Welcome to the 2026 GIS in Action Annual Conference hosted by the Oregon & SW Washington Chapter of the Geospatial Professional Network & Cascadia ASPRS.
Urban areas often experience higher surface temperatures due to impervious surfaces and limited vegetation. Evapotranspiration (ET) cools surfaces by transferring water from land and vegetation to the atmosphere. Understanding ET–climate interactions is important for designing green infrastructure that mitigates urban heat. This study investigates long-term relationships between ET and key climatic indicators in Portland, Oregon, comparing a highly urbanized downtown area with a densely vegetated reference site in Forest Park, located approximately 9.7 km away. Using Google Earth Engine, July mean values from 2000–2025 were derived for ET, land surface temperature (LST), maximum air temperature (Tmax), normalized difference vegetation index (NDVI), and surface albedo. Correlation analyses were used to evaluate ET–climate interactions. Results show clear climatic contrasts between the two landscapes. Daytime LST ranged from 28.7–34.2 °C in downtown Portland and 22.5–28.2 °C in Forest Park, while evapotranspiration was consistently higher in the forested site (18.6–26.3 mm/day) than in the urban core (8.2–16.5 mm/day). In the urban system, ET showed significant negative relationships with LST and Tmax, indicating measurable evaporative cooling effects. These findings suggest that increasing vegetation and green infrastructure may produce stronger marginal cooling benefits in water-limited urban environments than in already vegetated landscapes.
