Article

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

Monsoon clouds over desert mountains and saguaro cacti.

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

Overview

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

At Organ Pipe Cactus National Monument (NM) (Figure 1), Sonoran Desert 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. At Organ Pipe, we monitor climate, groundwater, and springs, among other vital signs.

Surface-water and groundwater conditions are closely related to climate conditions. Because they are better understood together, we report on climate in conjunction with water resources. 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., WY2021 runs from October 2020 through September 2021).

This article reports on results of climate and water monitoring done at Organ Pipe Cactus National Monument in water year 2021.

Map of Organ Pipe Cactus NM showing location of one weather station and eight groundwater monitoring wells found throughout the park.
Figure 1. Monitored weather stations and groundwater wells at Organ Pipe Cactus National Monument.

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. 

Findings for Water Year 2021

Precipitation

Annual precipitation at Organ Pipe Cactus NM in WY2021 was 11.80" (30.0 cm; Figure 2)—3.08" (7.8 cm) higher than the 1991–2020 annual average. This surplus primarily occurred in July and August, when the monument received 7.05" (17.9 cm) combined. January, June, July, and August each saw more than double the monthly precipitation of the 1991–2020 monthly averages. Precipitation during the rest of the year was much less than the 1991–2020 monthly averages.

Air temperature

The mean annual maximum air temperature at Organ Pipe Cactus NM in WY2021 was 87.2°F (30.7°C), 0.4°F (0.2°C) warmer than the average annual maximum for 1991–2020. The average annual minimum air temperature in WY2021 was 57.0°F (13.9°C), which was 0.7°F (0.4°C) warmer than the 1991–2020 average minimum. Average monthly maximum and minimum temperatures in WY2021 varied up to 6.9°F (3.8°C) relative to the 1991–2020 average monthly temperatures (Figure 2).

Bar-and-line graph showing precipitation was higher for three months in 2021 than for 1991-2020. Range: 0 to ~3.5 inches. Max and min temperature closely track between 2021 and 1991-2020. Range: ~100 and 75 degrees F (max); ~70 and 40 degrees F (min).

Figure 2. Climogram showing monthly precipitation and mean maximum and minimum temperature, WY2021 and the 1991–2020 means at Organ Pipe Cactus National Monument. Data source: GRIDMET via climateanalyzer.org.

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 Organ Pipe Cactus NM indicates that WY2021 was slightly wetter than the 1991–2020 average, from the perspective of both precipitation and potential evapotranspiration (Figure 3).

Bar graph of values for reconnaissance drought index ranging from ~-0.7 to 0.7 across water years 1991-2021. Blue represents values above 0. Red represents values below 0. There are more red bars than blue.

Figure 3. Reconnaissance drought index for Organ Pipe Cactus National Monument, WY1991–2021.  Data source: GRIDMET. Drought index calculations are relative to the time period selected (1990–2021). Choosing a different set of start/end points may produce different results.

Groundwater   

Groundwater is one of the most critical natural resources of the American Southwest. It provides water for drinking, irrigating crops, and sustaining rivers, streams, and springs throughout the region.   

Findings for Water Year 2021

Some quarterly measurements were not collected in WY2020 or WY2021 due to covid-19 disruptions to fieldwork. Average groundwater levels in five wells decreased between WY2020 and WY2021 (Figure 1, Table 1). The other three wells were missing data in either WY2020 or WY2021. Headquarters #5, Stack, USGS #1, and USGS #2 have shown similar rates of decline over the monitoring record, likely due to groundwater pumping south of the US–Mexico border. While the depth-to-water at Headquarters #5 is much deeper than the other wells, its water-level elevation is slightly higher, indicating it is upgradient but within the same aquifer. Groundwater levels in Corner well have also been declining, but much more gradually. Groundwater levels in Bates #2, Bonita, and USGS #3 have been more variable over the monitoring record, indicating that these wells are less impacted by recent groundwater pumping.

Line graph showing depth-to-water levels for eight wells from 1976 to 2021. Several wells show declines over time.

