Deforestation and Flooding

Deforestation – the intentional eradication of trees by felling to clear land of forested areas to make way for other human-created uses (eg houses, buildings, runways, motorways, tunnels, trains and agricultural) – is a major contributor to climate change in general, and to flooding in particular.

Between 1990 and 2016 alone, the Earth lost a staggering 1.3 million square kilometres (502,000 square miles) of forests, according to figures from the World Bank. Since humans first began cutting down forests, 46% of the Earth’s total trees have been felled. Woodland comprises less than a third of the Earth’s surface (30%), but this is disappearing fast as a result of deforestation – in the past 50 years alone, at least 17% of all rainforest has gone as a result of intensive tree felling, with the past 12 years alone accounting for record highs of deforestation in the Amazon.

A significant factor is also the types of trees needed, and why. Although some have argued there have in fact been recent gains in total global tree canopy due to melting polar regions and the growth of man-made forests through timber plantations, mature palm oil plantations, and zealous tree-planting programmes in China and other countries, man-made forests can never compensate for the loss of primary forest – specifically primary tropical forests and savannahs, which host a wealth of unique flora, fauna and vital ecosystems that are irreparably lost when the land is cleared.  

Tropical forests, such as those found in the Congo and Amazon river basins and Indonesia, are particularly critical to life on Earth as they are store the most carbon and are the most richly biodiverse regions on the planet, with some 90% of all species on Earth. Tropical forests are also home to many hardwood tree species that have no dormant period, and as such are vital to regulating the Earth’s atmosphere.

The UK is one of the least-forested (13%) nations in Europe (the total landmass of Europe is covered by 37% woodland), thanks to historic felling by the Romans and other invading peoples to clear land for roads and agriculture; further stripping of woodlands to provide ships during the height of Britain’s colonial and naval supremacy, and during the Second World War; and subsequent relentless felling for agriculture and building – including the current felling and irreparable destruction of 108 ancient woodlands to make way for the highly contentious high-speed railway (HS2) project, which some have referred to as ‘Britain’s Amazon’. Of this, most of the UK’s trees are in Wales and Scotland, with only 6.5% tree cover in Northern Ireland and 9.9% in England.

There are many impacts this substantial loss of tree canopy and forest cover will have on our planet if allowed to continue, not only because of their essential link to climate change and biodiversity loss, but because trees are also a vital deterrent to other ravages of a dramatically changing, overheated and destabilised climate, such as sea-level rise, water scarcity, drought and flooding. In this article, we will focus particularly on how deforestation contributes to flooding, both in the wider global picture and within the UK.

Deforestation and climate change

Deforestation accounts for 8% of the world’s greenhouse gas emissions – to put this into a proportional geographic context, this comes third below all of the emissions currently produced by the US and China.

Forests serve as the Earth’s temperature regulator and pollution filter. They not only provide shade, material for building and food for creatures including man, but they also act as a vital ‘carbon sink’, meaning they absorb carbon dioxide and monoxide molecules from the air and lock them in, re-releasing them as oxygen through the process known as photosynthesis. Thus, they are effectively nature’s air-conditioning units and weather regulators, as they recycle water, which then forms clouds and later rain, thus helping to cool and water the Earth and enable to plants to grow.

“Without vast tracts of woodland covering every continent on the planet, humans – and indeed, all (or most) other life forms on Earth – would be completely wiped out, as they would not have sufficient clean air to breathe or food to eat.”

–JANE CAHANE

Therefore, without vast tracts of woodland covering every continent on the planet, humans – and indeed, all (or most) other life forms on Earth – would be completely wiped out, as they would not have sufficient clean air to breathe or food to eat. Without trees, the presence of the harmful carbon emissions and other noxious gases that have intensified through human fossil fuel-burning would make the air unbreathable.

If the pollution alone did not kill us, the heat would. Without vital tree cover, incremental temperature rises would diminish the protective layer of ozone in the Earth’s atmosphere, thereby exposing our planet to the sun’s harmful radiation. The entire land surface would become a scorching, uninhabitable desert, where nothing could grow – as is currently the case in regions of the world that are covered in desert, whether hot or cold (note, at 33% of the Earth’s total landmass, there is already more desert than forest).

The lack of trees would also mean the planet would be unable to internally regulate weather patterns; coupled with the impact of the ozone reduction and rising heat, Earth’s weather would rapidly plunge into a wildly destabilised, crisis situation – as it is already showing signs of doing.

