Everything you always wanted to Know about the water in La Paz (but were afraid to ask)



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By Alejandra Campos

In Baja California Sur, including La Paz, we need to be very careful not to use too much water. The city of La Paz has a population of 272 711 habitants and the highest rate of population growth at the national level: 2.76%. Our only source of fresh water for consumption in the city comes from the La Paz aquifer and part of the Carrizal aquifer in the surrounding basin. In the watershed, there are no important surface waterfalls.

To better understand the current situation of the aquifer, we must understand the relationships that exist between the different factors andactors. Here are some of these:

Like the other 21 of the 39 existing aquifers in BCS, the La Paz aquifer
is overexploited. It also has a severe intrusion of seawater, calculated at 13
km inside the basin. To exemplify the above, the theoretical time of advance of
the salt intrusion is estimated between 150 and 200 meters per year.

Current status of the recharge
area of ​​the aquifer and its relationship with local precipitation cycles:

The infiltration capacity of thebasin has been reduced due to to the loss of vegetation cover and thesubsequent erosion of soil in its main recharging area. In addition to this, 56% of total rainfall in the basin comes from torrential rainfall effects whichare related to storms and hurricanes. When soils have no vegitation cover,erosion occurs and therefore, the rainfall drains into the sea instead ofentering the aquifer. 

The sum of these factors cause most of the rain to evaporate (80% of thetotal rainfall annually) or run off to the sea (5% of the total rainfall annually), leaving only the remaining 15% to infiltrate to the subsoil.

Infrastructure in the city:

  1. Infrastructure for water supply, measurementand quality: In terms of infrastructure, there are important areas to take intoconsideration but here, we will mention only a few: 1) A study done in 2006 estimates that about 40% the water that is distributed as tap water to homesand businesses is lost to leaks. Taking into account the limited investment ininfrastructure after 2006, it is possible that this percentage is even highertoday. 3) The percentage of water metering (the process of measuring water) isonly 31% for residential users, 52% for commercial users and 57% forindustrial. The scarce measurement presents important biases, which leads to inefficient resource management and consumption by users.
  2. Green infrastructure in the city: The city of La Paz is unprepared to receiverainwater that falls from the mountains and reaches the series of streetsbelow. This rainwater also tends to drag pollutants. Fallen water finds its wayto our beaches, causing havoc in daily life, health, safety and the economy ofthe population. Taking into account the factors already discussed (aquifer indeficit and with saline intrusion, torrential and insufficient annualprecipitation, natural elements for the recharge of the eroded aquifer,population growth, etc.) it becomes crucial to integrate in the city a seriesof elements designed to make the most of every drop of water and mitigate otherrisks.

Hard
data from the La Paz watershed and aquifer:

• The area of ​​the basin is 1,417 km2

• Baja California Sur is the driest state in
Mexico. The average annual precipitation of the La Paz basin is 178.8mm, with
most rainfall-taking place in the month of September with 68.9mm.

• The average annual recharge of the aquifer is 27.8 Mm3 and the concessioned volume of groundwater is 35.267748 Mm3, which results in a deficit of -7.46778 Mm3/year.

• Of the 653 officially declared aquifers in Mexico, the La Paz aquifer is one of the only 18 that present saline intrusion.

• The water that is extracted from the aquifer through the 257 wells is destined for urban public use, which represents the highest volume of extraction (63.46%) followed by agricultural use (28.18%)

In the Water and City Program of Niparajá, we promote and create synergies between different actorsto formulate solid strategies that allow us to preserve the natural resources that sustain life in the city of La Paz. We focus our efforts on issues of water governance and public spaces.

In order to understand the great challenge of having quality water for all, we must add other factors such as population growth, the overexploitation of the La Paz aquifer, its contamination by the saline intrusion and the progressive affectation of there charge zones. Addressing these challenges is fundamental to our well-being.We work to achieve efficient water management and of the several public spaces to promote an active and informed participation of the population.

Alejandra Campos is a graduate of biology at UNAM. She is currently coordinating the Water and City Program with Sociedad de Historia Natural Niparajá A.C. and is a member of the Consejo de Cuenca of BCS and la Junta de Gobierno of OOMSAPAS.

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