National Park Service

Department of the Interior

Natural Resource Stewardship and Science

Describing Trends in Past and Future Soil Moisture in 

the Mesa-Top Pinyon-Juniper Woodland Ecosystem 

in Bandelier National Monument

Natural Resource Report NPS/BAND/NRR—2020/2114 
ON THE COVER

TOP: Estimated past seasonal soil water patterns at Bandelier NM, described in detail in Figure 3. 

MIDDLE: Soil samples from different depths of a soil core taken from a long-term monitoring plot. NPS photo.

BOTTOM: Estimated current and future soil water patterns at Bandelier NM, described in detail in Figure 4.

BACKGROUND: Photo of Southern Colorado Plateau Network monitoring plot in the Bandelier NM mesa-top pinyonjuniper woodland ecosystem. NPS photo.
Describing Trends in Past and Future Soil Moisture in 

the Mesa-Top Pinyon-Juniper Woodland Ecosystem 

in Bandelier National Monument

Natural Resource Report NPS/BAND/NRR—2020/2114

Caitlin Andrews1, John Bradford1, Jodi Norris2, Jennifer Gremer3, Michael Duniway4, Seth Munson1, Lisa 

Thomas2

, and Megan Swan2

1 U.S. Geological Survey 

Southwest Biological Science Center

2255 N Gemini Dr. 

Flagstaff, AZ 86001

2

National Park Service

Southern Colorado Plateau Inventory and Monitoring Network

2255 N Gemini Dr. 

Flagstaff, AZ 86001

3

Department of Evolution and Ecology

University of California Davis

Davis, CA 95616

4

Southwest Biological Science Center

2290 SW Resource Blvd.

Moab, Utah 84532

April 2020

U.S. Department of the Interior 

National Park Service 

Natural Resource Stewardship and Science 

Fort Collins, Colorado
ii Describing Trends in Past and Future Soil Moisture in Bandelier National Monument

The National Park Service, Natural Resource Stewardship and Science office in Fort Collins, 

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Views, statements, findings, conclusions, recommendations, and data in this report do not 

necessarily reflect views and policies of the National Park Service, U.S. Department of the 

Interior. Mention of trade names or commercial products does not constitute endorsement 

or recommendation for use by the U.S. Government. 

This report is available from the Southern Colorado Plateau Network, and the Natural 

Resource Publications Management Web. If you have difficulty accessing information in this 

publication, particularly if using assistive technology, please email irma@nps.gov.

Please cite this publication as:

Andrews, C., J. Bradford, J. Norris, J. Gremer, M. Duniway, S. Munson, L. Thomas, and M. 

Swan. 2020. Describing trends in past and future soil moisture in the mesa-top pinyon-juniper woodland ecosystem in Bandelier National Monument. Natural Resource Report NPS/

BAND/NRR—2020/2114. National Park Service, Fort Collins, Colorado.

NPS 315/168208, April 2020
 National Park Service iii

Contents 

Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Acknowledgements . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

Introduction . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Discussion . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Page
iv Describing Trends in Past and Future Soil Moisture in Bandelier National Monument

Figures

Figure 1. Mesa-top pinyon-juniper woodland ecosystem in Bandelier NM. NPS photo. . . . . . . . 1

Figure 2. Map of Bandelier NM showing Southern Colorado Plateau Network 

monitoring plots in the mesa-top pinyon-juniper woodland ecosystem. . . . . . . . . . . . . . . . 2

Figure 3. Historical (A) and future projections (B) of soil water potential (SWP) in 

the mesa-top pinyon-juniper woodland ecosystem in Bandelier NM. . . . . . . . . . . . . . . . . 4

Figure 4. Panel A. Average seasonal patterns of climate in the mesa-top pinyonjuniper woodland ecosystem in Bandelier NM. Panel B. Average daily SWP for 

the current period (1970–2010), near future (2020–2059), and long-term future 

(2060–2099). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
 National Park Service 

v

Executive Summary

Variation in the structure and function of 

Colorado Plateau ecosystems is driven by 

seasonal moisture availability in the soil profile; however, the availability of soil moisture 

is expected to change in the coming decades 

as a result of climate change. To understand 

how ecosystems will be affected by this, we 

need to understand in more detail how these 

soil moisture patterns relate to plant productivity, and what changes in soil moisture are 

expected, both seasonally and at the range of 

soil depths that plants are adapted to use.

