Calling Durango, Colorado, “the desert” is a bit of a cheat. Located on the edge of the San Juan Mountains, it averages 20 inches or so (50 cm) of precipitation a year, well above what might formally qualify as desert. But Durango sits at a fulcrum in the complex interplay between climate and geography in the arid west.
With the intake structure for the Animas-La Plata Project, one of the west’s last great water projects, taking shape on Durango’s southern edge, the city also sits at a fulcrum of the complex interplay between climate, geography and engineering that has come to define life in the arid west.
I’m no expert on the Animas-La Plata Project, so I’m hesitant to wax too poetic about its importance, but it’s been described as quite possibly the last major water project in the west, so it’s worth using it, I think, to take stock of what lessons we’ve learned and what we haven’t.
Prowling the project’s Environmental Impact Statement this afternoon, I found something that was, to me, quite striking: the project’s planning is based on streamflow records on the Animas from 1929 to 1993.
I’m not aware of any tree ring reconstructions of the flow of the Animas, which is what you’d need to do this right. But there is a nice reconstruction of the Rio Grande at del Norte, which flows out of the same mountains and is strongly correlated during the period of instrumental record to flows in the Animas. The del Norte record shows droughts substantially more severe in the past than the 1929 to 1993 period. Once every 70 years or so, there has been a drought worse than the worst-case scenario on which the Animas-La Plata was based.