#15 Temperatures & Precipitation

Temperatures & Precipitation

Part 1: Heat Waves, Droughts, and Wildfires

Activity-based Carbon Brief Reading (5-10 min)

• Many climate attribution studies focus on the Global North, while regions like central Africa, Oceania, and South Asia are underrepresented.

  1. Why do you think this is, and how might the lack of studies in these regions affect our understanding of climate change impacts and global policy?

  2. Can you find a recent extreme weather event in an underrepresented region and see if any attribution research has been done?

Outline

• Heatwaves

• Droughts

• Wildfires

• Case Study: California 2025

What's the Difference?

• Climate Change

  • Refers to the increasing changes in the measures of climate over a long period of time, including precipitation, temperature, and wind patterns.

• Global Warming

  • Refers to the rise in global temperatures due mainly to the increasing concentrations of greenhouse gases in the atmosphere.

Heatwaves

• A heat wave is a period of abnormally hot weather generally lasting more than two days.

  • Heat waves can occur with or without high humidity.

  • They have the potential to cover a large area, often exposing a high number of people to hazardous heat.

Heat Wave Characteristics in 50 Large U.S. Cities (1961-2021)

Average Number of Heat Waves per Year

Heat Wave Frequency

• Change in number of heat waves per year:

  • ≤2

  • > 2-4

  • > 4-6

  • > 6-8

  • > 8

  • Not statistically significant

Change in Length of Season (in days)

• ≤20

• > 20-40

• > 40-60

• > 60-80

• > 80

• Not statistically significant

Expanding Footprint of Extreme Summer Heat

• Percent area of U.S. Southwest experiencing extremely hot daytime high temperatures over the years (1920-2020).

Heat Wave Magnitude Index Daily (HWMId)

Magnitude Scale

Impact of Heatwaves on Health

• Heat exhaustion and heat stroke

• Cardiovascular issues

• Respiratory issues

• Mental health concerns

• Other health concerns such as drug interactions

Increase in Average Temperature and its Effects

• Probability of occurrence

  • Previous climate

  • New climate

• Less cold weather, more hot weather, more record hot weather

Droughts

• A drought is a deficiency in precipitation over an extended period.

  • It can be a part of normal climate variability in many climate zones.

  • The duration of droughts varies widely.

Impacts of Droughts

• Increased evaporation

• Altered precipitation patterns

  • Impact on soil moisture

  • Longer drought periods

  • Impact on water availability

Massachusetts Drought Status (Effective October 1, 2025)

• Drought Levels:

  • Level 0: Normal

  • Level 1: Mild Drought

  • Level 2: Significant Drought

  • Level 3: Critical Drought

  • Level 4: Emergency Drought

• Statistics:

  • 1.6 Million Massachusetts residents in areas of drought, according to the Drought Monitor (↓11.5% since last week)

  • 20th driest August on record (since 1895), with 2.28 in. total precipitation (↓1.62 in. from normal)

  • 57th driest January-August on record (since 1895), with 28.67 in. total precipitation (↓0.84 in. from normal)

Data & Maps on Drought Conditions

• As of November 11, 2025, 37.24% of the U.S. and Puerto Rico, and 44.43% of the lower 48 states are in drought according to the U.S. Drought Monitor.

• Statistics:

  • 189.1 Million acres of major crops in the U.S. are experiencing drought conditions this week.

  • 126.8 Million people in the U.S. and 126.0 Million in the lower 48 states are affected by drought this week.

  • 45 U.S. states are experiencing Moderate Drought (D1) or worse this week.

Drought Level Within the United States

Cumulative Percentage of Continental U.S. by Severity

• Recorded from 2018 to 2022 across various drought levels: Moderate Drought, Severe Drought, and Extreme Drought.

Drought Patterns in the Southwest U.S.

Precipitation - United States Southwest (Water Years)

### Temperature - United States Southwest (Calendar Years)

Why Doesn’t a Drought End When It Rains?

• Temporary Relief vs. Long-Term Cure:

  • A single rainstorm is like one dose of medicine: it eases symptoms but doesn’t end the problem.

  • Light or Moderate Showers:

    • Provide short-term “cosmetic” relief; most water evaporates or runs off.

  • Thunderstorms:

    • Heavy but brief rainfall often runs off into streams rather than replenishing soil.

Global Drought Trends

• Area (%) of World Experiencing Drought Yearly Since 1951, by Duration:

  • At least one month

  • Three months

  • Six months

  • Increasing frequency noted, particularly since the early 2000s.

Four Types of Drought

• Agricultural Drought:

  • Occurs when there is not enough moisture in the soil to sustain the growth of crops.