We used a soil water model (SOILWAT2) to 

estimate historical, current, and future soil 

water availability in 300 vegetation monitoring plots in 13 ecosystems in the Southern 

Colorado Plateau Network of the National 

Park Service. In Bandelier National Monument, this included 47 vegetation monitoring 

plots within the mesa-top pinyon-juniper 

woodland ecosystem. The SOILWAT2 model 

used plot-specific vegetation and soil core 

data collected as part of the Southern Colorado Plateau Network’s long-term upland 

vegetation monitoring program to represent 

the environment.

Model simulations were run using climate 

data from the past (1916–2011) to provide 

historical context, the present (1980-2015) 

to create a current baseline for comparison. Model simulations were also run for 

two time periods in the future: a near-term 

period (2020-2059) and a long-term period (2060-2099). The future projections 

were made using nine general circulation 

models under two possible greenhouse gas 

emissions pathways: the 8.5 representative 

concentration pathway (RCP), and the 4.5 

RCP. Results of the 8.5 RCP simulations are 

presented here; this pathway corresponds to 

a comparatively high greenhouse gas emissions scenario. 

The soil-water model results provide a detailed look at historical patterns of soil water 

availability, and how soil water availability is 

projected to change in the future, both seasonally and at different soil depths. Model 

output included daily soil water potential 

estimates at multiple depths within the soil 

profile. This report describes results at intermediate (20–50 cm) soil depths.

A second goal of this work was to better 

understand how changes in seasonal soil 

water availability might affect vegetation. To 

do this, we initially examined how vegetation today is affected by seasonal differences 

in soil moisture by calculating correlations 

of annual NDVI (2001-2014) with soil water 

potential averaged over a range of moving 

windows. However, recent work (Norris 

and Walker, in review) has shown that the 

NDVI values in most pinyon-juniper ecosystems do not correspond with vegetation 

greenness. Therefore those analyses were 

discarded.

Key findings for the Bandelier NM mesa-top 

pinyon-juniper woodland ecosystem include 

the following: ● All of the climate models predicted 

increases in mean monthly and annual 

temperature in the near-term future 

(+2.3°C on average), and further increases in the long-term future (+4.9°C on 

average). Models had greater variation 

in their predictions of both the direction 

and the amount of future precipitation.

● Soil moisture is predicted to decline in 

the spring in the near-term future. In the 

long-term future, soil moisture in the 

fall, winter, and spring is predicted to 

significantly decline.

● The drying of soils in spring is predicted 

to occur earlier in the long-term future, 

and will shorten the length of time when 

soils are moist during the spring growing 

season. This will likely have a substantial 

impact on plant species reliant on spring 

soil moisture.
vi Describing Trends in Past and Future Soil Moisture in Bandelier National Monument

Acknowledgements

This report benefited from editorial improvements from Jean Palumbo and from 

reviews by David Thoma and Kathryn 

Thomas. Thanks to multiple years of Southern Colorado Plateau Network upland monitoring crews for vegetation and soils data 

collection. This work was supported by the 

National Park Monitoring Program of the 

U.S. Geological Survey and by the National 

Park Service Inventory and Monitoring Program, Southern Colorado Plateau Network.
 National Park Service 1

Introduction

In the semi-arid environment of the Colorado Plateau, soil water availability is an 

important driver of vegetation dynamics. 

Recent drought-associated tree mortality 

in the Southwest has highlighted the potential vulnerability of ecosystems to changing 

water availability. Climate change models 

predict continued warming and seasonally 

drier conditions over the next century.

How will changing soil water availability 

impact vegetation dynamics in these already 

water-limited ecosystems? To answer this 

question the U.S. Geological Survey (USGS) 

and National Park Service (NPS) have 

teamed up to model soil water availability 

under projected climate conditions in nine 

Southern Colorado Plateau national park 

units where long-term vegetation monitoring 

is underway.

