The Federal Reserve's Dan Tarullo has been a key player in post-Crisis U.S. bank reform and in the negotiation of Basel III, the set of international banking rules that guides regulation in major financial centers. In a speech made last Friday (May 3, 2013) Tarullo expressed some satisfaction with the U.S. and Basel III reforms -- and identified a risk needing further regulatory attention: runs on short-term wholesale funding.
Short-term funding has always constituted a vulnerability to the banking system. The traditional magic of banking involves the transformation of maturities -- banks borrow on a short-term basis and lend for the medium- or long-term. In ordinary times this works out splendidly -- as the short-term rates banks pay tend to be lower (over the long term) than the long-term rates they earn. And in ordinary times, short term funding is quite stable.
The dominant form of short-term funding was traditionally bank deposits. Deposits are essentially loans made to a bank by its depositors. Deposits are legally short-term, but practically rest in the hands of banks for substantial periods. Short-term funding becomes problematic, of course, when depositors systematically demand repayment: this is the old-style bank run. Post-Depression era deposit insurance has largely eliminated bank runs, at least in the United States, and so the ordinary insured bank deposit is (from the perspective of the bank) a trusty source of short-term funding.