Local Climate Trends in Salem, OR (1975-2024): Implications for Municipal Services

Understanding Our Changing Climate:

Salem, OR

Climate change is a global issue with local impacts we need to understand.
Analyzing our own historical data (50 years, 1975-2024) helps us see local trends. ¹
These trends affect how the city provides services (water, infrastructure, safety, etc.).
Our goal: provide data insights to help plan for future needs.

We often hear about climate change as a global phenomenon, and it is. But the impacts of climate change are felt very locally, affecting our specific environment and our community’s daily life. For a city like Salem, understanding these local changes is absolutely essential. Historical climate data provides us with a vital record, helping us identify patterns and trends that can inform how we anticipate and prepare for future challenges. This analysis covers 50 years of data for Salem, from 1975 through 2024, looking at key climate variables. The data for this analysis comes from daily summaries provided by the National Oceanic and Atmospheric Administration, or NOAA, covering that 50-year period from 1975 to 2024. Ultimately, these trends can directly affect how the city plans for and provides essential services – everything from managing our water supply to maintaining infrastructure and ensuring public safety.

Current Climate Baseline of Salem, Oregon

Temperature:

Average Annual High Temperature: Around 64°F
Average Annual Low Temperature: Around 43°F
Daytime Variations: Average monthly highs in the low 50s (°F) in Winter to the low 80s (°F) in Summer.
Nighttime Variations: Average monthly lows in the mid-30s (°F) in Winter to the mid-50s (°F) in Summer.

Precipitation:

Average Annual Precipitation: Approximately 42 inches.
Dry Summers: Summers are typically quite dry, with very little rainfall in July and August. For example, average precipitation in July and August can be less than half an inch.
Wet Winters: In contrast, December is often the wettest month, with an average of 7 inches of rain.

Snowfall:

Average Annual Snowfall: Approximately 4 inches.
Infrequent and Light Snowfall: Measurable snowfall is infrequent in Salem, typically occurring only a few days per year, averaging around 4 days. When it does fall, amounts are usually light, with most events seeing accumulations of 2 inches or less.

Decadal Temperature Shifts

Overall average temperatures are increasing over the decades, especially minimum temperatures.

Average temperatures in Salem have steadily increased over the past 50 years.
Nights are warming faster than days, with minimum temperatures rising more significantly.
The most recent decade was the warmest on average for both maximum and minimum temperatures.

Annual Temperature Swing Variability

Daily temperature varies annually, possibly with slightly more extreme maximums.

The typical year-to-year swing in daily temperatures has not been constant.
Variability in daily maximum temperatures appears to show a slight increase over the period.
Variability in daily minimum temperatures has been more stable.

Beyond just averages, we can look at how the variability of temperature within each year is changing. This graph shows the standard deviation of daily maximum [point to pink line] and minimum [point to blue line] temperatures for each year. Standard deviation is a measure of how much individual daily temperatures typically spread out from the average temperature of that year – in simpler terms, it gives us a sense of the typical temperature ‘swing’ within a year.

The key takeaway here is that the typical year-to-year swing in daily temperatures has not been constant; you can see the lines fluctuate quite a bit annually. We also see an indication that the variability in daily maximum temperatures [point to pink line] appears to show a slight upward trend over the 50 years. Variability in daily minimum temperatures [point to blue line], however, has been more stable, showing less of a clear trend upwards.

Seasonal Temperature Distribution & Variability

Summer maximum temperatures are significantly warming decade-over-decade, impacting the distribution and extremes, while Spring shows less clear warming.

Summer maximum temperatures show a clear warming trend across the decades.
Temperatures that were once unusually hot in summer are becoming much more common.
Spring maximum temperatures show less of a consistent warming trend compared to summer.

Now, let’s focus specifically on temperature patterns during our warmer seasons – Summer and Spring – and how they’ve changed by decade. This boxplot shows the distribution of daily maximum temperatures for Summer [point to blue boxplots] and Spring [point to pink boxplots] in each decade. The box represents the middle 50% of daily temperatures, the line in the box is the median, and the whiskers show the range, with dots indicating outliers or extreme days. The dashed lines show the 75th percentile of temperatures from the first decade, the 1970s.

