Understanding Extreme Precipitation: Risks, Impacts, and Climate Resilience

Zurich, December 10th, 2024

Extreme precipitation events are becoming more frequent and severe due to global warming, as rising temperatures increase the atmosphere's ability to hold more moisture. This intensification, shaped by both thermodynamic and atmospheric dynamics, poses significant risks to communities, infrastructure, and economies worldwide. Understanding these processes is crucial for mitigating impacts and building resilience in an increasingly volatile climate.

More frequent and severe precipitation events

From the devastating floods in Valencia in October 2024 to recent events in Germany, Nepal, and other regions, extreme precipitation is becoming more frequent and intense. These heavy precipitation events often induce floods in lower-elevation zones and areas with infrastructure that cannot withstand high amounts of water. In turn, they lead to significant impacts on communities, serious damage to infrastructure, disruptions in supply chains, food shortages, or damages to energy and electricity networks across entire regions. But what drives these heavy rainfall events?

The causes of extreme precipitation events

A key factor lies in atmospheric humidity and its relationship with temperature. As global temperatures rise, the air can hold more water vapor. The underlying physics is known as the Clausius-Clapeyron relationship, which states that for every 1°C increase in temperature, the atmosphere can hold about 7% more water vapor. This means warmer air carries more moisture, increasing the potential for heavy rainfall when conditions are right.

Generally, water vapor does not stay evenly distributed. Atmospheric moisture decreases with altitude and latitude, and under certain conditions—like slow-moving weather systems—this excess moisture can lead to local extreme rainfall. The effects are exacerbated by regional factors like ocean currents, topography, and urbanization. Combined, these elements make dynamic weather systems where small changes in temperature can have outsized impacts.

While the Clausius-Clapeyron relationship explains the foundational link between temperature and atmospheric water-holding capacity, the manifestation of extreme precipitation is far more complex. Articles such as that by Meyer et al. (2022) in Hydrology and Earth System Sciences and Fischer & Knutti (2016) in Nature Climate Change highlight that these events are shaped by a complex interplay of thermodynamic processes, atmospheric dynamics, and localized conditions, which can either amplify or modulate precipitation intensity.

Global warming not only increases the water vapor capacity of the atmosphere but also enhances the energy available for storms. Warmer air leads to greater latent heat release during condensation processes, fuelling storm intensification. This effect is particularly pronounced in systems where warm, moist air is rapidly uplifted, as seen in tropical cyclones and convective storms.

Moreover, dynamic processes in the atmosphere, such as slow-moving or stationary weather systems, act as primary triggers for heavy rainfall events. Key factors include:

Stationary Weather Patterns: When jet streams become “blocked” or meander, they can trap weather systems over specific regions, leading to prolonged rainfall.
Atmospheric Rivers: Narrow bands of moisture-laden air, often originating over the ocean, can release enormous amounts of rain when they encounter mountains or cold air masses.
Cut-off Lows: These isolated low-pressure systems can intensify local precipitation due to their slow movement and interaction with humid air masses.

Regional influences may also have strong impacts on precipitation patterns. For example:

Topography: Mountainous regions intensify rainfall through orographic lifting, where moist air is forced upward, cooling and condensing to release precipitation.
Regional Variability: In drier or arid regions, reduced evaporation rates can limit moisture availability, potentially offsetting the thermodynamic increase. Conversely, in humid regions with ample moisture, the amplification of extreme precipitation is more pronounced.
Urbanization: Urban areas disrupt natural water drainage systems, preventing water from being absorbed into the ground and causing it to flow over surfaces, which can intensify the local impacts of precipitation events.

Finally, another cause of extreme precipitation events is related to sub-daily intensification. While the Clausius-Clapeyron relationship predicts a 7% increase in atmospheric moisture per degree of warming, studies indicate that sub-daily rainfall intensities can exceed this rate. So-called convective processes, which dominate short-duration intense weather events, can amplify the overall scaling effect of the Clausius-Clapeyron relationship. For instance, localized downpours lasting minutes to hours may scale at 10% or more per degree of warming due to increased atmospheric instability and additional energy availability.

The rising frequency of extreme precipitation events under global warming

Global warming is expected to continue as greenhouse gas emissions rise, absorbing more energy and increasing temperatures, resulting in a cascade of impacts on the Earth’s climate systems. As a side note, even if emissions were to stabilize, the gases already in the atmosphere would continue to absorb and re-radiate energy, driving further warming and climate impacts. One of the most concerning outcomes is the increasing frequency and intensity of heavy precipitation events. These changes are already evident in the devastating floods seen worldwide, such as that in Valencia in October and November2024, which led to loss of life, severe impacts on the community, extensive property damage, and infrastructure disruption.

The frequency of heavy precipitation events will increase in a non-linear way with more warming, and this increase will be greater for rare events. With high confidence, it’s expected that at 4°C of global warming, the frequency of 10-year events could double, and 50-year events could triple compared to the recent past.

A recent study also highlights that, in general, the increase in frequency per degree of warming is much higher than the increase in intensity. This means that the overall change in extreme precipitation is driven more by the increase in frequency of these events than by their intensity, although that total changes in extreme precipitation are a result of combined changes in both intensity and frequency and both processes are important to consider.

Why it matters

Understanding the underlying physics of extreme precipitation is vital for accurately assessing the risks it entails. By delving into the scientific mechanisms, such as the Clausius-Clapeyron relationship and the dynamic processes that drive extreme weather, we can gain critical insights into the factors amplifying these events. This knowledge enables scientists, policymakers, and businesses to better predict when and where such events are likely to occur, ultimately improving early warning systems and reducing exposure to impacts.

Equally important is fostering a widespread understanding of these risks among communities and businesses. Extreme precipitation is no longer an abstract or rare occurrence; it is a growing global reality with social, environmental, and economic impacts. Raising awareness about the factors that drive these events helps both individuals and organizations recognize their vulnerabilities and empowers them to take proactive measures. This could involve upgrading infrastructure to withstand heavier rainfall, improving land use planning, or integrating climate risk considerations into business strategies.

By making the science behind extreme precipitation a common understanding, communities and businesses can transition from reactive responses to proactive risk mitigation. Such an approach minimizes disruptions, safeguards livelihoods, and builds resilience in the face of a changing climate.

Extreme precipitation assessments with Correntics

Correntics offers a cutting-edge platform for physical climate risk assessment, providing businesses with the tools to effectively navigate the growing challenges posed by extreme precipitation and other climate-related hazards. As highlighted in the preceding chapters, understanding the complex interplay of atmospheric dynamics, thermodynamics, and localized factors is critical for mitigating the risks posed by a warming climate. Our solutions are designed to bridge this scientific knowledge with actionable strategies for building resilience.

At Correntics, we integrate advanced climate risk analytics, regional hazard exposure assessments, and scenario modelling into a comprehensive risk assessment software. Our platform allows businesses to assess how extreme precipitation events, like floods and prolonged rainfall, could impact their operations, infrastructure, and supply chains. By identifying vulnerabilities and quantifying risks, companies can prioritize investments in adaptation measures and make informed decisions to safeguard their assets.

Beyond quantifying risks, Correntics aligns its assessments with global reporting standards such as TCFD and CSRD, ensuring that our clients can seamlessly incorporate climate considerations into their sustainability disclosures. From evaluating risks to developing proactive strategies, our platform empowers businesses and communities to adapt to an evolving climate landscape. By turning insights into action, Correntics helps organizations not only reduce vulnerabilities but also seize opportunities for sustainable growth in a changing world.