When drought and heat waves occur together
A 75-year observational analysis of compound drought–heat-wave occurrence, severity, and sensitivity to event definitions.
- Record
- 1951–2025
- Coverage
- CONUS
- Data
- nClimGrid-Daily
- Focus
- Compound events
The question
Where are drought and heat waves intensifying together?
This research uses NOAA nClimGrid-Daily observations to examine the frequency, magnitude, and regional structure of compound drought and heat waves across the contiguous United States.
Data & methods
A closer look at
the approach.
The primary definition combines one-month SPEI below −0.8 with heat waves lasting at least three consecutive days above the local 95th-percentile maximum-temperature threshold for 1961–1990. A compound month includes both drought and at least one heat-wave day. Sensitivity analyses compare SPEI with precipitation-only SPI and test alternative temperature reference periods.
Findings & context
What the work shows.
- Preliminary results indicate that the strongest long-term increases are concentrated in the western United States.
- The choice of drought metric changes estimated compound-event frequency substantially, illustrating why event definitions need to be explicit.
- Spatial trends, seasonal cycles, and a standardized compound magnitude index provide complementary views of changing drought–heat exposure.
Research in progress. Results and manuscript details may change as the analysis is refined.
From the analysis
Research figures.
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