Global estimates from 2016 show few adults (27.5%) and adolescents (19%) self-reported meeting guidelines for aerobic physical activity.1,2 Those who are insufficiently active miss the associated benefits of lowering risk of cardiovascular disease, diabetes, and several cancers as well as improvements to mental health, cognitive function, and sleep.3 Engaging in regular physical activity during childhood is critical since this health behavior may track into adulthood.4 Yet in the United States, only about one fifth (20.6%) of children self-reported meeting guidelines of 60 or more minutes of physical activity daily, in 2019–2020.5
For physical activity promotion among children, the Global Action Plan on Physical Activity 2018–2030 highlighted the need for school environments supportive of physical and health literacy.6 Recess—the regularly scheduled period on school days for physical activity and play supervised by staff7—has been shown to contribute up to 44% of children’s physical activity on school days in the United States.8 A systematic review identified 44 factors that may impact physical activity levels of children during recess, with consistent positive associations with number of facilities (eg, outdoor spaces), unfixed equipment (eg, balls), and perceived encouragement.9 Later studies have identified positive associations with adult engagement and supervision, schoolyard size, and schoolyards considered adequately equipped based on facilities, green areas, recreation areas, and surface material.10,11 With these factors in mind, school recess interventions (eg, equipment provision) have shown promise for physical activity promotion.12
An understudied factor that may affect physical activity levels of children is ambient temperature. Generally, studies have found a nonlinear association between ambient temperature and physical activity wherein temperature exhibits a direct association with physical activity until a certain point at which physical activity decreases,13 potentially due to thermal discomfort. A study of a hike and bike trail in Austin, Texas, United States, revealed that trail use was more likely by pedestrians until 27 °C (81 °F) and cyclists until 33 °C (91 °F) after which trail use decreases.14 Among the few studies exploring the temperature–physical activity relationship for children, summer months and days with higher temperatures exhibited negative associations with physical activity.15–18
Traditional schoolyard design—high amounts of impervious materials and few trees—results in high surface temperatures. For instance, average surface temperatures were 52 °C (126 °F) in September across 15 schoolyards in the City of Waterloo, Ontario, Canada.19 Children have been found to seek shade during high temperatures,20 and to engage in less physical activity under shade.21–23 A study in Western Australia found that children were more likely to use tables and seats under shade sails once temperatures reached 27 °C (81 °F),24 yet no studies have assessed how ambient temperatures relate to shade seeking and physical activity behavior of children.
Herein, we determined the relations between ambient temperature, shade, and physical activity of children during recess at elementary schools in a US city with a warm climate. Findings from this study can inform the development of heat-resilient schoolyards for physical activity, a growing concern with development patterns resulting in urban heat islands25 and climate change increasing overall temperatures and the intensity, frequency, and duration of heat waves.26,27
Material and Methods
Study Setting and Sample
This prospective cohort study is part of the Green Schoolyards Project, which was designed to evaluate how green features (eg, trees) impacted ambient temperatures and physical activity levels of children at school parks, and how children’s connection to nature relates to their social–emotional learning skills. The Green Schoolyards Project focused on 3 joint use parks at elementary schools serving greater than 85% economically disadvantaged Latino households in Austin, Texas, United States. Further detail on the design and methods of the Green Schoolyards Project are published elsewhere.20
The 3 elementary schools were located in postal codes with relatively low nature access,28 had joint use agreements between the school district and the Austin Parks and Recreation Department, and had equivalent park features including playgrounds, multipurpose fields, running tracks, and basketball courts covered by artificial shade structures. Each park was of comparable size: “intervention park” = 21,448 m2; “low-green park” = 27,923 m2; and “high-green park” = 16,187 m2. The intervention park had received new green features (ie, saplings, wildflower meadow, nature trail, rain garden, water cistern, outdoor classroom), while the low- and high-green parks had relatively low and high amounts of historical green features, respectively. We used the i-Tree Canopy tool to calculate the percentage of tree canopy cover for each park: intervention = 8.5%; low green = 11.5%; and high green = 22.5%.29 The relatively low percentage of tree canopy at the intervention park—calculated postintervention—can be attributed to the trees planted being saplings.
