In the mid-1980s, I got into an argument with my forest hydrology professor at the University of Georgia over whether forests make rain. He disagreed, saying rain only comes from the oceans.
He added that streamflow increases when forests are cut. But this is only a local-scale effect.
Studies done in the Amazon with oxygen and hydrogen isotopes demonstrate that intact forest ecosystems recirculate water to the atmosphere and enhance precipitation. In technical language, “positive feedback between the forest and rainfall promotes cascades of recycled moisture that precipitate across distant areas, allowing for forest cover expansion and playing a significant role in the maintenance of the northwestern Amazonian forest.”
Russian theoretical physicists provide the following less-technical explanation: In non-forested areas, precipitation weakens with distance from the ocean. Intact forests act as a “biotic pump,” creating ascending fluxes of air and sucking in additional moist air from the ocean. If deforestation breaks the pump, the water cycle on land is impaired.
They conclude that “a terrestrial water cycle compatible with human existence is unachievable without recovery of natural, self-sustaining forests on continent-wide areas.”
Authors of a 2012 article in Global Change Biology agree. They say that, “If mitigation is about energy, adaptation is about forests and water,” that “forest ecosystems represent global public goods that must find explicit expression in public policy,” and that “climate change mitigation and adaptation benefits of forest–water interactions remain poorly integrated into adaptation-related policy frameworks.”
Canada’s just-released National Adaptation Strategy illustrates this lack of attention to forest-water interactions. While it notes that “reforestation can improve water availability for agriculture and drought mitigation,” it lacks a commitment to maintain and restore natural forest ecosystems.
The forest industry would prefer the status quo of “managed forests.” Too often, this means single-species conifer plantations with natural vegetation suppressed and water cycling reduced. This leads to forest fires, as seen this summer. Fires, in turn, release huge amounts of carbon dioxide, making climate change even worse, further increasing drought, heat and fire risk.
Degradation of the Amazon forest and conversion to plantations, pastures and crop fields now causes it to burn regularly and act as a carbon source rather than a sink.
This deadly cycle can be reversed by increasing forest cover and restoring hydrologic cycling. Obviously, land is needed for food and timber, but getting the balance right between areas devoted to natural forests and to commodity production is critically important.
By maintaining freshwater resources, forest and wetland ecosystems sustain human health, agricultural production and economic activity. Without these natural ecosystems, the hydrologic cycle is reduced or even eliminated over large expanses of the terrestrial landscape. Restoring forests and wetlands should be central to climate change adaptation.
Unfortunately, Canada’s new strategy proposes as an indicator, “changes in land use, such as from forests to croplands and settlements.” This assumes that forest and wetland loss will continue. The “Nature and Biodiversity” section of the strategy contains no ecosystem restoration target.
If water is the critical issue for adaptation, we’re missing in action.
In attempting to address climate change in isolation from other issues, we suffer from “carbon tunnel vision.” Jan Konietzko of Maastrict University in The Netherlands has created a graphic to illustrate this.
Target 2 in the Global Biodiversity Framework adopted in Montreal last December calls on countries to “ensure that by 2030, at least 30 per cent of areas of degraded terrestrial, inland water, and marine and coastal ecosystems are under effective restoration, in order to enhance biodiversity and ecosystem functions and services, ecological integrity and connectivity.”
We need a group of “Citizens for an Abundance of Green Life on Earth.”
The federal government has another chance to get it right with its 2030 Biodiversity Strategy for Canada. The previous biodiversity strategy had no ecosystem restoration target, and a pathetic forest target: “By 2020, continued progress is made on the sustainable management of Canada’s forests.”
To prolong human habitation of this continent, we need to do better.
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