Targeted cooling of urban cycling networks for heat-resilient mobility

TL;DR

Cities confront increasing extreme heat that compounds risks for micromobility users. We couple a high-resolution urban microclimate framework (WRF--BEP--SOLWEIG) with 4.76 million Citi Bike trips in NYC to quantify cyclist heat exposure during a June 2024 heatwave and to test targeted cooling via tree canopy along high-exposure corridors. Targeted greening along the top 1,000 heat-exposed segments reduces heat-exposed kilometers by 19%, equivalent to about $4^{\circ}$C of cooling, and outperforms random citywide tree planting, particularly during midday when heat stress peaks; daytime exposure is higher in lower-income neighborhoods, underscoring equity considerations. These results provide a data-driven basis for designing heat-resilient and equitable cycling networks under warming conditions, highlighting the value of spatial prioritization and temporally focused cooling measures for urban mobility.

Abstract

Cities are increasingly challenged by extreme heat events, which pose serious risks to public health and urban livability. Micromobility users, whose numbers have increased rapidly in recent years, are particularly vulnerable to outdoor heat exposure. Yet, their exposure patterns and the effectiveness of mitigation measures remain poorly understood. Here, we couple a high-resolution urban microclimate model (WRF--BEP--SOLWEIG) with 4.76 million Citi Bike trips in New York City to quantify cyclists' thermal exposure during the June 2024 heatwave and to evaluate targeted cooling strategies. Results show that a small fraction of the street network concentrates the majority of rider heat exposure, and that localized interventions along these segments yield the greatest benefits. Targeted tree planting along just 1.5% of the city's street network reduces total heat-exposed kilometers ridden by 19%, equivalent to a thermal stress reduction of about 4°C, with its impact maximized during midday hours. In contrast, randomized citywide tree planting produces diffuse, resource-intensive cooling, highlighting the superior efficiency of spatially prioritized interventions. Baseline results further indicate that daytime heat stress is higher in lower-income neighborhoods, adding an important social dimension of urban heat exposure. Together, these findings provide a quantitative basis for designing heat-resilient and equitable cycling networks in a warming climate.

Figures (7)

• Figure 1: Street-level map of UTCI values across New York City. The inset presents a detailed view of the street network in Lower Manhattan. The integration of WRF-BEP and SOLWEIG provides a high-resolution representation of microclimatic variability, capturing features such as the oceanic cooling effect along southern Queens and coastal Brooklyn, where sea-breeze circulation lowers UTCI values relative to inland neighborhoods.
• Figure 2: Global distribution of the top 1,000 heat-exposed street segments. For each hour of the day, segments with UTCI values exceeding 32$^{\circ}$C were identified. For these segments, the number of Citi Bike trips passing through them was summed across all hours to determine the most heat-exposed segments citywide. Warmer colors indicate higher trip counts across heat-stressed segments. Major corridors include the Hudson River Greenway, Park Avenue, the East River bridges, and sections of Broadway Avenue.
• Figure 3: Land-cover comparison for Midtown Manhattan under the (a) Base and (b) Tree-Planting scenarios, showing added canopy cover across the hottest 1,000 street segments. Panel (c) shows the resulting reduction in heat-exposed kilometers (UTCI $\geq 32^{\circ}$C) across all cooling and intervention scenarios. The gray bar represents baseline exposure, green bars represent theoretical cooling scenarios, and the blue bar represents the targeted tree-planting intervention.
• Figure 4: Danger-zone comparison. Hourly share of Citi Bike trips exceeding the UTCI danger-zone thresholds ($\geq 32^{\circ}$C and $\geq 38^{\circ}$C) for three modeled conditions: the base scenario (left), tree-planting scenario (middle), and 10$^{\circ}$C cooling of the top 1,000 heat-exposed segments (right).
• Figure 5: Combined hourly heat-exposure patterns and mobility demand for the top 1,000 tree-planting segments. (Top) Hourly average heat stress (°C) under the baseline, tree-planting, and idealized-cooling scenarios. Tree planting produces modest nocturnal warming (+0.3--0.4°C) due to canopy heat storage but provides substantial daytime cooling of 1.5--2°C between 09:00 and 17:00, comparable to 3--5°C idealized-cooling equivalents. (Bottom) Total kilometers ridden per hour.