Colombia and Climate Change
by Peter Bunyard,* for LAB
2 December 2011
Its geographical location makes Colombia particularly vulnerable to climate change. The country is situated in the equatorial tropics, with the actual equator running through its Amazonian territory. It is poised, as it were, between the Pacific and Caribbean, with an isthmus joining it, via Panama, to Central America. Furthermore, it is the one South American country where the Andes divide into three distinct chains or cordillera. On the western, Pacific side, Colombia boasts the wettest tropical rainforest in the world, the Chocó, and to the East, over the three cordilleras, lies the Amazon Basin. The Colombian Amazon, some 40 million hectares, encompasses one third the total land area of the country.
There is little doubt that global warming is already affecting Colombia, which is feeling the devastating impacts of ENSO, the El Niño Southern Oscillation. Nothing could have illustrated this more than last year (2010), when, for the first few months, Colombia found itself suffering high temperatures and drought from a strong El Niño, which led to constraints on the use of irrigation, only to have that followed by an equally extreme La Niña, which in turn led to widespread flooding, momentous landslides, disruption to transport, considerable loss of life, and to agricultural losses which sent the cost of food soaring. All the signs are that, after a short respite, La Niña has now returned, bringing with it the usual round of flooding, landslides and deaths. (Indeed, the way ENSO is manifesting itself makes one wonder whether the climate models are correct in predicting a spate of El Niño events, rather than those of La Niña, as a consequence of global warming.)
Average surface temperatures over Colombia during the past 30 years have risen at approximately double the global rate, one tangible consequence being the rapid melting of the glaciers of the high peaks, such that all the ice will likely have melted within the next few decades. Global warming is often glibly blamed for the vanishing of the glaciers and it is undoubtedly true that higher air temperature is playing its part. But there is now growing evidence that deforestation, which has taken place at an alarming rate in Colombia over the past few decades, is beginning to have a big impact and, if it continues at the current rate, will have devastating consequences in coming decades. Last year, the country was shocked to discover that the annual rate of deforestation topped 300,000 hectares rather than the previously declared 100,000 hectares.
Let us look at the impact of this deforestation. To anyone versed in hydrology, it is vividly clear that tropical forests – whether humid, seasonal, pre-montane or cloud forest – play a significant role in Colombia’s climate and that widespread deforestation will therefore have a significant and considerable impact on the country. In a seminal study three Cololmbian scientists (Germán Poveda, Diana Álvarez and Óscar Rueda ) have shown the dramatic consequences of land-use changes (and hence deforestation) on the failing resilience of soils and vegetation to withstand periods of drought. In particular, they note significant changes in the amount of available water as measured by deficits in soil moisture, not just during different seasons and hydrological regimes, such as during an El Niño episode, but between soils covered with different types of vegetation (1). Consequently, they found marked soil deficits at the 20 cm level during the 1997-1998 El Niño in soils harbouring open-field, sun-lit coffee as distinct to coffee grown in the shade. Not surprisingly, they found that secondary growth forest was far better able to resist soil desiccation during that El Niño episode than open-field coffee and they came to the obvious but pertinent conclusion that Colombia would need to conserve its remaining forests and regenerate native woodlands in deforested, degraded areas, in order to mitigate the likely impacts of climate change and global warming.
The findings of Poveda and his colleagues make common sense: where forests exist, whether in the Tropics or elsewhere, they bring about an essential inversion of below-canopy temperatures, which serves to maintain and contain high levels of humidity (specific as well as relative) such that soils remain moist and can continue to provide water for vegetation growth, even during the dry season or during an episode of El Niño. With the forest cut down and the canopy gone, the soil is no longer protected from winds and from desiccation and, as a consequence, the hydrology resulting from that abrupt land-use change is severely altered. The roughness of the surface changes, as does the albedo, which is the amount of reflected solar energy compared to that which is absorbed and converted into heat, all of which alters substantially the transference of energy from the surface to the lower atmosphere. Given such changes in the energy balance, we should neither be surprised that surface temperatures have increased across the length and breadth of Colombia nor that the glaciers are fast vanishing.
Obsession with global warming
Even though global warming resulting from greenhouse gas emissions is a valid concern, the problem is that we have become obsessed with it, to the point where we are neglecting the massively important function of forests in modulating and tempering the dynamics of the lower atmosphere. We have therefore falsely come to the conclusion that a tree is a tree is a tree and that we can substitute plantation forests for native forests and get the same benefits. Far more important than whether or not vegetation is acting as a carbon sink, we must consider the consequences for the hydrological cycle and atmospheric dynamics of cutting down closed-canopy forests.
