Climate, Groundwater and Springs at Organ Pipe Cactus National Monument, Water Year 2021

At Organ Pipe Cactus National Monument, scientists from the National Park Service's Sonoran Desert Network track "vital signs" — key measurements repeated year after year, the way a doctor tracks a patient's pulse — to catch problems early enough for managers to act. Three of those vital signs are climate, groundwater and springs, reported together because desert water depends so closely on weather.

Reports run by water year: water year 2021 (WY2021) lasted from October 2020 through September 2021.

Monsoon clouds over Organ Pipe Cactus National Monument (NPS photo).

The weather station and groundwater wells monitored at Organ Pipe Cactus National Monument (NPS).

Weather: a wet summer

The monument has run a Cooperative Observer Program weather station since 1944. In WY2021 it was missing 65 days of data, so the report used GRIDMET — a gridded climate dataset at 4-kilometer resolution, built from weather stations, terrain and other data — together with 1991–2020 averages. GRIDMET values can differ from the weather at a particular spot.

• The surplus came mostly in July and August, which together brought 7.05". January, June, July and August each received more than double their usual rain; the rest of the year was much drier than normal.
• Monthly average highs and lows differed from their norms by up to 6.9°F.
• A reconnaissance drought index, which weighs precipitation against potential evapotranspiration (the water evaporation and plants would remove if supply were unlimited), rated WY2021 slightly wetter than the 1991–2020 average.

Monthly precipitation and mean maximum and minimum temperatures, WY2021 against the 1991–2020 means. Data: GRIDMET via Climate Analyzer (NPS).

Groundwater: steady declines near the border

Groundwater supplies drinking water, irrigates crops and feeds rivers, streams and springs across the Southwest. At Organ Pipe, park staff normally measure seven wells every quarter — Bates, Bonita, Corner, Stack, USGS #1, USGS #2 and USGS #3 — and the Arizona Department of Water Resources measures an eighth, Headquarters #5, once a year. Continuous monitoring began at four wells in WY2020. Some quarterly readings were missed in WY2020 and WY2021 because COVID-19 disrupted fieldwork.

• Levels fell in all five wells with data for both years; the other three lacked data for one year or the other.
• Headquarters #5, Stack, USGS #1 and USGS #2 have declined at similar rates over their records, likely because of groundwater pumping south of the U.S.–Mexico border. Headquarters #5's water lies much deeper below ground, but its water-level elevation is slightly higher — it sits upgradient in the same aquifer.
• Corner has also declined, but much more slowly.
• Bates #2, Bonita and USGS #3 have varied more, suggesting recent pumping affects them less.

Depth to water at the monument's eight monitoring wells (NPS).

Springs: four desert water sources

Springs, seeps and tinajas (small pools in rock basins) are rare, small hotspots of life in arid lands, the main meeting point of groundwater and surface water, and vital water for plants and animals. The network's key questions are how long a spring held water and how much. Crews describe each site, rate its disturbances, measure its water and test its quality. In WY2021 no non-native crayfish or bullfrogs turned up at any of the four sites.

Dripping Springs — visited March 22, 2021

Dripping Springs, with seeps on the cliff face (left) and its main pool near a cave at the foot of the cliff (right). NPS photos, March 2021.

A spring that rises as pools fed by seeps along the walls of a cave at the base of a cliff. In WY2021 hikers on the Dripping Springs Mine Trail left trampling and tracks through the springbrook and up to the cave, and the site's ratings for trails and human use jumped to "highly disturbed," up from slightly or moderately disturbed before. It was undisturbed in every other category. Two non-native plants, hedgemustard and dandelion, grew at low densities, as in 2019.

• Sensors showed water on all 123 days they worked.
• Flow was again too shallow to measure; the springbrook's size was within its past range.
• Chloride was 4 mg/L above any earlier reading — not considered a concern for wildlife or people — and sulfate was less than half its previous low.

East Arroyo Spring — visited March 24, 2021

A large, lasting tinaja at the foot of a 10-meter cliff in a big drainage below Ajo Peak. Signs of recent flooding earned a "slightly disturbed" rating, as in 2019, suggesting storm runoff sometimes pours down the channel. No non-native plants were found.

Figure 3. East Arroyo Spring (left), is located in a narrow canyon below steep cliffs (right; spring is at bottom center). NPS photos from March 2021.

• Sensors showed water on all 122 days they worked. In earlier years the pool held water 56.5–94.9% of the time, with dry spells in several years.
• Flow was too shallow to measure (it was 19.2 liters a minute in WY2019), and the steep sides made the pool unsafe to measure.
• pH reached 9.32, considerably more basic than before and above Arizona's 6.5–9.0 standard for body contact and for aquatic life and wildlife in other surface waters (there are no standards specific to most springs in Sonoran Desert parks). Dissolved oxygen was slightly above its previous high, and chloride nearly twice its previous maximum, though not considered a concern.

Quitobaquito Spring — visited March 25, 2021

Quitobaquito Spring, March 2021 (NPS photo).

A flowing spring that starts as a muddy seep at the foot of a low hill, runs through a short channel to a pool and a weir (a structure that measures flow), then travels more than 200 meters through a concrete channel to Quitobaquito Pond. The weir, a springbox and the cemented channel heavily modify its flow, and trail use and upkeep caused slight to moderate trampling and plant removal. Wildlife left tracks and trampling; no non-native plants were found, and wetland plants such as bulrush, cattails, rushes, sedges and spikerush grew there as in past years.

Figure 6. Left: An unlined springbrook flows from Quitobaquito Spring to a weir. Right: A cement-lined springbrook flows from below the weir to Quitobaquito Pond. NPS photos from March 2021.

• Sensors showed water on all 127 days recorded.
• Flow was 35 (± 1.3) liters a minute, within its usual range, and the brook, an estimated 200–500 meters long, again reached the pond.

Snake Pit Tinaja — visited March 23, 2021

A bathtub-sized pool in open bedrock in the north fork of Alamo Canyon, apparently filled mostly by runoff. Trash nearby — seen occasionally before — and, for the first time, a decaying bird in the pool earned "slightly disturbed" ratings. No wetland plants were seen, likely because of the bare rock around it.

Figure 8. Snake Pit Tinaja (left) is an isolated pool in Alamo Canyon (right). NPS photos from March 2021.

• Sensors showed water on all 125 days recorded; in earlier years it held water 84.8–99.5% of the time.
• There was no outflow; the pool's size was within its past range.
• The water was about 2°C colder than its previous low, and its pH, as in some earlier years, exceeded Arizona's 6.5–9.0 standard for other surface waters.

Sources

• National Park Service, Sonoran Desert Network: "Climate and Water Monitoring at Organ Pipe Cactus National Monument, Water Year 2021" (report by Kara Raymond, Andy Hubbard, Cheryl McIntyre and Laura Palacios). Pictures an earlier version of this page left out were restored on 2026-09-26.