US Extreme Weather and Climate Change Dashboard
Variables on this page
Every variable below is evaluated over a full reliable-trend window against this site's combined "detected change" standard (IPCC's likelihood criterion plus a magnitude-vs-variability check -- see the homepage or Methodology for the full definitions). Shown as alternative ways of characterizing this same phenomenon -- some from independent sources, others a different construction on the same underlying data (each variable's own note says which).
Palmer Drought Severity Index (PDSI), 1895–2026
National (contiguous 48 states) monthly PDSI from NOAA nClimDiv — a single meteorological/soil-moisture index, negative for dry conditions and positive for wet conditions. This is the long-record context layer alongside the US Drought Monitor panel below; full methodology on the Methodology page.
Source: NOAA NCEI nClimDiv (PDSI)
Shading shows dry months (below the zero line) versus wet months (above it) so the sign of PDSI is visible at a glance, not just readable from the number. The 2026 portion of the line reflects only the months observed so far this year and is not a full-year figure yet (see the Methodology page).
Drought
WeeklyUS Drought Monitor, weekly national area by severity category. Unit: % of CONUS.
USDM's whole record is used as the reliable window — 2000 is the record start, not a sub-window found within the data, so there's no earlier period to exclude here. USDM's native categories (D0 abnormally dry through D4 exceptional drought) are already cumulative ("this severity or worse") in the source data, not raw per-band values — D2+ is the level selector's default, chosen as the closest USDM analogue to a "1-in-10 or worse" severity cutoff (full rationale on the Methodology page), but every category is selectable.
Source: US Drought Monitor (USDM)
Computing trend…
Drought — SPEI
MonthlySPEI computation (Hargreaves PET, log-logistic standardization) -- a second, independently-derived drought index alongside PDSI, using a different PET formula specifically so a drought finding can be checked against a documented critique that PDSI's formula overstates warming-driven drying. Unitless; negative values are dry, positive are wet. Unit: SPEI.
Uses the same GHCN-Daily HCN station network that shows a reliable trend from ~1895; station count is exported per month so a thin-network period is visible rather than hidden. Uses a different, more defensible PET formula than PDSI (Milly & Dunne 2017) -- the two indices meaningfully diverge for 2021-2025 (PDSI strongly negative, SPEI only mildly so), a real finding disclosed on the Methodology page, not smoothed over.
Source: NOAA GHCN-Daily (temperature + precipitation), SPEI computed in-house
Computing trend…
Drought — Hydrologic (Low-Flow)
WeeklyThe mirror image of the Flooding page's high-flow index: % of HCDN-2009 reference gauges currently at or below the historical 10th percentile for the day of year -- a runoff-based drought signal, distinct from PDSI/USDM/SPEI's precipitation/soil-moisture basis. Unit: % of reference gauges below threshold.
Shares the high-flow index's 1957 reliable-trend window (the same underlying gauge-network coverage finding applies to either tail). 1934/1931 rank as the two driest years in the full record, and 1988/2012 both land in the reliable window's top 10.
Source: USGS NWIS daily discharge, HCDN-2009 reference gauges
Computing trend…