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Last updateFri, 09 Nov 2018 11am

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Tracking Lake Chapala changes

Lake Chapala invariably changes appearance as months roll by, rising with rainfall that comes principally from June through October and dipping though the drier months that follow.

pg12aSome years the seasonal variations are modest, in others quite extreme.

Chapala’s water content has been on a steady ascent over the past three years, a phenomena widely attributed to a presidential decree issued in 2014 that favors the lake over extractions from its tributaries for upstream agricultural production.

Expats new to lakeside may be unfamiliar with official methodology for evaluating Chapala’s status. The Comisión Nacional del Agua (Conagua) and Jalisco’s counterpart water watching agency CEA measure three related factors: volume, elevation and extension.

The estimated volume of water contained in the lake is expressed in millions of cubic meters. At full volume (Cota 97.80), the lake would hold 7,897,000,000 cubic meters of water, a figure usually abbreviated to read 7,897 Mm3. Some government specialists refer to 4,500 Mm3 as the lake’s “natural” volume and an optimum minimum figure for the end of dry season.

Another yardstick is the so-called Cota, a unique index relating the lake’s water level to the equivalent altitude. It is an arbitrary scale originally established in 1910 and modified in 1981 that sets a top measure of 100.00 on par with an altitude of 1,526 meters above sea level. At full capacity the lake would register at Cota 97.80, with the surface standing at 1,523.8 meters above sea level. At Cota 88 it would be completely empty.

The third gauge is surface area of the lakebed covered by water, usually cited in hectares. (One ha. is equal to 10,000 square meters or 2.47 acres.) The maximum extension of the vaso lacustre (lake vessel) is considered to measure 114,000 ha.

With all that in mind, let’s examine how radically Lake Chapala’s numbers have varied through history.

According to CEA data, the lake hit its all time peaked in 1926, with a volume of 9,663 Mm3 standing at Cota 99.38 on October 11, and flooding waters stretched over 116,092 hectares.

On the opposite end, Chapala bottomed out in 1955, when the volume fell to 954 Mm3 on July 1, registering at 90.80 on the Cota scale, with barely 67,008 ha. of the basin covered by a thin veil of water.

The lake’s second worst bad spell came in 2002. As of June 6 that year, the volume had dropped to a scant 1,138 Mm3, hitting Cota 91.07 with only 71,561 ha. under water.

It’s curious that both of these crisis eras were followed by abundant rainy seasons that brought about astonishing recoveries. During the 1955 rainy season the lake regained 3.42 meters in level over four months. In 2003, it jumped 3.23 meters between June and December.

As September closes, the lake now holds about 5,820 Mm3, standing at Cota 95.97, close to 73 percent its full capacity. The elevation level has increased by 1.65 meters since mid-June.

If you prefer to ignore the numbing numbers, simply trot out to the waterfront and open your eyes. Lake Chapala is looking good…and the rain keeps on coming.