We collected data in autumn of 2019 during school recess. The recess policy for the school district calls for a minimum of 30 minutes of supervised unstructured recess time daily. Furthermore, recess will not be taken away as punishment or for academic reasons, will not be viewed as a reward but as necessary educational support for all children, and is not part of the 135 minutes of required structured physical activity mandated and scheduled into the school day. Teachers receive annual training on these recess guidelines.30 To ensure sufficient temperature variability for testing relations with shade seeking behavior and physical activity of children, we designed the cohort study to span 10 consecutive school days in September (ie, period I) and 5 consecutive school days in November (ie, period II), months during the school year with substantial temperature differences over 1991–2020 (September: average = 27 °C, minimum = 21 °C, maximum = 33 °C; November: average = 16 °C, minimum = 10 °C, maximum = 22 °C).31
At the beginning of autumn of 2019, we recruited a convenience sample of 213 total third- and fourth-grade students aged 8–10 across the 3 elementary schools (intervention = 78, low green = 68, high green = 67 students) to participate in the cohort study. Each grade consisted of 3 classes, and each class had a separate teacher. Recess occurred at the same time for all classes in a grade, with teachers staggering when they released their children to recess a few minutes after another class in the same grade. The start time of recess varied by school and grade: intervention = 11:00 third grade, 13:40 fourth grade; low green = 13:50 third grade, 11:40 fourth grade; and high green = 12:00 third grade, 11:00 fourth grade. Prior to conducting any project activities, the institutional review board at The University of Texas Health Science Center at Houston (HSC-SPH-19-0502) and the school district reviewed and approved project protocols. We also received informed consent from participants’ parents and written assent from study participants.
Measurement of Weather
To measure air temperature and relative humidity during school recess at each park, we installed 10 HOBO MX2302A external air temperature/relative humidity sensor data loggers (Onset Computer Corporation), per previous research.32,33 We set the HOBO sensors to record air temperature and relative humidity data every 5 minutes and positioned sensors based on land cover, (eg, grass, pavement, mulch), land use (eg, soccer field, basketball court, playground), amount of shade, comparability across parks, and even spatial coverage. For this study, we calculated the average air temperature and relative humidity for each recess period from those HOBO sensors that were unshaded to represent typical conditions.
Measurement of Shade
Using GIS (ArcGIS 10.8, ESRI), we digitized polygons of shade from trees throughout the parks and artificial shade structures covering basketball courts at each park using four-band, high-resolution (60 cm) orthoimagery taken in November 2018 by the US Department of Agriculture’s National Agriculture Imagery Program.34 We excluded trees that did not provide shade, based on an in-person environmental audit of each school park. For each shade polygon, we geolocated its geographic centroid and determined its Euclidean distance-based radius, the latter of which we applied to estimate shade coverage. Since recess periods occurred between 11:00 AM and 2:00 PM, the sun was close to its solar noon when shade is immediately below the trees and artificial shade structures, which supports our process for shade estimation. We calculated relatively low amounts of shade at each park: intervention = 6.0% (trees = 4.2%, shade structure = 1.8%); low green = 11.1% (trees = 9.7%, shade structure = 1.4%); and high green = 17.8% (trees = 15.7%, shade structure = 2.1%).
Measurement of Shade Seeking and Physical Activity Behavior
From start to finish of recess periods on school days, we tasked the cohort sample with wearing elastic belts equipped with a Qstarz BT-Q1000XT global positioning system (GPS) monitor (Qstarz Intl Co) and an ActiGraph wGT3X-BT accelerometer (ActiGraph LLC) to measure geographic location and physical activity levels, respectively, over time.35,36 To not take time away from recess period, we assisted children with putting on the elastic belts 5 minutes before the start of recess then collected belts only after teachers ended recess.
