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.