Going with the flow

A press release from the University of California-Santa Barbara: Millions of Americans live in flood-prone areas. In 2012 alone, the cost of direct flood damage hit nearly half a billion dollars. However, because the factors contributing to flood risk are not fully understood, river basin management — and even the calculation of flood insurance premiums — may be misguided.

A new study by UC Santa Barbara’s Michael Singer and colleagues presents a paradigm shift in flood hazard analysis that could change the way such risk is assessed in the future. The results are published in the journal Geophysical Research Letters.

Existing analyses attribute flood hazard to how often high water flows occur. They don’t, however, take into account the ability of river channels to accommodate them. The researchers present a novel method that compares the effects of channel capacity and stream flow on flood hazard frequency. They also document how flood hazard has changed over time in more than 400 streams across the United States.

“Our results demonstrate that changes in river channel boundaries directly impact flood hazard trends across the U.S.,” said Singer, an associate researcher at UCSB’s Earth Research Institute. “We show that in order to accurately calculate flood hazard and insurance premiums for river basins, channel capacity needs to be considered jointly with stream flow.”

...The findings revealed that important trends in channel morphology through time were three times more common than those related to water quantity, indicating that changes in the channel’s geometry tend to offset increases in water flow. “That raised alarm bells,” Singer said. “It suggests that a lot of areas that we might not have considered to have trends in flood risk actually do.”...

Red represents increases and blue decreases in flood hazard frequency. Deeper colors indicate sites with statistically significant trends. Image from the UC Santa Barbara website

Making use of the hazard maps in the Phlippines

An editorial in the Cantanduanes Tribune (Philippines): All 11 municipalities, as well as the provincial government, have received sets of hazard maps under a disaster risk management project funded by the Australian Aid Program through the United Nations Development Programme (UNDP) and the National Disaster Risk Reduction and Management Council (NDRRMC).

Hopefully, the maps would guide them in helping save their constituents during calamities. The 1:50,000-scale maps indicate areas of each town facing various hazards such as earthquake, storm surge, landslide due to earthquake, landslide due to heavy rains, tsunami, flooding and liquefaction during earthquakes. The municipal DRRM offices were also given “soft” or digitized copies.

Now, the maps are nice to look at, especially if they are wrapped in plastic, framed and nailed on the walls of the MDRRM offices. But they should serve the purpose of saving the population from certain danger as envisioned under the Ready Multi-Hazard Mapping and Assessment for Effective Community-based Disaster Risk Management (Ready Project).

In the recent past, the national government also distributed hazard maps of smaller scale to several municipalities, but apparently the maps gathered dust in drawers or in the walls of their offices. None, or very few, people in the villages saw or even had the chance to understand the import of the hazard maps.

Thus, as soon as 2014 comes in, each of the municipal disaster bodies should open the digital copies and begin zooming in on each barangay. By doing this, they can pinpoint specific areas of the village which would be highly susceptible to the hazards. Hazard maps for each barangay could then be made, after which the barangay DRRM council as well as residents could be gathered at the plaza where the particular hazardous areas could be explained. Knowing where a hazard could hit hardest and how to avoid the threat and where to evacuate could save hundreds of lives....