Rethinking Extreme Heat and Urban Resilience through Scales Connectivity 

Rethinking the Rules of Urban Resilience

The climate is shifting faster than our response infrastructure can adapt. Extreme heat, unlike hurricanes or wildfires, is a silent, invisible killer and the leading cause of weather-related deaths across the U.S., responsible for 10,527 fatalities between 2004 and 2018. There were even higher tolls in recent years; for example, 1,600 deaths in 2021 alone (National Oceanic and Atmospheric Administration 2023; Vaidyanathan 2020). Its impacts fall disproportionately on vulnerable populations: the elderly, low-income households, and outdoor workers often lack access to adequate protection or reliable cooling (Bell, Gasparrini, and Benjamin 2024). But the risks extend far beyond public health.

Extreme heat places significant strain on energy systems, disrupts transportation infrastructure, and reduces labor productivity. These effects are especially acute in urban environments, where the urban heat island (UHI) effect—stemming from the dense concentrations of heat-retaining surfaces—exacerbates both temperatures and exposure durations (Tuholske et al. 2021).

What was once considered a rare and isolated threat is now emerging as a widespread and synchronized phenomenon (National Oceanic and Atmospheric Administration’s National Centers for Environmental Information (NCEI 2025). In the U.S., the past four consecutive summers (2021–2024) have shattered historical temperature records and expanded the geographic and temporal footprint of heat-related disruptions (Fischer et al. 2025). This growing convergence of heat extremes has exposed deep structural limitations in traditional emergency management systems, which were largely designed to respond to isolated, short-term hazards, rather than compounding, climate-driven events unfolding across multiple jurisdictions at once.

An effective response to extreme heat requires rapid mobilization of cooling resources, emergency personnel, medical aid, and public communication systems. Yet, given the relative rarity of such events in the past, it has been neither practical nor cost-effective for most cities to maintain dedicated reserves of heat-specific emergency resources. Instead, many of these assets, such as mobile cooling units, emergency medical teams, and federal disaster assistance, are housed at the national level and deployed reactively when cities issue requests for aid (Doan and Shaw 2019).

Historically, all requests for extreme heat disaster declarations under the Robert T. Stafford Disaster Relief and Emergency Assistance Act (the Stafford Act) have been denied, as the act has traditionally prioritized sudden-onset hazards that cause visible structural damage. However, in the context of a changing climate, this framework is beginning to evolve toward a broader definition of eligible events—those that exceed state and local capacity to respond and recover (Congress.gov 2024b).

When multiple cities are struck by extreme heat simultaneously—as was the case during the 2021 Pacific Northwest heatwave and the nationwide record-breaking heat domes of 2023 and 2024—demand for shared emergency resources can quickly outstrip available capacity (Congress.gov 2024a). In these situations, municipalities are often forced to compete for limited pools of support, stretching national response systems thin. This pressure is further compounded when extreme heat co-occurs with other climate-driven hazards, such as droughts, wildfires, and floods, or amid public health threats (Hyde et al. 2006).

This possibility raises a central policy question: How can climate science-based early warning signals be used to allocate scarce emergency resources more equitably and efficiently when multiple cities facing extreme weather simultaneously? One promising avenue lies in the emerging understanding of atmospheric resonance, a large-scale climate phenomenon capable of synchronizing weather extremes across distant regions.

This digest draws on our prior research on quasi-resonant planetary wave amplification (QRA), which demonstrates a robust link between resonant atmospheric circulation patterns and the occurrence of simultaneous extreme weather events (Li et al. 2024; Li et al. 2025; Mann et al. 2017; Mann et al. 2018). Planetary waves, or Rossby waves, are large-scale meanders in the jet stream. Under certain conditions, these waves can become effectively trapped and amplified within mid-latitude “waveguides.” When this occurs, the jet stream can slow and deform in ways that stall weather systems, locking regional patterns in place for days or even weeks (Mann et al. 2017; Mann et al. 2018), an atmospheric state referred to here as QRA.

