Misting as a key component of blue infrastructure for urban heat mitigation

Evaporative misters are widely used in urban outdoor spaces for heat mitigation, yet their impacts on thermal stress and optimal operating conditions remain unclear. To address this, we developed a misting model and integrated it into the Princeton Urban Canopy Model (PUCM) to evaluate the influence of microclimate and system design on misting performance. The PUCM-mist simulates sensible-latent heat conversion during mist evaporation and predicts corresponding changes in canyon air temperature and humidity. Validation against in-situ measurements at five sites in Tempe, AZ, demonstrates the capability of the model in capturing mist-induced cooling and humidifying effects. By varying flow rates, wind speeds, and misted area ratios, we assessed the potential of misters to mitigate thermal stress and identified optimization strategies. In Phoenix, AZ, misters reduced maximum canyon air temperature by up to 17.5^°C and human skin temperature by 0.48^°C; in more humid cities such as Houston, TX, misters still mitigate thermal stress although the cooling benefits were halved due to higher ambient humidity. Wind speed emerged as a key factor, with intermediate speeds yielding optimal cooling. Higher flow rates (e.g., 1 L/min) require moderate breezes for full evaporation, whereas lower flow rates (e.g., 0.01 L/min) are more effective in calm conditions. We also compared misting with other water-based cooling strategies, such as irrigation and sprinkling. Under abundant water availability, sprinkling and misting were most effective, cooling air and surfaces rapidly during midday and late afternoon, respectively. For water-limited scenarios, we propose a thermostatic control scheme that can save at least 10.5 m³/day of water compared to continuous misting for a 100-m stretch of street; the savings are equivalent to the water demand of about 20 Phoenix residents.