This graph clearly shows that Summer maximum temperatures are significantly warming decade-over-decade. Look at how the blue boxes and medians shift upwards over time. What’s particularly impactful is how temperatures that were once unusually hot in summer – represented by that dashed line, the 75th percentile of the 1970s – are becoming much more common; they are now within or below the typical range of summer temperatures in recent decades. By contrast, Spring maximum temperatures [point to pink boxplots] show less of a consistent warming trend across the decades

Summer Temperature Trends by Month

Summer months show a trend of increasing average maximum temperatures over the years.

Summer warming is evident when looking at average temperatures specifically in July, August, and September.
Average maximum temperatures in key summer months, like July and August, have increased notably in recent decades.
This contributes to extended periods of summer heat.

Decadal Total Precipitation and Snowfall

Total precipitation lacks a clear trend, while total snowfall shows considerable decadal variation.

Precipitation volume far exceeds snowfall volume in Salem in all decades.
Total precipitation shows high variability from decade to decade, without a clear overall upward or downward trend.
Total snowfall volume is extremely inconsistent and unpredictable across decades.

Switching gears to precipitation and snowfall, this graph shows the total volume of each by decade. The green bars are total precipitation, and the blue bars are total snowfall for each decade.

The first thing that stands out is that precipitation volume far exceeds snowfall volume in Salem in all decades; rain is our dominant form of water input by volume. When looking at total precipitation [point to green bars], you can see high variability from decade to decade – some are wetter, some are drier – but there is no clear overall upward or downward trend across the 50 years. However, total snowfall volume [point to blue bars] is extremely inconsistent and unpredictable across decades. Look at the dramatic differences in the blue bar heights, from a peak between 1985-1994 and again between 2005-2014 to very low amounts between 1995-2004.

Annual Precipitation and Snowfall Variability

Daily precipitation varies considerably, and daily snowfall is highly unpredictable from year to year.

The year-to-year variability in daily precipitation amounts fluctuates significantly, showing no clear trend in daily consistency.
Variability in daily snowfall amounts is extremely volatile and unpredictable annually.
The occurrence of snowy years leads to sharp spikes in daily snowfall variability.

Similar to temperature variability, we can look at the year-to-year variability in daily precipitation and snowfall amounts. This graph shows the standard deviation of daily precipitation [point to green line] and daily snowfall [point to blue line] for each year. Again, standard deviation gives us a sense of the typical daily variation within a year.

The green line shows that the year-to-year variability in daily precipitation amounts fluctuates significantly. There isn’t a clear trend towards more or less consistent daily rain amounts over time; it just varies annually. For snowfall [point to blue line], the variability is extremely volatile and unpredictable year-to-year. Many years show zero or very low variability (meaning little to no snow), while others have sharp spikes [point to spikes] indicating years with significant variation in daily snowfall amounts because snow events occurred within those years. The occurrence of snowy years leads directly to these sharp increases in daily snowfall variability.

Fall and Winter Precipitation Patterns

Steady precipitation contrasts with variable frequency and intensity of extreme rainfall events.

Fall and Winter are the primary wet seasons with significant daily precipitation.
Typical daily precipitation amounts in Fall and Winter have been relatively stable across decades.
However, the frequency and intensity of very heavy daily rainfall events vary by decade.

Focusing on our wet seasons, Fall and Winter, this boxplot shows the distribution of daily precipitation amounts by decade. This helps us see if the pattern of how rain falls in these seasons is changing.

You can see that Fall [point to Fall boxplots] and Winter [point to Winter boxplots] are consistently the primary wet seasons with significant daily precipitation. The medians and boxes for typical daily precipitation amounts in both Fall and Winter have been relatively stable across decades. However, looking at the outliers [point to dots], which represent very heavy daily rainfall events, you can see their frequency and intensity vary by decade. This suggests that while the amount on a typical rainy day hasn’t changed much, the occurrence of extreme wet days might be shifting over time.

Winter Precipitation Mix: Rain vs. Snow

Winter precipitation is mostly rain, with snowfall being a minor and erratic element.

