The evidence is compelling that our climate is changing.
www.climatechange.govt.nz/
Weather is getting more variable, with more storms and extreme weather like unseasonal heat waves or snowfalls. But overall it’s getting warmer and drier. This is the effect of global warming.
GLOBAL WARMING
The argument is no longer whether the world’s climate is getting warmer, but why and how quickly. Most scientists agree that it’s caused by human effects on the environment, in particular too much greenhouse gases. Others say it’s a natural short-term cycle and that it’ll get wetter again in twenty years or so. Or maybe ten years. Or maybe …
No one knows for sure. But as far as Canterbury’s water is concerned, it makes no difference who’s right or wrong. The fact remains that we are running out of water. There’s none to spare for further development without massive environmental impact. And already the environment is badly degraded from all the development that has taken place. It’s time to call a halt to further development that uses huge amounts of water and generates pollution.
DRIER CLIMATE - ANOTHER 'DOUBLE WHAMMY'
The biggest allocations of irrigation water in Canterbury have been made during the last 20 years. Many water rights have been issued for a 35-year period.
Unfortunately it now appears these allocations were based on optimistic forecasting of high mountain rainfall and river flows. More recent studies by the National Institute of Marine and Freshwater Research Ltd (NIWA) suggest the estimates were too high. But Water Rights Trust is not aware of any plans by ECan to review these consents.
This is another ‘double whammy’. If the climate gets drier, farmers who irrigate will need more water. But there may also be less rainfall, which means less water available.
If irrigation is already unsustainable, how much worse will it get in the future? Especially if irrigated farming keeps on the way it’s growing?
LESS RECHARGE
If there’s less rain falling, there is less water to soak into the ground and replenish the aquifers. The supply of water from under the ground will get smaller.
But there is more to it than that. To understand how aquifers get recharged, lets look at how aquifers work.
Cross Section through part of the Canterbury Plains Groundwater System (click image to enlarge)
You can see that aquifers can be quite complex. After many years of studying Canterbury’s aquifers, scientists still don’t quite know how they all work. They don’t know exactly where the recharge water comes from. Does it soak through from river beds or from rain falling in the foothills? They don’t know how the different aquifers are connected. If you draw water from one aquifer, will that affect other aquifers above and below? This means there is a lot of risk attached to taking more water out of a system we don’t fully understand. Like saltwater intrusion.
SALTWATER INTRUSION
The aquifers under Canterbury don’t just end at the shore. They extend out under the sea where they end in underwater springs. Or they used to. Now too much water’s being sucked out before it can get to the sea. Salt water is starting to back up into the aquifers. We could end up with salt in our drinking water if this gets worse.
WATER STORAGE - THE WAY OF THE FUTURE?'
Water storage schemes have been suggested as a solution to the problem of irrigation water supply. When rivers are running very high during floods, some water could be run off and stored in artificial lakes. Then, when rivers are low, no water would need to be taken. If enough water was stored, there would be no need to take so much from wells. The Central Plains Water scheme is an example that has been proposed in Canterbury.
But the idea of water storage schemes is to increase the amount of land that can be irrigated and intensively farmed. Which means more dairy farms.
As we’ve already seen, the problem isn’t just the question of where the water is to come from. Taking floodwater out of our rivers may in itself be sustainable, but there is no guarantee that the water will be used sustainably. More intensive farming will mean more pollution and there aren’t safeguards against this.
There may be another problem with ‘harvesting’ floodwater. There is evidence that floods play a major role in recharging aquifers, by spreading the water out widely where it soaks quickly and deeply into the ground. If we start reducing the size of our rivers when they flood, we may lose much of what we gain.