The resulting projections of soil water availability will allow us to develop hypotheses 

about how the dominant species in plant 

communities will respond to changing soil 

water conditions. This project will help park 

managers today by identifying the most sensitive ecosystems and informing strategies to 

improve long-term ecosystem resistance and 

resilience. Through continued monitoring 

over the coming decades we will also be able 

to compare observed vegetation dynamics 

to hypothesized responses, thus furthering our understanding of Colorado Plateau 

ecosystems.

For this project, USGS and NPS scientists 

used the range of variation in historical 

climate data to provide context for assessing the relative impact of projected future 

climate on water availability. We used a soil 

water model, SOILWAT2, to translate climate 

variability into site-specific estimates of 

soil water conditions that may drive plant 

responses. One of the valuable outputs of 

the model is daily soil water potential (SWP), 

which provides an estimate of water available 

for plants that reflects soil conditions. 

This report provides the results of modeled 

SWP at intermediate soil depths (20–50 cm) 

generated for the mesa-top pinyon-juniper 

woodland ecosystem in Bandelier NM, New 

Mexico (Figure 1). 

Figure 1. Mesa-top pinyonjuniper woodland ecosystem in Bandelier NM. NPS 

photo. 
2 Describing Trends in Past and Future Soil Moisture in Bandelier National Monument

Study Area

The Southern Colorado Plateau Network 

(SCPN) has been monitoring vegetation 

and soil stability in grasslands, woodlands 

and forests in network parks since 2007. In 

Bandelier NM, SCPN monitors the mesatop pinyon-juniper woodland ecosystem. 

The overstory of the plant community in 

this ecosystem ranges from a dense to sparse 

canopy of one-seed junipers (Juniperus 

monosperma). The understory is also variable; the most common understory species 

include grama grass (Bouteloua gracilis) and 

snakeweed (Gutierrezia sarothrae). Soils in 

this ecosystem are typically classified as sandy loam. We used data from soil cores taken 

from 47 plots in this ecosystem as inputs to 

the SOILWAT2 model (Figure 2).

Figure 2. Map of Bandelier NM showing Southern Colorado Plateau Network monitoring plots in 

the mesa-top pinyon-juniper woodland ecosystem. Plots from which soil cores were used are indicated as solid blue dots. NPS map. 
 National Park Service 3

Methods

Data were collected from the following 

sources for input into the SOILWAT2 model:

● texture and depth data from core samples that were taken during the establishment of SCPN upland monitoring plots 

(supplemented with NRCS SSURGO 

soil texture data when the soil cores did 

not extend to the full depth of the soil 

profile)

● vegetation species and functional group 

cover data from SCPN monitoring plots

● daily weather data estimates from 1920 

to the present 

■ Livneh (long-term historical weather; 1916–2011; 1/16th resolution)

■ DayMet (near-term historical 

weather; 1980–2015; 1 km × 1 km 

resolution)

● projected daily weather for 9 General 

Circulation Models (GCMs) for the periods 2020–2059 and 2060–2099, under 

representative concentration pathways 

(RCP) 8.5. RCPs, adopted by the International Panel on Climate Change, 

characterize potential future climate 

based on the hypothetical trajectories 

in the concentrations of greenhouse 

gases, with 8.5 demonstrating the highest 

potential concentrations. All projected 

climate data were downloaded from the 

Green Data Oasis (https://hpc.llnl.gov/

data-vis/green-data-oasis).

SOILWAT2 integrated these climate data, 

along with the soils and vegetation data, to 

generate the following simulations.

● long-term historical daily soil water potential (1915–2010) 

● near-term historical daily soil water 

potential (1980–2015)

● near-term future daily soil water potential (2020–2059)

● long-term future daily soil water potential (2060–2099)

We used box plots to represent annual variation in each of the seasonal soil moisture 

projections for the respective time periods. 

For future time periods, we used the mean 

projected soil moisture from the median 

ranked GCM.