Figure 1. Depth-to-water (feet below ground surface) at eight groundwater monitoring wells at Organ Pipe Cactus National Monument, 1963–2021. Depth-to-water for Headquarters #5 is shown on the right axis. Depth-to-water for all other wells is shown on the left axis. Measurements taken while groundwater pumping occurred are indicated in red. White indicates the well was dry.

Springs

Background

Springs, seeps, and tinajas (small pools in a rock basin or impoundments in bedrock) are small, relatively rare biodiversity hotspots in arid lands. They are the primary connection between groundwater and surface water and are important water sources for plants and animals. For springs, the most important questions we ask are about persistence (How long was there water in the spring this year?) and water quantity (How much water was in the spring?).

Findings for Water Year 2021

Dripping Springs | East Arroyo Spring | Quitobaquito Spring | Snake Pit Tinaja

Dripping Springs

Dripping Springs (Figure 1, left) was described in WY2017 as a limnocrene spring (emerges as one or more still pools) fed by numerous groundwater seeps along the bedrock walls of a cave located at the base of a cliff face (Figure 1, right). In WY2017, a small seep adjacent to the pool was present and a damp section of the trail extending about four meters from the cave suggested that the pool occasionally flowed over the lip of the cave opening.

Two photos. At left, desert cliff with black wash where water seeps into small pool at base, where monitoring equipment sits. At right, view of same area from above.

Figure 1. Left: Dripping Springs with cliff-face seeps. Right: Main pool of Dripping Springs, located near a cave at the base of a cliff. NPS photos from March 2021.

Site condition. In WY2021, Dripping Springs was rated as “highly disturbed” for hiking trails and evidence of human use due to impacts from hikers using the Dripping Springs Mine Trail. These ratings were increases from the “slightly” to “moderately” disturbed ratings in the past. There was evidence of trampling and tracks through the springbrook and to the cave entrance. The crew rated Dripping Springs as “undisturbed” for all other categories of human and natural disturbance.

The crew did not observe crayfish or bullfrogs (non-native, potentially invasive aquatic animals) in 2021. However, we did observe two non-native plant genera: hedgemustard (Sisymbrium sp.) and dandelion (Taraxacum sp.), both at low densities (1–5 plants each). Both invasive plant genera were also observed at similar densities in 2019.

We observed one native facultative wetland plant genus: monkeyflower (Mimulus sp.), which has been present since sampling began in 2017.

Color-block graph with blue representing wetted days and grey representing days with missing data, 2017–2021. About half of 2019, all of 2020, and most of 2021 are grey. The rest is blue.
Figure 2. Water persistence at Dripping Springs, 2017–2021.

Water quantity. The WY2021 sampling visit occurred on March 22, 2021. The spring contained water at that time. Temperature sensors indicated that Dripping Springs was “wetted” (contained water) for 123 of 123 days (100%) measured in WY2021. However, the sensors did not function all year (Figure 2). In prior water years, the spring was wetted 100% of the days measured.

The crew was unable to estimate spring discharge, as the outflow was too shallow for measurement. Discharge has not been measured for this reason at Dripping Springs during the entire monitoring period (WY2017–2021). Wetted extent was evaluated using a method for flowing water. For 2021, the springbrook length, width, and depth were all within the range of prior years (Table 1, below).

Water quality. The crew collected data on core water quality parameters and water chemistry within the pool inside the cave (Tables 2 and 3). The values for all parameters were within the ranges observed during prior years, with two exceptions: (1) chloride was 4 mg/L above any prior observation (with minimum detection level of 0.5 mg/L), but is not considered a concern for wildlife or human health, and (2) sulfate was less than half the previous low observed.

East Arroyo Spring

East Arroyo Spring (Figure 3, left) was described in WY2018 as a large, persistent tinaja (pool in a rock basin) that lies at the base of a 10-meter bedrock cliff within a large drainage below Ajo Peak (Figure 3, right).

Two photos. At left, an opaque green pool in pinkish bedrock. At right, a rocky desert landscape with a dark oval in the middle of the frame.

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.

Site condition. In WY2021, East Arroyo Spring was rated as “slightly disturbed” for recent flooding due to evidence of recent flooding in the channel. We also observed slight impacts from flooding in 2019, suggesting the channel is occasionally subject to substantial overland flow from storm runoff. The crew rated East Arroyo Spring as “undisturbed” for all other categories of human and natural disturbance.