We are all increasingly aware of the problem of climate change; we now know that if we do not act soon to reverse the ravages of climate change, our planet is on course for imminent untold disasters due to increasing wildfires, sea-level rise (SLR) and flooding, as well as decimation of vital plants, soils and species. The rise in global temperatures has accelerated the process of evaporation, which in turn has caused global wildfires to intensify in frequency, duration and prevalence, with some 8,100 wildfires in California alone in 2019–2020 and the fire season there now lasting 75 days longer than in the 1970s. Global SLR is also accelerating beyond predictions of the Intergovernmental Panel on Climate Change’s (IPCC’s) 2013 report, with more recent data showing SLR could reach up to (or even over) 2m by 2100.

“Along with sea-level rise, wildly fluctuating weather patterns will mean increased and more severe flooding, as higher oceans and air temperatures also mean higher concentrations of evaporation and cloud formation… this then leads to an increase in storms, levels of precipitation (frequency, intensity and duration) and severe flooding”

— JANE CAHANE

Along with SLR, wildly fluctuating weather patterns will mean increased and more severe flooding, as higher ocean and air temperatures also mean higher concentrations of evaporation and cloud formation, which further increase the moisture content in the air. This then leads to an increase in storms, levels of precipitation (frequency, intensity and duration) and severe flooding, with many regions already experiencing higher-than-average rainfall ­– for example, in October 2019, more rain fell in areas of the UK within a single span of 48 hours than would normally occur over an entire month.

Yet while forests could provide more than one-third of the total CO₂ reductions required to keep global warming below 2°C through to 2030, mankind unbelievably continues to chop trees down at an unprecedented rate. In the relatively short period between 2001–2015, over 300 million hectares (nearly the size of India) of tree cover was lost. Such short-sighted behaviour is essentially suicidal – if we continue chopping trees as we are, we will be unable to survive.

Deforestation and flooding

One of the biggest single causal factors in the devastating impacts of flooding is deforestation or de-vegetation. Deforestation contributes to the severity of flooding in a number of ways, both directly and indirectly, as described above in terms of the relation of the absence of trees to the overall impacts of climate change. Indirectly, forests also hold and use more water than agricultural lands or grasslands, which means some rainwater remains on the leaves and may evaporate directly into the air.

The most direct ways deforestation increases the impacts of flooding are by:

• increasing the speed and amount of sedimentary run-off;
• decreasing the amount of rainfall that is intercepted, as there are simply less leaves on trees and surrounding vegetation to absorb rainfall and reprocess it through photosynthesis; and
• the simple fact there is literally nothing physically present to stem the tide of a fast-flowing flood, which may or may not contain additional sedimentary elements.

The top two impacts are connected to the mechanisms by which plants absorb and expunge water. The process of photosynthesis means water is first absorbed via tree leaves and then transmitted to the roots beneath the surface of the ground, which in turn release nutrients into the soil. The water that is not used then travels up along the underside of the leaves and is re-released into the atmosphere as oxygen via evaporation.

When there are no trees and vegetation to absorb the precipitation, the quantity of water continues to increase, yet has nowhere to go. Also, roots absorb water from the soil and make it drier and able to store more rainwater, thereby making the surrounding lands less prone to flooding. Without the roots of trees and other vegetation deep absorbing precipitation deep below the ground, the water will remain on the surface and can more easily become a flood.

Deforestation also results in the top layer of soil becoming dislodged – a process known as erosion – because without the roots of trees and other plants and vegetation to anchor this topsoil in place, it becomes unstable and is no longer able to retain or reprocess any of the water that falls on it. This loose soil then becomes run-off– rain that is not absorbed by the soil. The increased surface run-off in turn increases the risk of flooding, because there is no soil layer to stop or absorb the flow of water. It therefore becomes a fast-flowing stream, with the loose sediment mixing with it to become a mudslide.

A flood of fast-flowing water or mud can also be more dangerous if the force of the current is strong enough to uproot and transport rocks or heavier items. Such items would have more likely been filtered or intercepted by the network of branches, roots and leaves of smaller trees, shrubs, hedgerows and other low-lying but substantial vegetation. Further, the movement of sedimentary run-off can shrink river channels downstream, thereby constricting the flow of rivers and causing them to overflow and burst their banks. Without forests and vegetation present to stem the tides of rising waters, the flood waters surge and move faster, ultimately becoming uncontrollable.

According to Janet Abramovitz of WorldWatch, deforestation in the Yangtze river-basin area played a major role in the massive flood of 1998, which occurred as a result of the region losing 85% of its trees. Although the Chinese government blamed El Niño and denied any complicity due to its logging activities in causing the regional devastation, it subsequently launched a $2bn plan to reforest the Yangtze basin. Says Abramovitz, “[This was] certainly… a very clear sign from the government that deforestation was [the] problem.”

Deforestation and flooding: the case against HS2

As previously stated, the UK is one of the least-forested nations in Europe, with less than 13% of tree cover. Therefore, any programme of deforestation for building, infrastructure and large-scale agricultural projects threatens to increase both the levels of climate change-related air pollution and the risk of flooding in the UK – not to mention severely impacting fragile wetland ecosystems and many unique, rare, threatened and protected species.

