NYCHA Climate Risk Index

Technical Methodology — encoding, normalization, parameters, data sources

1. Risk Formula

Risk is calculated independently for each of 4 climate domains, then averaged:

Per domain: adjusted = min_max(hazard × vulnerability) × (1 − effectiveness × mitigation)
Risk Index: = min_max( mean of 4 domain risks )

All values normalized to [0, 1]. Higher = more risk. A development with no hazard exposure in a domain scores 0 for that domain, pulling the overall average down.

2. Encoding Methods

Method	Formula	Output	Use Case
`min_max`	(v − min) / (max − min)	[0, 1]	Higher raw value = higher score (solar radiation, building count below DFE)
`min_max_inverse`	1 − (v − min) / (max − min)	[0, 1]	Lower raw value = higher score (groundwater depth: shallower = more hazard)
`boolean`	True → 1.0, False → 0.0	{0, 1}	Binary presence/absence (stormwater exposure, cool roof)
`categorical`	Lookup table	Custom	Ordinal categories (Tidal onset: 2050s=1.0, 2080s=0.67, 2100=0.33, no onset=0; Equipment: Yes=1.0, Partial=0.5, none=0)

3. Normalization

Stage	Method	Notes
Attributes	Encoded per method above	All output in [0, 1]
Sub-Indices	Weighted average of attributes, then min-max normalized	Missing attributes filled with 0.5 (neutral)
Indices	Per-site weighted average of sub-indices, then min-max normalized	Conditional sub-indices (vulnerability/mitigation) that are N/A for a site are excluded from both the numerator and weight denominator for that site. Non-conditional missing sub-indices filled with 0.5 (neutral).
Domain Risk	H × V product, min-max normalized, then mitigation applied	Per-domain before final averaging
Risk Index	Mean of 4 domain risks, then min-max normalized	Final output

Edge Cases

Condition	Behavior
All values identical	All set to 0.5
Single valid value	Set to 0.5
No hazard exposure in a domain	Domain risk = 0 (pulls overall risk down)
Hazard not present → vulnerability / mitigation	NaN (displayed as “Not applicable”); excluded from composite index aggregation for that site
Groundwater depth ≥ 16 ft	Capped before normalization → hazard scores 0; groundwater V and M set to N/A
Flood-exposed site with no buildings below DFE	Vulnerability floor of 0.1 applied (coastal, stormwater, groundwater)

4. Parameters

Parameter	Value	Purpose
Coastal DFE Buffer (2050)	40 inches (3.33 ft)	Buffer added to FEMA BFE; combined freeboard and sea level rise
Coastal DFE Buffer (2080)	52 inches (4.33 ft)	Buffer added to FEMA BFE; combined freeboard and sea level rise
Stormwater DFE Buffer	24 inches (2.0 ft)	Buffer added to stormwater BFE
Groundwater Depth Cap	16 ft	USGS HERA threshold; depths ≥ 16 ft = no hazard
Mitigation Effectiveness (default)	0.6	Max risk reduction for heat domain
Mitigation Effectiveness (flood)	0.9	Enhanced for coastal, stormwater, and groundwater (engineered flood-protection measures)
Basement Depth Below Grade	10 ft	Universal assumption for basement floor elevation (z_grade − 10 ft)
Vulnerability Floor	0.1	Minimum vulnerability for hazard-exposed properties with zero building vulnerability (applies to coastal, stormwater, and groundwater domains)
High-Rise Threshold	60 ft (≈ 6 stories)	Campus type classification
API Cache TTL	30 days	Auto-refresh for FEMA, coastal surge, building data

