Day: August 2, 2011

Read the full story in Environmental Protection.

While cool roofs and pavements have been found to cool the planet by preventing energy from being radiated back into the atmosphere, previous studies have not accounted for atmospheric feedbacks that may result from changing the surface reflectivity of urban areas. A new study from Lawrence Berkeley National Laboratory breaks new ground by using a high-resolution model of the continental United States that incorporates land-surface feedback to probe the effects of deploying light-colored roads and rooftops.

Full citation for the original article: Dev Millstein and Surabi Menon (2011). “Regional climate consequences of large-scale cool roof and photovoltaic array deployment,” Environmental Research Letters 6 034001. DOI: 10.1088/1748-9326/6/3/034001

Abstract: Modifications to the surface albedo through the deployment of cool roofs and pavements (reflective materials) and photovoltaic arrays (low reflection) have the potential to change radiative forcing, surface temperatures, and regional weather patterns. In this work we investigate the regional climate and radiative effects of modifying surface albedo to mimic massive deployment of cool surfaces (roofs and pavements) and, separately, photovoltaic arrays across the United States. We use a fully coupled regional climate model, the Weather Research and Forecasting (WRF) model, to investigate feedbacks between surface albedo changes, surface temperature, precipitation and average cloud cover. With the adoption of cool roofs and pavements, domain-wide annual average outgoing radiation increased by 0.16 ± 0.03 W m ^{− 2} (mean ± 95% C.I.) and afternoon summertime temperature in urban locations was reduced by 0.11–0.53 °C, although some urban areas showed no statistically significant temperature changes. In response to increased urban albedo, some rural locations showed summer afternoon temperature increases of up to + 0.27 °C and these regions were correlated with less cloud cover and lower precipitation. The emissions offset obtained by this increase in outgoing radiation is calculated to be 3.3 ± 0.5 Gt CO₂ (mean ± 95% C.I.). The hypothetical solar arrays were designed to be able to produce one terawatt of peak energy and were located in the Mojave Desert of California. To simulate the arrays, the desert surface albedo was darkened, causing local afternoon temperature increases of up to + 0.4 °C. Due to the solar arrays, local and regional wind patterns within a 300 km radius were affected. Statistically significant but lower magnitude changes to temperature and radiation could be seen across the domain due to the introduction of the solar arrays. The addition of photovoltaic arrays caused no significant change to summertime outgoing radiation when averaged over the full domain, as interannual variation across the continent obscured more consistent local forcing.