Forces of Nature: Water-related Environmental Extremes in a Changing Climate
A Common Home Spotlight by ECo Faculty Network member Dr. Marisa O. Ensor
January 9, 2025
The year 2024 ended with a stark reminder that destructive environmental extremes across the world have become the norm, not the exception. From October 29-30, eastern Spain was hit by exceptionally heavy rainstorms. Subsequent floods killed more than 200 people—the highest death toll in a flood event in Europe since the Lisbon flood of 1967.They also displaced more than 400 people, and left hundreds of thousands without water and electricity. Cyclone Chidodevastated the Mayotte archipelago, a French overseas territory located in the Indian Ocean between Madagascar and the coast of Mozambique, on December 14. It was the strongest cyclone to hit Mayotte in at least 90 years. A strong category 4 tropical storm, Chido also severely damaged parts of the Comoro Islands, northern Mozambique, and southern Malawi. Less than 2 weeks later, the international community marked the 20th anniversary of the 2004 Indian Ocean tsunami, one of the most destructive disasters in recent history, which claimed around 230,000 lives and wreaked havoc on 14 countries.
Importantly, the destructive events that marked the end of 2024 are not stand-alone. They are part of a larger phenomenon in which water-related, climate-induced events have killed, injured, and displaced thousands across the globe in recent years– despite significant advances in global hazard detection, forecasting, warning, and preparedness. Now, m id-way through the decade, translating the mounting frequency of climate impacts into a renewed sense of urgency amongglobal leaders and local communities to identify and implement effective solutions is increasingly critical as conditions worsen.
Water-related Environmental Extremes
Floods are the most common and widespread of all weather-related natural hazards, according to the US National Oceanic and Atmospheric Administration (NOAA). The US National Weather Service distinguishes between different kinds of floods, defined as overflows of water onto normally dry land. Floods are often caused by prolonged or intense rainfall, or snowmelt, and may last for days or weeks. Floods that occur when rivers or streams overflow their banks are calledriverine floods. Coastal flooding, on the other hand, is most frequently the result of storm surges and high winds coinciding with high tides. The most dangerous type of flood is flash floods. Rapid and extreme flows of high water across normally dry land can occur within a few hours or even minutes of torrential rainfall. They can also be caused by a sudden release of water from a dam or levee break and even mudslides. Densely populated areas are at a higher risk for flash floods because the construction of buildings, highways, and other infrastructure increases runoff by reducing the amount of rain absorbed by the ground. World Bank estimates show that 1.81 billion people, or 23 percent of the world population, are at risk of floods that pose significant risks to lives and livelihoods.
Tsunamis are another type of highly destructive water-related environmental hazard. The term “tsunami”—Japanese for “harbor wave”—refers to a series of giant ocean waves caused by the displacement of a large volume of water most commonly triggered by earthquakes or volcanic eruptions under the sea. Once generated, tsunamis radiate outward—i.e.,propagate—in all directions from their source. The height of the waves increases as they travel inland and the depth of the ocean decreases. The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave—i.e., the deeper the water, the faster they move. Although tsunamis are rare, the UN Office for Disaster Risk Reduction (UNDRR) classifies them among Earth’s deadliest natural hazards. In the past 100 years, 58 of them have claimed more than 260,000 lives, or an average of 4,600 per disaster, surpassing any other natural hazard. The highest number of deaths in that period was in the Indian Ocean tsunami of December 2004.
Tropical storms are called “typhoons” in the Western North Pacific, “cyclones” in the Western South Pacific and Indian oceans, and “hurricanes” in the Atlantic and Eastern Pacific oceans. They are rapidly rotating storm systems with a low-pressure center—i.e. the “eye of the storm”—and a spiral arrangement of thunderstorms that produce strong winds, heavy rain, and squalls. They derive their energy from the evaporation of water from the ocean surface, which then condenses into clouds and rain when moist air rises and cools to saturation. Since heat energy from the ocean acts as the accelerator for tropical storms, coastal regions suffer far more damage than inland regions. Coastal damage is often caused by strong winds and heavy rain, which could result in coastal flooding, as well as storm waves, and storm surges.
How does Climate Change Amplify the Risks of Water-related Disasters?
According to the most recent report by the Intergovernmental Panel on Climate Change (IPCC), disasters fueled by the climate crisis are already worse than scientists originally predicted. Celeste Saulo, Secretary General of the World Meteorological Organization (WMO), explained that “[a]s a result of rising temperatures, the hydrological cycle has accelerated. It has become more erratic and unpredictable, and we are facing growing problems of too much or too little water.” Climate change is amplifying the frequency and severity of water-related disasters, often compounding geophysical events like earthquakes and volcanoes. Furthermore, climate change is also impacting ocean patterns. Floods,tsunamis, and tropical storms are becoming stronger and more destructive as a result.
