03248nas a2200217   4500008004100000245012300041210006900164260001500233300001400248520249800262653002002760653002302780653002202803653001702825653002202842100002102864700002302885700003002908700002302938856006902961       2019                        eng d00aScale-dependent interactions between tree canopy cover and impervious surfaces reduce daytime urban heat during summer0 aScaledependent interactions between tree canopy cover and imperv  c2019/03/20  a2018175613 aCities worldwide are experiencing record-breaking summer air temperatures, with serious consequences for people. Increased tree cover is suggested as a climate adaptation strategy, but the amount of tree canopy cover needed to counteract higher temperatures associated with impervious surface cover is not known. We used a bicycle-mounted measurement system to quantify the interaction of canopy cover and impervious surface cover on urban air temperature. Daytime air temperature was substantially reduced with greater canopy cover (≥40%) at the scale of a typical city block (60–90 m), especially on the hottest days. However, reducing impervious surfaces remained important for lowering nighttime temperatures. Results can guide strategies for increasing tree cover to mitigate daytime urban heat and improve residents’ well-being.As cities warm and the need for climate adaptation strategies increases, a more detailed understanding of the cooling effects of land cover across a continuum of spatial scales will be necessary to guide management decisions. We asked how tree canopy cover and impervious surface cover interact to influence daytime and nighttime summer air temperature, and how effects vary with the spatial scale at which land-cover data are analyzed (10-, 30-, 60-, and 90-m radii). A bicycle-mounted measurement system was used to sample air temperature every 5 m along 10 transects (∼7 km length, sampled 3–12 times each) spanning a range of impervious and tree canopy cover (0–100%, each) in a midsized city in the Upper Midwest United States. Variability in daytime air temperature within the urban landscape averaged 3.5 °C (range, 1.1–5.7 °C). Temperature decreased nonlinearly with increasing canopy cover, with the greatest cooling when canopy cover exceeded 40%. The magnitude of daytime cooling also increased with spatial scale and was greatest at the size of a typical city block (60–90 m). Daytime air temperature increased linearly with increasing impervious cover, but the magnitude of warming was less than the cooling associated with increased canopy cover. Variation in nighttime air temperature averaged 2.1 °C (range, 1.2–3.0 °C), and temperature increased with impervious surface. Effects of canopy were limited at night; thus, reduction of impervious surfaces remains critical for reducing nighttime urban heat. Results suggest strategies for managing urban land-cover patterns to enhance resilience of cities to climate warming.10aair temperature10aecosystem services10alandscape context10aurban forest10aurban heat island1 aZiter, Carly, D.1 aPedersen, Eric, J.1 aKucharik, Christopher, J.1 aTurner, Monica, G.  uhttp://www.pnas.org/content/early/2019/03/19/1817561116.abstract