May 10 2012

2011: Year of the Flood, 2012: Year of the Drought?

A year ago at this time, the story in the U.S. was floods, floods, and more flooding to come. The story this year? Here is a quote from The Greeley Tribune on May 3:

Statewide snowpack as of May 1 was 19 percent of the 30-year average, according to a report released by the Natural Resources Conservation Services office in Colorado late Thursday afternoon.

That ties for the state’s worst snowpack on record for May 1.

Only May 1, 2002, — a historic drought year for the state — was as bad.

At 21 percent of average, the Colorado River Basin’s snowpack on May 1 of this year was at a record low.

What a difference a year makes. Take a look at these plots of the mountain snowpack (NRCS Snotel) in Western U.S. on April 1st in 2011 and 2012:

It will be hard to see unless you click on the individual image for each, but note that the legend for each is the same. We went from roughly 150% or more of the average last year to less than 50% of the average for this year. The map for May 1 of 2012 has not been posted yet, but it will be even more of a difference than looking at April! Last year was a wet and cold May while May this year was about as dry as April!

Take a look at the latest plot just for California (CDEC data):


These are the conditions in California even after a decent first half of April that helped boost numbers especially in the Northern Sierra. 

After all the flooding in the Missouri system last year, there are no such worries this year, barring any significant rain events. It doesn’t look nearly as bad as the southwest though, just a bit closer to average than last year (the plot is courtesy of the Corps of Engineers):


What stands out when looking at the Missouri River Basin is what an amazing snowpack last year was. 2012 is low but last year was simply unreal.  

What do we make of all this data? Is 2012 the year of the drought? Can just one water year create a drought? The reservoirs in the west were all nearly full after last year, what is with the panic this year?

Overall, total net storage in the two big reservoirs by the end of September is estimated to be 28.2 million acre feet, down 2.4 maf from the previous year. Remember that bodacious snowpack of 2010-11, all the bonus water filling both of the big lakes? 46 percent of last year’s bonus water will be gone by the end of this year, according to the new 24-month study. (jfleck at inkstain)

You may be startled to learn that California gets more water from the Colorado than any other state, 4.4 million acre feet a year. Of that 3.8 goes to the Imperial Valley and three other irrigation districts for agriculture. Now, if you will, prepare yourself to enter the looking glass world of water rights.

The behemoth Metropolitan Water District of Southern California has a fourth and fifth priority right on some of that water. Those four irrigation districts have water rights that predate the Colorado River Compact. Thus, they receive allocations every year, drought or no drought, before anyone else.   Other states, notably Arizona, hadn’t been using their full allocations in previous years, which made their water available to others. But that has changed. Colorado River states are increasingly using all their allotments.  California had been using the excess but that supply is quickly vanishing. (Bob Morris at IVN)

I think what is being exposed again is just how stressed the southwest is when it comes to water needs. If a monster snow year in the southwest like last year can be so easily dampened or erased by such a dry year, what might that say about the resiliency of the Colorado River Basin and the system we’re currently relying on?

One thing is for sure. Cadillac Desert by Marc Reisner should be required reading! Put it on your summer reading list and you won’t be disappointed!

Additional Resources

California Water Wars Spotlight: Colorado River (IVN)

Nearly Half of Last Year’s Colorado River “Bonus Water” Will be Gone by the End of the Year (jfleck at inkstain)

Statewide snowpack tied for lowest on record; Colorado River Basin at all-time low (Greeley Tribune)

Mountain Snowpack Maps for the Western United States (NRCS)

California CDEC Snow Information

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