Tuesday, August 3, 2010 - 10:50 AM

OOS 12-9: Evaluating the performance of model green roofs in a semi-arid urban ecosystem

Mitchell Pavao-Zuckerman, Margaret Livingston, Steven E. Smith, and Ronald Stoltz. University of Arizona


One of the key ways that local decision making intersects with global change processes is the modification of microclimates through the urban heat island effect in cities.  One strategy for ameliorating local elevated temperatures is to use green design to alter energy balances and reduce energy demands for cooling.  Despite interest in such approaches, little is known about how to balance needs for energy reduction with water costs associated with green roof installations in cities in arid environments.  We are conducting a pilot study to investigate strategies to implement green roofs in arid cities that are environmentally ‘responsible’ with respect to water consumption.  In this study we ask, (a) is green roof technology appropriate for a desert city, (b) if native plants and environmentally responsible watering regimes are used, will ecosystem services we seek from green roofs be supported.   Small-plot model green roofs are constructed on the campus of Biosphere 2, near Oracle, AZ.   The study design crosses two artificial soil types (a heavy and light mix made of different proportions of sand, organic materials, and a lightweight porous material [SOILMatrixTM], two irrigation regimes (ambient and drip irrigated), and three plant species (succulent: Hesparaloe parviflora; shrub: Calliandra eriophylla; grass: Cathestecum erectum) in initial tests.  To address the questions we are posing, we compare energy balance of the plots, water status and health of the plants, and soil water contents.     


Preliminary results from the first season of data collection will be presented and discussed here.  An important consideration is the meeting of building code requirements to keep the green roof installations below 40 lbs per square foot when saturated.  We also consider the ability to use Biosphere 2 as a place for scientific interpretation and the use of this experiment for the visiting public as a citizen science project.  The experimental plots are designed so that they can be reached by visitors (hence, not on rooftops) so that they can collect data with scientists.  Preliminary data at Biosphere 2 suggests that interaction with scientists and science projects improves visitor’s understanding and appreciation of the questions being addressed in research.   Our hope is that this interaction with scientists will contribute to enhanced science and environmental literacy.  With respect to our science questions, we argue that the trade-off between water and energy in urban environments is an essential consideration for the planning and implementation of sustainable and green design projects.