Rising sea levels not only make coastal communities more vulnerable to flooding from storms but also tsunamis. Increased volcanic and earthquake activity—a primary cause of tsunamis—has been associated with a phenomenon called “isostatic rebound”—the long-term uplift of land in response to the removal of ice sheets. The melting of permafrost(frozen soil) at high latitudes decreases soil stability, making it more susceptible to erosion and landslides. Global warming is accelerating the rate of iceberg calving. Wandering icebergs can trigger submarine landslides thousands of kilometers from the iceberg’s original source, as they hit unstable sediments on the seafloor. Tsunamis can be generated on impact as a landslide enters the water, or as water is moved by a rapid underwater landslide. More intense rainfall can trigger landslides too, as storms become more frequent and intense under the changing climate.
One of the most direct links between climate change and the increasingly frequent and severe impacts of tropical storms iscoastal flooding. Storm surges that accompany tropical storms can cause extensive flooding of coastal areas. A storm surge is a rise above normal sea level resulting from strong onshore winds and/or reduced atmospheric pressure. Tropical storms are now forming over higher sea levels, meaning that storm surges are higher and penetrate further inland than they would otherwise. Higher ocean surface temperatures and warmer, wetter atmospheric conditions provide a larger source of energy for tropical storms to draw on once they are formed. It is thus likely that they will become more intense—meaning, greater maximum wind speed and increased torrential rainfall. Climate change is also damaging manynatural coastal defenses, including coral reefs and mangroves, leaving communities and infrastructure more exposed.
A Call to Action
In the two decades since the tragedy provoked by the Indian Ocean tsunami, the international community has made significant strides in water-related disaster preparedness. In 2005, a year after the catastrophe, world nations convened under UNESCO’s Intergovernmental Oceanographic Commission (IOC-UNESCO) to establish the Indian Ocean Tsunami Warning and Mitigation System. The 10-year Hyogo Framework for Action was also adopted in 2005; it was the first comprehensive global agreement on disaster risk reduction.
Nonetheless, accelerated climate change, compounded by rapid urbanization and growing tourism in tsunami- and tropical storm-prone regions is getting ever-more people in harm’s way. According to UNESCO, 700 million individuals live in areas vulnerable to ocean hazards, including low-lying coastal areas and islands around the world. This number is expected to reach 1 billion by 2050. More risk reduction efforts are needed globally to achieve substantial reductions in disaster mortality. This is the primary goal of the Sendai Framework for Disaster Risk Reduction 2015-2030, the 15-year international agreement adopted in March 2015 to succeed the Hyogo Framework. The United Nations Office for Disaster Risk Reduction (UNDRR) coordinates the UN-wide implementation of the Sendai Framework. Today, 27 national tsunami warning centers can issue alerts within minutes of seismic and volcanic events. [1] [2]
Additionally, UN initiatives like the Tsunami Ready Programme and the Tsunami Project continue to empower local leaders and communities with life-saving knowledge and resources. Similarly, the Multi-Donor Trust Fund for Tsunami, Disaster and Climate Preparedness is developing vital early warning systems for all. Nevertheless, only half of countries worldwide report having adequate multi-hazard early warning systems to recent UN assessments. The impact is particularly severe in developing regions, where climate-related disasters cause fifteen times more deaths compared to other parts of the world. The UN Early Warnings for All initiative, launched in 2022, aims to reduce this critical gap by 2027. Despite these life-saving global efforts, the year 2024 suffered 24 billion-dollar weather and climate disasters—a total second only to the 28 annual disasters experienced in 2023. Among them, the US experienced one of its deadliest hurricanes as tropical storm Helene swept through the south-east and wreaked havoc across Appalachian mountain towns.
In his message to mark the 20th anniversary of the tsunami, Kamal Kishore, UN Special Representative for Disaster Risk Reduction exhorted the international community to continue engaging in effective disaster risk reduction. “It is crucial that we do not forget the 2004 Indian Ocean tsunami, and continue to do everything we can to protect ourselves, our children and our future generations from the impact of future tsunamis,” he emphasized. Climate, water, and environmental extremes respect no geographic or political boundaries, as often stressed by the World Meteorological Organization (WMO). This year marks a milestone for the WMO as it is the 75 anniversary of the convention that established this specialized UN organization. In his message for the new year 2025, the UN Secretary-General also reiterated the need for concerted climate action. As he urged, “[in] 2025, countries must put the world on a safer path by dramatically slashing emissions, and supporting the transition to a renewable future. It is essential—and it is possible.”