Climate and Groundwater Monitoring at Casa Grande Ruins National Monument: Water Year 2024 (U.S. National Park Service)

The black silhouette of the Casa Grande, ruins of an uneven adobe structure under a modern protective roof structure, in front of a blue and orange sunset. — Casa Grande Ruins National Monument
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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 Casa Grande Ruins National Monument (Figure 1), Sonoran Desert 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 resource problems, allowing managers to mitigate them before they become worse. At Casa Grande Ruins National Monument we monitor climate and groundwater, among other vital signs.

Groundwater conditions are closely related to climate conditions. Because they are better understood together, we report on climate in conjunction with groundwater. 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., WY2024 runs from October 2023 through September 2024). This web report presents the results of climate and groundwater monitoring at Casa Grande Ruins National Monument in WY2024.

Map showing the park boundary, a rectangle about one mile by 0.75 miles. The weather station is in the southwest part of the park at the end of the only road into the park. The monitored groundwater well is about 0.75 miles west of the NW park boundary. — Figure 1. Monitored weather station and groundwater well at Casa Grande Ruins National Monument.
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Climate and Weather

There is often confusion over the terms “weather” and “climate.” Weather describes short-term meteorological conditions (e.g., it’s currently raining or snowing, it’s a hot or frigid day), and 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 Cooperative Observer Program (NOAA COOP) weather station (Casa Grande #021314) has been operational at Casa Grande Ruins National Monument since 1906 (Figure 1). This station provides a reliable, long-term climate dataset for analyses in this climate and water report. Data from this station are accessible through Climate Analyzer.

Partially eroded ruins of a massive adobe structure with protective modern roof structure overhead. The sun sets out of frame, bathing the structure in orange light. Two saguaros stand tall in front of the ruins. — The Casa Grande from the northeast.
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Results

Precipitation

Highlight: Above normal cool season rains lead to above normal annual precipitation.

Annual precipitation at Casa Grande Ruins National Monument in WY2024 was 10.13″ (25.7 cm), 1.88″ (4.8 cm) more than the 1991–2020 annual average. This surplus primarily occurred in the cool season (October–March). While October was completely dry, precipitation in the other five cool season months was above the 1991–2020 average, resulting in 1.82″ (4.6 cm) more than average for the first half of the water year (Figure 2). The warm season (April–September) precipitation total was similar to the long-term average; however, warm season monthly precipitation was variable relative to the averages. April precipitation was near average. May was completely dry. June was over four times as wet as the average. July and September were substantially drier than average. August was twice as wet as the average. Extreme daily rainfall events (≥ 1.00″; 2.54 cm) occurred on 1 day, similar to the average annual frequency of 1.2 days. The single extreme rainfall event occurred on 07 August 2024 (2.05″; 5.2 cm).

Air Temperature

Highlight: Slightly cooler winter and hotter summer air temperatures than normal.

The mean annual maximum temperature in WY2024 was 88.3°F (31.3°C), 0.7°F (0.4°C) above the 1991–2020 average. The mean annual minimum temperature in WY2024 was 55.3°F (12.9°C), 0.3°F (0.2°C) above the 1991–2020 average. Mean monthly maximum and minimum temperatures in WY2024 differed by as much as 4.3°F (2.4°C; see June as an example) relative to the 1991–2020 monthly averages (Figure 2). Mean monthly maximum and minimum temperatures were above the 1991–2020 averages in eight months each. Cooler than average temperatures occurred in winter and spring months. Extremely hot temperatures (≥ 111.0°F; 43.9°C) occurred on 26 days in WY2024, about six more the average frequency of 19.6 days. Extremely cold temperatures (≤ 30.0°F; −1.1°C) occurred on 14 days, eight less than the average frequency of 21.9 days.

Climogram showing precipitation totals for WY2024 were higher than those for 1991-2020 in November-March, June, and August. Overall maximum and minimum temperature averages for WY2024 were higher than those for 1991-2020 in 8 months. — Figure 2. Climogram showing monthly precipitation and mean maximum and minimum air temperatures in water year (WY) 2024 and the 1991–2020 averages, at Casa Grande Ruins National Monument. Data source: climateanalyzer.org.
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Drought

Highlight: Modest recovery from the recent 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 Casa Grande Ruins National Monument indicates that WY2024 was wetter than the 1991–2024 average (for the second year in a row) 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.

Bar graph showing conditions in WY2023 and WY2024 were wetter than average. — Figure 3. Reconnaissance drought index for Casa Grande station at Casa Grande Ruins National Monument, water years (WY) 1991–2024. Drought index calculations are relative to the time period selected (1990–2024). Choosing a different set of start/end points may produce different results. N/A = insufficient data to generate reliable estimates. Data source: climateanalyzer.org.
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Casa Grande, a partially eroded large adobe structure, under a protective modern roof with saguaro cactuses and mesquite in the foreground. — Casa Grande Ruins National Monument
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Groundwater 

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