Water supply forecasters look to add sites to improve predictions

GUNNISON — Inflow into Blue Mesa Reservoir this year fell short of what forecasters expected after record winter weather, but provided insight into developing better predictions for the future.

A combination of elements, natural and man-made, contributed to an over-forecast of about 10 percent in 2008. As of Thursday, Blue Mesa was 88 percent full, according to the Bureau of Reclamation Web site.

While the outcome disappointed some, there wasn't a big effect on users because the year still brought considerable water, said Dan Crabtree, Bureau of Reclamation water resources group chief.

"If were having a dry or normal season and we missed it by 10 percent, we'd be more concerned about it," said Crabtree. "All (that happened) is that we didn't fill Blue Mesa as far as we wanted and the rafters didn't have as much water in the season as they would have liked."

Snow and precipitation account for  upwards of 90 percent of the year to year variability in runoff, according to Tom Pagano, water supply forecaster with the USDA's Natural Resources Conservation Service. Soil moisture and evaporation also play roles in forecasts and outcomes.

Pagano gave a presentation this past week at the Bureau of Reclamation meeting in Gunnison.

April and May precipitation, which helps boost snowmelt, did not measure up to those in years past, Pagano said.

The dry and warm spring weather may have also contributed to some evaporation, Pagano said. A slow start to the winter season, back in October and November, also didn't bring the precipitation that helps encourage runoff. "Usually there's a little bit of rain that primes the soils to help your runoff and that didn't really happen this year," he said.

These contributing factors combined with others threw off expectations for inflow from the past winter.

Pagano and others are looking into the gaps of their data network and have been scoping out new sites from which to measure snow pack and precipitation data.

He said there's also a need to supplement the quantitative data with local, anecdotal observations.

"There's always a need for a reality check in terms of whether there's somebody here on the ground that sees something obvious ... we always welcome input on our information and that helps us nudge things higher or lower and get a better forecast," Pagano said. Observations from individuals who have lived in the same place for a long time are especially helpful.

"The main things you can have are better data in terms of measurements of what is actually there," Pagano said. "That's actually more convenient when it comes to real time data. That sort of makes the forecast process easier and quicker than what you actually measure."