Second-wave Effects: A Global Health Perspective on Climate Change


“Tracking A Superstorm” by NASA is licensed under CC BY 2.0

Monsoon season in Southwest Asia generally stretches from early June until late September. While the annual rainfalls are known to replenish freshwater and maintain the vibrant green rice paddies that line hills, the last decade has seen a greater severity in the amount of rain, resulting in catastrophic consequences for the people of the south Asian subcontinent.

This past year, India, Nepal, and Bangladesh were hit hard by the monsoon rains. Entire villages were submerged by floodwaters, and the U.N. has estimated that 41 million people have been affected.[1] Flooding and landslides have displaced thousands of villages, and the death toll continues to ascend. In the poorest parts of the country, houses — huts made of mud — have completely disintegrated. Dirt roads that provide access to the region are now completely gone, making it increasingly difficult to provide foreign relief.

Over the last few months, extreme climate events on the Atlantic side of the United States have mirrored the tragedies in Southwest Asia. 2017 was one of the seven most active hurricane seasons in history, with 15 named storms, 10 hurricanes, and 6 category 3+ hurricanes as of mid-October.[2] Pummelled by one after the other, Houston, the Florida Keys, and Puerto Rico also suffered from the after-effects, including flooding, storm surges, and damage to infrastructure.

While it is obvious that the physical repercussions of natural disasters can destroy homes, displace communities, and take lives, a less frequently discussed consequence lurks in the background: vector-borne diseases. Post-storm conditions create the perfect environment for these transmitters of disease. The severity of these events is expected to grow over the next century under ideal conditions as a result of extreme climate events like the ones prevailing around the planet.


The “Canal da Malária” located in Olinda, Brazil
Image by Prefeitura de Olinda is licensed under CC BY 2.0

In order to understand the role that natural disasters play in the rise of vector-borne disease, we must first understand the role that climate change plays in extreme weather events. The trends in natural disaster severity worldwide are linked to anthropogenic climate change: the observed changes in climate systems resulting from human actions such as deforestation, burning fossil fuels, and heat and waste pollution.[7] The Earth has transitioned into a new geological epoch termed the Anthropocene, exemplified by the human impact on the world’s geology and ecosystems.

Both abnormal weather conditions and the development of human systems — like water storage and urbanization — have a direct effect on disease transmission dynamics. Vector propagation is dependent on warm temperatures, ideally ranging from 17-34°C, and aquatic breeding environments for larval development. Over the next century, a greater geographic area will have these optimal requirements for vector proliferation.[5] Global temperatures are expected to increase 1.0 to 3.5°C leading to a possible sea level rise of one meter by 2100.[3,4]

Coastal communities, especially in the developing world, become increasingly threatened by these changes. For example, the most recent Zika epidemic erupted in 2015, which was the “hottest year globally since record-keeping began 136 years ago.” [11] One study has revealed that Aedes aegypti mosquitoes, carriers of Malaria and Zika, are living year round as far north as Washington D.C. at Capitol Hill because they are now able to survive underground during the winter months.[6]

Think back to Houston after Hurricane Harvey: an estimated 27 trillion gallons of rain enveloped Texas and Louisiana in less than a week.[8] Houston immediately became submerged under multiple feet of stagnant water, the city becoming an enormous mosquito breeding ground. With A. aegypti mosquitoes and Zika harboring in the United States, eggs laid before the storm rapidly hatch, resulting in large populations of floodwater mosquitoes. These swarms hinder recovery efforts as people are encouraged to remain inside to protect themselves from the pests.

In an attempt to protect the citizens of Houston after Hurricane Harvey from Zika and West Nile virus, as well as aid recovery efforts, the U.S. Air Force reserve sprayed the city with a pesticide named Naled.[9] The Environmental Protection Agency has rated the chemical as safe for human contact, but the topic remains controversial as the insecticide can only have modest effects. The aerial spraying cannot kill the mosquito eggs that find refuge in small man-made containers or underground; these eggs can survive for months after the storm. Climate change will continue to exacerbate both the frequency at which these storms will occur and the severity of their aftereffects. The warmer and more humid it becomes, the faster vectors can proliferate, thus expanding the magnitude of swarms and pushing their geographic boundaries further north.


