Once fire-proof Amazon rainforests have become flammable, thanks to climate change

A forest fire in the Amazon. Image: Getty.

The Amazon rainforest is described as the planet’s lungs for good reason. So much carbon is locked up in its trees that protecting the forest is a must if we want to do something about global warming. However, reducing the CO₂ that is emitted when a tropical forest is destroyed depends not only on stopping the actual deforestation, but also on fighting wildfires within the forest.

In a new study published in Nature Communications we show that forest fires are responsible for a huge portion of the carbon emitted from the Brazilian Amazon. During drought years, these fires can emit around a billion tonnes of CO₂. That alone is double the amount of carbon effectively emitted through deforestation in the Amazon.

Humans are throwing vast amounts of CO₂ into the planet’s atmosphere. While in developed countries such as the US and UK most of the emissions come from industrial activities, in developing tropical countries such as Brazil, most come from forests being chopped down and burnt.

Yet while deforestation is already recognised as an important driver of carbon emissions, wildfires under the forest canopy present a less visible but still pernicious threat. To figure out just how bad the problem is, we combined satellite data on the current climate, atmospheric carbon content and the health of forest ecosystems. Our work revealed that emissions from tropical forest fires are growing, even though they are still not normally accounted for in estimates of national emissions.

Wildfires – but not natural fires

Wildfires in the Amazon are not natural events, but are instead caused by a combination of droughts and human activities. Both anthropogenic climate change and regional deforestation are linked to increases in the intensity and frequency of droughts over Amazonia.

Fires spreads into the forest during the 2015 drought. Image: Erika Berenguer/author provided.

This kicks off a nasty cycle: as trees have less water during such droughts, their growth slows and they’re less able to remove CO₂ from the atmosphere through photosynthesis. Trees then shed extra leaves or even die, which means more wood and leaves are ready to burn on the forest floor and, without a dense canopy to retain moisture, the forest loses some of the humidity which acted as natural fire prevention.

These changes are exacerbated by “selective logging” of specific tree species, which opens up the canopy and further dries out the understory and forest edges, which are drier than the interiors. The result: normally fire-proof rainforests become flammable.

A fiery future?

The resulting wildfires have reached a worrying level, burning millions of hectares during the recent El Niño. But the worst could still be to come, as the unusually warm conditions in the Atlantic or Pacific oceans that have caused previous droughts are expected to intensify.

So far this century the Amazon has already experienced three “droughts of the century”, in 2005, 2010, 2015-2016. If the climate science is accurate, and if no action is taken to efficiently predict and avoid fires occurring, we expect that carbon emissions from forest fires would be sustained even if deforestation ended overnight.

Smouldering tree trunk after a forest fire during the 2015 drought in eastern Amazonia. Image: Erika Berenguer/author provided.

As one of the signatories to the Paris agreement on climate change, Brazil is committed to reducing its emissions to 37 per cent below 2005 levels by 2025. A major reduction in deforestation rates over the past decade is a great start. However, deforestation policy doesn’t help reduce forest fires and consequently isn’t fully efficient in mitigating carbon emissions from the Amazon.

Brazil has made substantive advances in reporting emissions from deforestation. It now needs urgently to focus on incorporating CO₂ losses from wildfires into its estimates. After all, those fire emissions are expected to increase in future, thanks to more extreme droughts, an expansion of selective logging, and the ongoing use of fire to manage pasture or to remove regrowing vegetation on farmlands.

Kilometres of burned forests (magenta) spread across old-growth forests (green) in eastern Amazonia. White patches are clouds. Image: Celso Silva-Junior/USGS/author provided.

Given that fire is an essential part of many smallholders’ livelihoods, it is critically important to implement sustainable and socially-just policy responses. Brazil should start by reversing the budget cut to the organisation that oversees its only existing fire-prevention programme. It should also avoid selective logging in regions that are prone to fires, and ensure forest management always factors in long-term fire-prevention.

The ConversationIn summary, these findings are not only critical for policymakers in Brazil to strengthen the efforts of effectively quantifying and limiting carbon emissions from forest fires in the years ahead, but also to other tropical nations to tackle the potential impacts of drought-induced fires on their carbon budget. These new findings bring critical information for nations to help prepare for urgent actions aiming to mitigate the potential increase of fire emissions in response to the intensification of droughts in tropical ecosystems.

