Bent's Old Fort Weather, Water Year 2021: A Wet May, a Cold February and 33 Very Hot Days

Bent's Old Fort. NPS/Stuart West.

Climate and water shape how ecosystems work, above all in arid and semi-arid lands, and understanding changes in them is key to judging the condition of a park's natural — and often cultural — resources. At Bent's Old Fort National Historic Site, the Park Service's Southern Plains Inventory and Monitoring Network tracks ecological "vital signs" year after year, much as a doctor tracks a patient's, to give early warning of problems. Climate and weather are among them.

Weather is conditions at a moment — rain, snow, a hot or bitter day. Climate is the pattern of weather over seasons to years, and the main driver of ecological processes.

Reports follow the water year, which runs from October of the previous year through September: water year 2021 is October 2020 to September 2021.

Bent's Old Fort National Historic Site. NPS/Stuart West.

The data

All figures come from the National Oceanic and Atmospheric Administration's Cooperative Observer Program weather station at La Junta Municipal Airport, Colorado (#054720), 4.2 miles (6.7 km) west of the site, running since 1945. "Normal" means the 1991–2020 average. The data are available through Climate Analyzer.

Figure 1. The weather station near Bent's Old Fort. NPS.

Precipitation

• Total: 10.43 in (26.5 cm) — 0.91 in (2.3 cm) below normal.
• May brought more than half the year's total: 5.37 in (13.6 cm), over three times its normal.
• September got twice its normal; every other month was near or below normal.
• Just one day of extreme rain (1 in or more): May 29, 2021, 1.35 in (3.4 cm) — fewer than the normal 1.8 such days a year.

Temperature

• Mean maximum: 1.0°F (0.6°C) above the normal 70.0°F (21.1°C); mean minimum: 0.5°F (0.3°C) above the normal 39.6°F (4.2°C).
• Months swung widely. February was far colder than normal — its mean maximum 10.4°F (5.7°C) below. November and September were much warmer, with mean maxima 7.7°F (4.0°C) and 5.5°F (3.1°C) above normal.
• Extremely hot days (above 99.0°F / 37.2°C): 33 — almost twice the normal 18.0.
• Extremely cold days (below 11°F / −11.7°C): 17 — close to the normal 17.7.

Drought

The reconnaissance drought index (Tsakiris and Vangelis, 2005) compares precipitation with potential evapotranspiration — the water that would be lost to evaporation and plant transpiration if supply were unlimited — over seasons to years. By that measure, water year 2021 was slightly drier than the 1991–2021 average.

Sources

Based on K. Raymond and A. Ray, "Climate and Weather Monitoring at Bent's Old Fort National Historic Site: Water Year 2021," Southern Plains Network, National Park Service, 2023; a work of the United States government in the public domain. Its climate chart and drought-index chart, credited to Climateanalyzer.org, are not reproduced.