Both the GPS monitor and accelerometer were initialized to collect data every 15 seconds using the same start time.37 We developed a code in Python (version 3.8, https://www.python.org/) to time match the geographic location (GPS monitor data) and accelerometer data for each participant. We used the Pandas (version 1.0, https://pandas.pydata.org/) package to parse GPS and accelerometer data, Geopy (version 1.21, https://github.com/geopy/geopy) to process GPS data, and Scipy (version 1.4, https://scipy.org/) to time match GPS and accelerometer data. We used linear interpolation of GPS locations between 2 consecutive GPS fixes (recorded locations every 15-s epoch) to estimate location at each accelerometer epoch (15 s). We then categorized each epoch (15-s interval) as corresponding to a shaded location area by spatially matching their geolocation (GPS data) with the geolocation of shaded areas and estimated physical activity intensity of our sample using Evenson cut points for children.38 We focused on moderate to vigorous physical activity (MVPA) in this study, the activity intensity levels recommended by the Physical Activity Guidelines for Americans.39
Statistical Analyses
We first calculated summary statistics of study variables to be included in regression modeling. Second, we produced a graph using locally weighted smoothing to illustrate how average daily ambient temperature relates to the percentage of recess time in MVPA and under shade. Next, we calculated the percentages of recess time that children spent being sedentary and engaging in physical activity in both shaded and unshaded areas by tertile of ambient temperature. Last, we specified piecewise multilevel regression models to determine the relations between average ambient temperature during recess and percentage of recess time under shade and in MVPA. Piecewise multilevel regression properly accounted for the nonlinear relations between temperature, shade, and physical activity with temperature modeled as 2 pieces (ie, less than 33 °C [91 °F], greater than or equal to 33 °C) and for repeated day-level observations nested within each child (via a random intercept for each child). We employed a series of 4 models: (1) relation between average temperature and percentage of time in MVPA, (2) relation between average temperature and percentage of time under shade, (3) relation between percentage of time under shade and percentage of time in MVPA, and (4) how the interaction between average temperature and percentage of time under shade relates to the percentage of time in MVPA. All models adjusted for children’s school park, grade, gender, race, and ethnicity, along with average daily relative humidity during recess. We completed statistical analyses in Stata (version 17.0, StataCorp).
Results
The cohort sample had similar representation by school park and by gender and consisted of more third-grade students than fourth-grade students (56% vs 44%) and predominately identified as Latino (84%; Table 1). During recess periods that averaged 23 minutes, students were relatively active, spending about one half of the time (48%) engaging in light physical activity and about one third of the time (36%) engaging in MVPA. About two-thirds of the time (68%) children were not under shade. Air temperatures were 11 °C (20 °F) higher in period I (September 2019) than period II (November 2019), ranging 11 °C to 35 °C (53–96 °F) (see Supplementary Table S1 [available online]).
Summary Statistics of Study Variables
| % of Total (count) | Mean (SD) | |
|---|---|---|
| School park of child | ||
| Intervention | 37 (78) | |
| Low green | 32 (68) | |
| High green | 31 (67) | |
| Grade of child | ||
| Third | 56 (119) | |
| Fourth | 44 (94) | |
| Gender of child | ||
| Female | 51 (108) | |
| Male | 49 (105) | |
| Race and ethnicity of child | ||
| Asian | <1 (1) | |
| Black | 8 (18) | |
| Latino | 84 (178) | |
| White | 6 (14) | |
| Multiracial | 1 (2) | |
| School recess | ||
| Recess periods per child (no.) | 14 (2) | |
| Length of recess, min | 23 (10) | |
| Behavior of child during recess | ||
| Sedentary (% of recess time) | 16 (17) | |
| Light physical activity (% of recess time) | 48 (15) | |
| Moderate physical activity (% of recess time) | 22 (12) | |
| Vigorous physical activity (% of recess time) | 14 (12) | |
| Shade behavior of child during recess | ||
| Unshaded (% of recess time) | 68 (26) | |
| Shaded by trees (% of recess time) | 23 (24) | |
| Shaded by structure (% of recess time) | 9 (18) | |
| Weather during recess | ||
| Period Ia: Relative humidity, % | 53 (8) | |
| Period Ia: Air temperature, °C | 33 (2) | |
| Period IIb: Relative humidity, % | 50 (20) | |
| Period IIb: Air temperature, °C | 22 (4) |
aTen days in September 2019. bFive days in November 2019.
Rising ambient temperatures correlated with children spending a lower percentage of recess time in MVPA and a higher percentage of recess time under shade (Figure 1). Once temperatures at recess reached 33 °C, children spent more time under shade than in MVPA. Moving from lowest tertile (11–27 °C) to highest tertile (33–35 °C) of ambient temperature (see Supplementary Table S1 [available online]), the percentage of time being sedentary increased and the percentage of time engaging in MVPA decreased, both in and out of shade.
—Average daily ambient temperature and its relation to the percentage of recess time in MVPA and under shade. MVPA indicates moderate to vigorous physical activity.