By integrating expertise in climate science, sustainability, and energy policy, we propose an actionable, science-based tool to guide resource allocation decisions in the face of extreme heat. Such a tool could enhance urban resilience by informing coordinated emergency response planning at both local and federal levels, thereby:

1. Reducing competition for resources;
2. Improving equity in distribution; and
3. Mitigating the cascading impacts of extreme heat.

In the sections that follow, we summarize key findings from this work and outline the policy implications for building resilience across scales in an increasingly warming climate.

Planetary Waves and Urban Heat Extremes

Extreme heat events are no longer isolated or localized in nature. Increasingly, they are driven by large-scale atmospheric circulation patterns that can synchronize weather extremes across distant regions. QRA is one such mechanism: during resonant atmospheric states, phase-aligned planetary waves can produce simultaneous heat extremes across multiple metropolitan areas (Figure 1). 

During these resonant states, areas beneath persistent high-pressure ridges experience prolonged and intense heatwaves, while regions under low-pressure troughs may endure sustained rainfall or flooding. These quasi-stationary wave patterns act as atmospheric teleconnections, dynamically linking geographically distant cities so that extremes occur in tandem rather than in isolation.

For policymakers, the significance of QRA lies in its operational potential. Monitoring these atmospheric patterns can provide early signals that multiple regions may experience extreme conditions simultaneously. Such insights can help decision-makers anticipate surges in demand for cooling resources, medical personnel, and emergency response assets, allowing for earlier and more coordinated mobilization of support, especially when resource needs are likely to exceed supply across jurisdictions.

Resonant Waves as Early Warnings

Over the last four summers (2021–2024), QRA events have consistently coincided with record-breaking extreme maximum temperatures (EMXT) across a broad network of U.S. cities (Figure 2). These amplified planetary wave patterns repeatedly aligned with clusters of heat extremes, spanning not only traditionally hot cities but also cooler, northern metros that are historically less acclimated, and therefore less prepared, for prolonged heat. 

What sets QRA apart from other meteorological phenomena is its potential as an early warning indicator. When diagnosed in advance, these amplified planetary wave patterns can offer one to two weeks of lead time. This early warning provides a critical window for action, enabling:

• Public health systems to brace for spikes in heat-related illnesses;
• Utilities to scale power reserves; and
• Emergency response teams to pre-position mobile cooling and medical resources.

As climate extremes become increasingly synchronous across cities, QRA-based diagnostics offer a scalable, science-informed tool for proactive, cross jurisdictional resource planning. By transitioning from reactive crisis response to anticipatory coordination, we can better strengthen urban resilience, safeguard vulnerable populations, and reduce cascading impacts across interconnected urban systems.

Cooling Demand on Overdrive

Climate change is fundamentally altering the rhythm of the atmosphere. Over the past 75 years, the number of summer weather extremes linked to QRA has tripled (Figure 3). Once rare, these amplified jet stream patterns now occur with increasing regularity—rising from roughly one per summer in the 1950s to nearly three per summer today (Li et al. 2025). This sharp increase means more cities are likely to be hit by extreme heat at the same time, transforming what was once a localized hazard into a multi-regional challenge. As these atmospheric patterns become more persistent, the stresses they place on infrastructure, public health, and energy systems are becoming harder to manage.

Energy demand is particularly sensitive to these changes. In the U.S., space cooling already accounts for about 10% of total electricity use, and that share is rapidly growing. During a severe heatwave in July 2011, for example, space cooling alone accounted for up to 75% of Philadelphia’s peak electricity demand (Waite et al. 2017). Under QRA-driven heatwaves, multiple metropolitan areas can experience peak cooling demand simultaneously, placing unprecedented stress on regional power systems. Such synchronized demand increases the likelihood of grid instability, rolling blackouts, and cascading infrastructure failures as indicated by the Texas grid emergency in 2022 and blackout incidents during the 2023 Southwest heatwave.

A widely used metric to estimate cooling energy demand is the cooling degree days (CLDD) index, which measures the cumulative intensity and duration of daily temperatures above 65 °F (18.3 °C). The greater the number of CLDDs, the more energy is typically required to maintain indoor thermal comfort through air conditioning or fans. Across six northern and mid-latitude U.S. cities, statistically significant increases in CLDDs since 1950 point to steadily rising seasonal cooling demands (Figure 4).

