Zong-Liang Yang

The University of Texas at Austin

Introduction to Land Surface Introduction to Land Surface ModelingModeling

Prepared for the TCEQ MeetingMay 24, 2006

www.geo.utexas.edu/climate

Why Land Surface Modeling?

• An important component of the weather, climate or environmental system.– exchanges of momentum,

energy, water vapor, CO2, VOC, and other trace gases between land surface and the overlying atmosphere

– states of land surface (e.g., soil moisture, soil temperature, canopy temperature, snow water equivalent)

– characteristics of land surface (e.g., roughness, albedo, emissivity, soil texture, vegetation type, cover extent, leaf area index, and seasonality)

• Critical for weather, climate, hydrological, and environmental forecasts. NCAR CLM Website

The Development of Climate models, Past, Present and Future

Atmosphere Atmosphere Atmosphere Atmosphere Atmosphere Atmosphere

Land surfaceLand surfaceLand surfaceLand surfaceLand surface

Ocean & sea-ice Ocean & sea-ice Ocean & sea-ice Ocean & sea-ice

Sulphateaerosol

Sulphateaerosol

Sulphateaerosol

Non-sulphateaerosol

Non-sulphateaerosol

Carbon cycle Carbon cycle

Atmosphericchemistry

Ocean & sea-icemodel

Sulphurcycle model

Non-sulphateaerosols

Carboncycle model

Land carboncycle model

Ocean carboncycle model

Atmosphericchemistry

Atmosphericchemistry

Off-linemodeldevelopment

Strengthening coloursdenote improvementsin models

Mid 1950s Late 1960s Early 1980s Mid 1990s Present day Late 2000s?

John Houghton

Climate Change and Variability

P

E

Qs

Ss

Sg

Qg

Ig

Coupled Ocean-Atmosphere

Models

Hydrologic/Routing Models

Water Resources Applications

In Situ Data

Mesoscale Models

Air Quality Models

Soil-Vegetation-Atmosphere Transfer

Remote Sensing and GIS

Policy

Water Quality and Quantity

Air Quality

Integrated Environmental Modeling Framework

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Warnings & Alert Warnings & Alert CoordinationCoordination

WatchesWatches

ForecastsForecasts

Threats Assessments

GuidanceGuidance

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Forecast Forecast UncertaintyUncertaintyForecast Forecast UncertaintyUncertainty

MinutesMinutes

HoursHours

DaysDays

1 Week1 Week

2 Week2 Week

MonthsMonths

SeasonsSeasons

YearsYears

Initial Conditions

Boundary Conditions

Accurate Land Surface Modeling Is Critical for Seamless Suite of Forecasts

Paul Houser

Land-Atmosphere Coupling Strength

Koster et al. (2004), Science

What Are Land Surface Processes

Land surface processes function as– lower boundary

condition in Atmospheric Models

• Atmospheric Boundary Layer Simulation

• Climate Simulation• Numerical Weather

Prediction• 4-D Data Assimilation

– upper boundary condition in Hydrological Models

• Water Resources Estimation• Crop Water Use• Runoff Simulation

– interface for coupled Atmospheric / Hydrological / Ecological Models

Land Surface Models (LSMs)• Computer code describing land surface processes (also

called LSSs, LSPs, SVATs)– FORTRAN, C, … ...– Tens to thousands of lines

• There are a huge number of LSMs (100+ examples in literature)– many are just “research models’’, local-scale oriented, with

specific process emphasis– up to ~100 canopy, ~100 soil, ~100 snow, even ~100

atmosphere layers!