Citation: Journal of Physical Activity and Health 20, 2; 10.1123/jpah.2022-0405
From piecewise multilevel regression modeling (Table 2), we found that each 1 °C increase was associated with a 0.7 percentage point decrease (95% confidence interval [CI], −0.8 to −0.6) in time per recess spent in MVPA (P < .001), up until 33 °C when the association changed to a 1.5 decrease (95% CI, −2.7 to −0.4) (P < .01) (model 1). Each 1 °C increase was associated with a 0.3 percentage point increase (95% CI, 0.2 to 0.5) in time per recess spent under shade (P < .001), up until 33 °C when the association changed to a 3.4 increase (95% CI, 1.9 to 5.0) (P < .001) (model 2). There was no significant association between percentage of time under shade and percentage of time in MVPA (P > .05) (model 3), yet after adding interaction terms (model 4), there was a positive association between shade and MVPA that lessened as temperatures increased up until 33 °C (P < .05), with no interaction effect above 33 °C (P > .05). Children at the school park with the highest amounts of historical green features and tree canopy cover was associated with a 6.0 percentage point increase (2.1–9.9) in time spent in MVPA compared with the park with the least tree canopy (P < .01).
Model Output for Relations Between Ambient Temperature, Shade, and Physical Activity of Children During School Recess
| Model 1 | Model 2 | Model 3 | Model 4 | |
|---|---|---|---|---|
| Child-level variables | ||||
| Low-green park (1 = low green)a | −1.1 (−4.9 to 2.7) | −7.6*** (−11.4 to −3.8) | −0.9 (−4.8 to 2.9) | −1.0 (−4.8 to 2.8) |
| High-green park (1 = high green)a | 5.5** (1.6 to 9.3) | −24.4*** (−28.2 to −20.5) | 6.0** (2.1 to 9.9) | 6.0** (2.1 to 9.9) |
| Fourth grade (1 = fourth grade)b | −1.4 (−4.6 to 1.7) | −7.4*** (−10.6 to −4.3) | −1.3 (−4.4 to 1.9) | −1.3 (−4.5 to 1.8) |
| Female (1 = female)c | −9.4*** (−12.5 to −6.3) | −1.0 (−4.1 to 2.1) | −9.3*** (−12.5 to −6.2) | −9.3*** (−12.4 to −6.2) |
| Asian (1 = Asian)d | −0.1 (−23.4 to 23.2) | 13.4 (−9.8 to 36.6) | −0.4 (−23.7 to 23.0) | −0.4 (−23.7 to 22.8) |
| Black (1 = Black)d | −2.2 (−10.8 to 6.4) | −5.9 (−14.5 to 2.7) | −2.1 (−10.7 to 6.6) | −2.0 (−10.6 to 6.6) |
| Latino (1 = Latino)d | −3.2 (−10.2 to 3.8) | −0.4 (−7.4 to 6.5) | −3.2 (−10.2 to 3.8) | −3.3 (−10.2 to 3.7) |
| Multiracial (1 = multiracial)d | −2.5 (−19.9 to 14.9) | −15.1 (−32.5 to 2.2) | −2.2 (−19.6 to 15.2) | −2.2 (−19.6 to 15.2) |
| Day-level variables | ||||
| Relative humidity, % | 0.1* (0.0 to 0.1) | −0.1 (−0.1 to 0.1) | 0.1* (0.0 to 0.1) | 0.1** (0.0 to 0.1) |
| <33 °C | −0.7*** (−0.8 to −0.6) | 0.3*** (0.2 to 0.5) | −0.7*** (−0.8 to −0.6) | −0.5*** (−0.7 to −0.4) |
| ≥33 °C | −1.5** (−2.7 to −0.4) | 3.4*** (1.9 to 5.0) | −1.6** (−2.8 to −0.5) | −1.9* (−3.7 to −0.1) |
| Time under shade, % | 0.1 (−0.1 to 0.1) | 0.2** (0.1 to 0.3) | ||
| <33 °C × Time under shade | −0.1* (−0.1 to −0.1) | |||
| ≥33 °C × Time under shade | 0.1 (−0.1 to 0.1) | |||
| Constant | 58.7*** (50.5 to 66.9) | 37.2*** (28.3 to 46.1) | 58.0*** (49.7 to 66.2) | 53.4*** 44.4 to 62.5) |
| Constant lns1_1_1 | 2.4*** (2.3 to 2.5) | 2.3*** (2.2 to 2.4) | 2.4*** (2.3 to 2.5) | 2.4*** (2.3 to 2.5) |
| Constant lnsig_e | 2.7*** (2.6 to 2.7) | 3.0*** (3.0 to 3.0) | 2.7*** (2.6 to 2.7) | 2.7*** (2.6 to 2.7) |
| N | 2924 | 2924 | 2924 | 2924 |
Coefficients: 95% confidence intervals in parentheses. Dependent variables: (1) percentage of recess time in moderate to vigorous physical activity; (2) percentage of recess time under shade; (3) percentage of recess time in moderate to vigorous physical activity; and (4) percentage of recess time in moderate to vigorous physical activity.
