Engineering Urban Green Spaces for

Evapotranspiration: Vegetation and Climate

1 Department of Civil, Architectural and Environmental Engineering, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104

2 Center for Climate Systems Research/NASA Goddard Institute for Space Studies, Columbia University, 2880 Broadway, New York, NY 10025

Kimberly DiGiovanni1, Stephanie Miller1

Franco Montalto1 and Stuart Gaffin2

PA Stormwater Management Symposium 2013

Session 2b: Stormwater Control Measures -The Importance of Vegetation

Practical Motivation & Goal

• Engineer for ET

• ET is a significant flux that expands the capacity for GI facilities to capture stormwater and provide other ecosystem services

• NPDES permit holders seek to quantify ET volumes from different kinds of GI facilities (Philadelphia Water Department 2012; NYCDEP 2013)

2

Factors Impacting ET

• Meteorology

• Vegetation

• Media Moisture

3

Image adapted from Brouwer and Heibloem (1986)

Meteorology

Objective

• Quantify ET from in-situ urban green spaces and in laboratory studies

• Evaluate the role of vegetation and climate in influencing ET

4

Definitions

• Evapotranspiration (ET)

• Potential Evapotranspiration (PET)

• Reference Evapotranspiration (RET)

• Actual Evapotranspiration (AET)

5

Overview of presentation

• Field Studies – Monitoring Sites

– Methods

– Results

• Laboratory Studies – Methods

– Results

• Implications of Findings and Future Work

6

MONITORING AND DATA ACQUISITION

7

8

Google Maps and Bing9

Sites1. UP-Alley Pond (UP-AP)

2. Bio-Colfax (Bio-C)

3. GR-Columbia (GR-C)

4. GR- Fieldston (GR-F)

5. Air-John F. Kennedy (Air-JFK)

6. Air-La Guardia (Air-LG)

7. Bio-Nashville (Bio-N)

8. GR-Queens Botanical Garden (GR-QBG)

10

Monitored Sites

• Bioretention (Bio)

• Green Roofs (GR)

• Urban Parks (UP)

• Airports (Air)*

11

*Data sets acquired from NRCC

12

Bio-C

13

GR-F

14

UP-AP

15

Weighing Lysimeters

Weighing Lysimeters

16

GR-F

Green Roof

Sedum

species

Bio-N

Bioretention Area

(receives precipitation

and stormwater)

Juncus effusus

Bio-C

Bioretention Area

(right, receives

precipitation)

Juncus effusus

UP-AP

Urban Park (left)

Mixed natives

DETERMINATION OF EVAPOTRANSPIRATION

17

ASCE Standardized Reference Evapotranspiration Equation (short grass reference surface – well watered)

𝐸𝑇𝑠𝑧 =0.408 𝛥 𝑅𝑛 − 𝐺 + 𝛾

𝐶𝑛𝑇 + 273 𝑢2 𝑒𝑠 − 𝑒𝑎

𝛥 + 𝛾 1 + 𝐶𝑑𝑢2

ASCE-EWRI (2005)

18

Rn – net radiationG – soil heat flux Δ – slope of the saturation vapor pressure deficit curveγ – phsychrometric constant

Cn – numerator constantu2 – wind speed at 2 meters height es – saturated vapor pressure ea – actual vapor pressure Cd – denominator constant

Water Balance: Weighing Lysimeter

𝐸𝑇 =

𝑖=1

𝑥

𝑓𝑚𝑖 −𝑚𝑖+1𝜌𝐴

𝑖

• 𝑓 is a conversion factor

• 𝑚 is the mass of the lysimeter

• 𝐴 is the surface area of the lysimeter

• ρ is the density of water

19

RESULTS

20

Jul-2011 Sep-2011 Oct-2011 Dec-2011 Jan-2012 Mar-2012 May-2012 Jun-20120

1

2

3

4

5

6

7

8

9

10E

va

potr

ansp

iratio

n (

mm

/da

y)

21

Ref

eren

ce E

vap

otr

ansp

irat

ion

(m

m/d

ay)

Bio-C

22

327 non-consecutive days over one year period

Bio-C GR-C GR-F Air-JFK Air-LG GR-QBG

Ref

eren

ce E

vap

otr

ansp

irat

ion

(m

m/d

ay)

0

200

400

600

800

1000

1200

1 92 183 274 365

Cu

mu

lati

ve R

efer

ence

Ev

apo

tran

spir

atio

n (

mm

)

Day of Year

RET from Bio-C

RET from GR-C

RET from GR-F

RET from Air-JFK

RET from Air-LG

RET from GR-QBG

23

327 non-consecutive days over one year period

0

200

400

600

800

1000

1200

1 92 183 274 365

Cu

mu

lati

ve R

efer

ence

Ev

apo

tran

spir

atio

n (

mm

)

Day of Year

RET from Bio-C

RET from GR-C

RET from GR-F

RET from Air-JFK

RET from Air-LG

RET from GR-QBG

24

40%

0

200

400

600

800

1000

1200

1 92 183 274 365

Cu

mu

lati

ve R

efer

ence

Ev

apo

tran

spir

atio

n (

mm

)

Day of Year

RET from Bio-C

RET from GR-C

RET from GR-F

RET from Air-JFK

RET from Air-LG

RET from GR-QBG

Bio-C ≈ GR-F

25

26

Bio-C GR-F

27

Act

ual

Eva

po

tran

spir

atio

n (

mm

/day

)

