Excellent points - here are a couple more factors: - Often reservoirs are filled via gravity from elevations that are higher. If the precipitation at those hi

Excellent points - here are a couple more factors: - Often reservoirs are filled via gravity from elevations that are higher. If the precipitation at those higher elevations is falling as snow, you have to wait for it to melt before seeing the benefits. - When the ground is dry and the aquifers depleted, less of the rainfall will make it into the reservoirs. I'm from central PA and MOST of our water is actually stored in the natural aquifers (under my area of the state, it's water-fllled limestone caves). So to be fair to el Nino, you have to look at how the aquifers are responding to the rain. - California would be an unpleasant place if four years of drought were reversed in a single year.