When the sierra burns: wildfires, forests and Monterrey's water

65% of the water that reaches Monterrey's homes comes from the Sierra de Santiago and the Cumbres de Monterrey National Park. The forest's plant cover intercepts part of the rain and the soil has an enormous capacity to infiltrate and retain water. That forest works like a natural sponge: it captures the water we later drink. The Nuevo León 2050 Water Plan confirms it: it identifies the Sierra Madre Oriental as the best-conserved watershed in the state and an important water-capture zone, and notes that 43% of the water Nuevo León uses comes from underground sources, the aquifers we recharge when the soil infiltrates the rain.

When there are fires, that sponge is lost. Without plant cover, the water is no longer captured, and without capture there is no water in our homes. It's exactly what we lived a few years ago with the 2022 water shortage crisis.

Think of it this way: without forest or healthy soil, it's like dropping water onto a slide: it rushes down and is gone. What we want is the opposite: for the water to stay in the soil and seep into the subsoil, where there are rivers beneath the ground that later feed water sources like the Socavón de San Francisco in Santiago, or the dams. And although we tend to feel that it rains a lot, the reality is that rainfall here is scarce and irregular, and much of it falls concentrated in just a few days of the year. The goal is to capture as much as we can and use it over many years, instead of having rivers and dams fill up overnight and being forced to let it go, as happened with Tropical Storm Alberto in 2024, when the dams filled in a matter of days and we ended up spilling water. If we can get that water to soak into the subsoil, we'll have it for many more years.

After the great fires, around 21,800 hectares were affected in the basin; of those, the authorities designated some 3,800 hectares as priorities for restoration. The rest either recovers naturally or consists of cliffs and vertical walls that simply can't be reached. Organizations like Amigos de la Sierra A.C. have already worked hard in recent years and have restored more than ten thousand hectares.

A burned forest loses its beneficial role: it stops infiltrating water, regulating temperature and preventing floods. That's why, after 2021, every time it rained hard we saw runoff carrying black sediment and roads blocked by tons of rocks. This even led to a fatal case recently, when one of these torrents caused a deadly accident in the area. Without the protective effect of the forest and soil, the rain rushes down the basin and reaches the city with all its destructive force.

The problem is bigger than a single fire. The Nuevo León 2050 Water Plan estimates that the state lost 15.3% of its natural vegetation (969,828 hectares) in a little over a decade (1997-2013), and that the Río Bravo–San Juan basin, Monterrey's, loses on average 12,142 hectares of natural vegetation per year. And the floods that follow are not cheap: just four tropical cyclone events between 2010 and 2013 left losses of nearly 25 billion pesos in Nuevo León; Hurricane Alex, in 2010, cost on its own about 21.5 billion.

As hikers we can make a direct difference. Three concrete actions:

1. Never build campfires. The risk of the fire escaping is extremely high, even for trained brigade members and with no wind. It's also illegal: since the National Park and many of Monterrey's trails are private property, owners have the right to report you. Better bring food that needs no fire.

2. When you see a campfire mound, dismantle it. This is the golden rule: if you see rocks arranged in a circle with soil and half-burned logs, remove the stones and take the mound apart. Visually it's an invitation for the next person (often someone new to the sport) to build a fire there.

3. Don't leave glass or trash. Discarded glass can create a magnifying-glass effect and, under the right conditions, start a fire.