CLIMATE CHANGE INITIATIVE
Climate Change in Northwest Arkansas
Scientists agree, climate change is not something we will experience only in the future, but is something we are already experiencing today. While changes in climate have not been as pronounced in our region as along coastlines and in other parts of the country to date, we are experiencing change, and the change will only accelerate in future decades. Our hunters, fisherman, farmers, and outdoor enthusiasts have already noticed differences in the natural environment. And as change in other parts of the country and world bring “climate refugees” to Northwest Arkansas, the increase in population creates an added climate impact of its own. When we understand the expected changes our region faces, we gain an opportunity to mitigate negative impacts and protect our local landscapes for the future.
First Leaf Date
Tracking the timing of leaf emergence each season over time for different plant species provides valuable insight into our changing climate. Plant lifecycles respond to seasonal differences in weather, particularly temperature. Leaf emergence timing is a critical component of the food web and climate change has the potential to mismatch lifecycle timing for some species that are unable to adapt quickly enough.
For example, many insects, including pollinators, depend on the young leaves of specific plants for food. If leaves on these plants emerge earlier, insect species may not arrive in time to take advantage of their food supply. Many migrating birds depend on healthy insect populations to feed their young upon arrival to their breeding grounds. Citizen scientists are working with researchers to track timing of seasonal events in various plant and animal species to get a better understanding of how specific species may respond to changes in seasonal timing.
Researchers are already documenting changes in timing. For example, research by Courter et al. demonstrated that Ruby-throated hummingbirds are arriving at their spring breeding grounds 11-15 days earlier (depending on latitude) when comparing the data from 1880-1969 to data from 2001-2010. These birds rely on nectar for most of their nutritional needs. Scientists are uncertain just how much the changes in the timing of nectar blooms will affect their populations.
Source: EPA Climate Change Indicators
According to the EPA Climate Change Indicators, in Northwest Arkansas, the first leaf date is arriving on average approximately 8 days earlier than it did in the 1950’s. The map below shows trends in the timing of first leaf dates in lilacs and native honeysuckles across the contiguous 48 states. Blue circles represent later leaf dates, and red circles represent earlier. Earlier first leaf dates have been documented in much of the northern and western United States with trends in warming temperatures. Much of the Southeast region is experiencing later arrival of spring. The delay in leaf out date in this region may be due to a lack of chilling days needed by plants to respond to spring temperatures. Chilling day requirements refer to the number of cold hours a plant must experience before budding, generally the number of hours between 32 and 45 degrees Fahrenheit. Each species has different requirements.
Changes in Plant Hardiness Zone
Source: Arbor Day Foundation
Plant hardiness zones help farmers and gardeners decide which plants will likely survive in their area. The zones are based on average lowest temperatures recorded each winter. Plants are more sensitive to an extreme low temperature event than an extreme high temperature event. As temperatures warm in a location over time, new plants establish where they were previously unable to survive. These shifts in plant distributions affect the composition of the greater ecosystem. For example, as new plants move into or out of an area, wildlife species that depend on those plants often follow. From 1990-2015, Northwest Arkansas changed from plant hardiness zone 6 to zone 7.
Changes in Growing Season
Changes in the length of the growing season directly impacts which types of crops can be planted and when they should be planted. Agricultural practices must adapt to shifts in seasons to be successful. These changes also impact the types of plants that can be successful in our ecosystems. The map below show that nationally the growing season is about 15 days longer than at the beginning of the twentieth century. The western region has seen the greatest change. With warmer temperatures, the growing season in Northwest Arkansas has increased by approximately 10-15 days in the last century.
Allergies and Ragweed Season
Allergic illnesses, including hay fever, affect about 30% of the population in the United States. According to the EPA Climate Change Indicators, Northwest Arkansas has experienced an increase of approximately 11 days in the ragweed pollen season from 1995 and 2015. A study by Dr. Lewis Ziska and several colleagues found the longer pollen season is associated with the first fall frost appearing later in the season and longer frost-free periods. As temperatures continue to warm, Northwest Arkansas is likely to experience longer ragweed seasons.
