Large fires fill the river with water

Large fires fill the river with water

After a really large wildfires, river runoff may increase by up to ten years, which brings both pluses and minuses.

Researchers from the US analysed data for 168 major fires in the contiguous 48 States and found that after those of them that touched on a really large area, the level of water availability has changed markedly. Other things being equal she was growing up — apparently due to the reduction of water consumption by vegetation. The corresponding article is published in Nature Communications.

Forest and steppe fires in recent years have intensified in various parts of the world, including in the United States. One of the main reasons for this is the very fight fires. Efforts to extinguish a single fire indicate incomplete burning of dead wood and lack of natural cinders — between areas vulnerable to forest fire, which has already passed another fire. “Extinguished” the fumes from the “sanitary barrier” that isolates one forest from the other, turns into the bridge where the fire easily spreads throughout the dead wood from one forest to another. Because fighting fires will only increase, we can expect a strong increase in the frequency of wildfires. This makes it extremely important to study the consequences of such events for the places where they occur.

The authors studied the fires, past the basins of a number of American rivers, to understand how they affect the amount of water in them.

All data were processed 168 cases where a fire once destroyed the vegetation on more than one percent of the entire catchment area of this river basin. Among these cases were 32 and fire, at which the vegetation burned by 19 percent or more of the area of the river basin (especially large fires).

It was found that small fires and, in particular, managed fires — the good, they always burn just a modest part of the pool nearest the river do not affect the water content of the rivers. However, all 32 of the fire, affecting more than 19 percent of the pool nearest the river have significantly affected its water content. The effect is, depending on rainfall, was twofold.

Where following fires followed prolonged droughts, the water level in the river was falling, for example, it was in California. However, if after a fire, an anomalous drought was not the level of rainfall was close to normal or exceeded it — water rivers growing significantly.

Moreover, the level of water in it was raised not for one season, and for periods of 5-10 years. This means that the impact of fire on the region is much more durable than previously thought.

The authors of the new work to discuss the mechanism of increasing the level of water in the rivers after the fire. However, it is known that plants in the course of their life needs to absorb from the air carbon dioxide, which open the stomata, through which, as a result, evaporates part of the water. Compensate for its loss of the plant from the soil. After a major fire this channel of consumption of water is sharply reduced or disappears altogether. And all this moisture from plants previously infested territories, respectively, freely flows into the nearest river.


The researchers note that the increased level of water in the rivers after major fires can be both positive and negative. The main part of drinking and tap water in the US come from rivers, so the increase in their water content means a reduction in the severity of water supply problems — which is certainly positive news. However, in cases of rapid precipitation in the years following forest fires, increased water content of rivers — a negative phenomenon. The vegetation serves as a buffer, slowing down the ingress of rain water into the rivers. Without it, water gets into the river much faster. Almost all the rivers in the US are not controlled by dykes and dams, so to compensate for fluctuations in the level of water in them, nothing. Heavy rains combined with partial burning of vegetation can lead to flooding, which will be significantly stronger than usual.