The SOILWAT2 model, along with the soil 

moisture simulation for this report, is available at https://doi.org/10.5066/F7D50K6S.
4 Describing Trends in Past and Future Soil Moisture in Bandelier National Monument

Results

The outputs from our model show SWP for 

the past, present, and future, and highlight 

relatively moist and dry periods. These 

data can be considered in a variety of ways, 

including climate variability, variability 

among soil profiles, and relationships with 

plot-based vegetation monitoring data. Here 

we present seasonal and temporal patterns 

in soil water availability in the mesa-top 

pinyon-juniper woodland ecosystem in 

Bandelier NM.

Long-term trends in past and 

future water availability 

● Past SWP fluctuations highlight relatively 

moist and dry periods and allow us to 

compare the past variability in SWP to 

future projections (Figure 3A).

● Future projections (Figure 3B) suggest 

declining water availability in all seasons. 

Average spring SWP is expected to drop 

below -3.0MPa, indicating conditions of 

extreme water scarcity.

● In the future, SWP will remain the highest in the fall/winter. Spring soil moisture 

will likely be lower than those observed 

in summer, a pattern observed intermittently throughout the 20th century.

Historical and future climate 

patterns

● Currently, mean annual temperature 

(MAT) is 10.7°C. In the future, MAT is 

expected to increase under all climate 

models (near future +2.3°C, long-term 

future +4.9°C), underscoring the consistency of these projected rising temperatures across climate models (variation in 

temperature projections among models 

is reflected by the variation in orange and 

red values in Figure 4A).

● Mean annual precipitation (MAP) is 305 

mm, with concentrated rainfall during 

the monsoon. (Figure 4A). While future 

changes in precipitation are less consistent across models than temperature, 

the substantial projected increases in 

temperatures promote decreased soil 

moisture, especially during spring, and 

longer summer dry periods (Figure 4B). 

● Periods of meteorological drought occur when the precipitation line is below the temperature line in Figure 4A. 

The current period of meteorological 

drought spans from April to mid-July. 

In the future, the duration of these dry 

conditions will likely start earlier and 

last longer, primarily as a result of rising 

temperatures.

Figure 3. Historical (A) and future projections (B) of soil water potential (SWP) at intermediate soil depths (20–50 cm) in 

the mesa-top pinyon-juniper woodland ecosystem in Bandelier NM for three seasons: fall/winter (October–February), spring 

(March–June), and summer (July–September). Panel A shows historical annual variability (fine lines) and moving 10-year 

averages (thick lines) of drying and wetting from 1915–2010. Panel B compares variability amongst years for three time 

periods, current (C; 1970–2010), near future (N; 2020–2059), and long-term future (L; 2060–2099), grouped by season. Boxplot whiskers are 1.5 times the inter-quartile range of values, while dots are values outside this range. Dashed lines in both 

panels highlight plant-relevant SWP levels: traditional wilting point (-1.5 MPa) and a drylands wilting point (-3.0 MPa; Kolb 

and Sperry 1999a, 1999b).
 National Park Service 5

Future soil moisture

● Future soil moisture is predicted to be 

much lower in the first half of the year, 

particularly under the long-term scenario 

(Figure4B).

● Soil moisture in the latter half of the year 

is predicted to remain relatively unchanged in the near-term scenario, and to 

decrease under the long-term scenario.

● The drying of soils in spring is predicted 

to occur earlier in the long-term scenario 

and will shorten the length of time when 

soils are moist during the spring growing 

season. This will likely have a substantial 

impact on plant species reliant on soil 

moisture during this time of year.

Figure 4. Panel A. Average seasonal patterns of climate in the mesa-top 

pinyon-juniper woodland ecosystem in Bandelier NM. Climate diagram 

(Walter and Leith 1967) shows mean monthly temperature (°C) and 

precipitation (mm) in dark red and blue lines, respectively, in the current 

period (1970–2010). Shaded red and blue areas indicate the range of 

potential values in the near (darker area; 2020–2059) and long-term 

(lighter area; 2060–2099) future periods. Mean annual temperature 

(MAT) and mean annual precipitation (MAP) are derived from the mean 

monthly values. Panel B. Average daily SWP for the current period 

(1970–2010; black), near future (2020–2059; yellow), and long-term 

future (2060–2099; purple). For future time periods, thick lines represent 

the median value among climate models, while shaded areas represent 

the range of values from the 11th to 89th percentile, removing both the 

highest and lowest model values.
6 Describing Trends in Past and Future Soil Moisture in Bandelier National Monument

