At lunchtime on a wintry weekday, a bone-chilling southerly wind rips through the streets around Cathedral Square. This is the heart of Christchurch, a coastal city of 350,000 people.

A few tourists brave the cold to snap pictures of the ruined gothic-style cathedral which gives the square its name, but apart from that, it's eerily empty. There's simply not much here.

It has been four years since a 7.1 magnitude earthquake struck early on September 4, 2010. Despite the strong shaking, there was no loss of life. The bigger disaster came on February 22, 2011, when a violent 6.3 magnitude earthquake hit, killing 185 people.

About 80 percent of the buildings in the city center had to be demolished.

The climate challenge

Lyttelton Timeball Station was among buildings damaged in June 2011

While demolition has given way to reconstruction, Christchurch is still far from rebuilt. But the earthquake recovery is not the only challenge facing this low-lying, riverside city, much of which was established on a series of swamps and wetlands drained by European settlers from the 1850s.

Here in Christchurch, the effects of climate change have been fast-forwarded says Christchurch City Council's natural environment and heritage manager Helen Beaumont:

"The earthquakes have given us 100 years of climate change within two or three years. Not only have they lowered the land but they have changed the way that our rivers work. With the liquefaction [when sandy ground is turned to liquid by shaking], the river channels have narrowed, there's reduced capacity in those channels and that is exacerbating the flooding issues across the city," Beaumont told DW.

As a result of the earthquakes, the land across the city has sunk or settled in some areas half a meter (1 foot), and other areas 200-300 millimeters (6-9 inches). In certain areas, especially near the rivers, the land settlement has been more extreme.

While Christchurch has always been vulnerable to flooding, it's becoming increasingly common. The city has experienced three major floods this year alone.

"With climate change it's not only sea level rise, it is that intensity of storm events that is predicted to increase and perhaps Christchurch has seen that in the last year. It will be the meteorologists and climate change scientists who will tell us if what we have seen is just a quirk or if what we have seen is a sign of what's to come," Beaumont says.

Nonetheless, Beaumont says the rebuilding process has brought an opportunity to prepare for climate change.

"So we're looking and planning for much more intense rainfall events. We are protecting pond areas for storm water and rainwater further up in our catchments and protecting the built-up areas of the city."

In Christchurch, urban "holes" are plentiful where buildings once stood

Water from all directions

Residents in some parts of Christchurch are now anxious every time it rains.

Hugo Kristinsson lives in the suburb of South New Brighton, a thin finger of land between the ocean and estuary of the city's two main rivers, the Avon/Otakaro and the Heathcote/Opawaho. Floodwaters frequently creep up to the boundaries of his property, which he says has sunk significantly since the earthquakes.

"It's very stressful because of the fact that we are now behind a flood bank which gives us a little small buffer but if we have a combination of a low pressure zone and a significant rain event there is a very high probability that the water will exceed the height of the flood banks and that will generate flash flooding," Kristinsson told DW, adding that despite having enjoyed his scenic home for the past 19 years, he now wants to move on.

"Ideally we want to move to higher ground because we cannot see any future in staying when you see the bulk of water which we can see here through the windows it's highly concerning. Every significant rain event - this is nerve-wracking."

Kristinsson says he knew rising seas would one day claim his home, but he did not imagine it would be in his lifetime.

The memory of the Christchurch earthquakes was still fresh two years later for families who lost loved ones

Climate change on fast-forward

As well as fast-forwarding the effects of climate change, the earthquakes have also given Christchurch a unique opportunity to move get step ahead.

According to a report conducted for the city council by engineering firm Tonkin and Taylor, the city needs to prepare for a sea-level rise of at least one meter in the next 100 years. The report proposed a "managed retreat" from vulnerable areas. Because of the earthquakes, a retreat has already started.

Along the Avon River between the city center and the coast is 450 hectares of land – the largest of the areas which the New Zealand government decided were so badly earthquake-damaged, that houses couldn't be rebuilt there any time soon. The government called the areas 'red zones' and made residents an offer to buy them out, at a cost to the government of about $1.2 billion US dollars (950 million euros).

"Most of the residents have taken up that offer and a lot of that land is susceptible to increased tidal flooding. So that's given us an advantage in that we may have had to retreat from some of that land in the next 50 years but now we've got this opportunity to clear that land and use it more sensibly in the future," Beaumont explains.

The earthquakes also left behind a painful psychological legacy

The government's specially-created Canterbury Earthquake Recovery Authority (CERA) reports that more than 5,000 of about 7,000 red-zoned homes have already been demolished. A public consultation process is planned to help decide what to do with the red-zoned land.

The Avon-Otakaro Network community group is campaigning for the land along the river to become an ecological reserve, to create something positive from the painful experience of residents who had to leave their homes.

"The desire from the communities is to return the land to its natural habitat," the Network's co-chair Evan Smith told DW.

What will indeed happen with that land is the government's decision - after all, the government now owns it.

More than retreating

However, a sustainable rebuild isn't just about moving people off vulnerable land. The council's Helen Beaumont points to the need to build energy efficient buildings to replace those which were demolished.

She says the council is leading by example with its own facilities while providing advice and incentives to others, but it can be a challenge getting through the message of thinking about long-term sustainability issues when people are more concerned about rebuilding quickly. Still, Beaumont believes the council's efforts are making a difference.

"Even a basic brand new building today is going to be better than a lot of the buildings, which were destroyed through the earthquakes, because they were old very inefficient buildings," she said.

Community advocate Evan Smith gives the city a five out of 10 for its overall effort to rebuild sustainably.

"On the negative side, we still have to rebuild with our insurance monies. There is little opportunity with those insurance receipts to actually improve on what we've got unless it actually creates savings in the short term," he says, pointing out areas where the city may be missing opportunities to become more climate-change resilient. "When we have had to build a lot of new homes we have tended to do that in a way that just increased urban sprawl rather than look at medium density, more intensified levels of housing," he says.

Insurance money is paying for much of the rebuild

Not red zoned, still vulnerable

Perhaps the biggest issue is what the future holds for Christchurch residents whose land is vulnerable to flooding perhaps because of the earthquakes, but hasn't been red-zoned. Kristinsson, whose land was not red-zoned, says he's in limbo waiting for answers from authorities and insurers.

"It is like being in captivity, you can't do anything, I can't maintain the house, I can't plan, it's pretty pointless in maintaining the garden, that is just falling by the wayside... we have got nothing but uncertainty."

Despite this uncertainty, it's clear that after four years of hardship caused by the earthquakes, the people of Christchurch still have a strong desire to rebuild a sustainable city – a city which could be a positive example for the rest of the world as it faces the challenges of climate change.