Evaluating modifications of the soil module TERRA

1. Evaluating modifications of the soil module TERRA Felix Ament, MeteoSwiss COSMO General Meeting, September 2007

2. Dry soil moisture bias OPRerational COSMO, two-layer version Testsuite,multi-layer version Soil moisture T2m • Strong dry out bias! • Negative effect on T2m forecast.

3. Handling the dry out problem ECMWF.

4. Design of TERRA standalone experiments • Atmospheric Forcing: COSMO analysis data • Domain: see left; 64x61 gridpoints at 7km resolution • Period: year 2006 plus December 2005 for spin up • Initialization: Operational COSMO analysis Meteorological Forcing: T, p, u, q, Qdown COSMO analysis Precipitation RR SVAT „TERRA“ • Simulation of • Energy balance • Soil processes • Annual cycle of vegetation Working in the dark – nearly no or insufficient observations! time

5. Rain Evaporation Surface Runfoff Snow Intermediate Runfoff SM Ground Runfoff Nudged mulitlayer versus two layerAnalysis of the water budget Features of “Nudged Multilayer”: • Despite Nudging, LE is reduced in July/August and Tmax is higher. • Most of the nudged water (=residuum) is converted into runoff. • Remarkable: Less precipitation. Nudged multilayerOperational 2-layer

6. CTL standalone versus OPR 2-layer Features of “CTL standalone”: • Again, reduced LE in July / August (no response in T_2m due to external forcing) • Dry out in summer, but recovers until the end of the year. • Higher runoff. • Do we really have a dry-out problem? • Probably, the T_2m diagnosis is misleading? Doubts

7. Sensitivity experiments Lower boundary Drainage &diffusion Vegetation Exchange

8. Lower Boundary Condition I- concepts RIGIDGWATER dry wet medium rigid lid Free drainage ground water

9. Lower Boundary Condition IIGround water condition GWATER Problem: Definition of soil moisture gradient at top of water Solution: Solve Darcy equation with these simplifications: • F is constant below centre of lowest layer • D is constant there, too • K varies only linearly with Q :

10. Drainage and capillary rise I BROOKS1BROOKS2 • CTL: Rijtema (1969), e.g. for drainage K: • Brooks and Corey (1964) – much more popular • However, Brooks and Corey formulation requires three parameters to derive drainage and capillary rise (depending on soil moisture) – they are not well defined. • BROOKS1: 6 type DWD soil classification; lookup table adopted from R. Grasselt (UBonn) • BROOKS2: 6 type DWD soil classification; lookup table from J. Helmert (DWD) adopted from Shao and Irannejad (1999)

11. Drainage and capillary rise II Ecoclimap • PEDO • fields of soil pro-perties (e.g. pore volume) Rawls and Brakensiek, 1989 DWD classification USDA classification • BROOKS3 • 11 classes • Lookup by Shao • not fully done! • ECOSOIL • 6 classes • Lookup table by DWD

12. Runoff_g Drainage and capillary rise III MACROPOR Marcopores • help to infiltrate water rapidly during rainfall • might avoid runoff generation of saturated top layer Parameterization (adopted from VEG3d, e.g. Braun 2002) mit Fmax=10 und Qmin=0.5.

13. Vegetation I VEGPARA • Minimal / maximal stomatal resistance as well as plant albedo have constant value in TERRA CTL • VEGPARA uses spatially varying values depending on land-use CTL CTL

14. Vegetation II ECOVEG External vegetation parameters prescribed by ECOCLIMAP dataset (Mason et al., 2002): • Exhibits more variabilty • Systematic higher root depth • More detailed seasonal cycle (not shown) (all maps are valid for July)

15. Vegetation III ROOTDIST ROOTDIST • Linear root depth distribution CTL • Uniform root depth Recipe • Diagnose soil moisture stress function fSM,loc for each layer separately • Determine mean SM stress by average weighted by layer thickness Dz and root density rroot • Extract transpired water proportional to fSM,loc Dz rroot

16. Atmospheric exchange I ZOLOC Local roughness length z0,local • CTL roughness depends not only on local conditions, but also on variance of orography to account for gravity wave drag.  Very high roughness length over mountainous areas.

17. Atmospheric exchange II NP89 Top Layer SM at Lindenberg Dickinson, 1984: BATS scheme Designed for a two layer soil module! Noilhan and Platon, 1989 (NP89): ISBA scheme, Meso-NH

18. Rain Evaporation Surface Runfoff Snow Intermediate Runfoff SM Ground Runfoff Result I - bare soil evaporation NP89 • Significant reduction of Evaporation during spring and fall, … • … but no effect during summer!

19. Rain Evaporation Surface Runfoff Snow Intermediate Runfoff SM Ground Runfoff Result II – Budget Summary Deviations in mm

20. Conclusions • COSMO TERRA-ML is very robust; modifications have in general surprisingly small impact • TERRA-ML standalone has proven to be useful tool to asses the midterm effect of model modification. • However, objective decisions about implementation of modification is difficult, due to lack of observational data. • Scientifically the following modification can reasonably be recommended: • NP89 (removes high evaporation in spring & fall) • VEGPARA (better representation of forest) • (GWATER (counteracting dry-out)) • (BROOKSX (being state-of-the-art)) • Outlook: • Cross studies (e.g. BROOKS and GWATER) • Long term integration to reach model balance. • Combination with improved T_2m diagnosis.