Overall excellent validation Schär, ETH Zürich (Fischer et al. 2006) 31 Precipitation anomaly GPCC observed precipitation Spring 2003 Summer 2003 Low TWS is strongly affected by low preceding precipitation. Schär, ETH Zürich (Fischer et al. 2006) 32 Soil moisture experiments Schär, ETH Zürich (Fischer et al. 2006) 33 Soil-moisture induced temperature anomaly CTL-CLIM DRY25-CTL WET25-CTL Dry soil Æ larger (>2K) and spatially extended anomaly Schär, ETH Zürich (Fischer et al. 2006) 34 Soil-moisture induced 1000hPa height anomalies CTL-CLIM DRY25-CTL low-level heat low Dry soil Æ surface heat low Schär, ETH Zürich (Fischer et al. 2006) 35 Soil-moisture induced 500hPa height anomalies CTL-CLIM DRY25-CTL upper-level “heat high” Dry soil Æ positive 500hPa height anomaly POSITIVE FEEDBACK! Schär, ETH Zürich (Fischer et al. 2006) 36 Outline Introduction and motivation Large-scale observations of terrestrial water storage variations Sensitivity experiments of the European summer 2003 Role of terrestrial water storage for interannual variability • current climate • greenhouse gas climate Homogeneity of assimilation products Outlook Schär, ETH Zürich Climate Change Simulations 37 Greenhouse-Gas Scenario (IPCC SRES A2) Coupled GCM (HadCM3, ~300 km) Atmospheric GCM Regional Climate Model (RCM) (HadAM3, ~120 km) (CHRM /
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