Particularly in cities like Portland, Oregon, which historically have been considered temperate and less heat-prone, the combination of rising annual extreme temperatures and more frequent days exceeding 90 °F (32.2 °C) (Appendix Figures S1 and S2) underscores a widening mismatch between climate risk and existing infrastructure design.

Crucially, these surging demands are not borne equally. Higher-income households are more likely to have reliable access to air conditioning, well-insulated housing, and backup power during outages (Proussaloglou, Kane, and Tomer 2022). In contrast, low-income neighborhoods face greater exposure to heat-related health risks and energy insecurity, due to higher population densities, aging housing stock, and limited access to cooling technologies. In these communities, residents may be forced to choose between cooling their homes and affording other essentials, exacerbating preexisting health and economic disparities in the face of escalating heat stress. 

Rethinking Resource Allocation across Scales

As extreme heat events grow more intense and increasingly synchronized across regions, the existing emergency response architecture for extreme heat in the U.S. remains largely reactive and locally driven. The current response mechanisms are built to manage episodic, discrete hazards, such as hurricanes, rather than linked, slow-onset heat threats that can persist for days or weeks and increasingly unfolds across multiple regions at once.

In practice, most heat-risk management still occurs at the state and local levels. Local governments develop heat-health action plans, issue public risk communications, expand emergency medical staffing, distribute water and other essential supplies to vulnerable populations, provide emergency energy assistance, and open cooling centers (Congress.gov 2024a). These measures are critical, but their effectiveness depend heavily on local capacity.

Federal assistance typically enters only after an event exceeds state and local response capabilities. In such cases, the Federal Emergency Management Agency (FEMA) may reimburse certain heat-related response costs—such as air conditioning units or electric fans—through programs like the Individuals and Households Program (IHP), provided that the President issues an emergency or major disaster declaration under the Stafford Act. However, extreme heat is not explicitly listed as a qualifying incident type for a major disaster declaration, and historically, heat events have not received Stafford Act declarations, even though the law could theoretically be invoked if circumstances warranted.

Even when federal support becomes available, FEMA’s role remains primarily toward post-disaster recovery rather than proactive preparedness and response to extreme heat (Federal Emergency Management Agency 2025; U.S. Department of the Interior 2025; Keith et al. 2021). This current orientation reflects legacy assumptions about disasters as sudden, localized events. Yet climate-induced heat is fundamentally different: it unfolds gradually, spans large geographic areas, and requires sustained, proactive measures to prevent fatalities and protect public health.

As a result, states and local governments bear the brunt of frontline responsibilities during extreme heat events, often while operating with constrained budgets, outdated infrastructure, strained public health systems, and limited surge capacity. They must keep cooling centers open, deploy emergency services, and communicate risks to the public—all while managing rising electricity demand and mounting pressure on energy systems.

The challenge becomes even greater when heatwaves strike multiple cities or states simultaneously. In these cases, demand for federal support can quickly outpaces available capacity. At the same time, ongoing political and institutional uncertainty surrounding federal disaster management—including proposals to eliminate FEMA (The Guardian 2025) and recent legal disputes over disaster relief funding allocations (Frazin 2025)—underscores just how fragile the current support framework can be.

The result is a widening policy gap: the nation’s emergency management model remains largely reactive and fragmented, poorly suited to address the compounding, cross-regional nature of modern heat extremes. Without more forward-looking coordination—guided by climate science and centered on equity—the nation risks entering an era of shared scarcity, where jurisdictions are forced to compete for limited resources just as climate hazards are becoming more widespread, more connected, and more difficult to manage. 

