Crescent City, California, is in an area that is subject to tsunamis. Its harbor was severely damaged by the tsunami caused by the earthquake off the coast of Japan on March 11, 2011. The probability P (as a decimal) that no tsunami with waves of 15 feet or higher will strike Crescent City over a period of t years is given by the formula P = 0.99^t.
What is the percentage decrease of the probability for each one-year increase in the time interval?