Everyone remembers learning about the water cycle at school. We were all told about clouds coming over and raining. The water went down creeks and rivers into lakes and seas, where evaporation picked moisture up into the sky, where it became clouds again, endlessly ready to repeat the process.
What Miss Tyson forgot to tell us was the crucial bit about water cycle effectiveness, and what happens at the precise point where rain drops land from the sky. In particular, she forgot to mention that if the rain drop lands on land that you own or manage, you are responsible for it’s fate from that instant on.
On almost all land surfaces in the world the primary limiting factor to productivity is not the amount of rainfall received, but the effectiveness of the rainfall received. None of us can influence the amount of rain that lands on our land, but every land manager is responsible for the effectiveness of what rain does choose to fall on their land. The responsibility cannot be transferred to government, a church, or any other authority. It remains ours alone.
Effectiveness of rainfall is governed at the soil surface in two primary ways: First, on their arrival whether the raindrops go into the soil surface or run off; and second, if raindrops enter the soil, whether they are able to remain there or quickly evaporate away due to direct ‘sun to bare soil’ contact.
On arrival at the soil surface
A raindrop has to ‘choose’ its future immediately it impact with the soil surface, and it has just two choices—it will either enter the soil surface or it must run off. There are no other choices.
If the soil surface is covered in litter, and the soil surface underneath is friable and loose, and is not capped, then more of the rain will enter the soil. The water cycle is effective.
On the other hand, water cycle effectiveness is severely compromised if a raindrop moves away from its point of impact and flows into gullies, creeks and streams. Simply, when a raindrop moves from the point where it first landed it is of no further value there. Plants cannot benefit from water that is not retained!
Once the rain goes into the soil surface
The condition of the soil surface governs the degree of evaporation. If water moves into the soil but then rapidly evaporates out again, the water cycle effectiveness is diminished. A soil that is covered in a deep organic litter, like the photograph to the left, will prevent direct ‘sun to soil’ contact, thus minimising evaporation and increasing water cycle effectiveness.
A word about this photo: This property is in a 470 mm (18.8 inch) rainfall zone. It was taken on June 4, 2006, when the surrounding area was entering crisis mode, with impending drought.
The following Table is data from the official weather station at Narrandera, approximately 35 kilometres from where the photo was taken. The Table shows the actual rainfall by month (green bars), compared with the median by month (yellow bars) for the location.
Rainfall recorded at Narrandera for the period January to May 2006 was 33.1 mm, compared to the median rainfall of 125.8 mm. The actual rainfall recorded at this weather station during the full year of 2006 was 189.9 mm (7.6 inches).
The land owner concerned was able to retain his full breeding herd, and did not hand feed any animals during the year. This performance was mostly due to the effectiveness of the water cycle on the property, where every drop was retained and utilised.
Droughts and floods
Droughts and floods are the flip side of the same coin. If the water cycle is ineffective, run off is higher. Floods result when water that might have entered the soil surface does not. When water is unable to enter the soil surface and moves off the farm, the next drought has already begun. Plants cannot grow on water that isn’t there!
In a fully effective water-cycle, all the rain that falls on your land will go into the soil, and very little of the rainfall stored in the soil will be lost through evaporation. Eventually the stored water will move right through your soil profile, and you can expect to see streams and springs returning.
You achieve this glorious condition by focusing on the litter and overall condition of your soil surface. The target should be to maintain a soil surface that is covered with organic mulch (litter) every day of the year. Regrettably this notion is not yet widely accepted by either land-holders or bureaucracies, and so has rarely been achieved to date in low rainfall zones. This is a case of referring to Henry Ford's Quotation again:
Think of the soil surface as being like your skin. You know by experience, and probably instinctively as well, that losing skin cover is a painful experience. Lose enough and you will probably die. It is the same with the soil surface. Bare soil kills farm businesses stone dead.
Go here for Water cycle indicators of an effective and an ineffective water cycle
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