9.3 Impacts on hydrological cycle, sea level, and extreme events

Climate change is messing with our water cycle big time. It's causing more extreme rain in some places and worse droughts in others. This is happening because the atmosphere can hold more moisture as it warms up.

These changes are also affecting sea levels and extreme weather events. As oceans heat up and ice melts, sea levels rise, threatening coastal areas. Meanwhile, we're seeing more intense heat waves, stronger storms, and longer droughts in many parts of the world.

Precipitation Patterns and the Hydrological Cycle

Global Precipitation Changes

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• Global precipitation patterns show significant changes over the past century
  • Some regions experience increased rainfall
  • Other areas face more frequent droughts
• Intensification of the hydrological cycle leads to more extreme precipitation events
  • Particularly affects mid-latitude and tropical regions
  • Results in heavier rainfall and potential flooding
• Changes in atmospheric circulation patterns alter global precipitation distribution
  • Expansion of the Hadley cell impacts tropical and subtropical rainfall
  • Shifts in jet streams affect mid-latitude precipitation patterns
• Monsoon systems exhibit changes in timing and duration
  • Affects seasonal rainfall in regions like South Asia and West Africa
  • Impacts agricultural practices and water resource management

Atmospheric and Cryospheric Factors

• Atmospheric water vapor content increases due to higher global temperatures
  • Leads to changes in cloud formation processes
  • Alters precipitation intensity and frequency
• Alterations in snow and ice cover impact local and regional hydrological cycles
  • Particularly affects polar regions (Arctic and Antarctic)
  • Influences high-altitude areas (Himalayas, Andes)
  • Changes in snowmelt timing affect river flow patterns
  • Glacier retreat alters water availability in glacier-fed river systems

Climate Change Impacts on Coasts

Sea Level Rise Measurements and Causes

• Global mean sea level rises approximately 20 cm since 1900
  • Rate of increase accelerates in recent decades
  • Caused by thermal expansion of oceans
  • Melting of land-based ice (glaciers and ice sheets) contributes significantly
• Satellite altimetry and tide gauge measurements provide evidence of regional variations
  • Some areas experience rates significantly higher than the global average (Western Pacific)
  • Others show lower rates or even slight decreases (parts of Scandinavia due to post-glacial rebound)

Coastal Impacts and Adaptation

• Coastal erosion and inundation of low-lying areas increase
  • Threatens infrastructure (ports, roads, buildings)
  • Impacts coastal ecosystems (mangroves, salt marshes)
  • Affects human settlements in vulnerable regions (Maldives, Bangladesh)
• Salt water intrusion into coastal aquifers and estuaries occurs
  • Impacts freshwater resources for drinking and irrigation
  • Reduces agricultural productivity in coastal areas (rice paddies in Vietnam)
• Combined effects of sea level rise and storm surges increase flooding risks
  • Amplifies damage to coastal communities during extreme weather events (Hurricane Sandy in New York)
• Adaptation strategies implemented to mitigate impacts
  • Coastal protection measures (sea walls, levees)
  • Managed retreat (relocation of communities)
  • Nature-based solutions (restoration of mangroves and wetlands)

Extreme Weather Trends

Temperature and Precipitation Extremes

• Global warming increases frequency and intensity of heat waves
  • Record-breaking temperatures become more common (European heat wave of 2003)
  • Urban heat island effect exacerbates impacts in cities
• Extreme precipitation events become more frequent and intense
  • Heavy rainfall leads to increased flooding risks
  • Changes driven by increased atmospheric moisture content
  • Affects both urban and rural areas (Bangkok floods of 2011)

Tropical Cyclones and Droughts

• Tropical cyclones (hurricanes and typhoons) show regional variations
  • Some basins experience more intense storms due to warmer sea surface temperatures
  • Changes in frequency less certain and vary by region
  • Examples include Hurricane Katrina (2005) and Typhoon Haiyan (2013)
• Drought conditions intensify and become more prolonged in certain regions
  • Particularly affects subtropical and mid-latitude areas
  • Caused by changes in precipitation patterns and increased evaporation rates
  • Examples include California drought (2011-2017) and Australian Millennium Drought (1997-2009)

Wildfires and Compound Events

• Frequency and extent of wildfires increase in many regions
  • Exacerbated by warmer temperatures and prolonged dry periods
  • Changes in vegetation patterns contribute to fire risk
  • Examples include Australian bushfires (2019-2020) and California wildfires (2018, 2020)
• Compound extreme events become more common
  • Multiple hazards occur simultaneously or in close succession
  • Poses greater risks to human and natural systems
  • Examples include simultaneous heat waves and droughts, or successive hurricanes in the same region

Attribution of Hydrological Change and Extreme Events

Climate Modeling and Observational Evidence

• Advanced climate models and observational data improve attribution confidence
  • Allow scientists to link changes to human activities
  • Combine multiple lines of evidence (temperature records, satellite data, proxy records)
• Anthropogenic increase in greenhouse gas concentrations identified as primary driver
  • Explains observed changes in global precipitation patterns
  • Accounts for intensification of the hydrological cycle
  • Supported by paleoclimate records and model simulations

Attribution of Specific Phenomena

• Human-induced global warming significantly contributes to increased heat waves
  • Attribution studies show anthropogenic influence on frequency and intensity
  • Examples include Russian heat wave (2010) and European heat wave (2019)
• Anthropogenic climate change linked to tropical cyclone intensification in some regions
  • Warmer sea surface temperatures provide more energy for storm development
  • Natural variability still plays a significant role in cyclone activity
• Increased risk of extreme precipitation events attributed to climate change
  • Thermodynamic processes (increased moisture) play a major role
  • Dynamic processes (circulation changes) also contribute
  • Examples include increased monsoon rainfall intensity in South Asia

Land-Use Changes and Local Impacts

• Land-use changes exacerbate climate change impacts on hydrological cycles
  • Deforestation alters local precipitation patterns and water retention
  • Urbanization increases flood risks through reduced permeability
  • Agricultural practices affect soil moisture and evapotranspiration rates
• Human activities amplify extreme weather event impacts
  • Urban development in flood-prone areas increases vulnerability
  • Coastal development exacerbates risks from sea level rise and storm surges
  • Examples include increased flood risks in rapidly urbanizing areas of Southeast Asia