Act

ual

Eva

po

tran

spir

atio

n (

mm

/day

)

Bio-C GR-F

28

0

50

100

150

200

250

300

350

400

1 92 183 274 365

Cu

mu

lati

veA

ctu

al

Evap

otr

ansp

irat

ion

(m

m)

Day of Year

AET from Bio-C

AET from GR-F>25%

193 non-consecutive days

LABORATORY STUDIES

29

Objectives

30

• Quantify daily evapotranspiration (ET) rates from four species of vegetation commonly used in green infrastructure (GI) under uniform conditions

• Evaluate differences in seasonal ET trends for the four species

Plant Species

31

• Species chosen based on their popularity in GI installations in NYC

• NYC 2012 Interagency Bioswale Planting List consulted• Top 4 most frequent species

chosen for experiment

• 4 Carex lurida

• 4 Liriope muscari

32

• 4 Asclepias incarnata

• 4 Echinacea purpurea

Methods

33

• Use lysimeters to record daily weight changes of plants

• Replenished plant water supply every 4 days• Weighed plants before watering

and after gravitational drainage ceased

Water Balance: Weighing Lysimeter

𝐸𝑇 =

𝑖=1

𝑥

𝑓𝑚𝑖 −𝑚𝑖+1𝜌𝐴

𝑖

• 𝑓 is a conversion factor

• 𝑚 is the mass of the lysimeter

• 𝐴 is the surface area of the lysimeter

• ρ is the density of water

34

35

0

0.5

1

1.5

2

2.5

3

27-Jul 28-Jul 29-Jul 30-Jul 31-Jul 1-Aug 2-Aug

AET

(m

m/d

ay)

Date

Daily ET Values (8/19-8/29)

Carex Liriope Asclepias EchinaceaWatered 7/26

Watered 7/30

Results

Species Replicate 1 Replicate 2 Replicate 3 Replicate 4Avg

Cumulative ET

Carex 151.13 149.68 108.96 122.24 133.75

Liriope 124.30 110.20 110.40 106.89 112.95

Asclepias 102.39 105.96 139.40 107.69 105.35

Echinacea 159.67 105.28* 152.17 123.83 145.22

36

Results shown as depth in mm*This replicate began to senesce two weeks before the end of the experiment so it was not used in calculating average seasonal ET

Results

• Non-parametric statistics

• Kruskal-Wallis Median Test

• p value of .05 or below considered significant

37

38

0

20

40

60

80

100

120

140

160

27-Jun 4-Jul 11-Jul 18-Jul 25-Jul 1-Aug 8-Aug 15-Aug 22-Aug 29-Aug 5-Sep

Cu

mu

lati

ve A

ET (

de

pth

in m

m)

Date

Seasonal Evapotranspiration

Carex Liriope Asclepias Echinacea

39

Preliminary Conclusions

40

• There are significant differences between the four species

• Intra-species variability is very high forCarex and Echinacea• Further analysis is needed to explain

differences within species

Future Work

41

• Repeat experiment for 2014 growing season

• Determine relative influence of climatic factors, hours since irrigation, and species have on daily ET• So far only looked at seasonal totals

FINDINGS AND ONGOING WORK

42

Preliminary Conclusions

• Urban micrometeorological conditions dictate evaporative capacity from urban green spaces

– RET rates as determined at a daily time-step are statistically significantly differences across sites in an urban area

– Differences in cumulative RET up to 40 percent on an annual basis are observed between sites

43

Ongoing Related Work

• Micrometeorological variation across cities is an important factor in consideration of evapotranspiration

• Actual ET is influenced by other factors

– Vegetation Type

– Media Moisture Conditions

44

Vegetation Coefficients

45

𝑘𝑐 𝑅𝐸𝑇 = 𝐸𝑇𝑐𝑟𝑜𝑝

46

Ratio of Low Elevation AET to High Elevation AET (Furmanville Bioretention Area)

Future Objectives

• Engineer for ET

• Urban micrometeorological conditions dictate evaporative capacity from urban green spaces

• Vegetation selection controls ET

• Runoff routing dictates ability to fulfill ET capacity

47

Acknowledgements

48

Contact: Kimberly DiGiovanni – kad54@drexel.edu

49

50

1 92 184 275 3660

0.5

1

1.5

2

Day of Year

Actu

alE

T:R

efe

renceE

T

Kc

AET:RET

1: 1 𝑅𝑎𝑡𝑖𝑜

𝐾𝑐𝑎𝑣𝑔 = 0.59

𝑊𝑖𝑛𝑡𝑒𝑟

𝑆𝑝𝑟𝑖𝑛𝑔𝑆𝑢𝑚𝑚𝑒𝑟

𝐹𝑎𝑙𝑙

𝐾𝑐𝑎𝑣𝑔 = 0.83𝐾𝑐𝑎𝑣𝑔 = 0.95

𝐾𝑐𝑎𝑣𝑔 = 0.98

𝐸𝑇𝑐𝑟𝑜𝑝 = 𝑘𝑐 𝑅𝐸𝑇

51

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

7

8

9

10

Evapotranspiration by Method 1.1 (mm/day)

Evapotr

anspiration b

y M

eth

od 4

.1 w

ith M

eth

od A

Non-w

ate

r Lim

ited C

onditio

ns (

mm

/day)

1: 1 𝑅𝑎𝑡𝑖𝑜

52

Sanford and Selnick (2013)

53

Bioretention Cells Cross-Section from EPA (2013)