aReferent = intervention park. bReferent = third grade. cReferent = male. dReferent = White.
*P < .05. **P < .01. ***P < .001.
Discussion
At higher ambient temperatures in the warm climate of Austin, TX, children aged 8–10 years spent lower amounts of time in MVPA and more time under shade during school recess. Previous studies on the temperature–physical activity relationship of children corroborate our findings,15–18 Our study also had similar findings to those investigating the temperature–shade relationship20,24 including another study from the Green Schoolyards Project wherein researchers observed 11% more girls and 25% more boys under tree canopy during high temperatures.20 During extreme heat, children may be engaging in less MVPA and seeking shade for thermal comfort: on hot, sunny days in Texas, researchers measured higher levels of thermal comfort among children aged 9 to 13 in the shade compared with unshaded areas.40
The slope of the regression line significantly changed between temperature, shade, and physical activity at 33 °C, a higher value than in previous studies assessing the relation between temperature and physical activity. Using data from around the world, researchers found that temperatures above 20 °C (68 °F) exhibited a negative association with physical activity of children.16 In our study, children may be acclimatized to the warm climate and consequently have a higher behavioral threshold for heat than children in the global study that comprised countries with cooler climates. In another study in Austin, TX, researchers found pedestrians were more likely to use a hike and bike trail until 27 °C (81 °F) after which trail use decreased.14 The different temperature values at which the regression slope changes between this study and ours may be related to differences in setting and type (ie, active transportation vs scheduled free play) of physical activity41 impacting the behavioral threshold for heat.
We found a direct association between shade and MVPA that lessened as temperatures increased until 33 °C, after which children were more likely to spend time under shade and not engaging in MVPA. We posit that up until 33 °C, children felt thermally comfortable to engage in free play throughout the full play area available to them, most of which is unshaded. Once temperatures reached 33 °C, children may have been too thermally uncomfortable to be physically active, instead resting (ie, being sedentary) under shade for thermal comfort. Previous studies have also found children to engage in less physical activity under shade.21–23
The school park with the most tree canopy cover (ie, high-green park) was associated with children spending the highest percentage of recess time in MVPA. Previous studies have similar findings,21,42,43 with a study of children aged 10–11 in Bristol, United Kingdom, revealing the odds of engaging in MVPA in green space compared with nongreen space was 1.37 for boys and 1.08 for girls.43
To promote safe physical activity of children during school recess on extreme heat days, we recommend changes to school policy and the schoolyard environment that fit within what has been called HeatReady Schools.44 Schools and their districts should consider scheduling recess period during times of day when temperatures are cooler, and developing a formal procedure for adjusting, not canceling, recess programming on extreme heat days. Physical activity and thermal comfort of children may be maximized by scheduling recess during cooler morning hours when researchers have found more pedestrians using a hike and bike trail in Austin, TX, on extreme heat days than other times.14 In choosing when to schedule recess, schools should strike a balance between maximizing thermal comfort for physical activity promotion, providing a mental break from classroom instruction, and splitting up sedentary time during the school day.
