So anyways, I brought you a gift to make up for it. Close your eyes. No peeking! Okay, open them...
Happy New (Water) Year!!! Were you surprised? What... don't you like it? But it's the gift that keeps on giving! Oh, I get it, you're taking a "wait and see" attitude, huh? Well, OK then. Probably a smart move anyway, given the long-term commitment that a water year requires. I'll wait.
The hydrological water year starts every autumn (in the US, at least) on 1 October and extends to the following 30 September. The available description from the USGS does not explain why this is the period considered, so it might seem just as arbitrary as a budget year in various governmental and academic institutions and business. But at least there is some natural logic to the hydrological year: with the end of summer comes the (approximate) end of intense evaporation from reservoirs and the (approximate) beginning of the seasons in which the net water balance in a watershed is generally positive. That is, in general, precipitation > evaporation. Normally, from the beginning through about two-thirds of the water year (the following May-ish) water is stored in the higher reaches of large watersheds as snowpack, which melts and runs off through the rest of the water year. Stream flows generally continue to drop from October through winter, but then rise significantly at the start of the melt season. That imbalance, where precipitation > evaporation, applies over a period longer than a single storm and for the whole watershed, not just on a random wet or dry day in one's own neighborhood.
One of the more interesting areas to observe the water year is the Colorado River Basin (CRB) in the southwestern US. I've written before about the Colorado River, which has become so strictly regulated, in part because of gross over-allocation, over nearly a century of intensive use that it has become what I think is a consummate example of the coupled natural - human system. The CRB as a whole is governed by the Colorado River Compact, ratified by six of the seven basin states in 1922 (Arizona finally ratified in 1944) and amended significantly over time. Since its beginning, however, the fundamentals of the Compact have not been renegotiated, nor the river flows reallocated for accuracy, as that's a political hot potato in the US Southwest. There have been a number of proposals (e.g. from the Pacific Institute) to handle recent near-shortages and potential future shortages of water supply in the Lower CRB, and some careful approaches to informing efforts at Compact renovation by the USBR istelf.
Several web sites (e.g. here and here) provide measurements and statistics on CRB flows and the status of reservoirs and other river operations, including the US Bureau of Reclamation as the de facto engineer and watermaster for the Lower Colorado Basin. The Upper Colorado Basin, technically that area above Lee's Ferry AZ (USGS gauge 09380000) but effectively all the area contributing to Lake Powell, is managed by a jumble of entities that have become so tightly intertwined, and that have seemingly prioritized politics over science, that any "management" is difficult to discern (please, those of you who are more knowledgeable on the CRB, correct me where I am wrong). Of course, it's not like there aren't any water politics in the Lower CRB as well. The problem of water sharing and use in the CRB has resulted in some of the finest books on water issues in the past several decades, including Donald Worster's Rivers of Empire, Norris Hundley's Water and the West, and Marc Reisner's Cadillac Desert.
Earlier today I came across this fantastic map of the CRB natural and engineered system that was designed by 5W Infographics, who designed the map for National Geographic. A representative at 5W Infographics gave me permission publish this smaller version of their map, and you can find the full-resolution version at National Geographic's Map Collection. The detail and breadth of information that they've packed into this wonderful format is simply amazing! (I love maps, by the way... Can you tell?)
|Map courtesy of 5W Infographics, available in full size/resolution from the National Geographic Map Collection.|