Test Case: Scenario Planning for Joshua Tree National Park

By Katherine Waser | The University of Arizona | August 11, 2009

Why Joshua Tree?

Visitors from around the world are drawn to California’s Joshua Tree National Park, with its iconic namesake plants and massive, rugged rock formations.

But climate change impacts combined with pressures from outside development are posing a risk to the trees and park, which includes parts of the Colorado Desert—a western extension of the Sonoran Desert—and the Mohave Desert. Warmer winters caused by rising temperatures threaten the trees’ reproductive cycle, which requires a freezing period. Rising temperatures also promote increased frequency of fires and the spread of non-native, fire-adapted grasses. These grasses thrive under the changed fire regime, whereas the native Joshua trees are not adapted and are readily killed by fire.

Joshua Tree National Park was a good choice for early testing and introduction of the scenario planning process in the National Park Service (NPS) context, both because of the threat climate change poses to the Joshua trees in particular, and because of the importance of understanding fire regime/invasive species/climate change inter-dynamics for national parks overall.

Because scenario planning is a new tool for the NPS, this initial experiment had three goals:

1. test the feasibility of scenario planning as a viable tool for developing NPS management strategies in the face of climate change impacts.
2. familiarize top-level NPS managers and specialists, both from Joshua Tree National Park and from across the country, with the scenario planning process.
3. develop and vet a suite of plausible scenarios for Joshua Tree National Park specifically, as a basis for developing new management strategies.

Because NPS managers and specialists from across the country were involved in this experimental process, the actual scenarios were developed by a dispersed group via web-enabled communication tools over a period of several months. This approach proved to be very effective, enabling the participants to develop a suite of three preliminary scenarios prior to a final workshop at Joshua Tree National Park on November 13–14, 2007. Workshop participants could thus focus on further evaluating these three initial scenarios in terms of their ecological, managerial, and socioeconomic plausibility.

How the Scenario Planning Process for Joshua Tree Played Out

The initial focal question was discussed and negotiated online in April 2007. The online group ultimately defined the focal question, how should the NPS manage this national park in the face of climate change impacts?

Table 1. Summary of projected Climate Change for Joshua Tree National Park.

Climate Variable	General Change Expected	Specific Change Expected and Reference Period	Size of Expected Change Compared to Recent Changes	Seasonal Patterns of Change	Confidence	Source and Context
Temperature	Increase	2050: +2 +/-0.6°C 2100: +3.1 +/-1.1°C	Large	More pronounced in summer and early fall	>99.9% Virtually certain	Abatzoglou and Brown
Precipitation	No change/Decrease	2050: +2 +/-0.6°C 2100: +3.1 +/-1.1°C	Similar	More pronounced in winter and spring	Spring 99% Other seasons non-significant Likely	Abatzoglou and Brown
Relative Humidity	Decrease	2050: +2 +/-0.6°C 2100: +3.1 +/-1.1°C	Large	More pronounced in spring	Spring and summer 95% Likely	Abatzoglou and Brown
Wind Speed	Increase	2050: +2 +/-0.6°C 2100: +3.1 +/-1.1°C	Large	More pronounced in winter and spring	>99% Spring, >95% Annual Likely	Abatzoglou and Brown
Extreme Events: Temperature	Warm events increase/ Cold events decrease	2050: increase 3 to 6 times present; decrease to 1/5 to 1/3 of present 2100: increase 5 to 8.5 times present; decrease 1/12 to 1/8 of present	Large	Increase in frequency and length of extreme hot events (summer) greatest relative exceedances in summer; decrease in extreme cold events (winter)	Modeled and observed Very likely	Abatzoglou and Brown
Extreme Events: Precipitation	Decrease/Increase	2050: -20% to +50%	Large	Increase in frequency	Modeled and observed	Abatzoglou and Brown

The next step was to determine other important external drivers of possible future change at Joshua Tree in addition to climate change impacts. Two were identified: uncertainties about future budgets for park managers, which are subject to many factors outside the managers’ control, and potential changes in “park values.” This last driver alludes to the fact that public expectations and support of the objectives for any given park may shift over the decades, particularly in cases where these objectives were not defined in the park’s enabling legislation. Park values thus include such variables as visitor experience (for example, overall quality, number of visits to the park, personal contact with nature), wilderness services (solitude), ecosystem services (biodiversity, hydrologic cycle), cultural services, and infrastructure.

Once the group had agreed upon the most important external drivers, they developed more detailed tables summarizing the projected potential impacts each driver would have on the park. Related tables were developed that identified the various sectors making up the Joshua Tree system. The tables also identified specific potential impacts to each sector caused by climate change and interactions with changing budget allocations and resource values.

Table 2. Sectors and Potential Impacts to Joshua Tree National Park.

Sector	Sub-Sector	Impacts
Natural Resources	Hydrology and Water Resources	Increase in extreme runoff and flooding (especially in winter); decrease in total snowpack; decrease in soil moisture; limited surface and groundwater availability. Water shortage, decrease in water quality. Link between high precipitation events and increase in invasive species to increase in fire size and spread. Decrease in overall precipitation could lead to drought conditions. This could help eliminate the threat of invasive species as they could not cope with these conditions.
	Aquatic Ecosystems	Nitrogen eutrophication; increased pollution from runoff; lower streamflows in summer; warmer stream temps; loss of habitat and species.
	Vegetation	Changes in phenology and geographic range; increase in biomass (longer growing season). Increased invasive species. Stand-replacing fires result in loss of sources for recolonization of burned areas – e.g. it could take hundreds of years for pinyon-juniper woodland to recover (Brooks 158).
	Wildlife	Changes in phenology, migration, reproduction, dormancy, and geographic range. Threatened desert tortoise
	Disturbance (fire, pests, pathogens, avalanche)	Fire: Increase in length of fire season, severity of fires, and number of acres burned; non-native invasive grasses provide continuous fuelbeds and increase wildfire severity. Pest/Pathogen: increased winter temperatures facilitate pathogen/pest survival.

