Saturday, June 14, 2008

weather report

We have two side bets going on this summer's weather. We've each picked the number of days we predict the temperature to reach or exceed 100 degrees, and we've each picked the number of deaths that will be blamed on heat. I realize the latter is ghoulish, but it's a way of coping.

Historically, the Central Valley could count on around 14-18 days of 100+ degrees every summer. Last year there were 28. The year before there were around 25. This year it's looking like it's going to be the hottest summer ever recorded here. Yesterday was the fifth day of 100 degree weather already, and this isn't the hot part of the year.

Meanwhile, the Gov issued a drought emergency last month, after the driest spring ever, and has now issued a state water emergency. What this does is allow for quick transfers of water from municipal systems that supply residential drinking water into the aqueducts and canals that serve agriculture. So the "water emergency" plan is a plan to find ways to use more water, not conserve it.

If you think there's an ironic twist to this story that I'm about to reveal, then DING DING DING! You win!

The Central Valley is the agricultural heart of the state, and in some ways of the nation and the world. To achieve this, in what is basically an arid seasonal grassland, the rivers that feed the San Joaquin are all dammed to form a tremendous series of reservoirs. Those reservoirs feed canals, generally open trenches, that stretch down the hills into the valley, which ranchers and farmers tap to flood irrigate. Flood irrigation is an ancient, inefficient method of watering crops by, as the name suggests, flooding the ground with water and letting it seep in (in this climate, this means a whole lot of evaporation loss, but that's another story).

The irrigated water seeps through the ground, waters the parched roots of almond trees and tomatoes and whatnot, and eventually reaches the groundwater table. This used to be just a couple dozen feet down, but after droughts in the late 80s and early 90s, it fell to just above its record low, where it has remained, through wet and dry years, ever since (it recovered somewhat during the huge El Niño year, but has sank rapidly since). Up and down the Valley, municipal water departments dig wells to tap the groundwater to feed to residents as drinking water. So you see the pattern: dam the rivers, irrigate the fields, the water sinks into the groundwater, it's pumped up, and we drink it (the health implications of our drinking this water are another story).

In other words, the water emergency declaration allows rapid transfer of water from the municipal systems, pumping groundwater up from wells dug to reach the water table which is replenished by irrigation of crops from reservoirs, and we're doing this because there's not enough water in the reservoirs. Not only will we be depleting the groundwater by tapping it to supply agricultural irrigation that we rely on to supply the groundwater, but we'll be recirculating the groundwater through all the petrochemicals that the ag biz dumps onto crops out here!

This will all work out fine, of course, as long as we have 5 or 6 winters in a row of well-above-normal snowfall in the Sierras - a pattern of weather that we can count on every 50 or 60 years or so.

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