Actionable Pathways Forward

Addressing the growing threat of synchronized urban heat extremes requires moving from reactive crisis management toward a proactive, risk-informed system for allocating emergency resources. This transition must operate across all levels of government and be grounded in science-based early warning signals—such as atmospheric resonance diagnostics—that offer actionable lead times and clarify where extreme heat risks are likely to cluster. To improve resilience and equity, key recommendations include:

• Develop a tiered heat risk trigger system that activates shared protocols. This framework would translate early warning signals, like atmospheric resonance, paired with surface forecasts into predefined readiness actions across agencies and jurisdictions once thresholds for severity and/or duration are met (e.g., Tier 1–3). A tiered approach can reduce “late activation” in places that still rely on damage assessments or reimbursement triggers, and it enables earlier, equity-centered escalation when vulnerable communities face elevated risk.
• Authorize an emergency fund that provides advance assistance when Tier 2–3 thresholds are triggered. A standing, pre-approved funding mechanism would allow jurisdictions to act on forecasted risk rather than waiting for impacts to materialize. This action creates a practical decision shift: from “first come, first served” reactive support to rules-based, cross-scale coordination that prioritizes risk, vulnerability, and anticipated need.
• Establish heat-specific mutual aid mechanisms for jurisdictions forecasted to be affected simultaneously. While many mutual aid agreements already exist, few are designed for multi-region heat events that unfold in parallel. We recommend building “heat-capable” mutual aid frameworks tailored to cities likely to be phase-aligned within planetary wave patterns. Such agreements would facilitate rapid sharing of personnel, equipment, supplies, and operational expertise without triggering competition among jurisdictions. The tiered trigger system could also identify “aid corridors” and staging locations in advance to support timely mobilization during Tier 2–3 events.
• Treat power loss and critical infrastructure failure as first-order heat emergency risks. QRA-driven heat patterns increase the likelihood of simultaneous peak electricity demand across metropolitan areas, elevating grid stress and the risk that outages become multi-regional rather than local. Early warning signals should therefore trigger targeted protective actions before the peak—such as verifying backup power readiness at designated “critical cooling continuity sites” (i.e., clinics, shelters, senior facilities), hardening communications and transit access, and aligning public health operations with utility contingency planning. This focus is especially urgent given the limited federal assistance typically available for extreme heat emergencies.

By embedding science-based tools like QRA diagnostics into emergency planning and connecting resource systems across scales, we can begin to build a more agile, anticipatory, and equitable infrastructure for navigating an era of intensifying heat extremes. From the resonant patterns that signal risk to the policy levers that shape resilience, the path forward depends on bridging science, governance, and social equity. Only by doing so can we ensure that our cities—and the people who live in them—are not just surviving extreme heat but adapting, coordinating, and thriving in a warming world.

Acknowledgements 

We thank Iman Ali (School of Engineering and Applied Science, University of Pennsylvania) for her contributions to the preliminary data analysis presented in Figure 2.

Appendix

References

Bell, M.L., A. Gasparrini, and G.C. Benjamin. 2024. “Climate Change, Extreme Heat, and Health.” New England Journal of Medicine. 390(19), 1793-1801. https://doi.org/doi:10.1056/NEJMra2210769.

Congress.gov. 2024a. “Emergency Response to Extreme Heat: Federal Financial Assistance and Considerations for Congress.” https://www.congress.gov/crsproduct/R46873.

Congress.gov. 2024b. “Stafford Act Declarations for Extreme Heat.” https://www.congress.gov/crsproduct/IN12384.

Doan, X.V. and D. Shaw. 2019. “Resource Allocation When Planning for Simultaneous Disasters.” European Journal of Operational Research. 274 (2): 687-709. https://doi.org/10.1016/j.ejor.2018.10.015.

Federal Emergency Management Agency. 2025. “National Disaster Recovery Framework.” https://www.fema.gov/emergency–managers/nationalpreparedness/frameworks/recovery.

Frazin, R. 2025. “Court Temporarily Blocks Trump from Reallocating FEMA Disaster Preparedness Funds.” The Hill. August 5, 2025. https://thehill.com/policy/energy–environment/5437562trump–fema–disaster–preparedness–funds–bric/.

Fischer, E.M., M. Bador, R. Huser, E.J. Kendon, A. Robinson, and S. Sippel. 2025. “Record-Breaking Extremes in a Warming Climate.” Nature Reviews Earth & Environment. 6(7), 456-470. https://doi.org/10.1038/s43017–025–00681–y. https://doi.org/10.1038/s43017–02500681–y.

