American Society of Civil Engineers


Quantifying Evapotranspiration Rates for New Zealand Green Roofs


by Emily Voyde, (corresponding author), (Ph.D. Candidate, Dept. of Civil and Environmental Engineering, Univ. of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand E-mail: evoy001@aucklanduni.ac.nz), Elizabeth Fassman, Ph.D., A.M.ASCE, (Senior Lecturer, Dept. of Civil and Environmental Engineering, Univ. of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand. E-mail: e.fassman@auckland.ac.nz), Robyn Simcock, Ph.D., (Scientist, Landcare Research, Private Bag 92170, Auckland Mail Centre, Auckland 1142, New Zealand. E-mail: simcockr@landcareresearch.co.nz), and Julia Wells, (Undergraduate Student, Dept. of Civil and Environmental Engineering, Univ. of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand. E-mail: juliwells@gmail.com)

Journal of Hydrologic Engineering, Vol. 15, No. 6, June 2010, pp. 395-403, (doi:  http://dx.doi.org/10.1061/(ASCE)HE.1943-5584.0000141)

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Document type: Journal Paper
Special Issue: Low Impact Development, Sustainability Science, and and Hydrological Cycle
Abstract: Green roofs are an emerging storm-water management tool that has predominantly been analyzed for runoff volume reduction and peak flow mitigation. Little research has been completed on evapotranspiration (ET) in green roofs. Sedum mexicanum (Mexican stonecrop) and Disphyma australe (New Zealand iceplant) in a New Zealand designed, pumice- and zeolite-based substrate were analyzed to determine daily and hourly ET rates under both water-abundant and drought-stressed conditions. Water loss, and thus storage recovery of the substrate, was greatest in the first 9 days. Transpiration (T) by S. mexicanum contributed up to 48% of total ET (2.19 mm/day) and D. australe contributed up to 47% of total ET (2.21 mm/day). After the initial rate of rapid water loss, plants conserved water and ET was not significantly different from evaporation (E) from unplanted substrate. S. mexicanum had a greater ability to conserve water and thus a greater longevity of life than D. australe under harsh drought conditions.


ASCE Subject Headings:
Stormwater management
Roofs
Green buildings
Environmental engineering
Evapotranspiration
Evaporation
Best Management Practice
Vegetation
New Zealand

Author Keywords:
Stormwater management
Green roof
Environmental engineering
Evapotranspiration
Evaporation
Best management practice
Vegetation