Understanding the Connection Between Climate Change and Flooding

Flooding has always been a part of human history, but projections indicate a future with increasingly frequent and severe flooding events.

The imagery of individuals assessing the wreckage of their flood-damaged homes is heart-wrenching. Flooding is a widespread issue encountered annually by residents in mountainous areas, rural farmland, urban districts, and along coastal shores. The relationship between climate change and flooding is complex; flooding is a natural occurrence that began long before the Anthropocene era. So, how does climate change relate to flooding? The main link is that climate change enhances the frequency and severity of damaging flood events. Nonetheless, various forms of flooding exist, and climate change influences each type differently.

The Perils of Storm Surge

On the night of August 17, 1969, Ben Duckworth clung to an ancient oak tree in Pass Christian, Mississippi, as Hurricane Camille unleashed winds exceeding 175 miles per hour and a 24-foot storm surge. This devastating storm destroyed the Richelieu Manor Apartments, where Ben sought refuge. His desperate escape to the roof ended when the violent winds and water swept him away, but the tree ultimately saved his life. By dawn, only the foundation of the apartment building remained.

Fast forward to August 29, 2005, when Hurricane Katrina barreled through the Gulf of Mexico, delivering a 25-foot storm surge that breached New Orleans’ flood defenses, resulting in over 1,800 fatalities and a staggering $168 billion in damages.

Storm surge is just one type of coastal flooding associated with hurricanes. Its rapid onset and unpredictable destruction make it particularly dangerous. These surges are driven by low atmospheric pressure and wind rather than rainfall.

Mechanics of Storm Surge

Storm surge is influenced by two key elements: atmospheric pressure and wind intensity. The pressure at a hurricane's center is lower than in its outer regions, causing water to accumulate beneath the storm's eye. The lower the pressure, the higher the water rises. However, wind-driven surge often causes more devastation.

In the northern hemisphere, hurricane winds circulate counterclockwise around the storm's eye. When Camille and Katrina made landfall, eastern winds pushed water landward. The interaction between wind and ocean friction intensified the surge, making it comparable to a tidal wave rather than a conventional wave. The relentless pressure of the surge can devastate structures, pushing inland until the storm passes.

Climate Change and Storm Surge

While storm surges are fundamentally caused by wind and pressure, climate change exacerbates their danger through warmer oceans and more powerful hurricanes. Research indicates an increase in Category-3 storms since the 1980s, suggesting that while not every hurricane is stronger, the likelihood of encountering more intense storms each year is rising. This increased intensity elevates the risk of significant storm surge flooding, particularly for coastal communities.

Pluvial Flooding: A Prolonged Downpour

Hurricane Harvey's path exemplifies pluvial flooding, as it lingered near the Texas-Louisiana border for four days after making landfall on August 26, 2017. The storm unleashed over 40 inches of rain, inundating Houston and leading to damages of $130 billion, making it the second-costliest disaster in U.S. history.

Flooding types vary, but pluvial flooding arises from the convergence of heavy rainfall and flat terrain. In mountainous regions, rainwater flows downward, eroding land and directing runoff towards oceans. However, flatlands lack the topographical features necessary for efficient drainage, leading to water accumulation.

Urban settings are particularly vulnerable to pluvial flooding due to extensive concrete surfaces that hinder soil absorption, causing water to pool in the lowest areas. Cities like New Orleans, situated below sea level, resemble large bowls that fill rapidly with water, outpacing drainage systems.

Climate Change and Pluvial Flooding Risks

Significant pluvial flooding results from extreme rainfall paired with flat geography. Harvey struck as a Category 4 hurricane, drawing moisture from warm Gulf waters. Although the storm weakened upon landfall, it continued to extract moisture, resulting in catastrophic flooding.

Globally rising ocean temperatures fuel more powerful storms, heightening the threat of pluvial flooding in low-lying coastal cities. This trend poses a greater risk than storm surges in such areas.

Fluvial Flooding: Rivers Overflowing

In Nelson County, Virginia, remnants of Hurricane Camille in August 1969 serve as a stark reminder of the devastating impact of fluvial flooding. That night, over two feet of rain fell in just eight hours, leading to over 150 fatalities due to flash floods. While Camille caused destruction with its storm surge in Mississippi, it was the torrential rains that wreaked havoc in Virginia.

In 2019, the Midwest faced over five months of persistent flooding. Following an unusually cold winter, rapid spring warming and heavy rainfall led to overwhelming runoff. The frozen ground could not absorb the excess water, contributing to significant flood damage affecting millions.

Cumulative Flow Phenomenon

Flooding manifests in various forms, including storm surge, tidal flooding, pluvial flooding, and fluvial flooding. Both Nelson County and the Midwest experienced fluvial flooding, which results from cumulative flow. Rivers collect water from an extensive network of tributaries. When precipitation exceeds the rivers' capacity, flooding ensues.

Extreme Weather Patterns

Climate change is linked to an increase in extreme weather events, including catastrophic fluvial flooding. A warmer atmosphere retains more moisture, leading to greater precipitation. Additionally, the warming Arctic weakens the polar vortex, resulting in a meandering jet stream that drives extreme temperature variations and rapid snow melts.

Coastal Inundation: A Gradual Decline

The conversation about rising sea levels often highlights the fate of cities like Miami, which face gradual inundation rather than sudden disaster. The dual factors of thermal expansion and melting ice caps contribute to rising ocean levels. According to NOAA, the global sea level has risen by 9 centimeters over 25 years, with thermal expansion accounting for 40% of this increase.

Communities in low-lying coastal areas are increasingly affected by flooding from major storms as well as nuisance flooding, which occurs more frequently due to rising sea levels. NOAA reports that high-tide flooding has become 300% to over 900% more common than it was 50 years ago.

The Slow Spiral Downward

Nuisance flooding leads to initial inconveniences, such as inundated streets, which gradually escalate to structural damage in homes. As neighborhoods experience frequent flooding, property values decline, and homeowners face financial strain, exacerbating the community's deterioration.

The Core Issue: Heat

Global warming is the common thread connecting environmental shifts that result in both increased flooding frequency and intensity. Rising sea levels, fueled by melting ice caps and thermal expansion, contribute to heightened tidal flooding. Warmer oceans generate more powerful storms, while a warmer atmosphere leads to heavier rainfall and increased runoff, culminating in both fluvial and pluvial flooding.

The warming Arctic further disrupts weather patterns, leading to extreme temperature fluctuations and significant snow melts. While flooding has long been a natural occurrence, future projections indicate a rise in both the frequency and severity of flooding events, ultimately shaping our experience of this natural disaster.

The first video discusses how climate change is exacerbating flooding. It provides insight into the connection between rising temperatures and increased flood risks.

The second video explores why global warming is intensifying heavy rainfall events, highlighting its implications for flooding severity and frequency.