Climate Indicator Map Explorer: Southwest Case Study

Explore changes across the Southwest using climate change indicator datasets and guiding questions:

• Introduction to the Case Study
• What areas in the Southwest are experiencing changes in temperature and heat waves?
• How do changes in temperature in the Southwest compare to the rest of the United States?
• What other changes related to temperature are affecting the Southwest?
• Create Your Own Case Studies

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The Fifth National Climate Assessment (NCA5) reports:

Increases in extreme heat, drought, flooding, and wildfire activity are negatively impacting the physical health of Southwest residents (high confidence).

NCA5 Chapter 28: Southwest

An extreme heat event or heat wave is a persistent period of unusually hot days. “Unusually hot” refers to temperatures exceeding the 85th percentile of historical July and August temperatures. Heat waves are dangerous and can lead to illness and death. Older adults, small children, people with medical conditions, and other vulnerable populations, such as those without reliable access to air conditioning, are particularly vulnerable to heat dangers.

Let's explore changes across the Southwest using the climate change indicator datasets and a few guiding questions:

• What areas in the Southwest are experiencing changes in temperature and heat waves?
• How do changes in temperature in the Southwest compare to the rest of the United States?
• What other changes related to temperature are affecting the Southwest?

What areas in the Southwest are experiencing changes in temperature and heat waves?

Temperature in Southwest Cities

This map depicts annual anomalies, or differences, in average air temperatures in the Southwest from 2000 to 2020 compared to the long-term average of 1895 to 2023. An anomaly of +2.0°F means the average temperature was 2°F higher than the long-term average. States are divided into climate divisions, which are zones that share similar climate features.

Every part of the Southwest experienced warmer than average temperatures between 2000 and 2023 compared to the long-term average.

Los Angeles and San Diego are in the South Coast Drainage climate division, where temperatures from 2000 to 2023 were more than 2°F warmer than the long-term average.

Click on the map to explore how temperature is changing in the Southwest.

Heat Waves in Southwest Cities

This map depicts heat wave frequency, duration, season length, and intensity for large metropolitan areas. Cities in the Southwest have experienced an increase in heat wave frequency, duration, length of heat wave season, and intensity between 1961 and 2023. These trends are consistent with data averaged across the U.S.

To view how the different heat wave characteristics are changing in the Southwest cities, click on the map to explore layer options for Frequency, Duration, Season Length, and Intensity.

How do changes in temperature in the Southwest compare to the rest of the United States?

Now that you’ve explored the Southwest, let’s look at how temperatures are changing in other parts of the United States.

Rate of Temperature Change

This map shows how annual average air temperatures have changed from 1901-2023 by climate division. Some parts of the United States have experienced more warming than others. The North, West, and Alaska have seen temperatures increase the most, while some parts of the Southeast have experienced little change. Climate divisions in the Southwest have seen some of the largest increases in temperature.

Click on the map to see how temperature is changing across the United States.

Seasonal Temperature Change

Temperature changes vary by state, with larger seasonal increases occurring across the northern states and the Mountain West, and smaller increases in the South and Southeast. All 48 states experienced winter warming over this time period. Most states experienced warming in the spring, summer, and fall, but a few states had either little to no overall change or cooled slightly during those months. The Southwest experienced warming across every season.

To view how temperature is changing in different seasons, click on the map to explore layer options for Winter, Spring, Summer, and Fall.

What other changes related to temperature are affecting the Southwest?

As seen in the previous indicators, parts of the Southwest have experienced some of the largest increases in temperature in the United States. Warmer conditions are associated with drier conditions – as average temperatures rise, rates of evaporation increase, leaving less moisture available in the soil. Hotter and drier areas are more prone to drought and wildfires.

Drought

This map depicts total change in drought conditions across the contiguous 48 states, based on the long-term average rate of change in the five-year Standardized Precipitation Evapotranspiration Index (SPEI) from 1900 to 2023. Blue areas represent increased moisture; brown areas represent decreased moisture or drier conditions.

Drought conditions have increased the most in the Southwest.

Click on the map to explore how drought is changing across the United States.

Note: SPEI measures the combination of water supply (precipitation) and atmospheric water demand (evapotranspiration, which is based on temperature) to determine whether a certain area is experiencing extreme drought, extreme moisture, or conditions in between.

Wildfires

This map shows how the number of acres burned in each state as a proportion of that state’s total land area has changed over time, based on a comparison between the first half of available years (1984-2003) and the second half (2004-2022).

Parts of the West and Southwest show the largest increases in burned acreage.

Click on the map to explore changes in burned acreage by state.

Drought and Wildfires

The Climate Indicator Map Explorer includes an option to compare indicators. This is helpful when you want to view information side-by-side to compare data across multiple indicators, especially for area layers which would otherwise stack on top of each other.

Follow the steps below to explore how drought conditions and wildfires have changed in the Southwest region, which has the greatest increase in drought conditions and some of the highest increases in annual burned acreage.

Note: the Climate Indicator Map Explorer is included below for your convenience in following this tutorial, but it may be easier to view a larger version.

1. Dismiss the splash screen.
2. Select Compare Indicators under the All Indicators section of the Explorer tool.
3. On the left side of the screen, click on the eye icon for Weather and Climate, and toggle off all the layers besides Drought by clicking on the eye icon for each layer. Clicking on the eye icon can turn layers on or off to view additional information on the left-hand map.
4. On the right side of the screen, follow the same process for Wildfires, which is included in the Ecosystems section.

You can also drag and drop layers by clicking the six dots to the left of the layer title and dragging it to your desired draw order. If you drag one of the two maps to pan your view, the same panning action will apply to the other map. This is also true if you search for a specific address or place.

Create Your Own Case Studies

The EPA’s climate change indicator maps can be used to explore how climate-related trends are changing across the U.S. In addition to these examples, there are dozens more indicator layers related to weather and climate, oceans, snow and ice, health and society, and ecosystems.

• Determine your topic of interest; this step will help you select the relevant datasets. What climate topics or recent weather events spark your curiosity?
• Develop guiding questions to help further your exploration of the available data. For example:
  • What is your geographic region of interest?
  • How is winter temperature related to snowfall and lake ice?
  • How are leaf and bloom dates affected by changes in spring temperatures?
  • How does the length of the growing season compare to pollen seasons?
• Search the Climate Indicator Map Explorer to find relevant data. Think about other layers you might be able to display with EPA's climate change indicator data.