The Tropical Storm Harvey in the Unites States and the monsoon in South Asia have again shown how dangerous and destructive floodwaters can be.

　　More than 1,200 people have died across India, Bangladesh and Nepal as a result of flooding. In the American state of Texas, more than 40 people have died and at least 30,000 have been displaced.

　　These are the latest examples of powerful storms striking heavily populated areas, followed by extreme flooding. But storms alone are not the only cause of flooding.

　　Increasing development has been blamed for taking away natural drainage areas that used to limit flooding in cities.

　　The latest U.S. flooding following Hurricane Harvey was in Houston, Texas, America's fourth largest city. Areas around Houston have been hit with serious storm-caused flooding in the past, the last time in April 2016.

　　At the time, scientists and experts blamed the flooding on continued growth across the city, according to the Texas Tribune. They called on officials to pass laws limiting developers from paving land that used to take in large amounts of rainwater.

　　G.K. Bhat is head of the think tank Taru Leading Edge. On the flooding in India, he said "In a normal ground outside the city, nearly 80 percent of the rain would have got absorbed... with concrete and tarmac all around, we are creating almost a near-total impervious area. Thus, the flood gets amplified in urban areas."

　　Rising sea levels

　　Another big concern is rising sea levels that are predicted to put major areas of the world under water in coming decades.

　　Numerous scientific studies have confirmed that global sea levels began rising in the 19th century. The levels increased 14-17 centimeters during the 20th century and just keep rising.

　　In July, hundreds of scientists from around the world gathered in New York City for a major conference to examine sea-level rise. The conference was organized by the not-for-profit World Climate Research Programme, with support from the United Nations, the U.S. Space Agency NASA and other organizations.

　　In its closing statement, the group said global sea levels are currently rising at a rate of about 30 centimeters per century. The group predicted that if climate conditions stay the same, world sea levels could rise one meter or more throughout the 21st century, possibly reaching several meters by 2300.

　　A recent report by a group that analyzes climate changes in the Arctic said the area is currently warming faster than anywhere else on earth. The Arctic Monitoring and Assessment Programme said melting ice in the Arctic currently causes about 35 percent of global sea-level rise. Over a period of decades, experts say rising sea levels worldwide could cause disastrous flooding conditions.

　　Numerous U.S. communities face this same threat. Many coastal areas already experience regular flooding problems, according to the Washington-based Union of Concerned Scientists.

　　Erika Spanger-Siegfried is a senior analyst with the organization's Climate and Energy Program. She oversaw two reports that identified areas across the U.S. experiencing what the group calls chronic inundation. It defines this as flooding that prevents people or businesses from carrying out normal daily activities.

　　"What we see just in the next couple of decades is the expansion of areas that are chronically inundated to other currently unaffected parts of the coast. And really, mid-century and beyond is when we start to see major metropolitan areas affected by this chronic inundation as well."

　　What are the solutions?

　　Spanger-Siegfried suggested three main possible solutions to fight rising sea levels. The first is to build seawalls or levees. The second is to build homes elevated or create waterways to carry floodwaters. The third would be for people to relocate to areas not threatened by flooding. She says communities will likely use a combination of these methods in the short term.

　　"It is human nature to reach for defensive measures and to try and simply keep the water out and keep, maintain things as they are within communities, which is fully understandable."

　　Michael Bogin is a New York environmental lawyer. He told VOA that the US government under President Barack Obama had taken steps to give local officials more power to regulate development as a way to prevent flooding.

　　Bogin said one idea to deal with the problem is for governments to buy land from homeowners in areas with a high flood risk.

　　Such a program was used in Staten Island, New York, after Hurricane Sandy caused widespread damage in the area. Owners of destroyed or damaged homes were made offers to sell the property to the state. Buyers of the property were then required to follow post-Sandy flood rules when building new homes.

　　But Bogin says clearly that's not going to be a complete solution for cities with populations of four, six or eight million people, like New York or Houston.

　　He added that in New York City, officials have explored the building of more environment-friendly infrastructure. The idea is to take areas that have been paved over and turn them back into natural land areas that can take in extra water during floods.

　　I'm Bryan Lynn.

　　Bryan Lynn reported this story for VOA Learning English. Hai Do was the editor.

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