Mortgage Finance in the Face of Rising Climate Risk

Recent evidence suggests an increasing risk of natural disasters of the magnitude of hurricane Katrina and Sandy. Concurrently, the number and volume of flood insurance policies has been declining since 2008. Hence, households who have purchased a house in coastal areas may be at increasing risk of defaulting on their mortgage. Commercial banks have the ability to screen and price mortgages for flood risk. Banks also retain the option to securitize some of these loans. In particular, bank lenders may have an incentive to sell their worse flood risk to the two main agency securitizers, the Federal National Mortgage Association, commonly known as Fannie Mae, and the Federal Home Loan Mortgage Corporation, known as Freddie Mac. In contrast with commercial banks, Fannie and Freddie follow observable rules set by the FHFA for the purchase and the pricing of securitized mortgages. This paper uses the impact of one such sharp rule, the conforming loan limit, on securitization volumes. We estimate whether lenders' sales of mortgages with loan amounts right below the conforming loan limit increase significantly after a natural disaster that caused more than a billion dollar in damages. Results suggest a substantial increase in securitization activity in years following such a billion-dollar disaster. Such increase is larger in neighborhoods for which such a disaster is "new news", i.e. does not have a long history of hurricanes. Conforming loans are riskier in dimensions not observed in publicly available data sets: the borrowers have lower credit scores and they are more likely to become delinquent or default. A structurally estimated model of mortgage pricing with asymmetric information suggests that bunching at the conforming loan limit is an increasing function of perceived price volatility and declining price trends. A simulation of the impact of increasing climate risk on mortgage origination volumes with and without the GSEs suggests that the GSEs may act as an implicit insurer, i.e a substitute for the declining National Flood Insurance Program