Hazards

Hazards#

Hazard is the first term in the pipeline’s IPCC-aligned framework, \(R = H \times E \times V\): it describes the climate process itself, before any question of who or what it affects.

Definition

A hazard is a “process, phenomenon or human activity that may cause loss of life, injury or other health impacts, property damage, social and economic disruption or environmental degradation” (UNDRR, 2019). This pipeline covers two hydroclimatic hazard types: seasonal drought and seasonal excess wetness.

In this pipeline#

Drought hazard: H_dry
Excess-wetness hazard: H_wet
Combined hazard: H_overall = max(H_dry, H_wet)
High H_dry means a stronger drought signal from SPI, rainfall percentile, CDD, and CWD.
High H_wet means a stronger wetness signal from SPI, rainfall percentile, CWD, Rx1day, and Rx5day.
H_overall highlights where at least one hazard type is elevated.

Each is a per-ensemble-member field; H_overall is combined per member (max) before averaging, not averaged first and then maxed – see methodology.md for why the order matters.

Formula#

Weights below are the live values in config/weights.yaml, not illustrative numbers. Every sub-score is normalized 0-1 first (see “Standardization” below), then combined by the weighted sum.

\[ H_{dry} = 0.35 \cdot S_{SPI,dry} + 0.20 \cdot S_{rain,dry} + 0.30 \cdot S_{CDD,dry} + 0.15 \cdot S_{CWD,dry} \]

\[ H_{wet} = 0.20 \cdot S_{SPI,wet} + 0.20 \cdot S_{rain,wet} + 0.20 \cdot S_{CWD,wet} + 0.15 \cdot S_{Rx1day,wet} + 0.25 \cdot S_{Rx5day,wet} \]

\[ H_{overall} = \max(H_{dry}, H_{wet}) \]

Rx1day/Rx5day are wetness-only: a low value in either is not meaningful evidence of dryness, so they never enter H_dry. CDD is dropped from H_wet for the mirrored reason – see methodology.md for the full reasoning behind both design calls.

Standardization (turning a raw indicator into a 0-1 score)#

Percentile-based, using each grid cell’s own historical distribution for that calendar period (never a map-wide min-max):

\[ S_{rain,dry} = \mathrm{clip}\!\left(\frac{50 - P}{40},\ 0,\ 1\right), \qquad S_{SPI,dry} = \mathrm{clip}\!\left(\frac{-SPI}{2},\ 0,\ 1\right) \]

where \(P\) is the rainfall percentile (0-100) at that cell for that calendar period. CDD, CWD, Rx1day, Rx5day use the same clipped-percentile form against their own historical percentile rank. Full formulas for every sub-score, see the “Standardization formulas” section in methodology.md.

Data used#

H_dry/H_wet are computed per ensemble member from six indicators (rainfall percentile, SPI, CDD, CWD, Rx1day, Rx5day), produced upstream by the sibling indicator-calculation project and consumed as trusted input – see the “Hazard / probability inputs” table in data_provenance.md for the exact source files (corrected_1993_2025.nc, corrected_2026.nc, CHIRPS, and the sibling repo’s per-period GeoTIFF/NetCDF exports).

Result#

See the JJAS maps below, or the full per-period set (June-September) in results_gallery.md.

JJAS examples#

H_dry	H_wet

H_overall JJAS