Coinfluence of Green Space and Blue Space on Urban Outdoor Comfort by Using a Dense Urban Observation Network

Urbanization has continued growing dramatically in the past few decades, as more than half of the global population live in urban areas. The alternation of surface materials and morphologic characteristics in urban areas and anthropogenic emissions from daily activities have been evident with a considerable influence on a wide spectrum of local climate, hydrologic cycles, and ecologic patterns. Decades of research efforts have enlightened our physical understanding of the impacts of LULC on urban climates. In addition, such knowledge has provided a scientific basis for adaptation and mitigation strategies in cities to counteract the risks associated with adverse climate effects. Examples include the adoption of high albedo roofs and pavements to alleviate heat stress and harnessing the evapotranspirative cooling power of urban greenspace and bluespace (water bodies, including lakes, rivers, etc.) to provide a more comfortable thermal environment. This study uses multiple-year observations from more than 140 sites over the Madison metropolitan area, WI to assess the role of greenspace, bluespace and their interactions on the intra-urban spatial variability of local air temperature and moisture, as well as the combined effect on human comfort –Apparent temperature. The study unveils a universal greenspace cooling all year round, and the summer months, the greenspace cools more efficiently, substantially great at night up to 3.4 C. On the other hand, the greenspace elevated the moisture during the daytime. The bluespace cooling is only found during the daytime in spring and fall within 500m of the water shores. Often, bluespace plays a key role in nocturnal warming (as high as 1.1 - 2.3 C in the summer and fall) and diurnal humidification in its adjacent regions. The co-influence of green and blue space is found to an annual temperature spatial anomaly of 3.2 +/- 1.1 C at night and 1.5 +/- 0.4 C during the daytime. The strong positive relationship of temperature and moisture over the near-shore dense urban core implies a strong exacerbation of heat stress for urban residents, which can reach up to 4.1 C in the hottest month. In light of designing climate-sensitive cities using green-blue infrastructures, our findings offer an improved understanding of their independent roles and their compound effects on the urban thermal environment diurnally and seasonally. Results from this case study will inform more general mitigation and adaptation.