5. Design Flood Elevation (DFE)

DFE = max(LiDAR DEM elevation within flood zone intersection) + freeboard buffer

Domain	Flood Source	Buffer	Output
Coastal (current)	FEMA NFHL vector polygons	40 in	Inhabited floors & basements below Coastal DFE (counts)
Coastal (2050)	ArcGIS Coastal Surge 2050	40 in	Coastal_DFE_2050
Coastal (2080)	ArcGIS Coastal Surge 2080	52 in	Coastal_DFE_2080
Stormwater (2050)	Stormwater_2050_Moderate.tif	24 in	Inhabited floors & basements below Stormwater DFE (counts)
Stormwater (2080)	Stormwater_2080_Extreme.tif	24 in	Stormwater_DFE_2080

Calculation Steps

Identify flood zone overlap: Intersect the NYCHA development polygon with the flood zone geometry (FEMA NFHL vectors for coastal; stormwater raster cells > 0 for stormwater).
Sample ground elevation: Extract LiDAR DEM raster values within the intersection area. Only valid (non-nodata) cells are considered.
Determine Base Flood Elevation (BFE): Take the maximum ground elevation within the flooded portion of the development. This represents the highest point where floodwater is modeled to reach.
Add freeboard buffer: Add the domain-specific freeboard (40″ coastal, 24″ stormwater) to the BFE. This produces the Design Flood Elevation (DFE).
Count vulnerable buildings (inhabited floor): Using the Building Elevation Subgrade dataset (z_floor = first inhabited floor elevation, NAVD88), count buildings on the development where z_floor < DFE.
Count vulnerable buildings (basement): Estimate basement elevation as z_grade − 10 ft (universal assumption; configurable via BASEMENT_DEPTH_BELOW_GRADE_FT). Count buildings where basement_elevation < DFE. This captures vulnerability to building systems and infrastructure even when inhabited floors are above the flood line.

If a development has no flood zone overlap, DFE is not calculated and the building count defaults to 0. If the DEM has no valid elevation data within the intersection, DFE is also not calculated.

Raster Alignment

When the stormwater raster and DEM have different resolutions, the stormwater mask is resampled (nearest-neighbor) to match the DEM grid before combining. For coastal DFE using FEMA vectors, the development-flood zone intersection geometry is used directly as a DEM mask, avoiding raster-raster alignment.

6. Conditional Relationships

Vulnerability and mitigation sub-indices are only calculated when the corresponding hazard is present; otherwise set to NaN (“Not applicable”). When the composite hazard/vulnerability/mitigation indices are aggregated, N/A conditional sub-indices are excluded from both the numerator and the weight denominator for that site — so sites are not penalized by forced zeros for domains that do not apply to them.

Condition	Trigger (ANY)	Applies To
COASTAL_TIDAL_HAZARD	PFIRM=True, Surge 2050=True, Surge 2080=True, or Tidal ≠ empty	Coastal mitigation
STORMWATER_HAZARD	Stormwater 2020, 2050, or 2080 = True	Stormwater mitigation
GROUNDWATER_HAZARD	Depth_to_Groundwater_ft < 16 ft (the no-hazard cap)	Groundwater vulnerability and mitigation
HEAT_HAZARD	SolarRadGroundPct > 0, bldg_height_mean > 0, or Total_Roof_Area > 0	Heat vulnerability and mitigation

7. Data Sources

Auto-Refreshing (API, 30-day cache)

Data	API	Fields Used
FEMA PFIRM Flood Zones	hazards.fema.gov NFHL MapServer/28	FLD_ZONE, ZONE_SUBTY, SFHA_TF, STATIC_BFE
Coastal Surge 2050/2080 (NPCC projections)	NYC MOCEJ ArcGIS FeatureServer, serving New York City Panel on Climate Change (NPCC) sea-level-rise and coastal flood projections (reference link shows the 2050s 100-year floodplain; 2080s and tidal-onset layers are separate NPCC datasets published by NYC Open Data)	Geometry (boolean intersection)
Building Elevation Subgrade	NYC Open Data SODA (bsin-59hv)	the_geom, z_floor
NYC Building Footprints	NYC Open Data SODA (5zhs-2jue)	the_geom, height_roof; Shape_Area computed

