Effectiveness of Tree Planting Strategies to Mitigate Excessive Heat in Las Vegas Metropolitan Area

Many urban areas around the world suffer from excessive heat, associated with climate change, urbanization, among other factors, causing negative consequences for human health. Consequently, heat stress poses a great burden for decision makers, which are planning and implementing excessive heat mitigation and adaptation strategies. However, the effectiveness and associated cooling of each strategy depends on the local conditions and potential tradeoffs that may arise. Urban greening and tree-planting programs have been promoted in many urban areas due to their multiple benefits, including cooling, livability and carbon sequestration. However, the effect of trees on surface temperature has resulted in diverging findings, and most mesoscale models used for the evaluation of urban cooling strategies have a limited representation of urban trees. In this study, we use the BEP-Tree model coupled with WRF at urban-resolving resolution (900 m), which includes the effects of street trees on radiation and wind flow in the urban canyon. The model is implemented for Las Vegas Metropolitan Area, which is among the fastest-warming cities in the United States. The street tree cover in the model is represented based on a high-resolution (3 ft) tree dataset from the Southern Nevada Water Authority, derived from aerial imagery and LiDAR data. In addition, different tree-planting scenarios are implemented to evaluate their effect on near surface temperature and the wind flow. The developed scenarios are based on ongoing and planned projects, following guidelines for the preferred tree species, which consider the benefits of trees on the microclimate but having a low water consumption. The scenarios are designed to specifically target hotspots and areas suffering from excessive heat, using the Southern Nevada Extreme Heat Vulnerability dataset. This study is aimed at advancing our understanding of the effectiveness of street trees for cooling urban areas and providing decision makers with usable information.