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Rainfall

What

Rain is vital for life: our drinking water, our agriculture, our energy, our recreation, and our environment all rely on it.

Between now and the end of the century, the effect of climate change on rainfall in Canterbury/Waitaha is expected to vary, with different impacts depending on where in our region you are.

Exactly how our rainfall will change is less certain than for other impacts resulting from climate change such as temperature, and changes are expected to be seasonal rather than year-round. However, NIWA projections suggest that by 2090, if we don’t take action to curb greenhouse gas emissions, Banks Peninsula and our traditionally dry inland areas are expected to become drier, with 5% to 15% less rain.

On the other hand, winters could be wetter in some eastern, western and southern parts of Canterbury, with between 15% and 40% more rain.

The combination of drier summers and wetter winters could have real impacts on our environment and our economy.

Impacts

Canterbury’s diverse mahinga kai is at risk from changes in rainfall and the frequency of storm events. Likewise, warmer air and water temperatures can impact lake, freshwater, and coastal habitats.

Summer droughts significantly affect our water race network, which is thousands of kilometres long and supplied by rainfall, snowmelt, rivers, and springs. Some communities rely on these networks for irrigation, supplying water to stock animals and for fighting fires. Water races also serve as storm water drainage and are vulnerable to flooding during heavy rain.

In areas expected to have an increase in annual rainfall, rainwater can be collected by households for drinking water, reducing pressure on other sources.

Increasingly waterlogged soils can delay crop planting and cause significant crop damage, resulting in shortages, and therefore price increases, in our stores.

Māori have a special connection to freshwater, and freshwater bodies have their own mauri and identity. The availability and security of freshwater is affected by rainfall, and the mauri of waterways could be impacted by changes in river flow, increased water temperature, and more sediment.

Reduced snowfall has consequences for our mountain playgrounds, and flow-on tourism and environmental effects. In 2020, for instance, snow depths were roughly half that of a normal season, and several ski areas delayed opening or did not open at all.

Our special alpine tarns may become degraded, with habitat loss for alpine flora and fauna.

Increases in rainfall and warmer temperatures could change both the growing season and farming practices, while in areas where higher flows are projected, higher flowing rivers could improve irrigation and water storage.

Changes in annual rainfall, as well as drought and sea level rise, puts our groundwater, lakes, and rivers at extreme risk. If groundwater and surface water aren’t recharged by rainfall, there are flow-on impacts for agriculture and horticulture.

A longer, drier summer season in our inland areas and Banks Peninsula may bring economic benefits by way of increased tourism and different agricultural opportunities.

Our primary sector is predicted to be subject to ‘major impacts by 2050 and extreme impacts within a century’ if action is not taken now, due to changes in rainfall and temperature, seasonality, weather extremes and increased invasive species.

We are expecting more distinct seasonal changes in rainfall, bringing significantly more rain for some areas, and significantly less for others. The changes in river flows that follow put our freshwater biodiversity at major risk. When combined with higher air and water temperatures, habitats can be lost or degraded by lakes forming distinct layers of warmer and cooler water, and increased frequency of algal blooms.

More rain, coupled with warmer weather, encourages the beech trees in our high country to produce more seeds, known as a mast event. The increased food supply for predators rapidly increases their numbers, with drastic consequences for their other food source - our native birds and taonga species.