Storm clouds gathering

One of the greatest impacts of climate change is likely to be on water resources, according to the Ministry for the Environment. Jolene Williams investigates. 

The long dry summer of 2013 culminated in a drought that was New Zealand’s worst in 70 years. Farmers took an immediate hit, and the Treasury estimates the drought will reduce gross domestic product this year by 0.7 per cent.

Our wildlife, too, suffered immensely. Animals, big and small, suffered severe dehydration. Plants wilted, fish floundered on dry riverbeds, and starved kiwi in Northland made headlines because they couldn’t poke their beaks into the rock-hard ground to find food.

We need healthy freshwater systems to hold together our environment and economy. And yet scientists are warning to expect more disruptions like this year’s severe drought, as we increasingly see the effects of climate change take hold.

How will a warming climate affect our water systems?

National Institute of Water and Atmospheric Research (NIWA) surface hydrologist Daniel Collins says New Zealand’s variable weather makes it difficult to identify how climate change is already affecting our systems. “We’re a small island nation with a maritime climate. We’ve got natural fluctuations and things can be too variable to disentangle the data and detect what changes may be occurring,” he says.

“But we do have some good ideas about what might happen in the future. Never exact numbers but often the direction of change and a rough estimate of how much,” he says. One of the few certainties is that rising air temperatures (some say an increase of 2.6 degrees Celsius by 2099) will alter precipitation patterns.

As the Earth’s temperature rises, so do evaporation rates. The Earth’s average temperature has risen by 1degree Celsius in the past century, with most of the increase since 1980. And though that doesn’t sound like much, that 1degree has enabled the atmosphere to hold 8 per cent more moisture.

Higher evaporation rates and less rainfall mean less water in our waterways, which means more droughts. The more moisture that’s being held in the atmosphere also means when it does rain, it’ll do so with greater intensity.

So brace yourself for more intense storms and, with it, more intense floods.

Rather than using the term, “global warming”, Collins says New Zealand’s experience is better described as an intensification of local climate processes. In essence, eastern and northern areas will become drier, while western and southern areas will become wetter. And most of the changes will occur in winter and spring.

Forest & Bird Advocacy Manager Kevin Hackwell says increased rainfall in western regions such as the West Coast could create new wetlands. Across the Southern Alps, however, some of Canterbury’s already pressured rivers are likely to experience a drop in water levels.

And that’s not all. If the international studies are anything to go by, climate change will cause snowlines and glaciers to retreat, which could impact on water flows in South Island rivers.

What effect will this have on freshwater ecosystems?

The trickle-down effects on things such as stream temperatures, soil moisture levels, micro-organisms and river flows will have repercussions for the overall health of our natural ecosystems and native water-dependent species.

However, aside from NIWA’s extensive work on river flows, there’s little research in how exactly these changes will play out in the future.

Freshwater ecologist Mike Joy says we are already seeing changes in our waterways from intensive farming and these will be exacerbated by climate change. He says in the drying regions, water temperatures will rise, sedimentation will increase and there will be less available oxygen in the water.

More intense storms will also cause more erosion and debris to enter our river channels.

None of this is good news for the 68 per cent of our native freshwater fish listed as threatened.

Rising water temperatures in particular are a “really big issue” for our native fish, Joy says. “They don’t do well in warmer temperatures, neither do our invertebrates. Mayflies, caddisflies and stoneflies are all quite sensitive to temperature, and they’re the main food supply for our native fish.”

One of the few New Zealand studies is Dennis Trolle’s 2010 PhD study of three North Island lakes. Trolle estimates the expected effects of climate change will increase the lakes’ nutrient levels, making them increasingly eutrophic and “subject to more algal blooms”.

He projected that, by 2100, nutrient levels of those three lakes would be equivalent to a 25-50 per cent increase of nutrients at current levels.

What is the effect on our wildlife?

Hackwell says there will be significant impacts for our water-dependent wildlife. For a start, there’ll be a change in habitats as the vegetation that now fringes water bodies will be replaced by species better adapted to the drier or wetter conditions. Some animals will be forced to find more suitable habitats, others may undergo genetic changes to adapt to the new conditions. It’s not a stretch to say that local extinctions are almost certain.

“Imagine the fate of the endemic Canterbury mudfish if the climate becomes drier,” Hackwell says. “Mudfish can survive without water for up to two months in the muddy ground. Much of its habitat is already being destroyed from being drained and turned into pasture. If that dries up, it could really endanger it.”

Flood events, fine sediment and nutrient levels – there are a host of factors that determine habitats. University of Waikato’s Nicholas Ling’s 2010 research expects the distribution of cool temperate freshwater fish will change as fish try to escape the warming water temperature of their current habitats, largely by heading south. If they can, that is.

What can we do?

Ideally, get every country in the world to reduce carbon emissions. Reducing emissions to stem the warming climate is not impossible, but it’s neither wise nor practical to sit around and wait for countries to act.

And though we will need to respond with smart water storage and distribution schemes, it needs to proceed with the environment in mind.

Joy is concerned that some of the mitigation proposals such as reservoirs and dams will do more harm than good.

“The backers of these dams say that more continuous flows are good for our native fish. But we actually need the peak flows to clean things up ... [In one study] of radio-tagged native fish [we found] a population of them spend the vast majority of their time in the substrate between rocks and boulders. Natural variability [in water flows] is really important to some of these species.”

Forest & Bird is already committed to fighting the impact of climate change on our freshwater resources through a range of direct and indirect initiatives. Through engagement with policy-informing groups such as the Land and Water Forum and Sustainable Dairying:

Water Accord, we are helping to guide the development of future-proof water management strategies.

Our campaign work – fighting to stop the Denniston mine, protecting Canterbury rivers, advocating for more renewable energy resources – all in some way work towards buffering

Riparian planting or regeneration is really important. It not only helps keep the nutrients and sediment out of the water, it cools the water temperature. Kevin Hackwell

But one of the main ways we contribute, according to Hackwell, is through pest-control projects.

“Pest control creates forests that are much healthier. They have healthy leaf litter, duff and humus layers that absorb more rainfall, which reduces severe flooding and resists soil erosion. These layers also release the water more slowly, which will keep waterways flowing in times of drought.”

Humus, the organic matter made out of decomposed plants, holds its own weight in water. Just 5 kilograms of extra humus per square metre can give 50,000 litres of extra water storage per hectare.

In addition, pest control to improve our forests will allow more carbon dioxide to be sucked from the atmosphere into the vegetation and eventually our soils, which will work against the build-up of climate change-causing gases.

Riparian planting is also a simple way to slow down the impacts of climate change on freshwater. “Riparian planting or regeneration is really important. It not only helps keep the nutrients and sediment out of the water, it cools the water temperature,” Hackwell says.

These aren’t the silver bullet solutions to ward off the effects of climate change. We still need bigger picture initiatives such as developing ways to reduce water used for irrigation. But it’s heartening to know we can take the matter into our own hands. We can fight climate change