We present a model of an economy with heterogeneous banks that may be funded with uninsured deposits and equity capital. Capital serves to ameliorate a moral hazard problem in the choice of risk. There is a fixed aggregate supply of bank capital, so the cost of capital is endogenous. A regulator sets risk-sensitive capital requirements in order to maximize a social welfare function that incorporates a social cost of bank failure. We consider the effect of a negative shock to the supply of bank capital and show that optimal capital requirements should be lowered. Failure to do so would keep banks safer but produce a large reduction in aggregate investment. The result provides a rationale for the cyclical adjustment of risk-sensitive capital requirements.

[We compare various bank capital regulation regimes using a dynamic equilibrium model of relationship lending in which banks are unable to access the equity markets every period and the business cycle determines loans' probabilities of default. Banks hold endogenous capital buffers as a precaution against shocks that impair their future lending capacity. We find that Basel II is more procyclical than Basel I but makes banks safer, and it is generally superior in welfare terms. For high social costs of bank failure, the optimal capital requirements are higher but less cyclically varying, like those currently targeted by Basel III.]

We assess the procyclical effects of bank capital regulation in a dynamic equilibrium model of relationship lending in which banks are unable to access the equity markets every period. Banks anticipate that shocks to their earnings as well as the cyclical position of the economy can impair their capacity to lend in the future and, as a precaution, hold capital buffers. We find that under cyclically-varying risk-based capital requirements (e.g. Basel II) banks hold larger buffers in expansions than in recessions. Yet, these buffers are insufficient to prevent a significant contraction in the supply of credit at the arrival of a recession. We show that cyclical adjustments in the confidence level underlying Basel II can reduce its procyclical effects on the supply of credit without compromising banks’ long-run solvency targets.