Engineering Urban Green Spaces for Evapotranspiration: Vegetation and Climate Kimberly DiGiovanni 1, Stephanie Miller 1 Franco Montalto 1 and Stuart Gaffin 2 PA Stormwater Management Symposium 2013 Session 2b: Stormwater Control Measures -The Importance of Vegetation 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
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 Meteorology Image adapted from Brouwer and Heibloem (1986) 3
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
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Google Maps and Bing 9
Sites 1. 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)* *Data sets acquired from NRCC 11
Bio-C 12
GR-F 13
UP-AP 14
Weighing Lysimeters 15
Weighing Lysimeters UP-AP Urban Park (left) Mixed natives Bio-C Bioretention Area (right, receives precipitation) Juncus effusus GR-F Green Roof Sedum species Bio-N Bioretention Area (receives precipitation and stormwater) Juncus effusus 16
DETERMINATION OF EVAPOTRANSPIRATION 17
ASCE Standardized Reference Evapotranspiration Equation (short grass reference surface well watered) ET sz = 0.408 Δ R n G + γ Δ + γ 1 + C d u 2 C n T + 273 u 2 e s e a ASCE-EWRI (2005) Rn net radiation G soil heat flux Δ slope of the saturation vapor pressure deficit curve γ phsychrometric constant Cn numerator constant u2 wind speed at 2 meters height es saturated vapor pressure ea actual vapor pressure Cd denominator constant 18
Water Balance: Weighing Lysimeter ET = x i=1 f is a conversion factor f m i m i+1 ρa m is the mass of the lysimeter A is the surface area of the lysimeter ρ is the density of water i 19
RESULTS 20
Reference Evapotranspiration (mm/day) Bio-C 10 9 Evapotranspiration (mm/day) 8 7 6 5 4 3 2 1 0 Jul-2011 Sep-2011 Oct-2011 Dec-2011 Jan-2012 Mar-2012 May-2012 Jun-2012 21
Reference Evapotranspiration (mm/day) 327 nonconsecutive days over one year period Bio-C GR-C GR-F Air-JFK Air-LG GR-QBG 22
Cumulative Reference Evapotranspiration (mm) 1200 1000 800 600 RET from Bio-C RET from GR-C RET from GR-F RET from Air-JFK RET from Air-LG RET from GR-QBG 400 200 0 327 non-consecutive days over one year period 1 92 183 274 365 Day of Year 23
Cumulative Reference Evapotranspiration (mm) 1200 1000 800 600 RET from Bio-C RET from GR-C RET from GR-F RET from Air-JFK RET from Air-LG RET from GR-QBG 40% 400 200 0 1 92 183 274 365 Day of Year 24
Cumulative Reference Evapotranspiration (mm) 1200 1000 800 600 400 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 200 0 1 92 183 274 365 Day of Year 25
Bio-C GR-F 26
Actual Evapotranspiration (mm/day) Actual Evapotranspiration (mm/day) Bio-C GR-F 27
Cumulative Actual Evapotranspiration (mm) 400 350 300 250 200 150 100 AET from Bio-C AET from GR-F >25% 50 0 193 non-consecutive days 1 92 183 274 365 Day of Year 28
LABORATORY STUDIES 29
Objectives 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 30
Plant Species 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 31
4 Carex lurida 4 Asclepias incarnata 4 Liriope muscari 4 Echinacea purpurea 32
Methods 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 33
Water Balance: Weighing Lysimeter ET = x i=1 f is a conversion factor f m i m i+1 ρa m is the mass of the lysimeter A is the surface area of the lysimeter ρ is the density of water i 34
AET (mm/day) Watered 7/26 3 Daily ET Values (8/19-8/29) Carex Liriope Asclepias Echinacea Watered 7/30 2.5 2 1.5 1 0.5 0 27-Jul 28-Jul 29-Jul 30-Jul 31-Jul 1-Aug 2-Aug Date 35
Results Species Replicate 1 Replicate 2 Replicate 3 Replicate 4 Avg 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 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 36
Results Non-parametric statistics Kruskal-Wallis Median Test p value of.05 or below considered significant 37
Cumulative AET (depth in mm) 160 Seasonal Evapotranspiration Carex Liriope Asclepias Echinacea 140 120 100 80 60 40 20 0 27-Jun 4-Jul 11-Jul 18-Jul 25-Jul 1-Aug 8-Aug 15-Aug 22-Aug 29-Aug 5-Sep Date 38
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Preliminary Conclusions There are significant differences between the four species Intra-species variability is very high for Carex and Echinacea Further analysis is needed to explain differences within species 40
Future Work 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 41
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 k c RET = ET crop 45
Ratio of Low Elevation AET to High Elevation AET (Furmanville Bioretention Area) 46
Engineer for ET Future Objectives Urban micrometeorological conditions dictate evaporative capacity from urban green spaces Vegetation selection controls ET Runoff routing dictates ability to fulfill ET capacity 47
Acknowledgements Contact: Kimberly DiGiovanni kad54@drexel.edu 48
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2 ET crop = k c RET Kc AET:RET ActualET:ReferenceET 1.5 1 0.5 K cavg = 0.59 1: 1 Ratio Winter K cavg = 0.83 Spring K cavg = 0.95 Summer K cavg = 0.98 Fall 0 1 92 184 275 366 Day of Year 50
Evapotranspiration by Method 4.1 with Method A Non-water Limited Conditions (mm/day) 10 9 8 7 6 5 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 10 Evapotranspiration by Method 1.1 (mm/day) 1: 1 Ratio 51
Sanford and Selnick (2013) 52
Bioretention Cells Cross-Section from EPA (2013) 53