This study examined the relationship between annual precipitation and wildfires in California from 1959-2013. The researchers found a weak negative correlation between precipitation and total wildfires statewide, with precipitation explaining only 0.6% of the variance in wildfire counts. Similarly, there was a weak positive correlation between precipitation and total acres burned in Southern California, with precipitation explaining only 0.47% of the variance. Overall, the study found no strong correlation between precipitation and either wildfire counts or acres burned statewide or in Southern California. The researchers suggest focusing future studies on smaller geographic areas or additional variables that could influence wildfires.

1. A Study of Annual California Wildfires and Precipitation from 1959-2013
Paula Gluss1 and Allie Andrade2
University of Washington Department of Mathematics1, Department of Community, Environment and Planning2
INTRODUCTION
Times Series of Precipitation vs Total Wildfires
Figure 1: The time series chart depicts the total number of wildfires and the total
annual precipitation. We can see that there is a slight pattern between high rainfall
and a low number of wildfires and vice versa.
In the last decade, California has experienced a serious drought and a series of
raging wildfires. This research explores whether or not there is a correlation
between the average annual precipitation and the number of wildfires or acres
burned. We chose to examine the state of California as a whole and then honed in
on the Southern most district of California in order to reduce geographical variation.
Data Sources:
• Annual Precipitation in California: NOAA Climate Monitoring Data
• Annual Total Statewide Wildfires and Acreage Burned: CAL Fire Historical Wildfire Activity
Statistics
Collection Methods:
• We chose to examine data from 1959-2013 because earlier precipitation and wildfire data is not
complete or reliable.
• While fire data for California is complete, the districts change boundaries over the years, making
the data for one district inconsistent from 1959-2013
1. Is there a correlation between the average annual precipitation and number of
wildfires in California?
2. Is there a correlation between the average annual precipitation and the total
number of acres burned in Southern California?
Total Number of Wildfires and Precipitation Statewide
RESULTS
METHODS
RESEARCH QUESTIONS
y = -32.757x + 9175.4
R² = 0.0062
0
2
4
6
8
10
12
14
16
5 10 15 20 25 30 35 40 45
NumberofWildfires(thousands)
Total Annual Precipitation (inches)
Total Annual Precipitation and Wildfire Count from 1959-2013
Time Series of Precipitation vs Acres Burned
Total Acreage Burned and Precipitation in Southern California
Figure 2: The linear regression chart graphs the total number of wildfires and the
total annual precipitation. It shows a weak, but slightly negative correlation
between annual precipitation and total wildfires in CA. The R2 value is very small
and only 0.6% of variance in total wildfires can be explained by annual precipitation.
Figure 3: The time series chart depicts the total acreage burned and the total annual
precipitation. We can see that there is a slight pattern between high rainfall and a
low number of wildfires and vice versa.
y = 429.77x + 30931
R² = 0.0047
0
20
40
60
80
100
120
140
160
0 5 10 15 20 25 30
TotalAcreageBurned(thousands)
Precipitation (inches)
Southern California Total Annual Precipitation and Total Acres
Burned from 1959-2013
• Less than 80% confident that based on our data, total acreage burned is
positively associated with total precipitation in Southern California.
• No strong correlation between annual precipitation in inches and wildfire counts
or acreage burned in either California as a whole or in Southern California.
Average Acreage Burned per Decade with Standard Error Bars
Figure 4: The linear regression chart graphs the total acreage burned and the total
annual precipitation. It shows an even weaker, but slightly positive correlation
between annual precipitation and total acres burned. The R2 value is very small and
only 0.47% of variation in total acres burned can be explained by annual
precipitation. The significance level is less than 0.20.
The ANOVA results are not significant at a 0.05 or 0.01 level, which means that we
are not confident that there is a significant difference between acreage burned
each decade. Only 11.69% of the variation in acreage burned can be explained by
the decade. The ANOVA test revealed that there is a lot of variation in our data.
ANOVA Single Factor Test
CONCLUSIONS
• Focus on a particular city or country rather than a large district.
• Examine a particular class or size of fire and the resulting acreage burned.
• Examine previous year’s rainfall to see if it reduces the wildfire count or acreage
burned in the following year.
• Consider other variables in the cause of wildfires such as industrialization, clear
cutting, and reducing ground water reserves.
FUTURE RESEARCH
Figure 4
Figure 5: Due to high variation in our data, we chose to use standard error bars in
the bar chart of the average acres burned per decade.
State Total Wildfire & Total
Precipitation
Research Topic
SoCal Total Acres Burned &
Total Precipitation
Linear Regression
California Annual
Precipitation and Wildfires
Research Question Analysis Technique
ANOVA Test
Time Series Plot