75 Years of the Pacific's
Mood Swings: El Niño & La Niña

Every few years, the tropical Pacific Ocean shifts temperature, and the American West's rivers follow. This traces 75 years of those swings against measured streamflow in the Colorado, Columbia, and Sacramento rivers.

The Niño 3.4 region is a patch of ocean near the equator. When it runs warmer than usual for several months, we call it El Niño; cooler than usual, La Niña. Both change where rain falls across North America, and you can see the effects in river flows hundreds of miles away.

75 years of data · 902 months observed · 16 El Niño events · 21 La Niña events · record +2.15°C above normal · Feb 2026 neutral
El Niño (warmer than normal)
La Niña (cooler than normal)
Neutral
hover an event marker to explore river response ↓
↑ hover an event marker to see how western rivers responded
Data sources: NOAA PSL ERSSTv5 (sea surface temperatures) · NCEP/NCAR Reanalysis (atmospheric state) · NOAA CPC (oscillation indices) · USGS National Water Information System (streamflow) · NASA OISST v2.1 (gridded SST)
Method: ENSO events classified per NOAA CPC definition (±0.5°C Niño 3.4 anomaly sustained ≥5 consecutive months, 1981–2010 baseline). River values are z-scores relative to the 1951–2026 monthly mean discharge. All five sources were pulled into a PostgreSQL relational database built for this project.
Created by Noah Riego · University of Arizona · ISTA 322 · Spring 2026