The Salt/Verde, climate change and Upper Basin Envy

tl;dr – Heads up, Arizona. Less water headed your way!

longer version – Stuck out here in the Rio Grande Basin, I’ve long suffered Colorado River Basin Envy Syndrome. The Colorado is the sexy river, which means it gets all the cool science. I dream of an analysis this rich of uncertainties in my river’s streamflow.

Turns out that even within the Colorado River Basin there’s a little Envy Syndrome going on:

Numerous studies have assessed the potential impacts of climate change on the upper Colorado River basin… The lower basin is relatively less well studied, due mainly to the fact that most rivers in the lower basin were dammed during the 20th century and therefore do not contribute much surface water flow to the Colorado River basin (except in very wet years). Nonetheless, Colorado River tributaries in the lower basin (including two watersheds studied in this paper) are very important from a water supply perspective, providing totally 54% of the water used in the state of Arizona. (emphasis in original)

That’s Rajagopal et al., in On physical mechanisms related to climate-induced drying of two semi-arid watersheds in the southwest US. Their key finding:

The projections of this model ensemble indicate a statistically significant 25% decrease in streamflow by the end of the 21st century. The primary cause for this change is due to projected decreases in winter precipitation accompanied by significant (temperature driven) reductions in storage of snow and increased winter evaporation. The results show that water management in central Arizona is highly likely to be impacted by changes in regional climate.