The influence of climate change on California wildfires and type of vegetation burned

Abstract

Large California wildfire activity increased suddenly in the mid-1980’s and has been increasing ever since. The cause of this increase has not been clear. This thesis focuses on the correlation between number of acres burned in Mariposa County, California, and the type of vegetation burned under the influence of climate change. The research question is: “How are the number of acres burned by wildfires and type of vegetation burned connected to climate change in Mariposa County?” California data (wildfire frequency and number of acres burned) has been used to determine regional trends in acres burned. Thereafter, Mariposa County data has been analyzed to determine local trends in wildfire and the influence of weather on number of acres burned and type of vegetation burned. Wildfire data (number of acres burned, and type of vegetation burned) and average annual weather data (maximum temperature, minimum temperature and precipitation) in Mariposa County over a period of 1950 to 2013 have been used. Statistical analyzes using Pearson Correlations were performed. The main findings of the research are summarized as followed: first, a significant increase in Mariposa County and California area burned due to wildfires is found in the data. The influence of climate change on the weather in Mariposa county is less clear. The average annual minimum temperature shows a significant increase of over 1.5 degrees Celsius in the period of 1950-2013. The maximum temperature and precipitation do not show such a trend. Furthermore, no significant direct correlation between weather patterns and number of acres burned or type of vegetation burned has been found. A more indirect correlation between 9year moving averages of woodland area burned and minimum temperature could be found (Pearson’s r = 0.829, p < 0.01). If there is a causality, the increase in woodland area burned in Mariposa County could be caused by an increased minimum temperature. This increase in minimum temperature could be caused by climate change. Therefore, the increase in woodland area burned in Mariposa County could have been possibly caused by climate change.