The opening of a financial account of the balance of payments has been important during the last decade. Hence, financial flows such as direct investment and portfolio investment became more important. Usually financial flows are more volatile that enforce the necessity of higher reserves. Moreover, holding reserves, as a consequence of the increasing of financial flows, is known as Guidotti–Greenspan rule that states a country should hold liquid reserves equal to their foreign liabilities coming due within a year. For example, international wholesale financing relied more on Korean banks in the aftermath of the 2008 crisis, when the Korean Won depreciated strongly, because the Korean banks' ratio of short-term external debt to reserves was close to 100%, which exacerbated the perception of vulnerability.