We frequently drive north on Highway 89 as we head to the Grand Canyon, Williams or Flagstaff. On one of our first trips after moving to Prescott Valley in 2020, the sight along the road north of Paulden shocked me. Large numbers of Juniper trees in vast sections of the forest were dying or already dead. It was clear drought was impacting them.
The US Forest Service reported in 2021, approximately 50,000 to 100,000 acres of junipers had been affected. Mortality was reported to be 5-30% of trees with larger pockets from 1 to 15 acres even higher. The impact on our iconic juniper-pinyon forests is a sad reminder of climate change.
Trying to better understand the cause of our drought, I analyzed our historical weather looking at Annual Average Highs & Lows, Annual Days with Precipitation, Annual Precipitation and Annual Snow (see attached spreadsheet). The results surprised me a bit. Our rising temps were more strongly driven by gradually increasing lows than highs. While high temperatures have been rising steadily in the last 45 years, they have only in the last five years exceeded highs experienced in the 1930s and 1940s.
In addition, precipitation is not abnormally low. It is in a range experienced regularly. NOAA Research has confirmed this observation concluding in November 2024, the drought is driven from rising temperatures and not lack of rainfall. The rising temperatures increase evaporation and stress the soil leading to an increased need for precipitation. So “normal” precipitation is not enough. The rising temperatures may have also led to a change in how we are getting precipitation. The amount of snowfall has been low relative to history for the last 25 years. Snow and the way it slowly melts into the ground is the best type of precipitation for soil. Changing the form of precipitation also contributes to the stress on the land.
The climate and weather are definitely changing. Nature will continue to adapt over time. What the future consequences of these changes are is yet to be seen. The juniper forests warn us though that some change will be hard and costly.
References
* https://www.fs.usda.gov/detail/prescott/news-events/?cid=FSEPRD904406
* https://www.extremeweatherwatch.com/cities/prescott/average-temperature-by-year
* https://www.extremeweatherwatch.com/cities/prescott/most-yearly-snow
* https://www.extremeweatherwatch.com/cities/prescott/most-yearly-precipitation
* https://www.nps.gov/articles/pinyon-juniper-woodlands-climate-change-and-literature-cited.htm
* https://research.noaa.gov/new-study-finds-heat-not-lack-of-precipitation-is-driving-western-u-s-droughts/