Abstract
While the rain-driven evapotranspiration (ET) process has been well-studied in the humid climate, the mixed irrigation and rain-driven ET process is less understood for green roof implementations in dry regions, where empirical observations and model parameterizations are lacking. This paper presents an effort of monitoring and simulating the ET process for an irrigated green roof in a rain-scarce environment. Annual ET rates for three weighing lysimeter test units with non-vegetated, sedums, and grass covers were 2.01, 2.52, and 2.69 mm d−1, respectively. Simulations based on the three Penman–Monteith equation-derived models achieved accuracy within the reported range of previous studies. Compared to the humid climate, the overestimation of high ET rates by existing models is expected to cause a larger error in dry environments, where the enhanced ET process caused by repeated irrigations overlapped with hot, dry conditions often occurs during summer. The studied sedum species did not show significantly lower ET rates than native species, and could not effectively take advantage of the deep moisture storage. Therefore, native species, instead of the shallow-rooted species commonly recommended in humid climates, might be a better choice for green roofs in rain-scarce environments.
Highlights
Urbanization can perturb the natural patterns of streamflow, channel morphology, water quality, and ecosystem structure and function [1]
This study aimed to examine the ET behavior and to parameterize three ET models (FAO56, Thornthwaite–Mather equation (T–M), and P–M) for green roofs in a rain-scarce environment
A field experiment based on weighing lysimeter units was conducted in Salt Lake City, UT, USA, in 2014
Summary
Urbanization can perturb the natural patterns of streamflow, channel morphology, water quality, and ecosystem structure and function [1]. To address such an “urban stream syndrome”, the natural water balance needs to be restored via harvesting, infiltrating, or evapotranspiring the extra stormwater runoff caused by urbanization [1,2]. Green roofs bring other environmental benefits to the urban ecosystem, including heat island relief, air quality improvement, habitat and biodiversity provision, and food production [3,6,7,13,14,15,16,17,18,19,20,21]. In addition to its insulation [14,16,21], Water 2018, 10, 262; doi:10.3390/w10030262 www.mdpi.com/journal/water
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