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Runoff — filling our reservoirs — how much and when will it come ?

October 17, 2014

“… our ability to forecast seasonal water supplies derives from mixes of antecedent local hydroclimatic conditions and the distant echoes of El Nino. “

CNAP researcher Mike Dettinger provides an essay exploring runoff – the water we count on to fill our reservoirs here in the west.

http://tenaya.ucsd.edu/~dettinge/sources_of_forecast_skill_cnap.htm

Mike looks at forecast skill for runoff amount and timing. Three predictors are considered (and their associated colors): 1) water from the snowpack (current observations; blue); 2) runoff simulated just before the forecast period (green); and 3) El Nino status in the 3-month period leading up to the forecast (red). The triangles below show the darker the color the more skill the forecast has.

 skill90skill50skill10

The sample map shown below illustrates where the skill is in a forecast of April-July total runoff using the observed December snowpack (SWE, snow water equivalent), the runoff simulated for the season just before the forecast period (October through March) and the El Nino status (for January through March). This map shows knowing how much snow is on the ground in December (blue colors) leads to skill in the Pacific northwest mountain ranges as well as the Rockies. There is an influence from El Nino in the the southwest (light pinks) and the mountains. The greens indicate where the simulated runoff leads to some forecast skill.

skill_amj

Click on the link to the essay above for more information and more graphics!

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