Increasing atmospheric CO2 levels during the industrial age have gained a lot of exposure in the link with a changing climate. An area which has received far less attention are the significant changes to both local and global water cycles and vegetation patterns during the same period of time.
Water For the Recovery of the Climate – A New Water Paradigm (Kravcik et al, 2007) explores the science behind the very direct links between vegetation and both temperature and precipitation.
It’s a read I highly recommend and it can be downloaded by clicking on the title in the paragraph above. So that the time-poor can get the gist, I have included a number of the diagrams from the paper in a slideshow at the bottom of this article.
Here’s a very simple summary as well:
1) At any given time or place on the planet, there’s a certain amount of solar energy hitting the surface of the earth. That energy can be put to two very different uses.
At one extreme, a bare soil (or concrete, steel, etc), the majority of that energy is absorbed and re-radiated as (sensible) heat, warming the local environment.
At the other extreme, a saturated wetland, the majority of that energy is utilised by plants for photosynthesis, with the resulting transpiration drawing (latent) heat from the surrounding area.
So the sun’s energy is used to either power a landscape-scale radiant heater (above left) or a landscape-scale evaporative air conditioner (above right).
2) Of the average 720mm of precipitation that falls on land, the input from the sea is about 310 mm (the large water cycle). Hence, the land provides the larger part of its own precipitation (410 mm) from its own land-based evaporation (the small water cycle).
Therefore, a drained and dehydrated landscape, coinciding with relatively shallow rooted plants (ie conventional western agriculture) ultimately means less rain over the land, in a (not so) positive feedback loop.
A landscape which is primed to accept whatever rainfall or overland flow that arrives and to send that moisture through actively growing plants, means more rain over the land in a (more) positive feedback loop.
More soil moisture = more evapotranspiration = more precipitation = more soil moisture etc
The radiant heater mentioned previously means less rain; the evaporative air conditioner, more.
In closing, a couple of short paragraphs from the paper:
“The renewal of the domination of the small water cycle, which is advantageous for humanity, vegetation and the land, depends on the renewal of the functional plant cover of a territory and water surfaces in a country.”
“With sensible management of water and vegetation we can curb climatic change on the local level; if we can act in the same way across larger areas, perhaps we can expect a tempering of global climate change.”
Kravcik M., Pokorny J., Kohutiar J., Kovac M., Toth, E, 2007. Water For the Recovery of the Climate – A New Water Paradigm
Click here to download a pdf of the paper
Click on the images for a slideshow of the diagrams from the paper.