Hyde, J., B. Kim, L. Sprague Martinez, M. Clark, and K. Hacker. 2006. “Better Prepared But Spread Too Thin: The Impact of Emergency Preparedness Funding on Local Public Health.” Disaster Management & Response. 4(4), 106-113. https://doi.org/10.1016/j.dmr.2006.08.002.

Ladd, K., S. Meerow, D.M Hondula, V.K.Turner, and J.C Arnott. 2021. “Deploy Heat Officers, Policies and Metrics.” Nature. 598(7879), 29-31. https://doi.org/10.1038/d41586-021-02677-2.

Li, X., M.E. Mann, M.F. Wehner, and S. Christiansen. 2025. “Increased Frequency of Planetary Wave Resonance Events Over the Past Half-Century.” Proceedings of the National Academy of Sciences. 122(25), e2504482122. https://doi.org/10.1073/pnas.2504482122.

Li, X., M.E. Mann, M.F. Wehner, S. Rahmstorf, S. Petri, S. Christiansen, and J. Carrillo. 2024. “Role of Atmospheric Resonance and Land-Atmosphere Feedbacks As A Precursor to the June 2021 Pacific Northwest Heat Dome Event.” Proceedings of the National Academy of Sciences. 121(4), e2315330121. https://doi.org/10.1073/pnas.2315330121.

Mann, M.E., S. Rahmstorf, K. Kornhuber, B.A. Steinman, S.K. Miller, and D. Coumou. 2017. “Influence of Anthropogenic Climate Change on Planetary Wave Resonance and Extreme Weather Events.” Scientific Reports. 7(1), 45242. https://doi.org/10.1038/srep45242.

Mann, M.E., S. Rahmstorf, K. Kornhuber, B.A. Steinman, S.K. Miller, S. Petri, and D. Coumou. 2018. “Projected Changes in Persistent Extreme Summer Weather Events: The Role of Quasi-Resonant Amplification.” Science Advances. 4(10), eaat3272. https://doi.org/10.1126/sciadv.aat3272.

National Oceanic and Atmospheric Administration. 2023. “Weather Related Fatality and Injury Statistics.” https://www.weather.gov/hazstat.

National Oceanic and Atmospheric Administration’s National Centers for Environmental Information (NCEI). 2025. “Global Climate Report.” https://www.ncei.noaa.gov/access/monitoring/monthly–report/global.

Proussaloglou, E., J. Kane, and A. Tomer. 2022. “Data Shows 23 Million Americans Live in Places Most At Risk of Extreme Heat.” Brookings Institution. https://www.brookings.edu/articles/data–shows–23–million–americanslive–in–places–most–at–risk–of–extreme–heat/.

The Guardian. 2025. “Trump Plans on ‘Phasing out’ FEMA Disaster Agency After Hurricane Season.” June 11, 2025. https://www.theguardian.com/us–news/2025/jun/11/trumpfema–phase–out–hurricane–season.

Tuholske, C., K. Caylor, C. Funk, A. Verdin, S. Sweeney, K. Grace, P. Peterson, and T. Evans. 2021. “Global Urban Population Exposure to Extreme Heat.” Proceedings of the National Academy of Sciences. 118(41), e2024792118. https://doi.org/10.1073/pnas.2024792118.

U.S. Department of the Interior. 2025. “Natural Disaster Recovery.” https://www.doi.gov/recovery.

Vaidyanathan, A. 2020. “Heat-Related Deaths—United States, 2004-2018.” Morbidity and Mortality Weekly Report. 69(24), 729-734. https://www.cdc.gov/mmwr/volumes/69/wr/mm6924a1.htm.

Waite, M., E. Cohen, H. Torbey, M. Piccirilli, Y. Tian, and V. Modi. 2017. “Global Trends in Urban Electricity Demands for Cooling and Heating.” Energy. 127, 786-802. https://doi.org/10.1016/j.energy.2017.03.095.