Llonard Yap's List: Climate Change in the Philippines

• who is to blame?
• bogged down by politics and corruption in government exacerbates matters.
• about a fifth—of the 63,000 land area that makes up Metro Manila, is naturally flood prone
• To a great extent, this is caused by the fact that the water level at the Manila Bay, particularly during high tide, is higher than the elevation of many inland localities
• the annual rainfall in Metro Manila is one of the heaviest among metropolitan areas in the world. This normally ranges from 2,000 millimeters in the Manila Bay area to 3,000 millimeters over the mountains of Marikina, San Mateo, and Montalban (now known as Rodriguez)
• High tide normally prevents the flow of floodwaters through these natural drainage systems, causing water to spill over and swamp many low-lying areas.
• And the factors that made things worse are all man-made
• The Bankoff study noted that mean sea levels at Manila's South Harbor--which has been increasing by about two millimeters a year between 1902 to 1960--has accelerated sharply, reaching approximately 3 centimeters every year by 1991. Bankoff said such increase "cannot be explained as solely a consequence of global warming and bears a strong correlation to the rise in both ground water extraction and population growth."
• Rampant logging and quarrying in mountains along the outskirts of Metro Manila have made them highly vulnerable to erosion, causing higher-than-normal amounts of silt to settle in Manila's waterways.
• Silt deposits have already reduced the water-holding capacity of Laguna de Bay by as much as 64 percent, while surface run-off from denuded watersheds increased its level by 2.7 meters in the 1980s.
• Including the Marikina River, there are 13 tributaries that discharge into the lake. Bankoff noted, however, that there is only a single outlet that carries water from the lake to the sea at Manila Bay—the Napindan-Pasig River. 
• Palafox said a Metroplan drawn up in the 70s to address flooding in Metro Manila was supposed to include a Parañaque spillway to flush out the excess water to the Laguna de Bay and South China Sea. This was never done.
• Metro Manila’s predilection to flooding is only aggravated by the development of new subdivisions on former agricultural lands such as those in Marikina, Cainta, Pasig, Pateros and Taguig, according to Bankoff.
• acutely susceptible to flooding,
• Some 21,000 squatter families occupy shanties in these areas, further adding to the headaches of flood control officials.
• Daily, irresponsible city dwellers dump around 3,000 cubic meters (equivalent to 600 fully laden trucks) of garbage and other solid materials in rivers, drains and waterways in rivers drains, and waterways, thus clogging these drainage systems within weeks after being cleaned.
• Metro Manila has a number of pumping stations—including 15 high-capacity stations, each with the capacity to pump 18 cubic meters of water per second—hastening the discharge of floodwaters into the Pasig River and Manila Bay.
• The problem, however, is how to get floodwaters to reach these pumping stations, public works engineers said.

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• Experts consider San Antonio's anti-flood approach among the most innovative solutions to flooding in any metropolitan area.
• Between 1987 and 1996, federal and local governments funded the construction of a 16,200-foot concrete flood-diversion tunnel beneath the city. It siphons rainfall out of populated areas and carries it to the San Antonio River. Fully 24 feet in diameter, the tunnel was dug with a massive tunnel-boring machine, seen here in action beneath San Antonio.

  • Isn't this the same solution for Mandaluyong and Buendia, Makati during the Marcos era?

• Such  erosion can undermine bridge structures, levees, and buildings causing their collapse.
• Predicting River Flooding
• three main  approaches are taken to flood prediction
• Does this  make the statistical analysis unreliable?  The answer is no. 
• probability
• P_e = m/(n+1)
• P_e, is called the annual  exceedence probability
• Food hazard mapping is used to determine the areas susceptible to  flooding when discharge of a stream exceeds the bank-full stage.
• amount of rainfall, degree of ground saturation, degree of permeable  soil, and amount of vegetation
• In order to control floods, channel modification should involve  increasing the channel cross-sectional area, so that higher discharge will not increase  the stage of the river.  Straighter channels also allow higher velocity flow and,  enable the stream to drain faster when discharge increases.
• If the channelization results in decreasing the cross-sectional area of the  stream, as in the example above, then the same discharge that may not have produced  flooding prior to channelization, may overflow the banks and cause extensive flooding  after channelization.
• While this may prevent  local flooding of streets, it moves water more rapidly to the major stream systems and  thus decreases the lag time and increases the peak discharge of the streams collecting the  runoff from the storm sewers.
• Thus, extensive urbanization also decreases the lag time and  increases the peak discharge even further
• Floodways are areas where no construction is allowed, and where the land  is used for agricultural or recreational purposes when there is no threat of a flood, but  which provide an outlet for flood waters during periods of high discharge. 
• Floodplain zoning - Laws can be passed that restrict construction and  habitation of floodplains.  Instead floodplains can be zoned for agricultural use,  recreation, or other uses wherein lives and property are not endangered when  (note that I did not use the word if) flood waters re-occupy the floodplain.
• Floodplain buyout programs - In areas that have been recently flooded,  it may be more cost effective for the government, which usually pays for flood damage  either through subsidized flood insurance or direct disaster relief, to buy the rights to  the land rather than pay the cost of reconstruction and then have to pay again the next  time the river floods. 
• Mortgage limitations - Lending institutions could refuse to give loans  to buy or construct dwellings or businesses in flood prone areas.