Manual Refresh (local rasters)

File	Source	Update Trigger
Stormwater_2020_Light.tif	NYC Department of Environmental Protection (DEP) — NYC Stormwater Flood Maps	New DEP release or NPCC projection update
Stormwater_2050_Moderate.tif	NYC Department of Environmental Protection (DEP) — NYC Stormwater Flood Maps	New DEP release or NPCC projection update
Stormwater_2080_Extreme.tif	NYC Department of Environmental Protection (DEP) — NYC Stormwater Flood Maps	New DEP release or NPCC projection update
NYC_DEM_LiDAR.tif	USGS 3DEP / NYC DoITT	New LiDAR acquisition
nyc_groundwater_depth_interpolated.tif	USGS / NYC DEP	New interpolation
NYC_SolarRadiation_Merged.tif	NYC / CUNY Solar Map	New analysis

NYCHA-Maintained

File	Contents
NYCHA Development Data Book.csv	Administrative data, Sandy/IDA flags, completion date, building type
2025 Resident Data Book.csv	Demographics (Minors %, Seniors %)
Flood Protection Components.xlsx	Flood hardening inventory, critical equipment status
335 Developments Hazard Exposure desktop.xlsx	Tidal flooding timeline, Cloudburst designations
Developments with Replaced Roofs.xlsx	Cool roof installations
DFTA NYCHA Cooling Centers.xlsx	DFTA senior cooling center locations (union-flagged with DYCD into OnsiteCoolingCenter)
DYCD NYCHA Cooling Centers.xlsx (optional)	DYCD community/youth cooling center locations; OR-combined with DFTA into the OnsiteCoolingCenter attribute. Loads gracefully if absent.

8. Spatial Operations

Source	Method	Aggregation
Building Elevation Points	Spatial join (points within polygon)	min/max/mean z_floor; count below DFE
NYC Building Footprints	Centroid-in-polygon join	mean height, sum area, count
Rasters (groundwater, stormwater, solar)	Polygon mask extraction	Mean (groundwater depth), boolean any>0 (stormwater exposure), sum of ground-area pixels > 0 (solar radiation, continuous input to min_max)
FEMA NFHL / Coastal Surge vectors	Dissolved union, prepared geometry intersection	Boolean intersects + DFE via DEM sampling
Tabular (Excel, CSV)	Exact name match on DEVELOPMENT	First match or aggregated per domain rules

All spatial overlays use EPSG:2263 (NY State Plane). Vectors reprojected to match raster CRS before extraction. Invalid geometries repaired via make_valid before dissolve.

9. Ranking & Classification

All indices use descending rank (Rank 1 = highest/worst). For flood-related sub-indices, only exposed properties are ranked; zero-exposure properties show “N/A”.

third = ceil(total / 3)
Rank ≤ third → HIGH | Rank ≤ 2 × third → MEDIUM | Rank > 2 × third → LOW

10. Mitigation Action Matching

Mitigation action recommendations are tailored to each development based on its hazard exposure level. The system determines which recommendations to show using the tertile ranking of each hazard sub-index.

Decision Logic

Hazard Domain	HIGH (top third)	MEDIUM (middle third)	LOW (bottom third)
Coastal/Tidal	Full mitigation package	Full mitigation package	No section shown
Stormwater	Comprehensive package (H&H analysis + critical systems + site strategies + entrances + buffering)	Reduced package (H&H analysis + buffering only)	No section shown
Groundwater	Investigation steps	Investigation steps	No section shown
Extreme Heat	Shown for all exposed developments (any level except N/A)

Coastal Flood Mitigation Actions

BASELINE — Protect Critical Systems (boilers, electrical switchgear, generators, elevators, fire alarm, BMS, telecom):

Option 1: Elevate critical systems above DFE — relocate to higher floor, annex, or roof; replace with distributed systems (e.g., window heat pumps + centralized hot water above DFE)
Option 2: Flood-protect systems below DFE — dry floodproof rooms, permanent flood barriers, watertight doors and sealed penetrations, backflow prevention, sump pumps

Passive strategies preferred. Deployable strategies may be used where passive strategies are not feasible.