Luiz Aragão, Senior Lecturer in Earth Systems Sciences, University of Exeter; Jos Barlow, Professor of Conservation Science, Lancaster University, and Liana Anderson, Research Associate in Land Cover Dynamics and Carbon Emissions, University of Oxford.

This article was originally published on The Conversation. Read the original article.


 

 
 
 
 

What can other cities learn about water shortages from Cape Town’s narrow escape from ‘Day Zero’?

Cape town. Image: Pixabay/creative commons.

Cape Town was set to run dry on 12 April, leaving its 3.7m residents without tap water.

“Day Zero” was narrowly averted through drastic cuts in municipal water consumption and last-minute transfers from the agricultural sector. But the process was painful and inequitable, spurring much controversy.

The city managed to stave off “Day Zero,” but does that mean Cape Town’s water system is resilient?

We think not.

This may well foreshadow trouble beyond Cape Town. Cities across the Northern Hemisphere, including in Canada, are well into another summer season that has already brought record-setting heat, drought and flooding from increased run-off.

Water crises are not just about scarcity

Water scarcity crises are most often a result of mismanagement rather than of absolute declines in physical water supplies.

In Cape Town, lower than average rainfall tipped the scales towards a “crisis,” but the situation was worsened by slow and inadequate governance responses. Setting aside debates around whose responsibility it was to act and when, the bigger issue, in our view, was the persistence of outdated ways of thinking about “uncertainty” in the water system.

As the drought worsened in 2016, the City of Cape Town’s water managers remained confident in the system’s ability to withstand the drought. High-level engineers and managers viewed Cape Town’s water system as uniquely positioned to handle severe drought in part because of the vaunted success of their ongoing Water Demand Management strategies.

They weren’t entirely mistaken — demand management has cut overall daily consumption by 50 per cent since 2016. So what went wrong?


Limits to demand management

First, Cape Town’s approach to water management was not well-equipped to deal with growing uncertainty in rainfall patterns — a key challenge facing cities worldwide. Researchers at the University of Cape Town argued recently that the conventional models long used to forecast supply and demand underestimated the probability of failure in the water system.

Second, Cape Town’s water system neared disaster in part because demand management seemed to have reached its limits. Starting late last year, the city imposed a limit on water consumption of 87 litres per person per day. That ceiling thereafter shrunk to 50 litres per person per day.

Despite these efforts, Cape Town consistently failed to cut demand below the 500m-litre-per-day citywide target needed to ensure that the system would function into the next rainy season.

The mayor accused the city’s residents of wasting water, but her reprimanding rhetoric should not be seen as a sign that the citizens were non-compliant. The continuously shrinking water targets were an untenable long-term management strategy.

Buffers are key to water resilience

In the end, “Day Zero” was avoided primarily by relying on unexpected buffers, including temporary agricultural transfers and the private installation of small-scale, residential grey-water systems and boreholes in the city’s wealthier neighbourhoods. The former increased water supply and the latter lowered demand from the municipal system. These buffers are unlikely to be available next year, however, as the water allocations for the agricultural sector will not be renewed and there is uncertainty in the long-term sustainability of groundwater withdrawals.

For more than a decade, Cape Town has levelled demand, reduced leaks and implemented pressure management and water restrictions. This made Cape Town’s water system highly efficient and therefore less resilient because there were fewer reserves to draw from in times of unusual scarcity.

The UN Water 2015 report found that most cities are not very resilient to water risks. As water managers continue to wait for climate change models to become more certain or more specific, they defer action, paralysing decision-makers.

If we really want our cities to be water-resilient, we must collectively change long-held ideas about water supply and demand. This will require technological and institutional innovation, as well as behavioural change, to create new and more flexible buffers — for example, through water recycling, green infrastructure and other novel measures.

Although Cape Town avoided disaster this year, that does not make it water-resilient. Despite the arrival of the rainy season, Cape Town is still likely to face Day Zero at some point in the future.

The ConversationThere’s a good chance that the city is not alone.

Lucy Rodina, PhD Candidate, University of British Columbia and Kieran M. FindlaterUniversity of British Columbia.

This article was originally published on The Conversation. Read the original article.