Water Level and Surface Area

The depth of Lake Chapala has varied widely over time.  Some say these changes are part of the natural cycles that have recurred many times; others say the recent changes in the lake’s level are due to human interventions.  In any case, today's Lake Chapala contains only about one-fourth of its historic capacity.

The official definition of a “full” Lake Chapala has also changed over the years. Prior to 1991, the National Water Commission (CNA) considered the lake "full" when its level reached 8.125 billion m³. After 1991, CNA lowered its definition of “full” to 4.5 billion m³. Then, in 1997, CNA declared the level of 3.3 billion m³ as "critical". However the water level continued to sink to a low of 1.120 billion m³ in June 2002.

The Chapala pier in ...

1976                                   2002                                   2004
       

The main reasons why the lake level decreased so drastically in recent years are:

Varying precipitation levels. For instance, precipitation was less than normal in 2002 but exceeded the norm in 2003 and 2004.

Evaporation: The lake loses 1.0 - 1.5m per year through evaporation, ranging from about 3mm/day in Jan to about 8mm/day in Apr-May. Evaporation is the single most significant factor in water loss.

Diversion of water. Water that should empty into Lake Chapala from the Lerma River is being diverted to other locations. Water is taken out of Lake Chapala and the Lerma River for cities, agriculture, and industry. Some of this diversion is for lawful purposes, but some is illegal or clandestine. Below left, the pump station in San Nicolas provides water for Guadalajara residents. Below right, an example of illegal pumping in the city of Ocotlán.

 
  Pump station in San Nicolas                  Illegal pumps in Ocotlán

Upstream dams. The dams in the Lerma River, for example, reduce the amount of water that reaches Lake Chapala. These upstream dams each retain, on average, more than 100% of their technical volume.

 
A dam on the Rio Lerma                          ... and the resulting low water below

In addition, there is a great waste of water in the watershed due to:

Broken pipes and other infrastructure problems. For instance, as much as 40-50% of the water that goes to Guadalajara leaks into the ground before it ever reaches the residents or industries for which it is intended.

Outdated irrigation techniques. Many farmers use flooding-style irrigation that requires large quantities of water because of the tremendous run-off that occurs before the water ever reaches the roots of the crops.

An example of flooding-style irrigtion

Surface Area Of The Lake

The surface area of Lake Chapala has also decreased. For instance, while the lake’s surface area was 1150 km2 in 1972, it had declined to 812 km2 by 2001.

The map shown above is derived from the Landsat satellite imagery and illustrates changes in the lake between 1986 and 2001. The surface area of Lake Chapala in March 1986 occupied 1048 sq km and had diminished to 812 sq km by March 2001. Based upon bathymetric studies of the lake, this loss of almost 24,000 hectares of lake surface area corresponds to a lake level decline of 2-4 meters, to a level not observed since a prolonged drought in the mid-1950s.