Venice Mayor Luigi Brugnaro says his city is "on its knees" after facing an unprecedented flooding event this month.

Key points: Venice is composed of more than 100 small islands surrounded by a sea water lagoon

Venice is composed of more than 100 small islands surrounded by a sea water lagoon The sea level around Venice is rising while the city's foundations are also sinking

The sea level around Venice is rising while the city's foundations are also sinking The city is expected to experience more extreme flooding events in coming years

Water levels rose above 1.5 metres three times in a single week. It had never risen to that level even twice in a single year.

While the damage was still being assessed, there were fears there could be irreparable damage to some of Venice's historic treasures.

The famed Saint Mark's Basilica was flooded for just the sixth time in 1,200 years, but the fourth time in the past two decades.

The haunting sirens that warn Venetians of the acqua alta, or high waters, are becoming more frequent.

Mr Brugnaro has blamed climate change, saying Venice is "in the trenches" in the fight against rising tides. But is there more to Venice's woes, and is climate change entirely to blame?

What causes the Venetian lagoon to flood?

Venice's geography makes it susceptible to flooding and severe weather. ( Wikimedia Commons: Didier Descouens )

Venice is composed of more than 100 small islands surrounded by a sea water lagoon that is protected by a group of longer islands, known as the 'barene', with several narrow channels open to the Adriatic Sea.

This makes it especially susceptible to flooding and severe weather.

A key climatic factor that contributes to the lagoon flooding starts way down in North Africa.

Winds — known as the Scirocco in Italian — that form over the hot Sahara desert push up into the Mediterranean.

Venice is expected to experience more extreme flooding events in the years to come. ( REUTERS: Manuel Silvestri )

These mix with cooler oceanic air, and thrust powerful winds up into Southern Europe.

As they blow up the Adriatic Sea, they can sometimes combine with cooler winds coming from Eastern Europe that bear down on the Venetian lagoon.

When these winds — which peak in March and November — coincide with high tides, they can prevent water from flowing out of the lagoon.

If the winds are persistent, another high tide can enter the lagoon, accumulating even more water as Venice saw earlier this month.

Flooding usually happens when a high tide — exacerbated by a full moon or extreme weather — coincides with a rain event.

Is climate change to blame?

Venice faced an unprecedented flooding event this month. ( ABC News: GFX/Jarrod Fankhauser )

The sea level around Venice is rising; according to the city's tide monitoring service, the ocean is an estimated 26 centimetres higher than it was in 1870, an effect partly attributed to climate change.

Built on mud and marshland, the city's foundations are also sinking into the lagoon, a phenomenon made worse by decades of industry pumping water out of an aquifer beneath Venice until they were banned in the 1970s.

The 20th century was also a period of rapid industrialisation around the city; ports were constructed along the mainland and channels deepened and widened to allow larger ships to dock.

These manmade structures are thought to have disrupted and impeded the natural flow of water in and out the lagoon, possibly exacerbating high-tide events.

Can a failed project be revived to save the city?

The MOSE project involves building retractable sea walls along key points of the lagoon to prevent high tides. ( Reuters: Manuel Silvestri )

Venice is expected to experience more extreme flooding events in the years to come and the city is divided over what to do about it.

First proposed in 1988, a project dubbed MOSE — an acronym for Experimental Electromechanical Module, but also fittingly the Italian word for Moses — involves building retractable sea walls along key points of the lagoon to prevent high tides.

But it has been plagued by cost blowouts and corruption allegations that saw Venice's last mayor arrested and charged alongside a slew of other officials back in 2014.

It is not yet operational and is not expected to be until at least 2022.

It is little wonder many Venetians are cynical about the prospects of MOSE being their saviour.

Nonetheless the Italian Prime Minister Guiseppe Conte has vowed to complete the troubled project after touring Venice during the floods.

Mayor Luigi Brugnaro is also making a desperate bid to bring scientists to Venice to understand what is happening.

"We need scientists here, they need to come here and create a permanent place where they can study what is happening here, because of climate change, with all its effects … Venice is a frontier," he said.

For now, tourists continue to flock to Venice in their millions.

It is a city that has survived plagues, wars and destruction in the past, and is now under threat from mass tourism and a declining population.

The threat of extreme flooding may one day become an existential question for Venice, but for now, the city is scrambling for solutions.