Next, the group worked out visual flow charts that characterized the internal linkages between and among these various drivers, park natural resources, and park operations. Linkages were identified based not just on hard data and models, but also on the experience and insight of the scenario builders regarding Joshua Tree. These “internal dynamics schematics” were developed for climate drivers and budget drivers; a third schematic focused on climate drivers specifically as they relate to fire. Once completed, these tables provided the group with a powerful collaborative tool for conceptualizing and assessing the following:

• whether a driver is or is not impacting a given resource or operation at all
• whether the impact is direct or indirect
• how certain the impact is
• what feedback loops there might be within the system

Using this information, the group was able to identify a key climate uncertainty for Joshua Tree: the timing and intensity of precipitation, with the greatest variability coming from seasonal and episodic equatorial Pacific/Gulf of California events. Based on this key uncertainty, the group developed three preliminary scenarios that focused specifically on climate change and were linked to the global scenarios developed by the International Panel on Climate Change (IPCC) in its Fourth Assessment Report (Climate Change 2007). The three preliminary scenarios are:

The "Summer Soaker" Scenario

Precipitation decreases in winter and spring. Summer precipitation increases, mainly in the form of monsoons. Native grasses are actually favored with summer rains, but warmer temperatures begin to drive native annual grasses to higher elevations in the park. In this scenario, a major concern is the expansion of the Sonoran Desert ecosystem and the subsequent loss of iconic Joshua trees at lower elevations of the park.

The "When it Rains it Pours" Scenario

Wet and dry season variability increases: extreme inter-annual drought is punctuated by extreme precipitation events/years. Flash flooding events, erosion, and drought increase. In this scenario, the greatest concern is the impact of fire on the landscape due to increased invasion of non-native grasses. After a wet year, fires are big and burn fast because grass growth is stimulated. In turn, fire fertilizes the non-native annuals. This combination could set up a positive feedback loop in which Joshua Tree sees a widespread shift to a grassland ecosystem, and fires cover more and more of the landscape.

The "Dune" Scenario

This scenario is characterized by persistent dryness and drought. Wind increases overall, becoming more frequent and intense in spring and fall. Dune formation builds inside and just outside of the park due to increased wind and drought. Change in vegetation habitats due to drought and high temperatures leads to a loss of woody species. Ultimately, the park may end up with virtually no vegetation due to fire, water mining, wind, and higher temperatures.

The Workshop

At the workshop itself, the first task concerning Joshua Tree National Park was vetting these three preliminary climate-focused scenarios. Initially, participants found it difficult to accept and deal with the implications presented; ultimately, they were impelled by the plausibility of the scenarios to challenge and move beyond their current assumptions about the future. Once the scenarios were vetted, the group began considering how each might further be affected both by different park budgets and by different levels of public support for and expectations of the park. During this more detailed stage of planning, each preliminary scenario was given a specific budget and “park values” narrative, consistent with the goal of stretching the group’s thinking about the future. The “most bleak” (Dune) scenario, for example, was assigned a good budget and positive park values to help participants assess whether even these high levels of support would be sufficient to ensure the park’s ecological resilience under extremely adverse climate change impacts.

The two-day workshop did not allow enough time for full development of adaptation strategies for Joshua Tree. Nonetheless, this initial scenario planning process met all its outlined goals: The feasibility of scenario planning as a viable tool for the NPS was established, participants in the process gained a much greater understanding of the scenario planning process overall, and preliminary scenarios for Joshua Tree National Park were developed and tested as a basis for managing the park under the impacts of climate change.

Table 3. Comparison of the Three Scenarios for Joshua Tree National Park.

	Summer Soaker	When it Rains, it Pours	Dune
IPCC Emission Scenario	B1	A1B	A1F
Rate of CO2 emissions	Slowest rate of increase	Increases moderately	Steepest rate of increase
Temperature	Increases	Increases	Increases
Precipitation	Decreases in winter and spring; increases in summer; little or no change overall	Increase in extremes (drought in summer, storms in winter); overall decrease	Decreases overall and seasonally
Vegitation: non-native annual grasses	Decrease in current community; potential new suite of invasives emerge	Increase	Increase initially; decrease over time
Vegitation: native grasses	Increase	Decrease	Decrease
Vegitation: Joshua trees and other woody vegitation	Decrease and move to higher elevations	Decrease	Decrease
Fire regime	Slightly more intense, mosaic pattern	More intense, mainly after wet years	More intense initially, decrease over time as vegitation decreases
Native animal species	Decrease in Mojave species, increase in Sonoran species	Decrease	Decrease

What’s Next for Joshua Tree National Park?

At this point, the development of new strategies for managing Joshua Tree in the face of climate change is still underway. The preliminary tactics that have been proposed need to be analyzed in more detail and possibly tested on a small scale in the field. Specific next steps for the park have not been defined, but park managers have indicated their interest in continuing the process. Based on these initial results, the future of scenario planning for Joshua Tree National Park is bright.