Heavy rainfall events will likely increase. Photo / Peter de Graaf
Heavy rainfall events will likely increase. Photo / Peter de Graaf
Climate change is a big part of the conversation at the moment but it is easy to be overwhelmed and switch off. Over the next week, reporter Julia Czerwonatis takes an in-depth look at what it means for Northland, what the issues are, how you can make a difference and how the future is shaping up. Today we look at the science and Niwa's prediction for Northland.
Predicting the changes to our climate is highly complex and depends on many variables.
Mitigation measures that nations, organisations and individuals pledge to can change the outcome for the next 100 years and on.
For now, there are few guarantees but one is that the climate is changing.
Not everyone on the planet will experience the same changes, with some areas being more or differently affected than others.
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IPCC has developed a modelling system that includes four different scenarios called Representative Concentration Pathways (RCPs) that take into account different global mitigation strategies.
These range from a low-impact scenario, RCP 2.6, which assumes we'll have a low concentration of greenhouse gases in the atmosphere to a high-impact scenario, RCP 8.5, which assumes humans continue to produce the same amount or more emissions than they currently do.
In 2016 the National Institute of Water and Atmospheric Research (Niwa) compiled an extensive research paper analysing possible implications of climate change for Northland.
Niwa climate scientist Gregor Macara explains that RCPs have been put forward for what the future concentration of greenhouse gases might look like in the atmosphere.
"Greenhouse gases are obviously driving climate change. In simple terms, as you burn more coal and emit carbon dioxide into the atmosphere and our agricultural sector emits methane it increases the concentration of greenhouse gasses. It increases the amount of warming."
Northland won't notice a significant difference in change between the scenarios toward the mid-century but "when you push beyond that the changes start to emerge".
"Changes to Northland are similar to those for the rest of the country, which is mainly the temperature rise. This will probably be more notable for the region.
"The temperature increase that we expect will be greater at the end of the century, depending on the greenhouse gas concentration in the atmosphere."
In Northland, annual warming by 2040 can reach from 0.7C (under RCP 2.6) to 1.1C (RCP 6.0 and 8.5).
By 2090, the temperature rise varies from 0.7C on the low-end, between 1.4C-1.9C in the mid-range and up to 3.1C in the high-impact scenario.
Associated with temperature rise is also an increase in hot days, which are days where the maximum temperature exceeds 25C.
Northland is currently experiencing on average 25 hot days a year, which may increase to 99 days by 2090 under RCP 8.5.
"In addition to that, your days above 30C will be increasing as well," Macara said.
"The time of year when these hot days can occur will start to expand into spring and autumn. You can think of it as a lengthening of the summer heat season."
Related to rising temperature is an increased risk of drought.
"That comes from several factors but mainly it's relating to the higher temperatures because it enables greater evaporation of moisture from the soil and vegetation."
Northland can expect an increase in drought frequency of about seven per cent for 2030-2050 and 10 per cent for 2070-2090, compared to 1980-1999 levels.
Niwa suggests that higher drought risk and warmer temperatures will see farmers and growers start relying more on subtropical plants and introducing new commercial species that are heat- and drought-tolerant.
There will be a longer growing season for crops, but higher temperatures and less water availability may lead to decreasing yields.
A lack of cold winter temperatures could also be an issue for crops such as kiwifruit, and Kikuyu is likely to become the most prevalent forage grass in Northland due to its ability to spread readily and the fact that it is heat and drought-tolerant.
Vegetation fires will become a larger issue for the region.
Meanwhile, rainfall changes are expected to be small – at least by 2040. That could increase by 2090.
"The rainfall projection lies around plus/minus five per cent of the current rainfall," Macara said.
"That's not necessarily a significant change, when from year to year you see more variables. It falls within the current climate envelope that we observe in Northland."
However, heavy rainfall events are expected to increase.
"The warmer atmosphere has an ability to store or hold more moisture in the air. Therefore, it's able to deliver heavier rainfall events."
Warmer sea surface temperatures increase the evaporation of moisture from the sea, exacerbating the heavy rainfall events.
"The atmosphere is warmer – you can effectively think of it as having more energy, so there is more capability to generate and deliver stormier events."
Macara wasn't convinced that we would get more thunderstorms but said it wasn't well understood when they occur.
Dry spells can lead to increased fire risk and issues with water supply for the entire region. Photo / John Stone
While Niwa doesn't offer much data on rising sea levels, Northland Regional Council has undertaken extensive research and mapping.
NRC reports: "Over the past 100 years, around 20cm of sea-level rise has occurred, at an average rate of 2.2mm per year in Northland. However, recent estimates of sea-level rise are up to 3.6mm per year and are expected to approach 10mm per year in coming decades."
Under RCP 8.5, we could see a rise in sea levels up to 1.5m in the next 100 years.
Rising sea levels can displace coastal communities and put significant stress on infrastructure.
Groundwater levels near the coast are set by sea level, Niwa explains in its report.
As the sea level rises, coastal groundwater levels would increase to match, resulting in a reduction in groundwater flow rates.
This change would also be associated with an increase in the salinisation of the coastal aquifers.
Northland will also be faced with a range of new biosecurity challenges as higher temperatures allow new exotic pests, weeds and diseases to establish.
While Macara said we couldn't tell what scenario we are facing, it is clear that delaying mitigation efforts beyond those in place today through 2030 is estimated to substantially increase the difficulty in obtaining a longer-term low level of greenhouse gas emissions.
New Zealand has pledged to reduce its emission by 50 per cent of our 2005 emissions by 2030.
"But we haven't done that yet, so you need to track it to see if we are meeting what our pledges say we are going to do.
"There is a certainty that we have by emissions that we have already put into the atmosphere that we are going to see increasing of temperatures for a period of years ahead of the present day. We've locked in warming," Macara said.
"We've also locked in a certain level of sea-level rise just by the fact that we've increased the concentration of greenhouse gases in the atmosphere. But it takes time for various aspects to respond. The melting of ice doesn't all happen in one day.
"The temperature increase takes a bit of time to slowly feed through the water cycle and in the end increase the sea level."
We are certainly not going to see sea levels plateauing or temperatures remaining stable.
Planning depends on the kind of project and the level of ability to accept that things may or may not be damaged, Macara says.
When preparing for the future, taking RCP 8.5 into could be a safer bet, however taking low-impact scenarios into account signals a commitment to reduce greenhouse gas emissions and gives people hope.
The series Friday: How to encourage climate action Today: Niwa scientists predict Northland's climate Tomorrow: How can we help? Wednesday: What are our councils doing? Thursday: How we can fight for climate justice Friday: How to take industry into a sustainable future Saturday: Regenerative farming and growing techniques Monday: The future generation
