Planning for Systems Management & Operations as part of Climate Change Adaptation

2. Climate Change Effects to Transportation System Management and Operations

This section provides an overview of the expected climate change effects that will impact the transportation community, focusing on impacts that will require operational responses as opposed to long-term behavioral or planning level responses. The adjacent exhibit (Exhibit 1) illustrates how changes in future climate are determined through the use of General Circulation Models under a variety of scenarios.

The relevant climate change effects are separated into two general categories based on whether the effect is part of a climate trend (e.g., increasing annual average air temperatures) or it is associated with a distinct climate event (e.g., storm, flood, drought, heat wave), as these different categories of effects will necessitate different types of operational responses by transportation agencies Tables A.1 and A.2 list the full range of relevant climate change effects for the transportation sector in the continental U.S. (CONUS) and Hawaii for the 21^st century, along with the affected regions and projected date range for the effect to occur. Effects for Alaska are listed separately in Table A.3, since they are distinct in many ways from analogous effects in the tropics (Hawaii) and mid-latitudes (CONUS). When available, the associated certainty of an effect is also specified in Tables A.1-A.3. Certainty is designated using terms defined by the Intergovernmental Panel on Climate Change (IPCC) in their Fourth Assessment Report (Le Treut et al., 2007); these terms are listed in Table A.4 and Table A.5 in Appendix A. For simplicity, sources of the climate change effect information in this section were limited to summary reports, such as those from the IPCC, the Climate Change Science Program (CCSP), and U.S. Global Climate Change Research Program (USGCRP). Much of the data in the cited reports originated from the 2007 IPCC report; the next IPCC report is expected in 2013-14. The following sections highlight some of key climate trends and event-related effects of climate change.

Exhibit 1 – Climate Change Scenarios Changes in future climate are determined from the output of general circulation models (GCMs). GCMs are complex models that simulate atmosphere, ocean, and land processes. They typically project changes in temperature and precipitation, from which changes in related parameters (e.g., incidence of wildfires, changes in water quality) are derived. GCMs generally have relatively low spatial resolution, on the order of 400 to 125 km (250 to 80 mi), so a technique called downscaling is used to obtain projections on regional and local scales. GCMs simulate changes in climate under scenarios of future conditions. Scenarios are not predictions or forecasts of future events. Instead, a scenario represents a possible version of the future (IPCC, 2000). Scenarios are used when reliable projections of future conditions are not available, as is the case for climate change. They attempt to constrain the range of plausible future conditions, based on socio-economic variables and trends in global emissions of greenhouse gases and aerosols. Characteristics of the four basic scenario families used for current GCM projections are listed in Table 2.6 (IPCC, 2000). At present, it is not possible to predict which scenario is most likely to occur in the 21st century. As a result, GCMs are typically run under scenarios of high (A2) and low (B1) greenhouse gas emissions to provide a representative distribution of possible future climate conditions. Summary of Climate Scenarios. [Adapted from IPCC, 2000]
Scenario	Economic Development	Global Population	Technology Changes	Theme
A1	Very rapid	Peaks around mid-21st century and declines thereafter	Rapid introduction of new and more efficient technologies	Convergence among regions; increased cultural and social interactions
A2	Regionally oriented	Continuously increasing	Slower and more fragmented than A1, B1, and B2	Self-reliance and preservation of local identities
B1	Rapid change toward service and information economy	Same as A1	Introduction of clean and resource-efficient technologies	Global solutions to economic, social, and environmental sustainability
B2	Intermediate levels of economic development	Continuously increasing, but not as fast as A2	Less rapid and more diverse changes than A1 and B1	Local solutions to economic, social, and environmental sustainability

2.1. Effects Associated with Climate Trends

The following effects are associated with climate trends leading to changing conditions over time.

2.1.1. Air Temperature

Rising concentrations of greenhouse gases in the global atmosphere during the 21^st century are expected to cause a net warming of the Earth’s surface, leading to higher average air temperatures. In general, GCMs run under scenarios of high greenhouse gas emissions (A2) project larger increases in air temperatures than scenarios of low emissions (B1). Furthermore, the magnitude of increases in air temperatures is projected to be greater toward the end of the 21^st century. This acceleration in warming is a result of the cumulative effect of increasing levels of long-lived greenhouse gases in the atmosphere.

Since 1900, the global average temperature has increased by about 1.5 degrees Fahrenheit (USGCRP, 2009). GCMs indicate that average annual air temperatures across all of North America, including the CONUS and Alaska, will increase steadily during the 21^st century. In fact, by 2039, annual average temperatures are anticipated to be above the range of current natural variability (Christensen et al., 2007). Projections of annual average temperatures (Figure 2.1) suggest that increases will be in the range of 1 to 3°C (1.8 to 5.4°F) by 2039 (Christensen et al., 2007). These changes will vary by season, with the largest increases expected to occur across the northern regions during the winter and the largest increases expected to occur in the Southwest during the summer (Christensen et al., 2007). The magnitude of average temperature increases during the summer is projected to be 3 to 5°C (5.4 to 9°F) across most of North America by the end of the 21^st century (Christensen et al., 2007). Air temperature changes near the coasts are expected to show less seasonal variability due to warming of the oceans associated with climate change (Christensen et al., 2007).

Regional trends of annual and seasonal air temperatures in the CONUS are consistent with continental trends (Figures 2-2 and 2-3). Annual average air temperatures across the CONUS are expected to rise 7 to 11°F under the A2 (high) scenario and approximately 4 to 6.5°F under the B1 (low) scenario by 2100, and warming will be greatest during the summer (FHWA, 2010). By 2050, average air temperatures are projected to increase 2.5 to 4°F in winter and 1.5 to 3.5°F in summer in the Northeast (USGCRP, 2009) and 2.7°F ± 1.8°F in the Gulf Coast region (CCSP, 2008). In the Southeast and the southern and central Great Plains, increases in average air temperatures during the summer are projected to be larger than those in winter (USGCRP, 2009). In some areas of the Southwest, increases in air temperature during the summer are expected to be larger than annual average increases, and they will be exacerbated by localized urban heat island effects (USGCRP, 2009). Due to the increases in air temperatures across the U.S., electricity demand for air conditioning in most North American cities is anticipated to increase considerably in the 21^st century, in order to cool homes and indoor work and recreation spaces (Field et al., 2007).

2.1.2. Precipitation

Higher air temperatures associated with rising concentrations of greenhouse gases are expected to increase the amount of water vapor in the atmosphere, leading to overall increases in global precipitation during the 21^st century. It is important to note that GCM projections of temperature changes for a given region are generally consistent in sign and magnitude, but precipitation projections can vary widely across models due to the difficulty in simulating the myriad of factors that influence precipitation frequency, duration, and intensity. An additional complicating factor is that precipitation in the U.S. varies naturally on seasonal, annual, and inter-annual time scales. In model simulations, any precipitation changes associated with future climate change are overlaid on this natural variability, making it difficult for GCMs to resolve contributions from natural and anthropogenic influences. The result is increased uncertainty in expected precipitation changes associated with future climate change as compared to projections for temperature.

Figures 2.4 and 2.5 illustrate the expected range of regional changes in winter and summer precipitation in the U.S. through 2100. Model projections indicate that annual average precipitation will increase across the northern CONUS and decrease in the southern CONUS, particularly in the Southwest (Christensen et al., 2007; USGCRP, 2009). Overlaid on this annual change will be seasonal variations, with most of the increases in precipitation in the northern CONUS and most of the decreases in precipitation in the southern CONUS expected to occur in the winter and spring (ICF International, 2010).

Associated with the increasing air temperatures, snow season length and snow depth are projected to decrease across most of North America (Christensen et al., 2007). Figure 2.6 depicts projected changes in percent snow depth in North America during March in 2041-2070. The rain/snow line is expected to shift northward and to higher elevations, causing more winter precipitation to fall as rain and less as snow (ICF International, 2010). Furthermore, less overall snowfall and earlier snowmelt in the spring will lead to a general decrease in snow depth across snow-covered regions of the U.S. (Christensen et al., 2007), particularly in the Rocky Mountains.

2.1.3. Coastal Effects

Climate change is projected to cause a rise in global sea levels of between 0.18 m to 0.59 m (7.1 in to 23.2 in) by 2099 due to thermal expansion of ocean water and melting of glaciers, though the rise will not be uniform(TRB, 2008). This rise in sea level will impact the Atlantic and Pacific coasts of the U.S., leading to coastal inundation and accelerated rates of coastal erosion (Field et al., 2007). Coastal erosion is also expected to be exacerbated by reductions in the extent and duration of sea ice, which will allow for more open water during the winter storm season (Field et al., 2007).

Along the Gulf Coast, sea level is projected to increase by at least 1 ft and up to 6 to 7 ft in some locations, such as central and western Louisiana and eastern Texas, where subsidence rates are highest (CCSP, 2008). In the Northeast, model predictions under a high (A2) scenario suggest that sea level will rise along the Atlantic coast more than the global average, leading to severe coastal flooding (USGCRP, 2009). For example, what is currently considered a 100-year flood event may occur twice as often by 2050 and up to ten times as often (an average of once per decade) by 2099 (USGCRP, 2009). In the Northwest, the south Puget Sound region is particularly vulnerable to sea level rise and increasing coastal erosion, including the cities of Olympia, Tacoma, and Seattle in Washington State (USGCRP, 2009). A potential increase in the number of landslides on coastal bluffs in the Northwest is also a concern, associated with more saturated soils from increased precipitation (USGCRP, 2009).

2.1.4. Human Health Effects

It is projected that U.S. residents over the age of 65 will represent 20% of the U.S. population by 2030. This population shift along with projected increases in the frequency, intensity, and duration of heatwaves suggests a future increase in heat-related deaths, particularly in highly developed areas where the urban heat island effect is present (USCCSP SAP 4.6, 2008). A warmer climate in the U.S. is also expected to make conditions more favorable for increases in pollen, some air pollutants, and Lyme disease, thereby increasing risks to human health. Higher temperatures are generally favorable for the expansion of tick distributions and greater abundance of vector-borne diseases like Lyme disease (USCCSP SAP 4.6, 2008). Rising air temperatures and high atmospheric carbon dioxide (CO₂) concentrations are anticipated to increase pollen concentrations in the CONUS (Field et al., 2007). Higher air temperatures may also increase concentrations of tropospheric (surface-level) ozone (O₃) and non-volatile fine particulate matter (PM_2.5), due to increased rates of associated gas-phase reactions (Field et al., 2007), which in turn may exacerbate and intensify the occurrence of respiratory illness, such as asthma (USCCSP SAP 4.6, 2008). In addition, as air temperatures increase, trees and plants emit more O₃ precursors, such as isoprene, which will also enhance production rates of O₃ (Field et al., 2007). By 2050, daily average ozone levels are projected to increase 3.7 parts per billion by volume (ppb) in the eastern U.S., and the number of summer days that exceed the 8-hour O₃ regulatory standard is expected to increase by 68% (Field et al., 2007).

2.1.5. Ecological Effects

Climate change may also have significant impacts on ecosystems in the CONUS. Model projections indicate that the growing season will expand during the 21^st century, with earlier spring thawing and later fall freezing (Field et al., 2007). Less snow cover and more winter precipitation falling as rain will increase runoff, lengthen the erosion season, and enhance inland erosion (Field et al., 2007). Along the Atlantic and Pacific coasts, the salinity of estuaries, coastal wetlands, and tidal rivers is expected to increase due to saltwater intrusion, which will damage coastal ecosystems and possibly shift them farther inland (USGCRP, 2009). Climate change is projected to expand the geographic range of invasive species, which alter the structure and composition of ecosystems. Non-native insects that have expanded their ranges in the U.S. include the Asian long-horned beetle, hemlock woolly adelgid, the common European pine shoot beetle, and the emerald ash borer. Non-native invasive plant species have altered fire regimes in the western U.S.; cheatgrass is an invasive species now common in the Intermountain West, which has changed the fuel complex, increased fire frequency, and reduced habitat within this region (USCCSP SAP 4.4, 2008).

2.2. Impacts Associated with Climate Events

The following impacts are associated with events that are expected to occur as a result of changing climate trends.

2.2.1. Air Temperature Events

Rising air temperatures in the U.S. during the 21^st century mentioned in Section 2.1.1 are expected to cause increased incidences of heat waves and extreme temperature events. The frequency and duration of warm extremes are projected to increase across North America (Christensen et al., 2007). In the CONUS, the magnitude and duration of severe heat waves, characterized by stagnant, warm air masses and consecutive nights with high minimum temperatures, are predicted to increase in locations where heat waves already occur (Field et al., 2007). In the Gulf Coast region, the number of very warm days (high temperatures >90°F) is expected to increase significantly, and by 2050, there will be a 50% probability of 21 days per year with high temperatures ≥100°F (CCSP, 2008). Similarly, in the Northeast, GCMs run under the A2 (high) emissions scenario project that some cities, such as Hartford, CT, and Philadelphia, PA, will average almost 30 days per year with high temperatures >100°F (USGCRP, 2009). In the Midwest, the frequency, severity, and duration of heat waves are expected to increase, and by 2100, GCMs run under the A2 (high) emissions scenario project that severe heat waves could occur once every two years (USGCRP, 2009).

2.2.2. Precipitation Events

Changes in precipitation patterns associated with climate change will lead to changes in the incidences of extreme precipitation events and related phenomena, including floods and droughts. Extreme precipitation events, such as thunderstorms and heavy downpours, are projected to increase in frequency and intensity (Meehl et al., 2007; ICF International, 2010). Across the CONUS, the probability of a heavy downpour occurring in a given year is expected to increase from 5% to 20-75% by 2100 (ICF International, 2010). The intensity of individual rainfall events is projected to increase in the Gulf Coast region during the 21^st century (CCSP, 2008).

In the Northeast, GCMs run under the A2 (high) emissions scenario project that 1-3 month droughts will occur every summer in the Catskill and Adirondack Mountains of New York and across New England (USGCRP, 2009). The frequency, duration, and intensity of droughts are expected to increase in the Southeast, Midwest, and Southwest as well (USGCRP, 2009). In the Northwest, more precipitation falling as rain and not snow is anticipated to cause winter flooding on the west side of the Cascade Mountains (USGCRP, 2009).

2.2.3. Storms and Coastal Flooding

Changes in atmospheric circulation, in conjunction with increases in air temperature and altered precipitation patterns due to climate change, will affect the development of storms, including tropical cyclones (hurricanes and tropical storms) and extra-tropical cyclones (large mid-latitude snowstorms and rainstorms). Climate change is expected to shift the jet stream over the U.S. northward (ICF International, 2010), resulting in a slight shift in mid-latitude extra-tropical cyclone storm tracks toward the North Pole (Christensen et al., 2007). The intensity of extra-tropical cyclones is anticipated to increase, but they will occur less frequently (Meehl et al., 2007).

Trends for tropical cyclones are less clear. As surface water temperatures in the Atlantic Ocean and Gulf of Mexico increase due to climate change, the intensity of hurricanes is expected to increase, possibly by 10% (CCSP, 2008). Some GCMs predict that hurricanes’ peak wind speeds and rainfall intensity will increase (Meehl et al., 2007). Potentially stronger tropical cyclones combined with rising sea level are expected to result in higher storm surge and more severe coastal flooding (Field et al., 2007; USGCRP, 2009).

2.2.4. Wildfires

Warmer and drier conditions in the 21^st century associated with climate change will increase the potential for wildfires. Across the CONUS, higher air temperatures during the summer are projected to increase the risk of fire ignition by 10-30% by 2100 (Field et al., 2007). In the Northwest, earlier mountain snowmelt in the spring combined with higher air temperatures are anticipated to create dry conditions during the summer that will increase the risk of forest fires (USGCRP, 2009).

2.2.5. Landslides

Increased heavy precipitation in the winter and spring suggest an increase in soil saturation and a compromise in slope stability, which is projected to cause an increased occurrence of landslides and/or mudslides. In coastal areas, bluff landslides will be exacerbated by the rise in sea level (USGCRP, 2009).

2.2.6. Dust Storms

Temperature and precipitation changes are projected to decrease vegetation cover, which protects the ground from erosion. As a result, it is suggested the occurrence of dust storms will increase (USCCSP SAP 4.3, 2008).

2.3. Climate Change Effects in the Arctic (Alaska)

2.3.1. Air Temperature

Air temperatures in Alaska are expected to increase throughout the 21^st century, but at a faster rate than for the CONUS. Model projections indicate that the annual average warming in Alaska will exceed the global mean warming. The largest temperature increases are expected during the winter over northern Alaska, due to the positive feedback from reduced snow cover (Christensen et al., 2007) (Figure 2.3). The magnitude of warming is projected to vary from 7°C (12.6°F) in winter to 2°C (3.6°F) in summer by 2050 (Christensen et al., 2007; USGCRP, 2009).

2.3.2. Precipitation

Models are consistent in predicting an increase in annual average precipitation in Alaska, with most of the increase occurring during the winter months (Christensen et al., 2007; ICF International, 2010). As air temperatures rise, the ratio of rain to snow is expected to increase, so more precipitation should fall as rain and less as snow, particularly in locations in Alaska where average air temperatures are currently close to freezing (Anisimov et al., 2007). Changes in the frequency of extreme temperature and precipitation events in the Arctic are uncertain, but projections indicate that very warm and wet winters and summers will become more frequent in the 21^st century (Christensen et al., 2007).

2.3.3. Ice, Snow Cover, and Permafrost

Increasing air temperatures will have a profound effect on ice, snow cover, and permafrost in Alaska. Recent observations suggest that higher temperatures are already causing earlier spring snowmelt, reduced sea ice, widespread glacier retreat, and permafrost warming in Alaska (USGCRP, 2009). The extent and thickness of Arctic sea ice is expected to continue to decrease, with reductions of 22 to 33% in the extent of annually averaged sea ice projected by 2080-2100 (Anisimov et al., 2007; Christensen et al., 2007). Most of the reduction in sea ice is expected during the summer (Anisimov et al., 2007). Additional loss of snow cover on land is also projected (Figure 2.3), with reductions in snow residence times expected to be greatest in spring (Anisimov et al., 2007). Warmer conditions are anticipated to shrink the extent of terrain underlain by permafrost. By 2050, models project that the permafrost area in the Northern Hemisphere will decrease by 20 to 35%, due to thawing of permafrost in both discontinuous (10 to 90% of land frozen) and continuous (90 to 100% of land frozen) zones (Anisimov et al, 2007).