The types of hazards as they change over time can be best illustrated by using the following four temporal windows:

Before a hurricane, people’s anxiety, stress, and fear levels sharply increase. This leads people to hoard emergency supplies and to empty local supermarkets and drugstores within days. During Hurricane Sandy, one of the main reasons for emergency room visits was the inability to secure medications and other urgent medical supplies.

During a hurricane, most health hazards directly result from the destructive influence of the hurricane. Wreckage of roads and buildings from storms and flooding lead to injuries that cause death, and other non-fatal injuries such as falling, electric shock, lacerations, and crush injuries. From Hurricane Katrina, the Centers for Disease Control and Prevention (CDC) reported 2,018 non-fatal injuries; the leading causes were cuts, piercings from debris, and falling. The Louisiana Department of Health identified 971 Katrina-related deaths in Louisiana—40% of the deaths were from drowning and 25% were from injury and trauma.

Immediately after a hurricane, physical injuries are still a major concern, but this is caused more from the cleanup and restoration work. Those exposed to the greatest risk are cleanup workers who are residents themselves and don’t have proper knowledge or training. The onset of various infectious diseases is also common at this stage. Shortly after Hurricane Katrina, the CDC reported the spread of norovirus, cholera, and non-typhoidal Salmonella. The CDC also observed an unusual peak of Human West Nile virus in Katrina-affected regions in the weeks following Katrina. Wound and skin infections and mold exposures are others that commonly accompany flooding. Since the weather conditions and season of the Harvey-affected areas are similar to those of Katrina, we should anticipate and prepare for a replication of such a phenomenon in post-Harvey regions.

In the long term, the primary public health concern is the mental health of the affected populations, such as Post-Traumatic Stress Disorder (PTSD), chronic depression and anxiety, and addiction. Mental health issues are often underreported in the immediate aftermath because such symptoms are typically not expressed for weeks, if not months, after a traumatic event.

In the case of Katrina, studies showed that 30% to 50% of all Katrina survivors suffered from PTSD. Note that a study conducted by Columbia University found that 36% of Katrina-affected children showed serious emotional disturbances. In the case of Hurricane Sandy, over 20% of residents reported PTSD, 33% reported depression, and 46% reported anxiety. When groups were compared by the degree of exposure to the hurricane, the higher-exposed group showed 30% more PTSD than the less-exposed group.

Such mental health problems can give rise to a wide array of social problems—research showed that Katrina-affected communities experienced decreased population (over 50% one year after Katrina) and low birth weight in newborns. Sandy-affected regions showed higher prevalence of substance abuse, especially among adolescents. If not properly addressed, mental health issues will delay the community’s rebuilding efforts, and thus reinforce the vicious cycle.

The physical health issues that hurricanes cause directly are visible and treatable. However, we should also prepare for those problems that appear with progression of time, and thus build in flexibility in responding to such less immediate hazards. Prior hurricanes have demonstrated that mental health, particularly among children and adolescents, is one such example. We should seriously consider how to stabilize affected communities in this regard, in order to minimize Hurricane Harvey’s long-term influence that could develop into a society-wide challenge.

Hyun Kim is assistant professor in the Division of Environmental Health Sciences at the University of Minnesota.