Journal of the Japan Society of Erosion Control Engineering, Vol.55,No.4,p.23-28,2002

Evacuation decision making and quantitative accuracy of precipitation forecast

Hiroaki NAKAYA

Abstract
Decision]making of evacuation from natural disasters, especially sediment]related disasters is surrounded by many uncertainties. A simple response system and a simple decision model are introduced in order to specifically analyze the uncertainty of forecast precipitation, which has a significant impact on the decision. The response system has precipitation as its input variables, geomorphologic and geological aspects as its parameters, and a signal of occur/not occur as its output. The decision model constitutes of a decision node (evacuate/not evacuate), uncertainty nodes (rain exceeding a critical amount), and consequence nodes (presumed loss of lives and cost of evacuation). Operational forecast and actual precipitation used by Japan Meteorological Agency (JMA), which are calledgVery Short]Range Forecast of PrecipitationhandgRadar]Automated Meteorological Data Acquisition System (AmeDAS) Precipitationhrespectively, are examined to verify their quantitative accuracy for the period from January1998to January2001. Conditional probabilities of a precipitation amount exceeding a given critical amount when a certain amount of rain was forecast are obtained through the verification. The conditional probabilities have to go beyond the cost]loss ratio of evacuation decision]making in order for the evacuation decision to stand rational. The accuracy level of1]hour operational forecast precipitation barely meets the required level indicated by cost]loss ratio for5by5km square mesh, when a perfect response system is assumed. Importance of further research on (subjective) cost]loss ratios of actual decision]makers and sizes of areas in concern came to our attention.
Key words:evacuation decision making, accuracy of forecast, cost]loss ratio