For Latin America and no less Colombia it is therefore critical to understand that, despite the temptation to benefit from carbon trading and carbon sink projects associated with plantations on deforested and degraded lands, the emphasis for their own future survival
for maintaining a healthy hydrology. Therefore we have to question the real value of the clean development mechanism (CDM) associated with projects dedicated to tree plantations on land which had been deforested and degraded prior to the baseline date of 1990.
Colombia, no less than other developing countries, has looked to CDM projects as a means to benefit from certifiable emission reductions (CERs) in connection with carbon trading. One project, in total covering some 4,500 hectares, is already up and running, involving commercial forestry and agroforestry. In its entirety the project is expected to capture an estimated 38,000 tonnes of carbon dioxide annually and earn some US$3.5 million over the 20 years of accreditation. But, will such a project and others like it really serve to provide Colombia with some protection from the multifarious impacts of global warming and climate change? It is highly doubtful.
The obsession with carbon is particularly dangerous when applied to existing forests such as we find in the Amazon Basin. If greenhouse gases are believed to be the main factor accounting for climate change, then forests in themselves are only important for the amount of carbon they emit or they absorb. For instance, it were shown that the Amazon rainforest was a source rather than sink for carbon or even in a state of equilibrium with no net change in carbon flows between the atmosphere and surface, then the suggestion might be to substitute plantations of energy crops such as sugar cane or Africa palm for the forest. Indeed, this is already happening in Colombia’s Chocó where indigenous communities and Afro-Colombian communities have been expelled from their lands to make way for Africa palm plantations. But science is showing that, irrespective of their role in the carbon cycle, forests have a huge role in determining climate. It is only a combination of gross ignorance and greed that is permitting their destruction.
It is the forests’ role in hydrology that gives them their unique importance. Let’s take the specific case of the Amazon Basin. During the past few decades it has become clear that the hydrological path of the Trade Winds in both hemispheres, from their origin in West Africa and their traverse of the tropical Atlantic Ocean, all the way across the Amazon Basin to the Equatorial Andes, in what is known as the ITCZ – the Intertropical Convergent Zone – plays a critical role in the watering of South America as well as of other crucially important parts of the world, such as the Corn Belt of the United States and the even more distant South Africa.
The Trade Winds, in fact, dump some 12 billion (12×1012) cubic metres of water over the Amazon Basin each year of which about half flows back into the ocean via the Amazon River. A substantial quantity of that inflow of water vapour forms rivers such as the Orinoco which originates in the highlands of the Eastern Cordillera of Colombia and flows across the Eastern Plains to Venezuela and then into the Caribbean. Other flows of moisture occur in slow moving waves of air, such as the South American Low Level Jet Stream (SALLJ) which provide up to half the rainfall for the River Plate Basin countries, Argentina, Paraguay and Uruguay. Another stream of humid air passes to the Mid-West of the United States, its corn-belt, dumping the rains aptly in time for the growing season.
All this involves prodigious transfers of energy. Indeed, the rainforests of the Amazon are responsible for pumping an unsurpassed concentration of water vapour and energy, and they return up to 75 per cent of the solar energy received at the surface in the form of
water vapour, a transference of energy equivalent to that released by some 15 Hiroshima-sized atom bombs every second, including the hours of darkness. The destruction of the Amazon forests would therefore have a catastrophic impact. Just imagine the solar energy baking soils and converting them to laterite because the Amazon forests have vanished and whatever vegetation has replaced them can neither maintain an adequate degree of evapotranspiration to keep surface daily temperatures down nor provide the volatile chemicals such as isoprenes which on oxidation in the atmosphere provide the condensation nuclei upon which rain clouds form.
Partly because of the obsession with greenhouse gas emissions, the importance of the rainforest in determining global warming has been seriously underestimated – with potentially disastrous consequences. I have been in Colombia for the last year, working with colleagues to try and rectify this imbalance.
Data from radio soundings reveal the amount of water vapour – as precipitable water – in the column of air over different localities. The same data can be used to measure the quantity of that water which has condensed, presumably to form clouds, all of which should bear on the probability of rainfall in that same locality, particularly when measured over the course of a month so as to iron out differences between days when no rain falls and other days when as much as 120 mm (kg/m2) may pour out of the sky.
For the past year I have been reviewing daily radio soundings from distinct localities in the Sahara, across the tropical Atlantic, then over the Amazon Basin to the equatorial Andes of Colombia. I have discovered disturbing indications that deforestation on a local to regional scale is having a significant impact on lower atmosphere dynamics such as to reduce substantially the amount of atmospheric water vapour which condenses out of the air column. That reduction in condensation, at times by 50 per cent or more, during certain seasons and climate regimes, leads at times to an exponential reduction in rainfall.
