Minimal watering regime impacts on desert adapted green roof plant performance
Abstract
Roof tops can cover one-fifth of urban areas and can greatly alter the movement of matter and energy in cities. With traditional roofing methods and materials, roof tops readily absorb heat and as a result, buildings and the surrounding urban area heat to unnaturally high temperatures. It is hypothesized that extensive green roofs would have wide-ranging benefits for arid environments. However, little is known about the cost of water use associated with green roof installations and how to balance energy reduction needs with water costs in this water limited environment. We are conducting a pilot study to test whether a) green roofs with native plants and environmentally-responsible watering regimes will prove successful in arid environments and if b) green roofs provide ecosystem services with responsible water application. Three species of Sonoran Desert natives, Dyssodia pentachaeta (groundcover), Calliandra eriophylla (shrub), and Hesperaloe parviflora (succulent) have been planted in experimental plots [1 m2 model houses and roofs, replicated in triplicate] with two sandy, rocky desert soil mixtures (light mix: 60% expanded shale and heavy mix: organic and sandy mix with 50% shale) at the Biosphere 2 campus near Oracle, Az. The green roofs are watered by two different techniques. The first technique provides "smart watering", the minimal amount of water needed by green roof plants based on precipitation and historical data. The second watering technique is considered heavy and does not take into account environmental conditions. Preliminary data from the experimental plots shows a 30% decrease in daytime roof top temperatures on green roofs and a 10% decrease in interior temperatures in buildings with green roofs. This trend occurs with both watering regimes (heavy and light). This finding suggests that additional irrigation yields no extra heat reduction and energy savings. In order to explain this phenomenon more clearly, we use co-located temperature and soil moisture readings on each green roof to analyze the spatial and temporal covariance of water and temperature. We link these patterns in soil moisture to measures of plant performance with weekly hyperspectral images (NDVI - Normalized Difference Vegetation Index) of each green roof. The data will allow us to determine the minimal amount of water use required for successful green roofs and healthy green roof plants. Preliminary data from a five week pilot study in the 2011 summer monsoon has shown a variation in NDVI by species. H. parviflora displayed the highest NDVI values, while D. pentachaeta and C. eriophylla shared similar, lower NDVI values. In general, the comparison of soil moisture and NDVI values expressed a very weak positive relationship but stronger species specific responses. D. pentachaeta demonstrated the strongest response to soil water and H. parviflora displayed the weakest response.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMGC33B1059K
- Keywords:
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- 1637 GLOBAL CHANGE / Regional climate change