Protect entrances and exits: protect or relocate ground-floor spaces below DFE; install passive barriers at entrances.

BETTERMENT — Buffering strategies to reduce flood impacts: elevated curbs or floodwalls, regraded site to direct water away from buildings, vegetated berms along waterfront edges.

Stormwater Flood Mitigation Actions — HIGH Risk

BASELINE — All coastal baseline actions plus:

Hydrologic and Hydraulic (H&H) analysis to refine DFE per NYCHA Stormwater Design Manual
Option 3: Site-based strategies — retrofit landscape for stormwater conveyance/retention; install subsurface retention/detention in parking lots and wasteyards

BETTERMENT — Buffering per NYCHA Stormwater Design Manual: elevated curbs, adapted topography, vegetated berms, subsurface tanks and nature-based solutions.

Stormwater Flood Mitigation Actions — MEDIUM Risk

BASELINE — Build H&H Model to refine DFE per Stormwater Design Manual.

BETTERMENT — Same buffering strategies as HIGH risk.

High Groundwater Mitigation Actions

Mitigation credit is given to properties with the following measures (weights for the Groundwater Mitigation sub-index):

Sandy resiliency retrofits (0.45) — Sandy work included below-grade waterproofing, foundation repairs, and drainage improvements that reduce groundwater intrusion.
IDA recovery risk reduction (0.30) — post-Ida recovery addressed basement flooding and sewer-backup failures that correlate strongly with shallow groundwater.
Elevated/protected critical equipment (0.25) — elevating boilers, electrical switchgear, and other critical building systems above grade protects against chronic groundwater seepage.

Recommended further investigation steps for high-groundwater sites:

Review existing geotechnical surveys and soil borings
Consult geotechnical engineer on groundwater impacts
Install groundwater monitoring wells
Evaluate active subsurface drainage strategies

Extreme Heat Mitigation Actions

BASELINE:

Reduce indoor temperatures: heat pumps (window, through-wall, or central) in coordination with electrification assessment; retrofit community centers with cooling, refrigeration, device charging, and 24-hour backup power
Ensure egress during brownout: install Automatic Voltage Regulators

BETTERMENT:

Reduce ambient outdoor temperatures (combine options): expand shaded areas via trees/structures; use high-albedo/heat-reflective materials; install water misters
Ensure egress during power outage: install BESS for one elevator + common-area lighting per building

11. Key Assumptions

Relative ranking: Scores rank NYCHA properties against each other, not against external safety standards.
Equal domain weighting: Each hazard domain contributes 0.25 to the final Risk Index.
Hazard-present gating: Mitigation only assessed where hazard exists; otherwise “Not applicable.”
Residual risk: Full mitigation reduces risk by 90% (flood) or 60% (heat), never to zero.
Near-term weighting: Current conditions (2020) weighted more heavily than distant projections (2080).
Freeboard buffers: 40 inches coastal (current, 2050 scenarios), 52 inches coastal (2080 scenario), and 24 inches stormwater — conservative margins above the computed base flood elevation (FEMA BFE for coastal, derived stormwater BFE for stormwater).
Groundwater vulnerability proxy: Estimated from building age (1.0) since direct below-grade condition data is unavailable. Applied only to sites where groundwater is a concern (depth < 16 ft).
Basement depth assumption: Every building is assumed to have a basement 10 ft below grade (z_grade). This universal assumption may be replaced with site-specific data when available from NYCHA engineering teams or verified subgrade observations.
Vulnerability floor: Flood-exposed properties with zero building vulnerability (no inhabited floors or basements below DFE) receive a minimum vulnerability score of 0.1, reflecting site-level risks such as access disruption, grounds flooding, and infrastructure damage.