Tres Esquinas, in the Caquetá province of Colombia, lies in the western Amazon Basin just ne degree North of the Equator and close to the piedmont of the Eastern Cordillera. Its geographical position implies a hydrological regime of bounteous rainfall, more than 3,000 mm per year, as the air currents associated with the East-to-West Walker Circulation over the Basin begin to feel the orographic updraft of the nearby Andes. But this is not the case. Instead – and the results are particularly apparent during the phenomenon of ElNiño – Tres Esquinas displays meteorological characteristics which have more in common with the dry tropics than with the forested regions of the Amazon Basin, such as Manaus in the central Amazon of Brazil or Leticia which, as Colombia’s most southerly point, lies some thousand kilometres further upstream on the Amazon River.
Does that difference between Tres Esquinas and Leticia in any way matter? We know from the original studies of Eneas Salati and his colleagues that the forests further to the West of the Amazon Basin depend on the recycling of water through the agency of evapo-transpiration whereby water is drawn up into the roots of the rainforest vegetation and, as water vapour, passes out of the leaf stomata. A drop of water evaporated from the Tropical Atlantic and carried inland by the Trade Winds may therefore get recycled some five or six times just over the Legal Amazon of Brazil.
That fact, in itself, would suggest that widespread deforestation in the eastern and central part of the Amazon basin, by causing a substantial reduction in evapotranspiration and therefore in the quantity of recycled water, would have repercussions on the viability of the forests in the western reaches of the Basin. At this moment in time, Tres Esquinas is still benefitting from the thousands of kilometres of forests stretching eastwards to the Atlantic Ocean and consequently the amount of precipitable water in the air column over the degraded cattle lands is not substantially different from that over Leticia or Manaus. However, primary, closed-canopy forest, with the maintenance of a temperature inversion below the canopy such as to conserve humidity, will mine water at much greater depths, even metres below the surface, and can resist extended dry periods of several months, whereas Tres Esquinas, shorn of its natural vegetation, no longer has that luxury and is displaying characteristics more in common with the open-field coffee plantations as studied by Germán Poveda and his colleagues in the Cauca Valley and central part of Colombia.
Until we look carefully at the dynamics of the lower atmosphere, we may jump to the conclusion that deforestation will cause changes but not necessarily devastating ones. The majority of climate models that have been modified to look specifically at the consequences of widespread deforestation in the Amazon Basin predict a reduction in rainfall, particularly in the western reaches, perhaps of some 20 per cent, such that the land once occupied by humid tropical rainforest turns to savannah and scrubland.
But the preliminary findings in my research suggest that these models might be wrong. The Russian physicists, Anastassia Makarieva and Victor Gorshkov of the Nuclear Physics Institute of St Petersburg, believe that the trade winds, with their gentle flow across the Amazon Basin, are actually sucked in by the forest as a result of the pressure changes caused by evapotranspiration and cloud-forming. If the Russians are right, rainfall could decline by 99 per cent or more, thereby leading to desertification. I have been investigating their theory of a forest-induced Biotic Pump from primary forest locations in Costa Rica and am finding statistically significant correlations between the evaporative force of the biotic pump and the local wind-speed.
Were research to reveal the validity of the biotic pump theory, it should certainly lead to a new appraisal of the role of forests in their essential hydrological role of drawing in the rains that feed the interior of continents. The corollary to the theory, which is that deforestation leads inevitably to a devastating reduction in rainfall as one proceeds from the coast inland, would mean that South America, the continent with the most rivers and fresh water resources, would rapidly come to resemble drought-bedevilled Africa.
Ultimately we must come to realise that climate, as experienced at the Earth’s surface, is contingent on the functioning of the planet’s ecosystems and that forests, particularly those covering large expanses of continents, are crucially important in regulating the ebb and flow of rain for the benefit of species such as our own.
(1) Germán Poveda, Diana Álvarez and Óscar Rueda , Hydro-climatic variability over the Andes of Colombia associated with ENSO: a review of climatic processes and their impact on one of the Earth’s most important biodiversity hotspots, Clim Dyn (2011) 36:2233–2249
*Peter Bunyard, Lawellen Farm, Withiel, Bodmin, Cornwall, PL30 5NW. Tel: 01208 831205; mobile: 07740404819; email: email@example.com & firstname.lastname@example.org. He is science editor of The Ecologist, a fellow of the Linnean Society of London, and a research fellow at the University Sergio Arboleda in Bogota, Colombia.