Farmed fish dying, grape harvest weeks early – just some of the effects of last summer’s heatwave in NZ

Queensland groper, typical of coral reefs off Queensland at 27°S were found in the Bay of Islands, north of Auckland, at 35°S.
from http://www.shutterstock.com, CC BY-ND

Jim Salinger, University of Tasmania and James Renwick, Victoria University of Wellington

As the Australian heatwave is spilling across the Tasman and pushing up temperatures in New Zealand, we take a look at the conditions that caused a similar event last year and the impacts it had.

Last summer’s heatwave gave New Zealand its warmest summer and the warmest January on record. It covered an area of four million square kilometres (comparable to the Indian subcontinent), including the land, the eastern Tasman Sea and the Pacific east of New Zealand to the Chatham Islands.

In our research, we looked at what happened and why, and found that the heatwave affected many sectors, leading to early grape harvests and killing farmed fish in parts of the country.

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Drivers of warmer than average conditions

We used a combination of land and ocean temperature observations, large-scale analyses of the atmospheric circulation, and ocean modelling to understand the drivers of the 2017/18 summer heatwave. It was memorable for a number of extreme events and statistics.

The average air temperature was 2.2°C above the 1981-2010 normal of 16.7°C, and it was the warmest summer ever recorded in more than 150 years. The number of extreme warm days and warm nights was also the highest recorded, going back several decades.

The peak month was January 2018, 3.2°C above normal and the warmest month recorded in observations as far back as 1867. Ocean surface temperatures were similarly extreme, with a marine heatwave that lasted about five months, at 2.0°C above normal at its peak.

The combined New Zealand annual land and sea surface temperature record, in °C, from 1867 to 2018, compared with the 1981-2010 average. The blue bars represent individual years, and the red line trends over groups of years.
Jim Salinger, CC BY-ND

The warming was mostly the result of very settled conditions over the country, especially to the east, bringing light winds, plenty of sun, and warm air from the subtropics. Such conditions in summer are associated with the positive phase of a polar ring of climate variability known as the Southern Annular Mode (SAM), which brings high pressures (anticyclones) to New Zealand and parts of other southern hemisphere countries in the mid-latitudes, including southern Australia and Tasmania, southern Chile and Argentina.

The SAM was strongly positive throughout last summer, especially in January, and weak La Niña conditions were prevalent in the tropics. The light winds in the New Zealand region allowed the ocean surface to warm rapidly, without the usual turbulent mixing to transport the heat away. The warmest waters in the Tasman Sea formed an unusually thin layer near the surface.

Impacts and repercussions

New Zealand was affected by more than its normal share of ex-tropical cyclones, notably Fehi and Gita. They brought strong winds, storm surges and heavy rainfalls that caused flooding as they passed through. The warm ocean waters around New Zealand would have helped maintain the intensity of the storms and supply moisture to drive the heavy downpours.

The warm conditions caused massive ice loss in South Island glaciers, estimated to be the largest annual loss of glacier ice in nearly 60 years of records for the Southern Alps. Satellite data from end-of-summer snowline measurements at the Tasman Glacier suggest that the Southern Alps lost 9% of glacier ice during last summer alone.

The Franz Josef glacier on New Zealand’s West Coast advanced during the 1980s and 1990s but is now retreating.
Andrew Lorrey/NIWA, CC BY-ND

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A bird’s eye view of New Zealand’s changing glaciers

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Warm air temperatures had a marked effect on managed and natural ecosystems. The Marlborough grape harvest was unusually early in 2018, two to three weeks ahead of the normal maturation time. Marine ecosystems were significantly disrupted. Coastal kelp forests struggled to grow in the warm sea. In southern New Zealand, the temperature threshold was breached three times, resulting in substantial losses of kelp canopies.

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For the first time, Atlantic salmon had to be imported as farmed fish died in salmon farms in the Marlborough Sounds. Commercial fishers reported that snapper was spawning approximately six weeks early off the South Island coast, and Queensland groper was reported in northern New Zealand, 3000km out of range.

Past and future

The summer of 2017/18 shared some characteristics with another hot summer, way back in 1934/35. That season was so warm that it prompted a special report by the New Zealand Meteorological Service. Conditions were similar: persistent high-pressure systems in the New Zealand region, positive SAM conditions, light winds over and around New Zealand, warm ocean surface and air temperatures. While those two summers shared some natural variations in the local climate, the recent summer was warmer for two reasons.

First, climate in the region is now more than half a degree warmer now than in the 1930s. Second, the SAM has been trending towards its positive phase over the last few decades, making settled conditions over New Zealand more frequent now than in the 1930s. That trend is mostly related to the ozone hole that occurs in spring and early summer, cooling the polar atmosphere and driving the strongest winds farther south towards Antarctica, leaving lighter winds and higher pressures over New Zealand.

