Bent's Old Fort National Historic Site21쪽 중 6쪽

Climate and Weather Monitoring at Bent's Old Fort National Historic Site: Water Year 2023

The morning sun is glowing radiantly through green leaves on large trees scattered through a grassy area.

Bent's Old Fort National Historic Site, Colorado NPS/STUART WEST

Overview

Together, climate and hydrology shape ecosystems and the services they provide, particularly in arid and semi-arid ecosystems and across the Southern Plains (Woodhouse and Overpeck 1998). Understanding changes in climate, groundwater, and surface water is key to assessing the condition of park natural resources—and often, cultural resources.

At Bent’s Old Fort National Historic Site (Figure 1), Southern Plains Inventory and Monitoring Network scientists study how ecosystems may be changing by taking measurements of key resources, or “vital signs,” year after year—much as a doctor keeps track of a patient’s vital signs. This long-term ecological monitoring provides early warning of potential problems, allowing managers to mitigate them before they become worse. We monitor climate, among other vital signs at the park.

Climate and weather reporting is by water year (WY), which begins in October of the previous calendar year and goes through September of the water year (e.g., WY2023 runs from October 2022 through September 2023). This article reports the results of climate monitoring at Bent’s Old Fort National Historic Site in WY2023.

Reference: Woodhouse, C. A., and J. T. Overpeck. 1998. 2000 years of drought variability in the central United States. Bulletin of the American Meteorological Society 79(12): 2693–2714. https://doi.org/10.1175/1520-0477(1998)079%3C2693:YODVIT%3E2.0.CO;2.

Go to Climate and Weather, Past Findings

Climate and Weather

There is often confusion over the terms “weather” and “climate.” In short, **weather **describes instantaneous meteorological conditions (e.g., it’s currently raining or snowing, it’s a hot or frigid day). Climate reflects patterns of weather at a given place over longer periods of time (seasons to years). Climate is the primary driver of ecological processes on earth. Climate and weather information provide context for understanding the status or condition of other park resources.

Methods

A National Oceanic and Atmospheric Administration (NOAA) Cooperative Observer Program (COOP) weather station (La Junta Colorado Municipal Airport #54720) located 4.2 miles (6.7 km) west of Bent’s Old Fort National Historic Site has been operational since 1945 (Figure 1). This station provides a reliable, long-term climate dataset used for analyses in this climate report. Data from this station are accessible through Climate Analyzer.

Walls of an old fort viewed through fall leaves and a field of milkweed pods open with seed.

Bent's Old Fort NPS

Precipitation

Annual precipitation near Bent’s Old Fort National Historic Site in WY2023 was 14.20″ (36.1 cm), which was 2.86″ (7.3 cm) more than the 1991–2020 annual average. Above average precipitation occurred in every month except October, November, December, and March, which received no (or trace amounts of) precipitation or substantially less precipitation than the 1991–2020 average (Figure 2). Extreme daily rainfall events (≥ 1″; 2.54 cm) occurred on 4 days, twice the average annual frequency of 1.8 days. Extreme rainfall events occurred on 26 April 2023 (1.28″; 3.3 cm), 24 May 2023 (1.21″; 3.1 cm), 05 July 2023 (1.72″; 4.4 cm), and 20 July 2023 (1.10″; 2.8 cm).

Air Temperature

The mean annual maximum temperature near Bent’s Old Fort National Historic Site in WY2023 was 68.0°F (20.0°C), 2.0°F (1.1°C) below the 1991–2020 average. The mean annual minimum temperature in WY2023 was 37.6°F (3.1°C), 2.0°F (1.1°C) below the 1991–2020 average. Mean monthly maximum and minimum temperatures in WY2023 differed by as much as 7.5°F (4.2°C; see June as an example) relative to the 1991–2020 monthly averages (Figure 2). Air temperatures were generally cooler than normal throughout the year. Warmer than average mean maximum and minimum monthly temperatures occurred only in August and September. Extremely hot temperatures

(≥ 99°F; 37.2°C) occurred on 13 days in WY2023, approximately half the average frequency of 23.2 days. Extremely cold temperatures (≤ 11°F; −11.7°C) occurred on 30 days, which was more than the average frequency of 17.9 days.

Bar and line graph showing overall monthly max and mean temperatures were cooler than average and monthly precipitation totals were wetter than average in eight months.

Figure 2. Climogram showing monthly precipitation and mean maximum and minimum air temperatures in water year 2023 (WY2023) and the 1991–2020 means at La Junta Colorado Municipal Airport weather station near Bent’s Old Fort National Historic Site. Data source: climateanalyzer.org. NPS

Drought

Reconnaissance drought index (Tsakiris and Vangelis 2005) provides a measure of drought severity and extent relative to the long-term climate. It is based on the ratio of average precipitation to average potential evapotranspiration (the amount of water loss that would occur from evaporation and plant transpiration if the water supply was unlimited) over short periods of time (seasons to years). The reconnaissance drought index for Bent’s Old Fort National Historic Site indicates that WY2023 was wetter than the 1991–2020 average from the perspective of both precipitation and potential evapotranspiration (Figure 3).

Reference: Tsakiris G., and H. Vangelis. 2005. Establishing a drought index incorporating evapotranspiration. European Water 9: 3–11.

Figure 3. Bar graph showing that water year 2023 was wetter than average following five drier than average years. The 1990s had wetter than average years and after that there are more dry years than wet.

Figure 3. Reconnaissance drought index for the La Junta Colorado Municipal Airport near Bent’s Old Fort National Historic Site, water years 1991–2023. Drought index calculations are relative to the time period selected (1990–2023). Choosing a different set of start/end points may produce different results. “N/A” = insufficient data to generate reliable estimates. Data source: climateanalyzer.org. NPS

Go to Climate and Weather, Past Findings

Report Citation

Authors: Kara Raymond, Andy Ray

Raymond, K., and A. Ray. 2024. Climate and Weather Monitoring at Bent's Old Fort National Historic Site: Water Year 2023. Southern Plains Network, National Park Service, Pecos, New Mexico.

Past Reports

Water Year 2022 Climate and Weather Monitoring at Bent’s Old Fort National Historic Site

Water Year 2021 Climate and Weather Monitoring at Bent’s Old Fort National Historic Site

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