Schools in our study follow district-level guidelines for physical education and recess periods in hot weather: at 38 °C (100 °F), limit to 60 minutes of exposure with one 5-minute water break; at 41 °C (105 °F), limit to 45 minutes of exposure with a 5-minute water break every 15 minutes; and at 43 °C (110 °F), do not permit.45 These guidelines are well above 33°C (91 °F), what we identified as the tipping point for children to be more likely to decrease physical activity and seek shade during recess. In addition, the guidelines for exposure time are well above the 23 minutes, on average, that children spent at recess in our study as well as the minimum recess time of 30 minutes required by the school district.30 District guidelines for hot weather can be updated such that at and above 33 °C, teachers encourage children to play in park areas shaded by tree canopy and artificial structures, and can do so by organizing games and sports in these more thermally comfortable areas. On extreme heat days, schools that have available climate-controlled settings for physical activity (eg, air-conditioned gyms) may be inclined to shift recess to these settings; however, removing outdoor time means children will forgo potential contact with nature and its associated benefits for their health and well-being.46
In schoolyards, we recommend providing shade at areas intended for physical activity (eg, playgrounds, basketball courts). School community members have advocated for shade: teachers, parents, and administrators in Canadian schools have identified lack of shade as a limiting factor for active play on school grounds,47 and parents/guardians watching their children in neighborhood parks in London stated that lack of shade was a main deterrent to park use.48 Yet shade was limited at each of our study parks (intervention = 6.0%; low green = 11.1%; high green = 17.8%), and the same has been found at playgrounds in Mannheim, Germany (22% of play areas covered by shade, on average)22 and schoolyards in Boston, Massachusetts (10% of schoolyards covered by shade, on average).49
Selection of shade type should be based on what is most appropriate for the function of the space. For example, trees planted in the center of a multipurpose field may interfere with organized activities (eg, soccer, football) while an artificial shade structure may be a better choice if its posts are clear of activities. An opportunity that may significantly increase physical activity levels during recess is to add shade to previously uncovered spaces intended for MVPA; however, shading of large spaces would be a considerable investment that may not be practical with limited school resources. Just as critical as shading areas intended for physical activity may be the provision of shaded rest areas since children are less tolerant of heat than adults, placing them at higher risk of exertional heat illness when at play.50
Schoolyard greening may be optimal for physical activity in extreme heat. In our study, children at the school park with the most tree canopy spent the highest percentage of recess time engaging in MVPA. This is consistent with studies showing a positive correlation between nature play and physical activity,51 and an evaluation of a playground greening project at an elementary school in Los Angeles, CA, that found individuals’ participation in vigorous activity increased 48.5% after playground greening.42 Along with encouraging physical activity, trees are proven to reduce urban heat,20,25,33 with air temperatures at playgrounds shaded by trees up to 4 °C (7 °F) cooler than unshaded playgrounds.20 Yet trees and their benefits to human health are not distributed evenly, with low-income communities and communities of color in cities across the United States having less tree canopy cover than their higher income and white counterparts.52 Low-income communities and communities of color should be prioritized for tree planting in city and school district planning efforts. Protecting existing large trees should also be prioritized, as previous research has shown that living in areas with large trees, as measured by crown volume, may be more beneficial to cardiovascular health than having a higher number of smaller trees.53
This study was not without limitations. By focusing on 3 schools in the same city, the temperature threshold of 33 °C (at or above which children were most likely to decrease physical activity and seek shade) may not be the same for locations in different climate zones, which have their own physical, social, and cultural adaptations that require different thresholds to be set.54 Second, our study parks had limited variation in which types of areas (eg, basketball court, multipurpose field, playground, swings) were covered by shade. For instance, basketball courts at each park were covered by a shade structure, which prevented us from identifying whether children were attracted to the shade or the basketball court during high temperatures. Last, we did not collect information on types of activities occurring at recess (eg, teacher-led soccer games, talking groups at picnic tables), which may impact child behavior in extreme heat.
Conclusions
At joint-use elementary school parks in Austin, Texas, United States, we found that high ambient temperatures associated with children aged 8–10 spending less time in MVPA and more time under shade during school recess, with 33 °C (91 °F) serving as the threshold at which the strength of these associations intensified. We also found that green schoolyards were associated with children spending more time in MVPA. Study findings suggest that high temperatures are a barrier to children engaging in physical activity during recess due to thermal discomfort, and during high temperatures, children rest under shade as refuge from the heat. To encourage physical activity in the face of extreme heat, we recommend that schools consider scheduling recess during more thermally comfortable times of day, urging teachers to organize children’s play in shaded park areas, and adding shade to areas intended for physical activity where feasible, with priority given to planting shade trees for their cobenefits. School policy updates and shade retrofits have the potential to encourage safe and comfortable physical activity of children and ultimately create heat-resilient schoolyards, a key tool as society confronts urban heat islands and climate change.
Acknowledgment
This work was supported by the Robert Wood Johnson Foundation (grant number 76576).
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