• Socioeconomic Drought:

  • Occurs when the water supply is too low to support human and environmental needs.

• Hydrological Drought:

  • Occurs when there is a lack of surface and subsurface water supply.

• Meteorological Drought:

  • Region-specific; occurs when an area receives less rainfall than normal.

The Relationship Between Droughts and Floods

• Warmer worldwide temperatures mean increased rainfall in some areas and decreased rainfall in others, leading to both increased flooding and more droughts.

Effects of Warming on Drought Severity

• Normal water cycle includes periods of dry or wet weather, but with rising temperatures, dry periods can become more intense.

• Increased evaporation from the land and ocean enhances drought severity.

Drying Effects of Warming on the Water Cycle

• More precipitation falls as rain, leading to:

  • Less snowmelt

  • Reduced soil moisture

  • Lower water table

  • Increased evaporation overall.

SOURCE: Meteorological Office, United Kingdom

Ecological Impacts of Droughts

• Vegetation Decline

• Species Decline

• Altered Food Webs

• Increased Fire Risk

• Soil Degradation

• Disrupted Water Cycles

Societal Impacts of Droughts

• Water Scarcity

• Agricultural Losses

• Economic Impacts

• Energy Production Disruptions

• Public Health Concerns

• Migration and Displacement

Wildfires

• A wildfire is an uncontrolled fire that burns in a natural area, such as a forest, grassland, or prairie.

• Can be caused by:

  • Natural events (e.g., lightning)

  • Human activity (e.g., discarded cigarettes).

Positive and Negative Effects of Wildfire

Positive Effects:

• Decreases disease

• Kills pests and burns away diseased organic matter

• Renews forest floor

• Clears space for new growth

• Can benefit certain tree propagation.

Negative Effects:

• Ecosystem damage

• Erosion

• Air pollution from smoke and greenhouse gases.

Wildfire Statistics in the U.S.

• The overall number of wildfires has remained fairly constant, yet land area burned has increased over time.

• Yearly Statistics (1983-2023):

  • Number of wildfires: (Data from National Interagency Fire Center)

  • Amount of land area burned (in acres)

Human Impact on Wildfires

• Humans cause nearly 90% of wildfires in the United States through prohibitive activities such as:

  • Discarded cigarettes

  • Unattended campfires

  • Burning debris or equipment malfunctions.

(Source: Western Fire Chief Association, Congressional Research Service 2022)

The Vicious Cycle of Wildfires

• Rising pollution from industry and traffic

• Deforestation reducing the absorption of CO₂ and production of oxygen

• Ice melting and changes in climate leading to hotter, drier environments, increasing wildfire occurrence.

Wildfire Seasons and Climate Change

• Wildfire season has extended by 105 days since the 1970s.

• Average wildfire area burned has also increased significantly.

Specific Cases of Wildfires in California

• As of March 19, 2025:

  • 545 wildfires burning 58,085 acres

  • 16,251 structures destroyed and 29 fatalities recorded.

  • Significant wildfires include the Palisades Fire, Eaton Fire, and Hughes Fire.

Factors Driving Wildfire in California

• Rising temperatures

• Drought conditions

• Dryer vegetation

• Longer fire seasons and increased burned area.

Understanding the Changing Fire Season in California

• Historical patterns show a shift in rainy seasons and prolonged dry periods.

Heatwaves in California

• Heatwaves per year are increasing in frequency, intensity, and duration from 1960 to 2020.

Observed and Projected Temperature Changes in California

• Average temperatures have increased overall, reflecting the impact of emissions.

Wildfire Health Impacts

• Negative effects include:

  • Poor air quality

  • Contaminated water quality

  • Soil erosion

  • Loss of vegetation

  • Health impacts on firefighters and vulnerable populations.

Measures to Avoid and Prevent Wildfires

• Recommendations from GREENPEACE to avoid actions leading to wildfires.

Wildfire Technologies

• Fire Urgency Estimator in Geosynchronous Orbit (FUEGO): A planned technology involving drones and satellites.

• Infrared Cameras: For heat detection.

• I4F Instant Foam: Eco-friendly fire-retardant foam.

• Supported Sensor Networks: Providing real-time data for firefighting activities.

Case Study: Australia's Bushfire Crisis

• Noteworthy statistics from the June 2019 to January 2020 bushfire season known as Australia’s Black Summer, including landscape and wildlife losses.

Frequency of Extreme Heat Events in Australia

• Data reflecting trends from 1910 to 2020.

Climate Change as a Driver in Australia’s Wildfires

• Factors affecting the bushfire crisis include rising temperatures, drought, and dryer vegetation.