Summertime response of temperature and cooling energy demand to urban expansion in a semiarid environment

This article explores regional impacts on near-surface air temperature and air conditioning (AC) electricity consumption due to projected urban expansion in a semiarid environment. In addition to the modern-day urban landscape setting, two projected urban expansion scenarios are analyzed with the Weather Research and Forecasting Model coupled to a multilayer building energy scheme. The authors simulate a 10-day extreme heat period at high spatial resolution (1-km horizontal grid spacing) over Arizona, one of the fastest-growing regions in the United States. Results show that replacement of natural land surfaces by buildings and pavement increases the local mean near-surface air temperature considerably. Furthermore, present-day waste heat emission from AC systems increases the mean nighttime 2-m air temperature by up to 1°C in some urban locations, but projected urban development aggravates the situation, increasing nighttime air temperatures by up to 1.5°-1.75°C. The contribution of anthropogenic heating due to AC systems is computed through comparison of two different types of numerical experiments: in one case, a specific urban scenario is simulated with the AC systems turned on and expelling heat into the outdoor environment, and in the second case, the same urban development (with the AC systems turned on) is simulated but with no heat expelled into the outdoor environment. The results demonstrate that projected urban expansion significantly amplifies local cooling energy demands for the Phoenix and Tucson metropolitan regions and therefore highlight the need for sustainable future energy needs to maintain thermal comfort levels.