Destruction and flooding in Port Arthur, Texas in the wake of Hurricane Harvey
This image by the SC National Guard is licensed under public domain

Anthropogenic climate change presents the greatest threat for the tropics and subtropics, which encompass parts of Africa, South America, the Caribbean, and South Asia. By no coincidence, socioeconomically poor populations living in these areas retain the greatest risk and burden for infectious diseases due to climate conditions that are most suitable for transmission. Paired with a lack of public health infrastructure, these communities’ ability to manage outbreaks and provide curative treatment is minimal. While the United States has the resources to respond to health crises immediately following the storm, the developing world depends on foreign aid which is often delayed and only palliative. Rather than inhabitants taking refuge in shelters, they are stuck living in under plastic tarps on the land that used to contain their farms and homes. These camps harbor disease, and the length of stay is indefinite.[10]

Natural disasters are typically portrayed on a short-term scale, with a definite beginning and end. A storm begins to form thousands of miles off coast and slowly encroaches on land. Citizens who have the means can respond: they board up their homes and try to evacuate. Upon landfall, the storm engulfs the location, and people around the world watching on television wait to hear news of the destruction the next day. In the following weeks, recovery efforts commence to repair the geographic area made victim to nature’s forces.

However, this rhetoric about natural disasters often fails to address both the principal causes of our current climate trends and the long-term effects on human health systems in both the developed and developing world. Emphasizing the increasing danger of vector-borne diseases post-storm must stand alongside the current reasons to act against anthropogenic climate change. Beyond another defense of the severity of climate change, these second-wave effects should present another motivation to take action and understand how the human-induced changes in climate dramatically impact the wellbeing of people worldwide.


  1. Penn, D. (2017, August 24). Floods, landslides affecting 41 million in Bangladesh, India and Nepal. Retrieved November 18, 2017, from
  2. Erdman, J. (2017, October 09). 2017 Atlantic Hurricane Season Now Seventh Most Active in History. Retrieved November 18, 2017, from
  3. Githeko, A. K., Lindsay, S. W., Confalonieri, U. E., Patz, J. A. (2000). Climate Change and vector-borne diseases: a regional analysis (Bulletin of the World Health Organization, 2000). (Ref. No. 00- 0737). Kisumu, Kenya.
  4. Rahmstorf, S., Morgan, J., Levermann, A., & Sach, K. (n.d.). Scientific understanding of climate change and consequences for a global dea. In H. J. Schellnhuber (Ed.), Global Sustainability – A Nobel Cause (pp. 67-79). Cambridge: Cambridge University Press.
  5. Ryan, S. J., Mcnally, A., Johnson, L. R., Mordecai, E. A., Ben-Horin, T., Paaijmans, K., & Lafferty, K. D. (2015). Mapping Physiological Suitability Limits for Malaria in Africa Under Climate Change. Vector-Borne and Zoonotic Diseases, 15(12), 718-725. doi:10.1089/vbz.2015.1822
  6. Erdman, J. (2017, October 09). 2017 Atlantic Hurricane Season Now Seventh Most Active in History. Retrieved November 18, 2017, from
  7. Mann, Michael E., and Kerry A. Emanuel. “Atlantic hurricane trends linked to climate change.” Eos, Transactions American Geophysical Union, vol. 87, no. 24, 13 June 2006, p. 233., doi:10.1029/2006eo240001.
  8. Griggs, Brandon. “Harvey’s devastating impact by the numbers.” CNN, Cable News Network, 1 Sept. 2017,
  9. Christine Crudo Blackburn Postdoctoral Research Fellow, Scowcroft Institute of International Affairs, Bush School of Government and Public Service, Texas A&M University, et al. “Harvey and Irma present nearly perfect conditions for Zika-Spreading mosquitoes.” The Conversation, 15 Nov. 2017,
  10. Gettleman, Jeffrey. “More Than 1,000 Died in South Asia Floods This Summer.” The New York Times, The New York Times, 29 Aug. 2017,
  11. National Oceanic and Atmospheric Administration . (2016). State of the Climate. Accessed