Data shows Boulder’s dry years are getting drier, while its wet years are getting wetter
Climate change is known to increase uncertainty when it comes to weather expectations - a trend we are seeing in Boulder County. Thirty years of precipitation data show that dry years are getting drier, wet years are getting wetter, and drought and flood events are becoming increasingly difficult to predict.
Rain on a mountain road. Photo by Zachary Spears / Unsplash
Knowing what to expect, in terms of annual precipitation, is helpful for our community. It helps growers plan their crops, ski lodges plan their season, and visitors plan their trip. But Matt Kelsch, Associate Scientist IV at the University Corporation for Atmospheric Research (UCAR), and John Brown, at NOAA’s Earth System Research Lab, have been tracking precipitation in Boulder daily for the last 30 years, and the data raise some complicated questions about Boulder’s climate future.
The data, presented below, show consecutive years with significant departures from the 30-year average in annual precipitation. The data suggest that our late winters and springs are getting wetter, while our summer months are getting drier (Figures 1 and 2). It’s unclear how much these changes are connected to climate change and how long this pattern may hold. Climate cycles typically run on decadal scales. However, cycles can be shorter, and much longer too.
Ultimately, this data set is a huge accomplishment and is pivotal to understanding climate trends in Boulder. However, the data raise more questions than they answer about our climate future, and it’s clear that uncertainty is an increasing part of the equation.
explore the data
Annual precipitation in the city of Boulder, from 1991 to today
Figure 1. This chart presents the percent departure from the average in annual precipitation each year (0% represents 21.22”, the annual average precipitation across the last 30 years). We can see consecutive “wet” years (i.e. years with significant departures above the average, represented by blue bars). For example, from 1995-1999, we had record-breaking highs in annual precipitation. And again in 2013, the year of the September floods in Boulder County, we saw a stretch of wet years that lasted until 2015. We can also see consecutive “dry” years (i.e. years with significant departures below the average, represented by red bars). A large portion of 2000-2010 was dry, which includes the severe drought of 2002. Dry years combined with high temperatures provide the ingredients for drought, which has important implications for the intensity of fires we will see in the years to come. Data provided by Matt Kelsch, Associate Scientist IV at the University Corporation for Atmospheric Research (UCAR) and John Brown, NOAA’s Earth System Research Lab.
Monthly precipitation in Boulder, from 1990 to 2020
Figure 2. This chart represents monthly precipitation values measured within the city of Boulder from 1990 to 2020. Each vertical bar is divided into lots of little rows or horizontal bands, with each band showing the total precipitation (in inches) for that month in a single year. The band on the bottom of each vertical bar is 1991; the band on the top of each vertical bar is 2019. Notice the months are organized in an unusual order along the horizontal axis of the figure. This is what is known as the water year. The term ‘water year’ is used by the U.S.Geological Survey to calculate surface-water supply within a 12-month period, starting October 1st through September 30th of the following year. (Learn more about how the U.S. Geological Survey uses this measurement). These data highlight that precipitation is extremely variable among years, i.e. some bands are narrow, and some bands are wide. The more precipitation, the wider and darker the band. Note: Months with precipitation of 0 in any given year are not represented in this figure. Data provided by Matt Kelsch, Associate Scientist IV at the University Corporation for Atmospheric Research (UCAR) and John Brown, NOAA’s Earth System Research Lab.
recommendations
Stay informed on the impacts of precipitation trends and get involved in community science projects
At 30 years, the data set presented here isn’t enough to quantify climate change or reliably predict our future climate. Thus, it is essential that we keep an ongoing record of precipitation and study emerging patterns.
To learn more about local weather phenomena and further understand how these fit into longer-term climate trends, educate yourself by reading the National Weather Service Denver/Boulder blog, with up-to-date information on Front Range weather.
You may also want to get involved in a community science project that tracks precipitation. A popular one that deploys volunteers across the country is the Community Collaborative Rain, Hail and Snow Network which reports a robust community database used by “meteorologists, hydrologists, emergency managers, city utilities (water supply, water conservation, storm water), insurance adjusters, USDA, engineers, mosquito control, ranchers and farmers, outdoor & recreation interests, teachers, students, and neighbors”.
This general-interest community records and maps precipitation rates across the nation.