Discussion

These results present a long-term historical 

and future perspective on soil moisture in 

the mesa-top pinyon-juniper woodland ecosystem in Bandelier NM. Predicted changes 

in SWP are likely to affect vegetation community dynamics in the future. Spring soil 

moisture is predicted to decline by the end 

of the 21st century. When compared to other 

woodland ecosystems examined in SCPN 

parks, the soil moisture here is expected to 

change more in response to climate change. 

This ecosystem is warmer and receives much 

less precipitation than other woodland 

ecosystems examined within the SCPN and, 

currently, soil moisture for this site is consistently below important thresholds of plantwater availability for much of the year.

The projections of future soil moisture 

provided here can be used in conjunction 

with species-specific vegetation monitoring 

data collected by the SCPN to (1) contribute 

to hypotheses about how individual species 

within an ecosystem may respond to changing soil water availability and (2) inform 

future management decisions in the face of 

changing and increasingly variable climate. 

Furthermore, the SWP estimates here have 

been published as a data release (Andrews 

and Bradford 2017) and can be used to 

inform future research. A recent example of 

this is a study by Gremer and others (2019) 

that used these SWP values to model the balance between grasses and shrubs in SCPN 

parks. The model created in that study predicted that in the future, climate change will 

favor greater relative abundance of shrubs 

across most Southern Colorado Plateau 

Network parks, including for the long-term 

future predictions (2060–2099) for the Bandelier NM mesa-top pinyon-juniper woodland ecosystem described in this report. 

The modeled soil moisture values are influenced by both the logic embedded within the SOILWAT2 model and site-specific 

weather, soil, and vegetation. This approach 

provides a consistent, process-based framework for assessing climate change impacts 

on soil moisture, and projections of change 

in SWP are robust. The variation among climate projections displays the uncertainty in 

the magnitude of SWP change, but modeled 

SWP patterns consistently point to earlier 

and drier spring periods. These changes in 

both the timing and amount of soil moisture 

are certain to affect the communities that 

rely on them. 
 National Park Service 7

Literature Cited

Andrews, C., and J. Bradford, 2017. Simulated Soil Water Potential in National Parks and 

Monuments of the Southern Colorado Plateau, 1915-2099—Data: U.S. Geological 

Survey data release, https://doi.org/10.5066/F7D50K6S. 

Gremer, J. R., C. Andrews, J. R. Norris, L. P. Thomas, S. M. Munson, M. C. Duniway, and 

J. B. Bradford, 2018. Increasing temperature seasonality may overwhelm shifts in soil 

moisture to favor shrub over grass dominance in Colorado Plateau drylands. Oecologia, 

188.4:1195-1207. 

Kolb, K. J., and J. S. Sperry. 1999a. Differences in drought adaptation between subspecies of 

sagebrush (Artemisia tridentata). Ecology, 80:2373–2384.

Kolb, K. J., and J. S. Sperry. 1999b. Transport constraints on water use by the great basin 

shrub, Artemisia tridentata. Plant, Cell and Environment, 22:925–935.

Livneh B., E. A. Rosenberg, C. Lin, B. Nijssen, V. Mishra, K. M. Andreadis, E. P. Maurer, and 

D. P. Lettenmaier. 2013. A Long-Term Hydrologically Based Dataset of Land Surface 

Fluxes and States for the Conterminous United States: Update and Extensions, Journal 

of Climate, 26, 9384–9392.

Norris J. R. and J. J. Walker. In Review. Solar and sensor geometry, not vegetation response, 

drive satellite NDVI phenology in widespread ecosystems of the western United States. 

Walter, H., and H. Leith. 1967. Climate diagram world atlas. Fischer Verlag, Jena, Thuringia, 

Germany. Oakley, K. L., L. P. Thomas, and S. G. Fancy. 2003. Guidelines for long-term 

monitoring protocols. Wildlife Society Bulletin 2003, 31(4):1000–1003.

The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides scientific and 

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