TreeBenefits-UrbanHeatIsland

Code associated with a manuscript analyzing the cooling effects trees have on urban areas worldwide and impacts of climate change on that cooling.

Manuscript submitted summer 2025

Title: Global risk of precipitation deficits for tree-based cooling in cities

Authors: Christine R. Rollinson[1*], M. Ross Alexander[2], Jessica B. Turner-Skoff[3], Melissa Custic[4], Lindsay Darling[1,5,6], Ayo Andra J. Deas[7], Trent W. Ford[8], Renata Poulton Kamakura[9,10], Natalie Love[11] Zach Wirtz[5]

Affiliations: [1] Center for Tree Science, The Morton Arboretum; Lisle, IL 60532 USA [2] Consortium for Advanced Science and Engineering, University of Chicago; Chicago, IL 60637 USA [4] Science, Longwood Gardens; Kennett Square, PA 19348 [4] Illinois Landscape Contractors Association; Oak Brook, IL 60523 [5] Chicago Region Trees Initiative, The Morton Arboretum; Lisle, IL 60532 USA [6] Forestry and Natural Resources, Purdue University; West Lafayette, IN 47907 USA [7] Earth and Environmental Sciences, The Graduate Center, City University of New York; New York, NY 10016 USA [8] Illinois State Water Survey, Prairie Research Institute, University of Illinois, Urbana-Champaign; Champaign, IL, 61820 USA [9] Nicholas School of the Environment, Duke University, Durham, NC 27710 USA [10] 10Gulf of America Coastal Ocean Observing System, College Station, TX 77843 [11] Negaunee Institute for Plant Conservation Science and Action, Chicago Botanic Garden, Glencoe, IL, 60022

*Corresponding author. Email: crollinson@mortonarb.org

Abstract: Trees provide critical cooling services in natural and urban ecosystems globally1,2, and increasing tree cover is a widely adopted nature-based strategy to mitigate excessive urban heat3. However, evapotranspiration (ET), a key cooling mechanism, relies on water availability, which climate change may threaten in many regions4. We analyzed urban tree cooling and water sustainability in 2,091 global cities by comparing summer ET with precipitation under current and increased canopy cover. Most cities currently receive sufficient summer precipitation to support urban canopy cover increases that can significantly reduce urban heat. However, climate change projections indicate that 40% of cities could be at risk for summer precipitation deficit by 2100 given current canopy extent and composition. Our findings highlight the need for climate adaptation strategies that reduce water demands of urban forests so that cooling benefits can be sustained as water balances shift with changing climate conditions.

One-Sentence Summary: Urban tree cover and the cooling it provides may require more water than will be available from summer precipitation in many regions.

Repository Contents All data is publicly accessible through the sources cited in the manuscript. Scripts are numbered in the order to be executed. Note: All scripts are workflows designed to be worked interactively as numbers are generated within them. The final scripts largely follow the order of the submitted manuscript with specific language from the manuscript to aid in transparency of how particular values were calculated.