What is the role of public health in times of Population Crises and Emergencies?

What is the  role of public health in times of Population Crises and Emergencies?  How does the National Response Plan relate to the role of public health. Offer some strategies to improve inter-agency communications and coordination between local, state, and the federal government.This question is pertaining to Emergency Medical Services. Please respond with at least 200-250 words. Thank you.