Looking to the future, we can compare the conditions experienced in 2017/18 with what climate models predict for the future. We estimate that the extreme warm conditions of New Zealand’s last summer would be typical summer conditions by the end of the century, for an emissions scenario associated with a couple of degrees of global warming above pre-industrial temperatures. If emissions keep increasing as they have done in recent years, last summer will seem cool by the standards of 2100.

Jim Salinger, Honorary Associate, Tasmanian Institute for Agriculture, University of Tasmania and James Renwick, Professor, Physical Geography (climate science), Victoria University of Wellington

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Damning royal commission report leaves no doubt that we all lose if the Murray-Darling Basin Plan fails

Jamie Pittock, Australian National University

In the wake of revelations of water theft, fish kills, and towns running out of water, the South Australian Royal Commission into the Murray-Darling Basin has reported that the Basin Plan must be strengthened if there is to be any hope of saving the river system, and the communities along it, from a bleak future.

Evidence uncovered by the Royal Commission showed systemic failures in the implementation of the Murray-Darling Basin Plan. The damning report must trigger action by all governments and bodies involved in managing the basin.

The Basin Plan was adopted in 2012 to address overallocation of water to irrigated farming at the expense of the environment, river towns, Traditional Owners, and the pastoral and tourism industries.

The Commission has made 111 findings and 44 recommendations that accuse federal agencies of maladministration, and challenge key policies that were pursued in implementing the plan.

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Aboriginal voices are missing from the Murray-Darling Basin crisis

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What did the report find?

The commission found that the Basin Plan breached federal water laws by applying a “triple bottom line” trade-off of environmental and socioeconomic values, rather than prioritising environmental sustainability and then optimising socio-economic outcomes.

I and my colleagues in the Wentworth Group of Concerned Scientists provided evidence to the commission from our independent assessment of the Basin Plan in 2017, which the commission’s findings reflect.

Contrary to current government practices, the Commission recommendations include:

• prioritising environmental sustainability
• basing the plan on transparent science
• acquiring more water for the environment through direct purchase from farmers
• meeting the water needs of the Basin’s 40 Indigenous nations
• ensuring that state governments produce competent subsidiary plans and comply with agreements to remove constraints to inundating floodplain wetlands
• addressing the impacts of climate change
• improving monitoring and compliance of Basin Plan implementation.

Resilience in decline

The Murray-Darling Basin is not just a food bowl. It is a living ecosystem that depends on interconnected natural resources. It also underpins the livelihoods of 2.6 million people and agricultural production worth more than A$24 billion.

The continued health of the basin and its economy depends on a healthy river – which in turns means healthy water flows. Like much of Australia, the Murray-Darling Basin is subject to periods of “droughts and flooding rains”. But over the past century the extraction of water, especially for irrigation, has reduced river flows to a point at which the natural system can no longer recover from these extremes.

That lack of resilience is evidenced by the current Darling River fish kills. More broadly, overextraction risks the health of the entire basin, and its capacity to sustain productive regional economies for future generations.

From the perspective of the Wentworth Group, we support the commission’s main recommendations, including increasing pressure on recalcitrant state governments to responsibly deliver their elements of the plan, and to refocus on the health of the river.

We particularly support recommendations related to the use of the best available science in decision-making, including for managing declining water availability under a changing climate.

We welcome the recommendation to reassess the sustainable levels of water extraction so as to comply with the Commonwealth Water Act. These must be constructed with a primary focus on the environment.

In line with this, the 70 billion litre reduction in environmental water from the northern basin adopted by parliament in 2018 should be immediately repealed. So should the ban on direct buyback of water from farmers for the environment.

We also recognise that the Basin Plan’s water recovery target is insufficient to restore health to the environment and prevent further damage, and would welcome an increase in the target above 3,200 billion litres.

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A good plan to help Darling River fish recover exists, so let’s get on with it

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South Australian Premier Steven Marshall has taken a welcome first step in calling for a Council of Australian Governments meeting to discuss the commission’s findings. Our governments need to avoid the temptation to legislate away the politically inconvenient failings exposed by the commission, and instead act constructively and implement its recommendations.

This is not only a challenge for the current conservative federal government. The Labor side of politics needs to address its legacy in establishing the Murray-Darling Basin Authority and the Basin Plan, as well as the Victorian government’s role in frustrating the plan’s implementation by failing to remove constraints to environmental water flows.

Now, more than ever, we need strong leadership. If the Murray-Darling Basin Plan fails, we all lose.

Jamie Pittock, Professor, Fenner School of Environment & Society, Australian National University

This article is republished from The Conversation under a Creative Commons license. Read the original article.