8 February 2024

Between floods and forests is a matter of probability


Properly managing forests and preventing floods requires a paradigm shift, a Canadian study explains. That means replacing the deterministic approach with probability analysis and take all factors into account

by Matteo Cavallito


“It’s time to recognize the power of healthy forests in managing global growing flood risk, and to shift towards more sustainable forestry practices and policy,” say two researchers from the University of British Columbia (UBC) in Vancouver, Canada. The call is part of a study published in the journal Science of the Total Environment.

The survey, in particular, states how for decades hydrology studies have “severely and consistently underestimated” the impact of deforestation on flooding. And it explains, at the same time, how necessary it is to rely on a new paradigm for analyzing the problem.

A change in approach is needed to prevent floods

For more than a century, explained Younes Alila, a UBC professor and co-author of the study with fellow researcher Henry Pham, scientists have chosen a deterministic approach in studying the link between deforestation and floods. But the truth, the researchers point out in a statement, is that flood risk is influenced by many factors that interact over time in complex ways.

“The causes of floods are multiple and chancy and, hence, can only be investigated via a probabilistic approach,” the study states.

“Here we call for a causal inference framework to advance the science and management of the effect of any forest or its removal on flood severity and frequency.” Moreover, “We use the stochastic hydrology literature to infer a blueprint framework which could guide future research on the understanding and prediction of the effects of forests on floods in environments where rain is the dominant form of precipitation.”

Consider all the elements involved

To understand how deforestation can increase flood risk, scientists who rely on a deterministic approach are committed to describing the cause/effect relationship between the two phenomena. The probabilistic paradigm, on the other hand, assumes that flood risk is influenced by many factors. These include, for example, the amount of snow on the ground, whether or not it melts. But also the amount of rain that falls, and the characteristics of the landscape.

The probability-based approach, consequently, aims to consider these complexly interacting aspects as a whole over time. In this way, a more accurate overall picture can be provided. “The probabilistic approach is already well established in other disciplines such as climate change science,” spiega Pham says. “It is the most accurate method for evaluating the effects of deforestation on floods.”

Extreme rainfall events are becoming more frequent

The use of a new paradigm and, consequently, a better understanding of the problems can help prevent flooding by better protecting forest cover. This is a key issue in today’s picture of increasing frequency of the phenomenon. Early last year, a report released by the Global Water Monitor Consortium, an initiative of the Australian National University, highlighted how global warming is altering the water cycle. Thereby increasing the incidence of the most extreme phenomena.

That is, times when rainfall is either too abundant, to the point of increasing flood risk, or excessively scarce, such that it triggers drought phenomena.

At the same time, Pham notes, deforestation causes more severe and much more frequent floods, which can have severe consequences. “They can negatively impact river ecosystems, degrade water quality in community watersheds, and cause sedimentation issues downstream,” he say. “Thousands of lives and many ecosystems further downstream of clear-cut logging stand to be affected.”