Estado de la Vivienda

The threatened area is defined as the area that can possibly flood based on the forecasts and the area in which the consequences of the flood can occur (where there will be a breakdown of all kinds of services). The threatened area is based on the possible (worst credible (ten Brinke et al. 2010), as defined in Table 1) floods using information available at the moment of decision making for evacuation using realistic forecasts. Up to 24 hours before the onset of the flood, the entire coast is expected to be at risk. No areas can be excluded because of the uncertainty in the development of the weather (Kolen and Wouters 2007).

Inside the threatened area, different zones are identified based on the possible impact of and their vulnerability to the threat, using the knowledge of water depth, the velocity of the water

Figure 26: National Concept Traffic Management presenting routes from west to east and north to south and shelter areas (circles) (Holterman et al. 2009)

and the breakdown of services. These zones represent more or less vulnerable areas and are used for several strategies for evacuation. These are shown in Figure 27:

 A high threat area: The high threat area is the area that could be flooded in one of the worst credible flood scenarios;

 A low threat area: The area that could flood with low probability. For example, breaches at unexpected places could cause flooding. In this area, almost all services (electricity, gas, waste water, drinking water, telephone, etc.) are assumed to break down. The threatened area (Figure 27) is divided into areas that are assumed to be independent:

 North Netherlands;

 Flevoland and surroundings;  North and South Holland;

 Islands of Zealand and South Holland;  Zeeuws Vlaanderen.

For the strategy ‘National concept traffic management’, the complete combined area is used as one zone.

Number of people for which the evacuation strategies apply.

The number of people for which the evacuation strategies apply can be determined by a combination of the threatened area and the number of people in an area. In Table 13, the population to be evacuated is presented, divided into those who evacuate preventively and those who stay inside the area (using shelter-in-place or vertical evacuation) for each strategy.

Figure 27: Threatened area (BZK and VenW 2008a)

The population to be evacuated is based on the number of people in postcodes and the different zones of the threatened area. About 11% of the total population is estimated to be unable to evacuate without requiring medical assistance and is not considered self-reliant; they will need the support of emergency services to evacuate (CBS 2008; RIVM 2008).

All other citizens are assumed to evacuate on their own, supported by family or other citizens, and are considered self-reliant.

Table 13: Number of people in each strategy (x 1,000 people)

Preventive evacuation Vertical evacuation and shelter in place

Maximum preventive evacuation 3.900 900

High preventive evacuation 2.900 1.900

Low preventive evacuation 2.700 2.100

Minimum preventive evacuation 1.200 3.600

Citizen response

The response of each citizen depends on several factors, such as experience, trust in the government, and the safety of family, friends, and pets (van Duin et al. 1995; Kok et al. 2007; Perry and Mushkatel 1984). At the start of the evacuation, people are assumed to be in their homes, and roads are assumed to be empty. Before the decision to start an evacuation, other measures, decisions and crisis communications have been executed based on forecasts in accordance with national and regional emergency planning. People who evacuate spontaneously are assumed to be compensated by people who enter the area to support family and friends. Each scenario uses a departure curve that defines the moment when people leave their homes and take part in the traffic (Friso et al. 2008; Doef M. van der 2006). After 5 hours, 20% of the people leave their home for preventive evacuation; after 7 hours, 50%; 9 hours, 80%; and after 15 hours, 99% of the group that evacuates preventive have left their homes. These departure curves are based on experience in the United States and are appropriate for the Netherlands (Friso et al. 2008). These curves take into account the time needed to respond and the influence of changing information in the response of the public. This case study assumed that 20% of the people will not adhere to the desired strategy as announced by the government. The remaining 80% of the population will follow the instructions of the government’s evacuation strategy. This 20% estimate is based on an enquiry by ‘TNS NIPO’ (NIPO 2006) in the Netherlands as well as what has been learned from the experience during hurricanes induced evacuation in New Orleans.

Table 14: Different figures of % of people who evacuate preventive or will stay behind

Percentage of people in The Netherlands who say they will evacuate preventive when advised (or forced by law) by the authorities (NIPO 2006) Preventive Evacuation Do not know yet Stay inside the threatened area No opinion

River area with experience of evacuation of 1995

68% 28% 3% 1% River area without experience of evacuation

of 1995

63% 34% 1% 2% Coastal area that flooded in 1953 56% 38% 2% 4% Other parts of coastal area 47% 49% 2% 2%

Percentage of people in New Orleans (%) Preventive Evacuation Stay inside the threatened area

Survey 2004 (Van Heerden and Streva 2004) 69% 31% Hurricane Katrina 2005 (Wolshon 2006) 80% 20% Hurricane Gustav 2008 (Cole 2008) 95% 5%

The Dutch enquiry Table 14 shows the different willingness of citizens to evacuate preventively in the Netherlands if ordered by the government. A large group of citizens indicate that they do not know as yet what they will do and require more information. Personal experience with evacuation or living in an area which is more at risk, such as rivers with relatively high discharges every year, have relatively little effect on these choices. Experience in New Orleans shows that the number of people who would evacuate preventively changes over events (as 80% during Hurricane Katrina and 95% during Hurricane Gustav). Because of the large possible impact of the different choices of the public, more research is necessary to have a better understanding of public choices and their impact. The results can be integrated into planning documents and used for communication with the public.