The historic storm that struck Houston on Monday may have caused as much flooding in some areas as Tropical Storm Allison did 15 years ago, suggesting the possibility of billions of dollars in economic and insured losses. While it will take days for flood waters to recede and the damage to become clear, some figures are beginning to emerge. Ratings agency A.M. Best, citing the Insurance Council of Texas, said insured automobile losses alone could top $200 million. Catastrophe modelers Aon Benfield described the flooding in some parts of the city as a 1-in-200-year event.