The crew did not observe crayfish or bullfrogs (non-native, potentially invasive aquatic animals) or any non-native plants during surveys in 2021. As in past years, we did observe the facultative wetland plant genus Mimulus (monkeyflower).

Color-block graph with blue as wetted days, yellow as dry days, and grey as days with missing data, 2017–2021. Much of 2021, and parts of 2020, 2018, and 2017 are grey. The rest is blue except for parts of 2020, 2019, 2018, and 2017.
Figure 4. Water persistence at East Arroyo Spring, 2017–2021.

Water quantity. The WY2021 visit occurred on March 24, 2021. The spring contained water. Temperature sensors indicated that East Arroyo Spring was “wetted” (contained water) for 122 of 122 days (100%) in WY2021, but sensors were not operational at the start of the water year. In prior water years, the spring was wetted 56.5–94.9% of the days measured, with an extended dry period in the summer of WY2018, and shorter dry periods in the fall/winter of WY2019 and 2020 and mid-summer of WY2017 (Figure 4).

We were unable to estimate spring discharge, as the outflow was too shallow for measurement. During the last sampling of East Arroyo Spring (WY2019), discharge was estimated at 19.2 L/min (Table 4, below). Wetted extent was also not evaluated in WY2021, as the tinaja’s steep sides prevented safe access for measuring pool dimensions.

Water quality. The crew collected data on core water quality parameters and water chemistry within the downstream edge of the pool (Tables 5 and 6). Most values were within the range of prior years, with some notable exceptions: (1) at 9.32, pH was considerably more basic than in prior sampling, (2) dissolved oxygen was slightly higher (~2.8 mg/L) than the previous high value, and (3) chloride was nearly twice as high (+20 mg/L with minimum detection level of 0.5 mg/L) as the previous maximum value, but is not considered a concern for wildlife or human health. While there are no water quality standards specific to East Arroyo or most other springs in Sonoran Desert parks, pH in WY2021 exceeded the Arizona water quality standard of pH (6.5–9.0) for three designated uses for other surface waters (rivers, streams, lakes, and reservoirs): full- and partial- body contact (humans), and aquatic and wildlife.

A small pool surrounded by a grassy dirt bank and a small pile of rocks.
Figure 5. Quitobaquito Spring in March 2021. NPS photo.

Quitobaquito Spring

Quitobaquito Spring (Figure 5) was first described in 2017 as a rheocrene spring (emerges as a flowing stream) that emerged at the foot of a low hill as a muddy seep. It then feeds into channel 16 meters long and then into a larger pool and weir (discharge monitoring instrument modifying the channel; Figure 6, left). Beyond that, the springbrook flows more than 200 meters through a concrete channel (Figure 6, right) that supports Quitobaquito Pond.

Two photos. At left, a thin stream of water passes through dried grasses and desert shrubs. At right, an even thinner squiggly stream passes over cement.

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.

Site condition. Visitor access and site development contribute to a number of impacts at this spring. Flow is heavily modified by installation of a permanent weir and springbox, and the springbrook is cemented to limit infiltration ahead of the outflow to Quitobaquito Pond. Additionally, hiking trails and their maintenance (vegetation clearing) resulted in slight-to-moderate impacts during WY2021 due to vegetation trampling and removal. Wildlife use of the spring was also evident in tracks and trampling. The crew did not observe crayfish or bullfrogs (non-native, potentially invasive aquatic animals), nor did they detect any non-native plants.

The crew observed the facultative wetland plant, mulefat (Baccharis salicifolia), and several obligate plant genera or families: bulrush (Schoenoplectus sp.), cattail family (Typhaceae), rush family (Juncaceae), sedge family (Cyperaceae), and spikerush (Eleocharis sp.). Each of these wetland plants has been detected in one or more prior years of sampling at Quitobaquito Spring.

Color-block graph with blue representing wetted days and grey representing days with missing data, 2017–2021. Much of 2021 and part of 2020 is grey. The rest is blue.
Figure 7. Water persistence at Quitobaquito Spring, 2017–2021.

