effects of land cover modifications in mm5 on surface energetics in phoenix susanne grossman-clarke,...

Effects of Land Cover Modifications in MM5 on

Surface Energetics in Phoenix

Susanne Grossman-Clarke, Joseph. A. Zehnder,William L. Stefanov,

Harindra J.S. Fernando, Sang-Mi Lee

Environmental Fluid Dynamics ProgramArizona State University

Introduction

Focus on PhoenixCentral-Arizona Phoenix (CAP)

Long-Term Ecological Research (LTER) Project.

Mesoscale Meteorological Modeling GroupNeighborhood scale distributions of near-

surface meteorological variables.

Introduction - Applications

Urban heat island

Water use (evaporation & transpiration)

CO2 dome

Air quality

Urban design

Biogeochemical cycles

Introduction – Characteristics of Phoenix

Fastest growing city in the US.

Mostly suburban core, surrounded by irrigated agricultural land and dry sparsely vegetated desert, embedded in complex terrain.

Irrigated vegetation in suburban neighborhoods is important for urban energy balance.

Introduction - Land Surface Representation in MM5

Land use and soil data Land use and soil classes Physical and biological parameters Physical approach for describing

energy, momentum and matter exchange between land surfaces and the atmosphere.

Land Use Data Preparation

Land cover data 30 meter resolution

Based on 1998 Landsat Thematic Mapper satellite images for Phoenix (visible and shortwave infrared & vegetation index).

Postclassification using additional data sets in expert system.

Land Use Data 1998

Land Use Data Preparation

Reprojecting land use data according to the grid information of USGS 30-second data in GIS.

Zonal summing of the 30 m data set within 30 second grid cells.

Land Use Data Preparation

Three urban classes in 25-category USGS land cover classification: Built-up urban, mesic and xeric

residential.

Composition of mesic and xeric residential areas in terms of typical fractions of irrigated and total vegetation. MM5 water availabilty factor.

Surface Parameters

Albedo

Roughness length

Moisture availability

Emissivity

Heat storage capacity

LU class USGS class

1 Cultivated veget.

3 - Irrigated agric.

2 Cultivated grass 3 - Irrigated agric.

3 River gravels 19 - Bare soil

4 Compacted soil 19 - Bare soil

5 Vegetation 11 - Decid. forest

6 Com./Industrial 1 - Urban and built-up

7 Asphalt/concrete 1 - Urban and built-up

8 Undisturbed desert

8 - Shrub land

9 Compacted soil 19 - Bare soil

10 Mesic residential New

11 Xeric residential New

12 Water 16 – Water

Land Use Class Characteristics

(LTER - 200 point survey)

Irrigated vegetatio

n

Xeric vegetatio

n

Bare soil

Asphalt,

concrete

Mesic residenti

al

40 - 2 58

Xeric residenti

al

3 22 2 73

Build-up urban

0-18 - 0-3 79-100

Native desert

- 38 62 -

1km x 1km Land Use: 1998 Satellite Data

2km x 2km Land Use: 1998 Satellite Data

2km x 2km Land Use: 1976 USGS Data

MM5 (a) 1976 USGS (b) 1998 Land Use Data

Design of Numerical Simulation

1700 LST May 28 – 1700 LST May 30, 2001Spatial dimension

Nested Run of MM5: 54 Km 18 Km 6 Km 2 Km 32 vertical layers

Meteorological data Initial & Boundary conditions : NCEP Eta Analysis 40 km

Elevation and land use data resolution: 30 sec. MRF boundary layer scheme & 5 layer soil model.

Surface Energy Balance Equation

)( gTfEGHnRtgT

gC

Tg … Ground temperature [K]

Cg … Heat capacity of the ground [J m-2 K-1]

Rn … Net radiation balance [W m-2]

H … Sensible heat flux [W m-2]

G … Soil heat flux [W m-2]

E … Latent heat flux [W m-2]

Latent Heat Flux

)/(ln

)(

0Lz

z

z

qTqkuME

aha

vagvsa

M … Moisture availability factor [-]

z0 … Roughness length [m]

h … Stability function [-]

qvs … Saturation specific humidity [-]

qva … Specific humidity at za[-]

Sensible Heat Flux

)/(ln

)(

0Lz

z

z

TTkucH

aha

agpa

Ta … Air temperature at za [K]

u* … Friction velocity [m s-1]

L … Monin Obukhov length [m]

k … von Karman constant [-]

cp … Specific heat capacity of air [J K-1 kg-1]

