Boulder County’s human population has increased nearly 600% in the last 70 years, with implications for watershed health.
2020 Trends | Watershed Health
The types of land cover in a watershed strongly influence the quality and amount of runoff. As the human population in Boulder County has substantially increased over the past several decades, there have been dramatic changes in land cover and land use, both of which may influence watershed health.
The human history of Boulder County can be traced back several thousand years to Paleo-Indian hunter-gatherers whose activities and livelihoods are revealed in the presence of archaeological sites.
By about 500 years ago, groups of Ute, Cheyenne, and Araphaho peoples resided in Boulder County, and riparian areas such as Boulder Creek were particularly important wintering grounds. In the mid 19th century, gold and silver deposits began to be exploited by European settlers, leading to the establishment and growth of mountain towns in western Boulder County, such as Gold Hill, Caribou, and Nederland.
During that period, the city of Boulder grew to support the mining industry and the city of Longmont developed primarily as a center of agricultural activity. The 20th century was a period of rapid population growth in Boulder County, fueled by the post WWII economy, the establishment of several US government laboratories and high-tech industries, and the growth of the University of Colorado.
Between 1950 and 2020, the population of Boulder County increased from about 48,000 residents to just over 330,000 residents; an increase of nearly 600% (Figure 1).
explore the data
Boulder County human population size, from 1870-2020
Figure 1. Boulder County human population size from 1870-2020. Source: https://worldpopulationreview.com/us-counties/co/boulder-county-population
The increase in the number of Boulder County residents clearly translates into more houses, roads, schools, and commercial infrastructure to support our communities. The maps shown below (Figure 2) display the areas of annexed urban land cover in the cities of Boulder, Longmont, Superior and Louisville, which have all increased substantially between 1950 and 2020.
These increases in urbanization result in greater area of impervious surfaces and new forms of inputs to surface water and groundwater in Boulder County.
Although the relationships between urban land cover and watershed health have not been extensively studied in Boulder County, we know from other urban centers that increasing urbanization can impact the watershed via greater inputs of potential pollutants in runoff, such as nutrients from lawn fertilizers, pesticides from lawn and garden chemicals, petroleum by-products from vehicles and roadways, and bacteria from human and animal waste that may move into our surface water and groundwater. The increase in human population may also increase the probability of human-ignited forest fires, which may also influence watershed health.
Figure 2. Urban land cover in Boulder County in 1950 (left panel) and 2020 (right panel). Yellow, orange, and red polygons represent areas annexed from 1872-1945, 1946-1993, and 1994-2020, respectively. Source: Data compiled by Boulder County Land Use Department staff from city of Boulder data and recorded ordinances for Longmont, Lafayette, Louisville, Lyons, and Superior.
recommendations
Boulder County must continue to prioritize ethical, sustainable population growth.
Boulder’s population is projected to continue to grow over the next few decades. Efforts that prioritize ethical, sustainable population growth are likely to provide a continued, high quality of life for Boulder residents.
Urbanization typically results in more concrete and more built structures, but there are ways to increase population density while decreasing per capita human impact.
Relevant to watershed health, it’s important to support activities that minimize or reduce urban land cover and impervious surfaces.
For example, converting lawns to pollinator gardens or other native landscapes, as well as decreasing the area of impervious surfaces in your residential landscape, will reduce potential pollutants that flow into nearby creeks and streams.