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• The 2D version of CCHE-FLOOD can be efficiently used for studying flood propagation due to dam-break, and embankment or levee breaching.
• literally exploded
• 14 minutes
• A 5km reach of the valley has been reproduced on a 1:100 scale physical model. The experimental data (topographic data, inflow hydrographs, hydraulic conditions and physical parameters and water elevations measured at 32 gauging stations) is available as benchmark data for testing numerical models. Two different dam-break test cases are available; one with the flood wave overtopping a reservoir located in the middle of the valley, and the other without overtopping. The case with overtopping of the reservoir was used to validate CCHE-FLOOD. 

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• flash floods, floods due to dam-break or levee breach
• discontinuities (hydraulic jump, traveling positive wave)
• mixed flow regimes over complex terrain topography.
• Use these state-of-the-art numerical models to assist government agencies and private institutions in conducting flood risk assessment studies, planning and designing flood control project, and establishing early warning system and emergency action plans.

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• Using the radiation emitted from lightning flashes, we’ve developed a system that can give adequate warning to the public ― and save lives
• Eventually, the Flash system may be used to send messages to cell phones, RSS feeds, GPS units and other devices to warn people in the path of a flash flood and avert disaster.
• By measuring the radiation emitted by lightning, researchers can pinpoint the most intense thunderstorms, and the resulting rainfall can be located and tracked.
• This data has been used to predict both the path of a storm and where heavy rainfall will appear ― crucial predictions, since the impact of flash floods depends on ground topography, slope and vegetation cover. “Nowcasting,” which predicts what conditions will be in the next few hours, versus “forecasting” a day or two in advance of expected weather conditions, is critical.

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• Cities incite thunderstorms, researchers find
• Summer thunderstorms become much more fierce when they collide with a city than they would otherwise be in the open countryside, according to research led by Princeton engineers.
• based their conclusion on computer models and detailed observations of an extreme thunderstorm
• Their modeling suggests that the city of Baltimore experienced about 30 percent more rainfall than the region it occupies would have experienced had there been no buildings where the city now sits.
• climate change is expected to make such events more frequent, according to the fourth assessment report of the Intergovernmental Panel on Climate Change
• Precipitation events like gully-washing rainstorms are expected to increase in intensity as the world warms due to the buildup of greenhouse gases
• This means that warm-season thunderstorm systems will probably increasingly lead to more flash flooding, which can be very dangerous
• Hydrologists have observed evidence in the past that urban environments alter the behavior of storms. But they have mostly noted average increases in rainfall over long periods of time.
• The scientific consensus so far has been that, during a storm, greater rainfall occurs on the downwind part of the city than on the upwind side.
• Exactly how does the urban environment have the potential to alter the evolution of thunderstorms?
• often 2 to 5 degrees Fahrenheit hotter
• this "heat island" can provide fuel for a modest thunderstorm
• The tall buildings increase wind drag on the city, resulting in vertical velocities – essentially a boiling action – that can enhance rainfall
• Analyses of the lightning and flood peak data also show a close link between the occurrence of major thunderstorms systems and flash flooding on a regional scale.

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• Forecast Flash Floods
• People living near vulnerable creeks and rivers
• NCAR Front Range Flash Flood Prediction System
• combines detailed atmospheric conditions with information about stream flows to predict floods along specific streams and catchments
• We want to increase the lead time of a forecast, while decreasing the uncertainty about whether a flood will occur."
• Flash floods are difficult to predict because they happen suddenly, often the result of heavy cloudbursts that may stall over a particular watershed.
• But whether a flood hits a specific river or creek also depends on soil, topographic, and hydrologic conditions that are characteristic to particular watersheds. Thus, emergency managers may not know that a flash flood is imminent until the waters begin to rise.
• It is designed to pinpoint whether a particular stream is likely to overflow, as well as forecast the likelihood of flash floods producing events across a larger region.
• proof-of-concept test
• To predict weather events, the system utilizes National Weather Service radar observations of current conditions and short-term computerized weather forecasts.  The weather forecasts are generated by NCAR's Weather Research and Forecasting (WRF) model, which produces highly detailed simulations of the local atmosphere.
• The system integrates the weather information with datasets about hydrology and terrain. These datasets incorporate information about land surface conditions, such as terrain slope, soil composition and surface vegetation. They also include information on stream flow and channel conditions.
• By combining information about the land and the atmosphere, the system can project whether an intense storm is likely to stall over a specific area of the Front Range and how that may impact the flow of water on the ground.
• This new system is unique in that it provides a detailed forecast of the location and duration of a severe storm, as well as the watershed's likely response to the heavy rain
• Since flash floods are complex and fast-moving events, we need to know about both weather and ground conditions in order to predict them

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