The role of soil moisture in influencing climate and terrestrial ecosystem processes

Transcription

1 1of 18 The role of soil moisture in influencing climate and terrestrial ecosystem processes Vivek Arora Canadian Centre for Climate Modelling and Analysis Meteorological Service of Canada

2 Outline 2of 18 The structure of the climate model. How soil moisture is modelled as a prognostic variable. The role of soil moisture in determining various climate system processes. Introduction of vegetation as a dynamic component of the climate system. Vegetation processes that are affected by soil moisture. Soil moisture requirements.

3 The structure of the climate model 3of mb Atmosphere 31 levels Interactive clouds Dynamic sea ice Ocean 29 levels Interactive land surface (3 levels) 3.75 resolution Global climate models (GCMs) solve mathematical equations describing the complex coupling of atmosphere, land surface and the oceans.

4 Structure of the Canadian land surface scheme (CLASS) 4of 18 e t P F c e c P Canopy Canopy P P e s r cs r cg Snow r sg e g e g P The four sub-areas snow-covered F gs F cs vegetation-covered F cg 3.75 m bare soil F g vegetation-snow covered 0.10 m G r o u n d 0.25 m r o r g

5 The structure of the land surface scheme 5of 18 Both evapotranspiration and runoff are non-linear functions of soil moisture Infiltration Evapotranspiration 0.10 m 0.25 m Runoff Liquid and frozen soil moisture contents are calculated prognostically 3.75 m

6 Land-atmosphere interactions and feedbacks 6of 18 Insolation Outgoing long wave radiation Precipitation Net Radiation Cloudiness Boundary layer thickness and heating Atmospheric moisture Atmosphere Albedo Latent heat flux (evapotranspiration) Sensible heat flux Surface/Soil temperature Land Soil moisture Ground heat flux

7 Land-atmosphere interactions and feedbacks 7of 18 What is the strength of this feedback loop? How is it modulated by soil moisture? How does vegetation affects this loop? Precipitation Evapotranspiration Atmosphere Land Soil moisture

8 Relationship between soil moisture and the state of the atmosphere 8of 18 Relative humidity (RH) Low cloud cover (LCC) Net longwave radiation LW net (W/m 2 ) Soil moisture index (Surface Layer) Soil moisture index (Surface Layer) Results from ECMWF reanalysis over southwestern Amazon Basin Betts A. K., P. Viterbo (2005), Land-surface, boundary layer, and cloud-field coupling over the southwestern Amazon in ERA- 40, J. Geophys. Res., 110, D14108, doi: /2004jd

9 Relationship between soil moisture and the state of the atmosphere 9of 18 Observations from ARM facility sites in Oklahoma and Kansas. Dirmeyer, P.A., R.D. Koster, and Z. Guo, Do Global Models Properly Represent the Feedback between Land and Atmosphere? J. Hydrometeorology, 7(6),

10 Structure of the Canadian Terrestrial Ecosystem Model (CTEM) 10 of 18 G = photosynthesis, GPP A S = carbon allocated to stem from leaves A R = carbon allocated to roots from leaves R gl = Growth respiration for leaves, and similarly for stem (S) and roots (R). R ml = Maintenance respiration for leaves and similarly for stem (S) and roots (R) R hd = Heterotrophic respiration from the litter or debris pool R hh = Heterotrophic respiration from the soil carbon (humus) pool C D H = carbon transferred from the litter to the soil carbon pool Leaf litter, D L G Leaves, C L A S R gl R ml Stem litter, D S CTEM 1.0 Plant Functional Types 1 2 Needleleaf Evergreen Needleleaf Deciduous Stem, C S R gs R ms 3 Broadleaf Evergreen R hh R hd 4 Broadleaf Cold Deciduous A R R gr R mr 5 Broadleaf Dry Deciduous 6 C 3 Crop Litter Pool, C D 7 8 C 4 Crop C 3 Grass C D H Roots, C R 9 C 4 Grass Soil Carbon Pool, C H Root mortality, D R

11 CTEM provides CLASS all vegetation related attributes 11 of 18 CTEM CLASS Since vegetation biomass is time variant and model climate dependent Leaf biomass Stem biomass Root biomass Canopy mass Albedo Depends on the specified land cover maps, which may be constant or time varying e.g. with increasing crop cover. Leaf Area Index, LAI (used in water and energy balance calculations) Vegetation Height (determines roughness length and thus drag) Root distribution profile and rooting depth (determines fraction of roots in each soil layer and thus transpiration) Determines canopy heat capacity Determines net radiation and net downward SW flux. All these vegetation attributes also become time variant and climate dependent (except for the land cover which has to be specified). CTEM 1 doesn t model the competition between PFTs and thus the fractional coverages of PFTs in a grid cell has to be specified.

12 Land-atmosphere interactions and feedbacks 12 of 18 Insolation Outgoing long wave radiation Precipitation Net Radiation Cloudiness Boundary layer thickness and heating Atmospheric moisture Atmosphere Albedo Latent heat flux (evapotranspiration) Sensible heat flux Surface/Soil temperature Land Ground heat flux Vegetation biomass, height and LAI Photosynthesis Fire Soil moisture

13 How CTEM grows vegetation? 13 of 18 Annual vegetation growth for a Broadleaf Cold Deciduous plant functional type in Germany

14 How CTEM grows vegetation? 14 of 18 Annual cycle of leaf area index for a Broadleaf Cold Deciduous plant functional type in Germany

15 How CTEM grows vegetation? 15 of 18 Annual cycle of leaf area index for a Broadleaf Cold Deciduous plant functional type in Germany

16 How CTEM grows vegetation? 16 of 18 Simulated annual cycle of leaf area index Annual cycle of satellite-derived normalized difference vegetation index (NDVI) Model-simulated annual cycle of NDVI (derived from grid-averaged LAI, m 2 /m 2 ) NDVI-LAI relationship from Buermann, W., et al. (2002): Analysis of a multi-year global vegetation leaf area index data set, J. Geophys. Res., 107(D22), /2001JD

17 In near future, combined analysis of soil moisture and states of vegetation and atmosphere is planned 17 of 18 Compare model simulated and observation-based behaviour of and relationship between Soil moisture, Vegetation state defined in terms of LAI or NDVI, and State of the atmosphere Observation-based information about states of vegetation (satellite-based NDVI) and atmosphere (reanalysis) is available. But no information is available for root zone soil moisture at large spatial scales.

18 Summary 18 of 18 Soil moisture affects the state of the atmospheric boundary layer (ABL) by influencing the partitioning of net radiation into latent and sensible heat fluxes. In a coupled vegetation-climate model, soil moisture additionally influences the state of vegetation and in particular the LAI which also interacts with the ABL. Quantification of soil-vegetation-atmosphere feedbacks is important to understanding the behaviour of coupled models, but hindered by the lack of observation-based root zone soil moisture data.