Rain is the overwhelming primary component of total volume in winter months.
Snowfall contributes a relatively small portion to total winter monthly volume.
The contribution of snowfall is highly variable and unpredictable by month and decade.

Finally, let’s look closely at the composition of our winter precipitation. This stacked bar graph shows the total monthly volume for January, February, and March in each decade, broken down into precipitation (rain - solid color) and snowfall (patterned).

This chart clearly shows that rain is the overwhelming primary component of total volume in winter months across all decades. Snowfall contributes a relatively small portion to the total winter monthly volume compared to rain. However, the contribution of snowfall is highly variable and unpredictable by month and decade. You can see how much the patterned blue section varies, showing significant inconsistency in the winter rain/snow mix over time. This means planning for winter conditions needs to consider both the overall volume (mostly rain) and the highly volatile potential for snowfall.

Implications for Municipal Services

Warming (Heat): Increased heat stress (public health), higher cooling demand, potential infrastructure impacts.
Warming (Milder Winters): Reduced heating demand, less reliable snow cover (recreation), potential freeze-thaw near 32F?
Precipitation Variability: Challenges for water supply (drought risk), stormwater management (intense rain), potential for both drier and wetter years/periods.
Snowfall Variability: Unpredictable demand for snow removal, budgeting challenges, less reliable snow-dependent planning.
Variability Overall: Planning for wider swings in conditions.

So, what do these observed climate trends mean for the services the city provides?

The warming temperatures, particularly the increase in summer heat, have implications for public health due to increased risk of heat stress, potentially higher energy demand for cooling, and impacts on infrastructure sensitive to heat. Milder winters could mean reduced heating demand, but also less reliable snow cover for any related activities, and potentially more damaging freeze-thaw cycles for our roads and sidewalks if temperatures fluctuate around freezing more often.

The precipitation and snowfall variability presents challenges. The high year-to-year and decadal variability in total precipitation, along with potential changes in extreme rainfall patterns, impacts water supply management and stormwater infrastructure. The extreme inconsistency in snowfall volume creates unpredictability for winter maintenance planning, budgeting for snow removal, and managing related infrastructure impacts.

Overall, the observed changes in both temperature and precipitation/snowfall variability suggest that planning may need to account for wider swings and more unpredictable conditions throughout the year.

Next Steps:

Further Analysis and Planning

This analysis provides a foundation; continued monitoring is needed.
Recommend further analysis:
- Snow Depth: Important for infrastructure load, water supply from melt.
- Analysis of freeze-thaw cycle frequency.
- Geospatial Analysis: Understand localized impacts within Salem.
- Analysis of other variables or extreme event metrics.
Use these insights to inform adaptation strategies and build a more resilient city.
Full analysis details available in the accompanying technical report.

Full analysis details available in the accompanying technical report: Assessing Local Climate Trends in Salem, Oregon (1975-2024): Implications for Municipal Services.

This analysis provides a foundational look at key climate trends in Salem over the past 50 years. To further enhance preparedness for future climate impacts, I recommend several areas for additional analysis.

It would be beneficial to investigate snow depth in addition to snowfall volume, as depth is critical for assessing infrastructure load and the contribution of snowmelt to our water supply. Analyzing the frequency of freeze-thaw cycles would provide crucial data for anticipating infrastructure maintenance needs related to pavement damage. A geospatial analysis looking at data from individual stations across Salem would help us understand if climate trends or impacts are localized in specific areas of the city. Further analysis of other variables or specific extreme event metrics could also provide valuable insights.

More detailed findings from this analysis, including methodology and all visualizations, are available in the accompanying technical report.

Utilizing these data-driven insights is key to informing targeted adaptation strategies and contributing to building a more resilient community here in Salem.

About the Presenter

Selene Faire

Graduate Student, Truman State University
- Studying Data Science and Analytical Storytelling
Business & Operations Analyst, UC Santa Cruz
- Applying analytical skills to operational challenges in a public sector environment.
This analysis was developed as part of graduate coursework focusing on data-driven communication.
Approach: Using the scientific process and data analysis to understand complex systems and inform planning.