Nighttime warming acceleration
~2x faster
Nighttime minima are rising roughly twice daytime highs in urban regions.
Zhao et al. 2014
NHVI Data Story
Why nights are becoming deadlier, and for whom
The Night Heat Vulnerability Index combines thermal exposure, urban form, and social determinants into a 0-100 score that reveals where heat injustice is compounding fastest.
Equity Gap
0.0
NHVI-point difference between highest and lowest risk neighborhoods
Heat mortality timing
Predominantly nocturnal
A large share of deaths occur during nighttime and early morning windows.
Murage et al. 2017
Urban amplification
Significant attributable burden
Urban heat island intensity materially increases mortality risk in heat events.
Heaviside et al. 2017
Formula Breakdown
Night Heat Vulnerability Index (NHVI)
NHVI = NighttimeTemp + CanopyDeficit + BuildingAge + PovertyRate + ElderlyPop + ACDeficit + SurfaceAlbedo
Nighttime Temp
27% weight
Higher nighttime minimums indicate failed physiological recovery windows.
Canopy Deficit
18% weight
Lower canopy means weaker shade and weaker evapotranspiration cooling.
Building Age
14% weight
Older envelopes release stored daytime heat into occupied nighttime periods.
Poverty Rate
16% weight
Higher poverty increases heat exposure and lowers adaptive options.
Elderly Population
8% weight
A larger older adult population increases physiological vulnerability.
AC Deficit
12% weight
Low cooling access raises uncompensated overnight heat strain.
Surface Albedo
5% weight
Dark, low-albedo surfaces absorb and re-radiate more heat after sunset.
Selected Neighborhood Profile
Thorncliffe Park
East York
NHVI Score
75.8
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Neighborhood Ranking
Highest NHVI neighborhoods
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Historical Divergence
20-year widening night-heat divide
The most vulnerable neighborhoods are climbing faster, with accelerating divergence from high-canopy, high-resource neighborhoods.
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AI Advisor
AI NHVI Analyst
Interpret score drivers, equity gap pressure, and trend divergence to produce decision-ready adaptation recommendations.
Risk Tier Classification
Standardized risk bands
0-25
Low Risk
26-50
Moderate
51-75
High Risk
76-100
Critical
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