National Park Service

Department of the Interior

Natural Resource Stewardship and Science

Describing Trends in Past and Future Soil Moisture 

in the Shallow Loamy Mesa-Top Pinyon-Juniper 

Woodland Ecosystem in Mesa Verde National Park

Natural Resource Report NPS/MEVE/NRR—2020/2117
ON THE COVER

TOP: Estimated past seasonal soil water patterns at Mesa Verde NP, 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 Mesa Verde NP, described in detail in Figure 4.

BACKGROUND: Photo of Southern Colorado Plateau Network monitoring plot in the Mesa Verde NP shallow loamy 

mesa-top pinyon-juniper woodland ecosystem. NPS photo.
Describing Trends in Past and Future Soil Moisture 

in the Shallow Loamy Mesa-Top Pinyon-Juniper 

Woodland Ecosystem in Mesa Verde National Park

Natural Resource Report NPS/MEVE/NRR—2020/2117

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 Mesa Verde National Park

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

Colorado, publishes a range of reports that address natural resource topics. These reports 

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

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

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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 shallow loamy mesa-top 

pinyon-juniper woodland ecosystem in Mesa Verde National Park. Natural Resource Report 

NPS/MEVE/NRR—2020/2117. National Park Service, Fort Collins, Colorado.

NPS 113/168219, 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 Mesa Verde National Park

Figures

Figure 1. Shallow loamy mesa-top pinyon-juniper woodland ecosystem in Mesa 

Verde NP. NPS photo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. Map of Mesa Verde NP showing Southern Colorado Plateau Network 

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

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

the shallow loamy mesa-top pinyon-juniper woodland ecosystem in Mesa Verde NP 

for three seasons: fall/winter (October–February), spring (March–June), and summer (July–September). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Figure 4. Panel A. Average seasonal patterns of climate in the shallow loamy mesatop pinyon-juniper woodland ecosystem in Mesa Verde NP. 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 pro-

file; 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 produc-

tivity, 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 monitor-

ing plots in 13 ecosystems in the Southern 

Colorado Plateau Network of the National 

Park Service. In Mesa Verde National Park, 

this included 10 vegetation monitoring plots 

within the shallow loamy mesa-top pinyonjuniper woodland ecosystem. The SOILWAT2 model used plot-specific vegetation 

and soil core data collected as part of the 

Southern Colorado Plateau Network’s longterm 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 compari-

son. Model simulations were also run for 

two time periods in the future: a near-term 

period (2020–2059) and a long-term pe-

riod (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 emis-

sions scenario. 

The soil-water model results provide a de-

tailed look at historical patterns of soil water 

availability, and how soil water availability is 

projected to change in the future, both sea-

sonally 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 inter-

mediate (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 eco-

systems do not correspond with vegetation 

greenness. Therefore those analyses were 

discarded.

Key findings for the Mesa Verde NP shallow 

loamy 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 

(+2.5°C on average), and further increas-

es in the long-term future (+5.2°C on 

average). Models had greater variation 

in their predictions of both the direction 

and the amount of future precipitation, 

except for June, for which low precipita-

tion is consistently predicted.

● By the end of the 21st century, average 

spring soil water potential is expected 

to drop to approximately -3.0MPa, 

indicating conditions of extreme water 

scarcity. Soil moisture is also predicted 

to decrease from September through 

December. 

● The drying of soils in spring is predicted 

to occur earlier in both scenarios, and 

will shorten the period when soils are 

moist during the spring growing season. 

This will likely have a substantial impact 

on plant species that rely on spring soil 

moisture.
vi Describing Trends in Past and Future Soil Moisture in Mesa Verde National Park

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 shallow loamy mesa-top 

pinyon-juniper woodland ecosystem in 

Mesa Verde NP, Colorado (Figure 1). 

Figure 1. Shallow loamy 

mesa-top pinyon-juniper 

woodland ecosystem in 

Mesa Verde NP. NPS photo. 
2 Describing Trends in Past and Future Soil Moisture in Mesa Verde National Park

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. Shallow 

loamy mesa-top pinyon-juniper woodland 

is one of two upland ecosystems that SCPN 

monitors at Mesa Verde NP. The plant community in this ecosystem is characterized 

by a dense pinyon-juniper (Pinus edulisJuniperus spp.) overstory and an understory 

dominated by muttongrass (Poa fendleriana) 

and antelope bitterbrush (Purshia tridentata). Forbs and cacti are also present. Soils 

in this ecosystem are typically classified as 

loam. These shallow soils often occur on the 

mesa shoulders. The second ecosystem is the 

loamy mesa-top pinyon-juniper woodland 

ecosystem, which is addressed in a separate 

report. We used data from soil cores taken 

from ten plots in the shallow loamy mesatop pinyon-juniper woodland ecosystem as 

inputs to the SoilWat2 model (Figure 2).

Figure 2. Map of Mesa Verde NP showing Southern Colorado Plateau Network monitoring plots 

in the shallow loamy 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 Mesa Verde National Park

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 shallow loamy 

mesa-top pinyon-juniper woodland ecosystem in Mesa Verde NP.

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, particularly 

in the spring. By the end of the 21st century (L), average spring SWP is expected 

to drop to approximately -3.0MPa, 

indicating conditions of extreme water 

scarcity.

● Future seasonal differences in soil 

moisture will remain similar to current, 

with the highest moisture in winter and 

the lowest in summer. Spring soils will 

become increasingly drier, with conditions approaching those observed in the 

summer now.

Historical and future climate 

patterns

● Currently, mean annual temperature 

(MAT) is 9.4°C. In the future, MAT is 

expected to increase under all climate 

models (near future +2.5°C, long-term 

future +5.2°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 401 

mm. Bimodal precipitation is received 

during the monsoon and fall/winter 

(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 mid-May to August. 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

shallow loamy mesa-top pinyon-juniper woodland ecosystem in Mesa Verde NP 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 

higher in January through March under 

both the near and long-term scenarios 

due to the earlier onset of snowmelt. Under the long-term scenario, April through 

August will be drier (Figure 4B).

● Soil moisture is predicted to decrease 

from September through December, 

and to a greater degree in the long-term 

future.

● The drying of soils in spring is predicted 

to occur earlier in both scenarios and will 

shorten the period 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 4B).

Figure 4: Panel A. Average seasonal patterns of climate in the shallow 

loamy mesa-top pinyon-juniper woodland ecosystem in Mesa Verde 

NP. 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 Mesa Verde National Park

Discussion

These results present a long-term historical 

and future perspective on soil moisture in 

the shallow loamy mesa-top pinyon-juniper 

woodland ecosystem in Mesa Verde NP. 

Predicted changes in SWP are likely to affect vegetation community dynamics in the 

future. In the future, more moisture will 

be available in the winter due to the earlier 

onset of snowmelt. However, drying of soils 

is predicted to occur earlier in spring, which 

would shorten the period when soils are wet 

during this time. Compared to other woodland ecosystems examined in the SCPN, the 

soil moisture here is expected to change less 

in response to climate change, likely due to a 

relatively cooler, wetter climate. Compared 

to the second ecosystem monitored at Mesa 

Verde NP, soil moisture here is slightly wetter, due to differences in soil texture.

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 Mesa 

Verde NP shallow loamy mesa-top pinyonjuniper 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.

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