Average annual temperature (°C) Annual precipitation (cm) 100 200 300 400 -10 0 10 20 30 Subtropical desert

Biosphere 2

The Environmental and Natural Resources 2 (ENR2) building at the University of Arizona is a state-of-the-art facility designed to promote interdisciplinary research and education in environmental and natural resource management.

The building was completed in 2015 and has a total floor area of 120,000 square feet. It features a range of sustainable design features, including a green roof, rainwater harvesting, and a high-performance building envelope to reduce energy consumption. The ENR2 building also incorporates a range of energy-efficient systems, such as natural ventilation, radiant heating and cooling, and solar shading.

In 2020, a photovoltaic solar array and garden were installed on the roof of the building to create one of the first rooftop agrivoltaic gardens in the world. The garden was seeded with 21 desert-adapted and native species and provided with a minimal amount of irrigation. Study plots were installed in the full shade of the solar array, in the transition zone between shade and sun, and in the full sun beyond the solar array.

Rooftop gardens are challenging in the harsh climate of the southwest United States. The ENR2 rooftop agrivoltaic garden was designed to alleviate the environmental pressures on the plants by creating a microclimate beneath the solar array. The immediate results made it clear that this was effective as vegetation thrived in the shade before establishing in the sun.

Over time, and with the use of irrigation, the species originally seeded began differentially growing in the sunny and shaded area of the garden. There were phenological differences, with not only different species and abundances in the treatments but flowers opening at different times within a season depending on whether the plants were growing in the shade or in the sun.