• LSMs in GCMs and Hydrological Models are less diverse– one dimensional, with 1-2 canopy, 1-10 soil, 1-10 snow layers– three general classes

• “Bucket” Models (no vegetation canopy)• “Micrometeorological” Models (detailed soil/snow/canopy

processes) + Greening• “Intermediate” Models (some soil/snow/canopy features)

Four Basic RequirementsFrequently-sampled (hourly or sub-hourly) weather

“forcing data” to “drive” LSMs• precipitation (rate; coverage, large-scale/convective)• radiation (shortwave, longwave)• temperature• wind components (u, v)• specific humidity• surface pressure

Initialization of state variables• soil moisture (liquid, frozen)• deep soil temperature

Specification of surface characteristics• vegetation cover percent and composition (ET, BVOC…)• soil type (soil moisture & hydrology)• topography (hydrology)• albedo (solar radiation & energy balance)• roughness (turbulence & momentum exchange)• root depth (water holding capacity & hydrology)

Validation of simulations of state variables and fluxes• soil moisture• sensible/latent heat fluxes• skin temperature

Best Known Examples

– “Biosphere-Atmosphere Transfer Scheme (BATS)”

– “Simple Biosphere Model (SiB)”– Community Land Model (CLM)– Noah

Community Land Model

Hydrology

Drainage

Canopy Water

Evaporation

Interception

SnowMelt

Sublimation

ThroughfallStemflow

Infiltration Surface Runoff

Evaporation

Transpiration

Precipitation

Soil Water

Redistribution

Ocean Lake

Snow

Soil Water

Ground Water

River Flow

Surface Runoff

Direct Solar

Radiation

Absorbed SolarRadiation

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Pho

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Biogeophysics

NCAR CLM Website

Community Land Model Dynamic Vegetation

Vegetation Dynamics

0

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Ecosystem Carbon Balance

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0 15 30

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g C

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Foliage Water Potential (MPa)

g C

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Vapor Pressure Deficit (Pa)

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PPFD (molm-2s-1)

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Litterfall

NutrientUptake

NCAR CLM Website

Noah

NCEP Noah Website

Research Issues

• Obtaining and applying relevant “pure biome” data to test or calibrate LSMs

• Dealing with spatial/temporal heterogeneity• area-average parameters or tiling of land covers?• defining space-time structure of atmospheric inputs

• Making best use of remote sensing data for initialization, specification and validation

• Improving key processes• Snow/Frozen soil• Runoff generation/routing• “Greening” of LSMs (carbon balance and

vegetation dynamics)• Urban

CLM Subgrid Structure

Gridcell

Glacier Wetland Lake

Landunits

Columns

PFTs

UrbanVegetated

Soil Type 1

Keith Oleson

CLM Subgrid Structure

Gridcell

Glacier Wetland Lake

Landunits

Columns/PFTs

Vegetated

PerviousShaded WallRoof Sunlit Wall Impervious

Urban

Canyon Floor

Industrial

Medium Density

Suburban

Keith Oleson

Climate Science Program at UT-Austin

NOAA, Understanding and Simulation of the Effects of Vegetation on North American Monsoon Precipitation.

NASA/NOAA, Parameterization of Snow Cover Fraction in Climate and Weather Prediction Models.

EPA, Impacts of Climate Change and Land Cover Change on Biogenic Volatile

Organic Compounds (BVOCs) Emissions in Texas.

DHS, Regional Scale Flood Modeling for the San Antonio River Basin, 3-yr Graduate Fellowship to Marla Knebl.

NSF, Including Aquifer into the Community Land Model, 3-yr Graduate

Fellowship to Lindsey Gulden. [Groundwater and Runoff]

NASA, Using MODIS Data to Characterize Climate Model Land Surface Processes and the Impacts of Land Use/Cover Change on Surface Hydrological Processes.

www.geo.utexas.edu/climate

Climate Change and Variability

P

E

Qs

Ss

Sg

Qg

Ig

Coupled Ocean-Atmosphere

Models

Hydrologic/Routing Models

Water Resources Applications

In Situ Data

Mesoscale Models

Air Quality Models

Soil-Vegetation-Atmosphere Transfer

Remote Sensing and GIS

Policy

Water Quality and Quantity

Air Quality

Integrated Environmental Modeling Framework

Coupling Land Surface with Other Processes

NCAR CLM Website