Driest Rio Grande flow on record

Updating my “drought and climate change” lecture each fall is a useful exercise – this year more useful than most. Much like the year itself, my slide deck is setting all time records for new data visualizations needed to make sense of the remarkable 2026.

Update

Great questions from the comments. (I love my commenters.) First, a request to include a smoother to make the trend more legible:

Now with bonus smoother.

Second, an observation that it looks like it tracks the Pacific Decadal Oscillation, a large scale pattern linked to drier conditions in the southwest. Good eye! A quick run of the numbers based on prior-year fall PDO shows a statistically significant but small (r squared explaining 6 – 9 percent of the variance) relationship.

Worth noting that this is all of the water flowing past Otowi, which is a function of climate and all the many human activities upstream (irrigation reducing flow, San Juan-Chama adding to flow). So it’s not solely a climate signal.

Weirdly, when I redid the analysis for the Del Norte gage, which is above the San Luis Valley diversions and should be a clearer climate-alone signal, the relationship disappears. No correlation at all with PDO, which surprised me.