What's making the floods worse in Manila?

Lashed each year by typhoons and stuck with outdated drainage systems, the Philippine capital has been hit by ever-worsening floods. Population growth, inadequate infrastructure, corruption, deforestation and even trash build-up combine to exacerbate the impact. It's a trend experts expect to continue.

Here's why:

"NO EXIT FOR WATER"

Manila is located in a catch basin sandwiched between Manila Bay and Lake Laguna to the southeast. The city was built on waterways, canals and creeks that have for centuries channeled floodwaters into the sea.

But half the 40 kilometers (25 miles) of narrow waterways and canals that would drain rainwater - constructed and modified during the Spanish colonial period - have been lost, cemented or paved over, said architect and urban planner Paulo Alcazaren. Many of the remaining ones are clogged with garbage and ill-maintained, teeming with squatter colonies occupying riverbanks and coastal areas.

Much of Manila, once known as the "Pearl of the Orient," was lost in heavy bombardment at the end of World War II. The haphazard, poorly planned urban reconstruction coupled with the 10-fold jump in population to nearly 12 million today has severely strained the city's ability to cope with flooding.

The capital's flood control system is outdated, incomplete and poorly designed, said Felino Palafox, Jr., another urban architect who has closely studied flooding in Manila.

He said that starting in the 1970s, he and international development agencies had unsuccessfully called for the construction of a major spillway that would drain excess water during the typhoon season from Lake Laguna to Manila Bay. The lake has become heavily silted, decreasing its capacity to hold water and often overflows and floods outlying towns and cities, including Manila.

"There's no exit for water," Palafox said.

TYPHOONS PACKING MORE POWER:

Each year, about 20 typhoons hit the country, and they have become stronger over the past decade, said Edna Juanillo, head of the Philippine government weather agency's climatology division. That prompted the agency about a decade ago to add a fourth category to public storm warning system for typhoons with sustained winds of more than 185 kilometers per hour (115 mph).

"It has not been concluded if this is caused by global warming and climate change, but we've been seeing more powerful tropical cyclones with winds of 150 kph and above in the last decade," Juanillo said.

Four of the strongest typhoons that hit between 2008 and 2012 caused damage of $2.2 billion compared to $828 million for the four of the most devastating typhoons between 1990-1998.

The most ferocious storm to ever hit Manila was Typhoon Ketsana in 2009, which dumped more than a month's worth of rain in 12 hours with floodwaters reaching 7 meters (23 feet). That and a second typhoon on its heels killed about 1,000 people and caused more than $1 billion in damage.

Last year, the annual monsoon and thunderstorms unleashed nonstop rains over eight days, flooding the same areas again, destroying thousands of homes, roads and submerging about 90 percent of Manila.

This week's deluge, brought by a monsoon and a tropical storm, dumped about the same amount rain as Ketsana but over 24 hours and wider area, submerging half of the city and shutting it down for two days. About a million people were affected.

Excessive logging on the Sierra Madre mountains north of the city has also made things worse. The rainwater rushes down the denuded slopes into the Pasig River, which runs through Manila and typically overflows.

POLITICS, CORRUPTION AND TRASH:

Several proposals to dredge Lake Laguna failed to materialize. One such $430 million contract was signed by former President Gloria Macapagal Arroyo's government and a Belgian company but was shelved by her successor, Benigno Aquino III, on suspicion of corruption and irregularities.

Aquino has authorized a plan to relocate slums from the city's waterways to ease flooding. Public Works Secretary Rogelio Singson revealed in June that local politicians sought the delay of the operation ahead of the May congressional elections, making it too late for the onset of this year's rainy season.

The governing structure of Metro Manila also makes it difficult to get decisions covering the whole area. The metropolis is made up of 16 cities and one municipality, each headed by a separately elected mayor and city councilors.

The increasing volume of trash is also a problem. Most of the garbage ends up in landfills, but a substantial amount is discarded into drainage. One estimate by Metro Manila Development Authority is that the city dumps daily 3,000 cubic meters (equivalent to 600 trucks) of garbage and other solid materials in rivers, drains and waterways.

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Associated Press writers Jim Gomez and Oliver Teves contributed to this report.

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Follow Hrvoje Hranjski on Twitter at twitter.com/hmanila

FILE - In this Aug. 19, 2013 file photo, a truckload of stranded commuters cross a flooded street in Manila, Philippines. Lashed each year by typhoons and stuck with outdated drainage systems, the Philippine capital has been hit by ever-worsening floods. Population growth, inadequate infrastructure, corruption, deforestation and even trash build-up combine to exacerbate the impact. Itís a trend experts expect to continue. (AP Photo/Aaron Favila, File) Enlargephoto

FILE - In this Aug. 19, 2013 file photo, a truckload of stranded commuters cross a flooded street in Manila, Philippines. Lashed each year by typhoons and stuck with outdated drainage systems, the Philippine capital has been hit by ever-worsening floods. Population growth, inadequate infrastructure, corruption, deforestation and even trash build-up combine to exacerbate the impact. Itís a trend experts expect to continue. (AP Photo/Aaron Favila, File)