The DEC have a set of criteria which are used to determine whether we will launch an appeal after a disaster has occurred. Details of these criteria can be found by following this link.
These criteria have been established to ensure that a DEC appeal is launched only when there is dire need for international response, the capability to run an effective response and enough public sympathy and awareness to make an appeal a viable option.
This is not to say that the DEC do not want to see everyone affected by disaster being helped, but that a DEC appeal is not always going to be the most effective way to respond to a disaster. In many instances, international humanitarian aid will not be called for at all, so there would not be programmes for DEC funds to be used for. Further to this, most of the DEC member charities are international humanitarian aid organisations working in the poorest and most undeveloped countries in the world, so if a disaster happens in a more developed country the lack of DEC member presence will mean that there is nowhere for DEC appeal funds to go.