Declining Colorado

Paul Miller and Tom Piechota have assembled a new set of data suggesting a decline in precipitation in the West, and more particularly in the basin that feeds the Colorado River.

For this work, they looked at SNOTEL stations, the network of snow measurement sites run by NRCS that feed data into streamflow forecasts. For the period of record at the various sites (which varies in length) they found:

  • 86 percent of the 398 sites around the western United States show decreasing water year precipitation
  • 87 percent of the 79 sites in the Colorado River Basin showed decreasing water year precipitation

It is important to note, as Miller and Piechota do, that the time series here is too short (less than 30 years in most cases, with few stations having data going back 40 years) to find statistical significance in the decline. But less precipitation is less precipitation.

Their data also point to another important characteristic. In recent years, for a given amount of peak snow water equivalent (essentially depth of snowpack), streamflow tends to be lower. Which is to say, less of what falls from the sky is ending up in the West’s rivers – a finding consistent with climate change projections.

h/t the the JAWRA blog for bringing this paper to my attention, and to the always-helpful Paul Miller for helping me understand what he and Tom had done.

Importantly, while the primary focus is on the Colorado River, Miller and Piechota also looked at the rest of the West, noting the interlocking water management systems via which we now share these problems.


  1. …and if we include tributaries, the inter-locking mechanism of climate change and water resource management is even more obvious (San Juan/Chama project).
    What’s really odd to me is that I keep reading authors claiming that the era of big projects is over, and yet everywhere I look, states and municipalities are planning more inter-basin transfers. Dams aren’t the only way to steal water, and I’m reminded of this on a daily basis whether in New Mexico or in Colorado.
    Can we geoengineer our way out of climate change? Is that adaptive? Does further hardscape engineering lead to greater resilience or greater vulnerability?
    Tough questions… for all of us.

  2. Eric –

    Thanks for dropping by.

    I think one of the problems in the upper basin is that we don’t know yet where the upper bound is on water supply. The recent discussions sparked by Eric Kuhn’s work really show that. Things are very different in the lower basin, where all the states know exactly how much the upper bound on their possible diversions is. They know they’re not going to get any more, and they’re being forced to adjust behavior accordingly. One might not like the choices they’ve made in response – Southern California diverting more from the Sacramento Delta, for example, in response to reduced Colorado River allocation, or the Las Vegas groundwater grab. But both are examples of what happens when a boundary condition is imposed. In the upper basin, the question of how much water is available seems downright fuzzy, and as a result no one’s being forced to adjust.

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