This is a brief discussion of the water cycle that elaborates on the information provided in Overview - Soil, Water, Vegetation And Climate Change. We feel it is important to have an appreciation of these topics as, ultimately, the health of any land and its inhabitants is highly dependent on water. And this, in turn, underpins wildlife conservation work.
Both the carbon cycle and the water cycle, which are intertwined, have been compromised through habitat clearance and inappropriate agricultural practices. The good news is that restoring the carbon cycle through native habitat restoration, regenerative land management approaches and, particularly here in Australia, minimising wildfire will also enhance the water cycle. This ultimately is our aim here at Heron Hill.
The water cycle can be thought of as being both regional or large and local or small. The former involves the cycling of water between land and sea, while the latter occurs on the land where plants move moisture from the soil to the air which ultimately becomes rain, if conditions are suitable. As mentioned earlier, both small and large water cycles, are degraded through habitat loss and land management practices which destroy the permeability of the soil and ultimately its health.
Small water cycle
Plant transpiration drives the small water cycle. But for this to occur, the soil surface needs to be well covered in vegetation. As this vegetation photosynthesises, water is released into the air. If the soil is bare, there is no transpiration and, accordingly, there is no release of water vapour into the atmosphere. The small water cycle is effectively impaired. This heats up the surrounding area as plant transpiration is absent and the bare earth radiates heat from the sun. An example of this is a person walking from a bare field into an adjacent forest. It is significantly cooler in the latter due to plant transpiration and lack of radiated heat from the ground.
When vegetation is absent and there is a lack of transpiration, weather patterns are altered. Judith Schwartz in her book, Water in Plain Sight, explains that water vapour that is transpired forms around nuclei (often bacteria). This in turn drives most of the rain in the small water cycle through cloud seeding. In fact, Professor Clive McAlpine from the University of Queensland has observed a strong correlation between clearing of southeast Australia’s forests over the past two hundred years and rainfall decline. Rainfall decreased from 4 to 12 percent. His modelling determined that the cause was large scale tree clearing. This same modelling showed that large-scale reforestation increased rainfall, in a positive feedback loop, where more trees made more rain which, in turn, increased the number of trees.
In relation to the small water cycle, excessive runoff from degraded soils and impermeable infrastructure like roads, carparks and buildings has led to a deficiency of water in the soil and too much being flushed down rivers and into the ocean. As explained in Overview – Soil, Water, Vegetation And Climate this has led to a half hydrological cycle or water cycle with a myriad of ecological consequences that lead to ecosystems being far more fragile to stressors like droughts.
Repairing the water cycles
The repair of our dysfunctional small water cycle begins with both land rehabilitation through tree planting and appropriate land management practices that keep vegetative cover and increase soil carbon. In relation to the former, once you re-establish appropriate vegetation cover, increased transpiration leads to improved rainfall, which in turn stimulate soil biodiversity. This is needed to build soil carbon. As Schwartz points out, fixing the water cycles will also start the process of fixing the carbon cycle, and vice versa.