Water quantity. The WY2021 visit occurred on March 25, 2021. The spring contained water. Temperature sensors indicated that Quitobaquito Spring was “wetted” (contained water) for 127 of 127 days (100%) measured up to the WY2021 visit. However, data were not available for the start of WY2021. In prior water years, the spring was wetted 100% of the days measured (Figure 7).

Discharge (Table 7, below) was estimated at 35 (± 1.3) liters (9.3 ± 0.3 gal) per minute in WY2021, within the range observed in past years.

Wetted extent was evaluated using a method for flowing water (Table 8). The total brook length was estimated at 200–500 meters and, as in all previous years, flowed into Quitobaquito Pond. Width and depth averaged 37.9 centimeters and 9.4 centimeters, respectively, within the first 100 meters. Length, width, and depth values were within the ranges observed in past years.

Water quality. The crew collected data on core water quality parameters and water chemistry at a pool just upstream of the weir (Tables 9 and 10). Dissolved oxygen, pH, and most chemical parameters were slightly above the range of values observed in past years. Potassium and magnesium were comparable with past values. Water temperature, specific conductivity, and total dissolved solids were slightly below any values observed at Quitobaquito Spring in the past. All observed values were well within Arizona water quality standards.

Snake Pit Tinaja

Snake Pit Tinaja (Figure 8, left) was described in 2017 as an isolated, bathtub-sized tinaja (small pool in rock basin) in the middle of a wide canyon in the north fork of Alamo Canyon (Figure 8, right). It is located within a wide expanse of bedrock and appears to be primarily fed by overland flow.

Two photos. At left, an opaque green pool in pink bedrock. At right, a view of the area from above. A tall deciduous tree grows next to the pool in a rocky desert landscape.

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

Site condition. Snake Pit Tinaja was rated as “slightly disturbed” for evidence of human use due to trash observed near the spring, as has been observed occasionally at this site in past years. The crew also rated the tinaja as “slightly disturbed” for wildlife impacts for the first time in 2021, as they observed a decaying bird in the tinaja. Snake Pit Tinaja was rated as “undisturbed” for all other human and natural disturbances.

The crew did not observe crayfish or bullfrogs (non-native and potentially invasive aquatic animals) or non-native plant species in 2021. Obligate or facultative wetland plants were also not observed, likely due to the expanse of bedrock around the spring.

Color-block graph with blue as wetted days, yellow as dry days, and grey as days with missing data, 2017–2021. Much of 2021, and parts of 2020 and 2019 are grey. The rest is mostly blue except for occasional periods during summer 2020, 2019, and 2017.
Figure 9. Water persistence at Snake Pit Tinaja, 2017–2021.

Water quantity. The WY2021 visit occurred on March 23, 2021. The spring contained water. Temperature sensors indicated that Snake Pit Tinaja was “wetted” (contained water) for 125 of 125 days (100%) measured up to the WY2021 visit, with some data missing early in the water year. In prior water years, the spring was wetted 84.8–99.5% of the days measured (Figure 9).

There was no discharge from Snake Pit Tinaja at the time of sampling. Wetted extent was evaluated using a method for standing water (Table 11, below). Width averaged 99.7 centimeters. Length averaged 218.5 centimeters, and depth averaged 65.5 centimeters—all within the ranges measured in prior years.

Water quality. The crew collected data on core water quality parameters and water chemistry within Snake Pit Tinaja along the downstream edge of the pool (Tables 12 and 13). All parameters were within the ranges observed in past years at this location, except for water temperature, which was about 2°C colder than the previously observed low temperature. While there are no water quality standards specific to Snake Pit Tinaja or most other springs in Arizona, pH in WY2021 and some previous years exceeded the Arizona water quality standard of pH (6.5–9.0) for three designated uses for other surface waters (rivers, streams, lakes, and reservoirs): full- and partial- body contact (humans), and aquatic and wildlife.

Authors

Information prepared by Kara Raymond (Southern Arizona Office) and Andy Hubbard, Cheryl McIntyre, and Laura Palacios (Sonoran Desert Network).

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    Organ Pipe Cactus National Monument

    Last updated: October 24, 2024