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Depleted groundwater can cause drier conditions that lead to more severe wildfires.

Researchers find that low water can dry ecosystems, leading to conditions that encourage fires to spread

A connection between groundwater depletion and increasingly destructive and frequent forest fires — like the recent ones in the American West — might seem tenuous at first glance, but in fact such a connection has been observed not just in United States but also across the globe.

Groundwater Dependent Ecosystems

In the West, riparian forests, forests adjacent to rivers and streams, depend on both surface water and groundwater for survival. Forests that rely entirely or in part on groundwater for survival are known as groundwater dependent ecosystems.

Inadequate monitoring and study of these ecosystems corresponds with a general lack of awareness that they and other nearby ecosystems are in trouble, especially during parching summers and droughts.

Groundwater dependent ecosystems are resilient against water stress, but they begin to decline, sometimes irreversibly, if there is little groundwater available and when there’s also a shortage of surface water. This loss of habitat cascades into trouble for the structure and function of the ecosystem by interfering with reproduction, growth, recruitment, and mortality.

For example, tree mortality has been on the increase in the Sierra Nevada region, with 66 million trees lost since 2011. In California, 66 million trees have been lost since 2015 alone. Tree loss on this scale has never before been recorded, and each dead tree provides more fuel for wildfires.

Rainforest Fires in Borneo

Southeast Asian rainforests have been drying up for the past 20 years, creating conditions conducive to fires that have led to many deaths related to smoke pollution. Some estimates place the number of casualties as high as 400,000. In Borneo, researchers have found a correlation between forest fires and groundwater dynamics.

During lengthy dry periods, the researchers have found that groundwater levels become so depleted that underground capillary action is effectively halted, creating a “hydrological drought.” When fires happen during hydrological drought, there’s a tenfold increase in the area of forest loss. This discovery is likely to improve predictions on when fires will happen and how extensive they will be.

Fire’s Effects on Groundwater

Not only do groundwater dynamics affect fires, but fires affect groundwater too.

  • Wildfires can contaminate irrigation water with sediment and ash, potentially changing its pH level.
  • Nutrients and carbon released by fires could enter the water table.
  • Losing forest canopy to fire eliminates shade, leading to hotter ground, which could affect evaporation and aquifer recharge.
  • Sediment from fires may block routes that stormwater takes on its return to groundwater.

These dynamics are hard to measure because they take place underground, so some researchers are measuring water in karstified limestone caves to study it on its movement from the surface to aquifers. In the years after a significant wildfire, researchers note more evaporation, less aquifer recharge, and nutrient spikes that are eventually moderated by regrowth.

Some researchers in Italy, however, have noticed that in coastal areas, fires actually decreased saltwater intrusion into aquifers, presumably by allowing more water to pass into the ground. It is hard to know if that is a net plus.

Perhaps the most hopeful news for groundwater globally is new technology for decentralized wastewater treatment that produces water suitable for reuse. One example of this is Fluence’s Smart Packaged Aspiral™ solution, utilizing MABR technology, which can treat water for reuse in recharging aquifers, helping to maintain the balance of a healthy ecosystem.

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