Boundary Layer Height

])([

)( 2

sv

vacr hg

hURibh

h … Boundary layer height

Ribcr … Critical bulk Richardson number (0.5)

va … Virtual potential temperature at za

v … Virtual potential temperature at z=h

s … Virtual potential temperature at ground level z=0

U(h) … Wind speed at z=h

Simulated Ground Temperatures (a) USGS (b) 1998 Land Use Data

29 May 2001 14:00 LST

Differences in Ground Temperatures

Simulated Latent Heat Fluxes (a) USGS and (b) 1998 Land Use Data

29 May 2001 14:00 LST

Differences in Latent Heat Fluxes

Simulated Sensible Heat Fluxes (a) USGS (b) 1998 Land Use Data

29 May 2001 14:00 LST

Differences in Sensible Heat Fluxes

Simulated 2m Air Temperatures(a) USGS (b) 1998 Land Use Data

29 May 2001 14:00 LST

Differences in 2m Air Temperatures

Simulated Boundary Layer Heights (a) USGS (b) 1998 Land Use Data

29 May 2001 14:00 LST

Differences in Boundary Layer Heights

Results

Results

Results

Results

Results

Results

15

20

25

30

35

40

45

0 4 8 12 16 20 0 4

Time of day

Ob

serv

ed t

emp

erat

ure

[oC

]

Stat. 1

Stat. 2

Stat. 3

Stat. 4

Stat. 5

Stat. 6

Results

15

20

25

30

35

40

45

0 4 8 12 16 20 0 4

Time of day

Sim

ula

ted

tem

per

atu

re [

oC

]

Stat. 1

Stat. 2

Stat. 3

Stat. 4

Stat. 5

Stat. 6

Summary

Urban land use is likely to have a significant impact on the simulated near surface temperatures and PBL heights in MM5.

Model validation is necessary.

Summary

Problems

Physical representation of urban surfaces in MM5.

Slope flows in complex terrain (timing, strength), eddy diffusivities.

Nitrogen Dry Deposition Modeling

Assess indirect and direct effects of urban vegetation on nitrogen dry deposition in the CAP LTER study area, including Phoenix metropolitan area.

Is N deposition significant input to N mass balance of the area.

Changes in biogeochemical cycles. Effects on ecosystems.

Nitrogen Dry Deposition Modeling

Models-3/CMAQ – Problems: Physical approach of describing matter

transport in urban roughness sub-layer. Land use data.

Diagnostic model Make use of long-term measured pollutant

concentrations and weather variables Investigate seasonal changes of dry

nitrogen deposition.

Nitrogen Dry Deposition Modeling

Assess indirect and direct effects of urban vegetation on nitrogen dry deposition in the CAP LTER study area, including Phoenix metropolitan area.

Is N deposition significant input to N mass balance of the area.

Changes in biogeochemical cycles. Effects on ecosystems.

Vertical Dry Deposition Flux

0zCrzCadvdF

z0 Sink height at the surface

zr Reference height in the atmosphere

C(zr) Pollutant concentration at reference height

C(z0) Pollutant concentration at the surface

vd Deposition velocity

a Air density

Deposition Velocity

srbrardv

1

ra Aerodynamic resistance

rb Boundary layer resistance

rs Surface resistance

Aerodynamic resistance

ku

L

z

L

dz

z

dz

r

hh

rh

h

r

a

0

0

ln

L Monin-Obukhov length

k von Karman constant

u* Friction velocity

h Similarity function for heat (Holtslag & van Ulden, 1983 and Dyer & Hicks,1970)

Monin-Obukhov Length

kgH

TcuL apa

3

H Sensible heat flux

k von Karman constant

u* Friction velocity

Ta Air temperature

Sensible Heat Flux

GARS

SH n1

1

s

p

dq

dTcS

Rn Net radiation

G Soil heat flux

A Anthropogenic heat production

Water availability factor

Water Availability Factor

222.0610.0 if

fi Fraction of irrigated vegetation cover (Oke, 2001)

Canopy Resistance

minmax

0max

0max

max

min

min0

2

2001min

TT

TT

s TTTT

TTTT

Rrcr

rmin Minimum canopy resistance

Rs Incoming solar radiation

T Air temperature

Tmin Cold limit (–5 – 0 C)

Tmax Heat limit (45 - 50 C)

To Optimum temperature (30 C)

Air quality monitoring station Phoenix Supersite.

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 50 100 150 200 250 300 350

Julian Day 1998

C(N

O2)

[p

pm

]

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

F(N

O2)

[kg

N h

a-1

d-1

]

NO2 dry deposition flux (FNO2 —) and measured NO2 concentrations (CNO2 --- )

Nitrogen Dry Deposition Modeling

Contribution of individual land cover types to the estimated

annual NOx dry deposition at Phoenix Supersite

0

10

20

30

40

50

urban irrigated veg. bare soil shrubs & xeric

% o

f to

tal

NO

x d

epo

site

d

Urban Irrig. Veg.

Bare soil

Xeric

Cover [%] 59 21 8 12

FNOX[%] 31 41 6 22

Nitrogen Dry Deposition Modeling

Modeling Nitrogen Dry Deposition

Spatial distribution of total nitrogen dry deposition flux 1998