A disaster is an event that goes beyond the scope of local resources.
Normally, response agencies like Fire, Police, Public Works, and Parks & Community Services can handle emergencies, but during a disaster these agencies may be overwhelmed or unable to respond normally. Emergency Management provides coordination and control between responders, City departments, volunteers, and other stakeholders to respond effectively to disasters and emergencies.
This video is a good summary of Emergency Management's role in Kirkland: