Climate extremes put millions of people living in port cities, some of which are also included among the largest cities of the world, at increasing risk. Storm-surge flooding, damaging high winds, rising sea level and local land subsidence threaten large cities’ populations as well as billions of assets. An ongoing study being conducted by the Organization of Economic Cooperation and Development (OECD) ranks port cities according to exposure and vulnerability to such climate extremes, as reported by Bloomberg News via the Environmental Health News.

Port cities are thriving today, constituting more than half of the world’s largest cities. Many of these are already exposed to challenges like coastal flooding and rising seas. The study focused on 136 port cities that have populations exceeding one million in 2005. The study also assessed how each port city is likely to be impacted by increased risk of coastal flooding due to climate change by 2070.

Findings show that about 40 million people are already vulnerable to 1 in 100 year coastal flood event. Cities that are at most risk are shown to be almost equally divided between developed, wealthy nations and developing nations. Based on populations at risk, the top ten cities were predominantly those in Asian regions like Mumbai, Osaka-Kobe, Shanghai, and Ho Chi Minh. In terms of assets at risk, cities in developed countries rose to the top of the list likeMiami,Amsterdam, and Tokyo as wealth of the cities became crucial in calculation. Three wealthy nations (the USA, Japan, and the Netherlands) contained 60% of the total exposure in terms of assets.

The top 20 cities at risk from climate change extremes are:

Alexandria, Egypt – this city flourishing by the Nile Delta ranks least among the top 20, but by 2070 Alexandria’s population at risk are estimated to be at 4.4 million, with an estimated $563.3 billion in assets at risk.

Virginia Beach, U.S. – intensifying Atlantic hurricanes, coastal inundation, and shoreline retreat will put estimated $581.7 billion assets and 794,000 people at risk by 2070 in this area.

Qingdao, China – according to OECD’s study, Qingdao might have the highest proportional increase in population at risk from climate change extremes, Bloomberg reports. Estimated 2070 population at risk: 1.9 million; assets: $601.6 billion.

Nagoya, Japan – has a history of vulnerability and exposure to extreme weather, as when over 3,000 people were killed in a 1959 typhoon. Estimated 2070 population at risk: 1.3 million; assets: $623.4 billion.

Ho Chi Minh, Vietnam – a city that is barely above sea level, Ho Chi Minh is especially vulnerable to risks from climate extremes. Estimated 2070 population at risk: 9.2 million; assets: $652.8 billion.

Rotterdam, the Netherlands – Bloomberg mentions an aside about the Netherlands’ name, which has the original meaning of “lower lands”. The city is already working to address its climate change risks by upgrading infrastructure and flood security measures. Estimated 2070 population at risk: 1.4 million; assets: $825.7 billion.

Amsterdam, the Netherlands – has a history of flood control measures attesting to its vulnerability to climate change extremes. Projected climate change effects are expected to be a significant challenge to cities like Amsterdam. Estimated 2070 population at risk: 1.4 million; assets: $843.7billion.

Osaka-Kobe, Japan – vulnerability to climate change extremes are worsened by land subsidence partly due to groundwater pumping. Estimated 2070 population at risk: 2 million; assets: $969 billion.

New Orleans, Louisiana, U.S. – local land subsidence continues to add to the risk of flooding from climate change extremes. Estimated 2070 population at risk: 1.4 million; assets: $1 trillion.

Ningbo, China – Bloomberg reports that Ningbo might have the highest proportional increase in assets at risk from climate change extremes according to OECD’s report. Estimated 2070 population at risk: 3.3 million; assets: $1.1 trillion

Bangkok, Thailand – monsoon flooding continues to putBangkok’s thriving auto and technological industries at risk, with floods in July 2011 causing billions in damage. Estimated 2070 population at risk: 5.1 million; assets: $1.1 trillion.

Hong Kong, China– with 450 miles of coastline and 19 sq. mi of water in its territory, an estimated 687,000 people and $1.2 trillion in assets by 2070 are at risk.

Tokyo, Japan – has overtaken security measures against flooding by other wealthy cities, according to the study. Estimated 2070 population at risk: 2.5 million; assets: $1.2 trillion.

Tianjin, China – is exposed to dangers from severe flooding, putting an estimated 3.8 million people and $1.2 trillion in assets by 2070.

Mumbai, India –India’s entertainment and commercial capital is vulnerable to annual monsoon flooding. Estimated 2070 population at risk: 11.4 million; assets: $1.6 trillion.

Shanghai, China – heavy storms in 1997 flooded over 170 roads and cost Shanghai millions in economic losses. The city established flood security measures in the last decade. Estimated 2070 population at risk: 5.5 million; assets: $1.8 trillion.

Kolkata, India – Bloomberg reports that Kolkata has the third highest GDP among Indian cities, but remains vulnerable to annual flooding during rainy seasons. Estimated 2070 population at risk: 14 million; assets: $2 trillion.

New York and Newark, U.S. –New York lags behind Amsterdam, Tokyo, London, and Shanghai in flood security measures, though it ranks as the second wealthiest city on the study’s list. Estimated 2070 population at risk: 2.9 million; assets: $2.1 trillion.

Guangzhou, China – over $500 million in damages due to recent “meteorologically unusual,” heavily damaging storms exposed this wealthy city’s vulnerability to climate extremes. Estimated 2070 population at risk: 10.3 million; assets: $3.4 trillion.

Miami, Florida, U.S. – Bloomberg describes southeast Florida as being on the “front line of climate change,” at risk from rising sea levels due to warming temperatures. Miami tops the list with an estimated 4.8 million population and $3.51 trillion in assets at risk by 2070.