One of the UK government’s most ambitious, expensive and deeply controversial infrastructure projects is the high-speed railway (HS2), phase 1 of which is currently being built, with an escalating cost to taxpayers of some £106bn. The HS2 railway scheme proposes to connect London and Birmingham (and, at a later stage, areas of the Midlands, the North of England and Scotland). To build it, engineers have drawn straight lines bisecting large swaths of countryside, including several Areas of Outstanding Natural Beauty (AONB), such as the Chilterns; HS2 officials have also contentiously seized houses and farms and evicted families along the proposed route, citing a World War Two law that allows the government to grab land and houses for ‘a national emergency’.

Yet, according to a survey conducted by the Wildlife Trusts, the work will destroy or irreparably damage 108 irreplaceable ancient woodlands (these once covered Britain, but now only 2.5% remain), plus 693 local wildlife sites, five internationally protected wildlife sites and 33 legally protected sites of special scientific interest (SSIs).

While some see the proposed train route as an advantageous – even ‘green’ – development, both for facilitating business and reducing the amount of car traffic through ostensibly providing faster connections between major UK cities, the journey from London to Birmingham will only be 20 minutes shorter, which hardly seems to justify such excessive expenditure and destruction.

“Perhaps the flooding in
areas already deforested
for HS2 is a sign that
if even if the government
refuses to halt this work,
nature herself may have
the final say”

—Jane hurd cahane

Also, HS2 will in fact add carbon dioxide (1.49 million tonnes of carbon emissions) rather than reducing it over its projected 120-year lifespan. And then there is the fact that overall, rail travel is down – the pandemic has proven that remote working not only could become the norm, but for many workers, is preferable. Indeed, even long before the pandemic, train use was in decline; it is hardly likely demand will ever justify its construction.

But despite the risks and the clear lack of viable green credentials, the project poses an even greater risk: increased flooding. This is because several areas across which HS2 is being built are floodplains, and without the farmland and forests – which HS2 is commandeering all across the route – to soak up the surface water and serve as a natural flood defence, this leaves these flood-prone areas even more exposed to the freakish extremes of the weather and precipitation patterns, which have clearly increased in recent years.

Understandably, many residents, particularly in the Midlands and areas of the North of England along the proposed HS2 route, are fearful that its construction will put their homes at even greater risk of flooding. Some critical MPs and reporters such as BBC News Chief Political Correspondent Norman Smith have even suggested that HS2 itself will be a casualty of flooding. Indeed, a map produced by the Environment Agency revealed that areas already severely hit by flooding run an almost indentical course to the proposed rail line, including a 45-mile section of Staffordshire and a large area around Leeds station. In fact, had the rail line already been built through this section, it would likely have been submerged several times over.

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While various spokespersons for HS2 have claimed, and continue to claim, that drainage systems near the construction locations will be put in place as works continue, recent flooding of what was formerly the South Cubbington Woods – home to ancient woodlands and the beloved Cubbington 2015 ‘Tree of the Year’ pear tree, which were recently felled to make may for HS2 – makes such claims vastly unreliable. In view of such evident increase of flooding in an area that would have otherwise been soaked up by these woods, local residents are justifiably angry that money being spent on what many see as a ‘white elephant vanity project’ has not instead been directed towards erecting greater flood-prevention defences.

Speaking after the major flooding incidents caused by Storms Desmond and Eva during the Christmas 2015 holidays, which saw record-breaking rainfall hit Lancashire, Cumbria, southern Scotland and parts of Wales, former UK MEP for Yorkshire and the Humber Mike Hookem said: “Flood defences are not something that the government can palm off on charities and communities… rather than pouring billions of pounds into projects like HS2 – while at the same time cutting the flood defence budget, as it did in its recent spending review – the government must get its priorities right and make protecting the homes and businesses of hundreds and thousands of people from flooding an absolute priority.”

As an island nation normally subject to intensive rainfall, it is clear flooding is about to become even more intense for the UK due to rising sea levels, increasingly erratic and dangerous weather patterns, and the other issues of climate change-induced flooding made infinitely worse through deforestation. While the government has recently agreed to new 2050 targets for achieving net carbon neutrality and becoming a net-zero emitter of greenhouse gases, its continued support for the HS2 project is in direct opposition to these goals, due to the fact the project itself is adding to rather subtracting carbon emissions.

Perhaps the flooding in areas already deforested for HS2 is a sign that even if the government refuses to halt this work, nature herself will ultimately have the final say.

This article was originally written for the Earth Fast 2021 website in relation to this year’s theme on water – please see here for further articles and information about how to join the fast, and how to fast safely.