Changes in growing season 1895-2015 Source: Climate Central
Change in Ragweed Pollen Season 1995–2015
Scientists have developed different models representing changes to our climate based on different emissions scenarios and how well, or not, we do on that front. According to the NOAA Climatic Data Center, historical average temperature for Arkansas ranged from 58 to 63 degrees between 1895 and 2013. The Climate Wizard, an interactive map produced by The Nature Conservancy, examines projections in temperature based on sixteen different models and three different greenhouse gas emission scenarios throughout the United States. The average temperature increase for Northwest Arkansas based on averages of these models and scenarios is approximately seven degrees Fahrenheit by the end of the century.
This graphic from EPA’s report Climate Change Impacts Southeast and Caribbean shows that the number of days reaching temperatures over 95°F in the Southeast is projected to increase during this century. This graph compares historic patterns from 1971-2000 to future estimates for 2041-2070 under a scenario with high greenhouse gas emissions. The predicted increase in number of days over 95 degrees in Northwest Arkansas ranges from 20-40 depending where you are in the region.
The National Climate Assessment projected water availability to decrease in availability for 2010-2060 with the western portion of the Southeast region, including Northwest Arkansas, experiencing the largest reduction in water availability.The data indicates our water availability will likely decrease 5-6.4% from climate change impacts.
In addition to reduction from increased evaporation with higher temperatures and changes in precipitation, our region faces additional stress in water supply with increased urbanization and potential increases in irrigation needs from local farmers. The report also indicates that our region is expected to experience an increase in extreme weather events, particularly prolonged drought conditions and heavy flooding.
Impacts in Northwest Arkansas
Plant and animal species adapt slowly over time to live within a particular range of environmental conditions including temperature, water, soil type, and light levels. When the conditions of their local environment change, therefore, many species must shift to a new location to survive. According to research (Chen et al.), species are already moving to escape rising temperatures in search of more favorable habitat conditions. Species have shifted in elevation at a rate of 11 meters (about 36 feet), and toward the north and south poles at a rate of 17 kilometers (about 10 miles), per decade. Animal populations shift more rapidly than plants, because plants must spread their seeds to relocate. However, animals depend on certain plant communities for food and shelter, so this misalignment of habitat needs disturbs the balance of the ecosystem on which these species rely. Furthermore, some animals can cover ground more quickly than others. Birds, butterflies, and mammals are more mobile than small terrestrial creatures such as snails and frogs.
Northwest Arkansas is known for its abundant recreational opportunities, scenic views and biodiverse forests that provide invaluable ecosystem services for our region, including water filtration, air filtration, and carbon sequestration.
Ecosystems in Northwest Arkansas are currently experiencing multiple forms of stress, however, from urbanization, invasive species (including non-native plants and insects), diseases, and habitat loss and fragmentation. These stressors threaten the health of our Ozark ecosystems, and climate change exacerbates the region’s vulnerability.
For example, higher temperatures mean longer insect and pest seasons. Woody vines and shrubs can grow faster than trees, overtaking habitats with their fast-growing expansion. One study by Lewis Ziska measured how poison ivy grew in environments with higher levels of carbon dioxide and concluded higher carbon dioxide levels significantly increased leaf size and the amount of urushiol produced, the chemical that causes an itchy rash. Changes in temperature also enable pests from the south the extend their range northward.
Urban development and habitat fragmentation create barriers to movement for plant and animal species, which weakens their ability to migrate and adapt as their habitat ranges shift with changes in temperature and precipitation. Current urbanization has decreased water quality by reducing the natural buffers responsible for filtering out pollutants. In the future, these negative impacts on water quality will be compounded during extreme flooding events associated with climate change.
This report by Audubon documents the range shift of birds in North America over the past 40 years.
Invasive honeysuckles like Japanese honeysuckle (above) and bush honeysuckle were brought to the U.S. from eastern Asia in the 1880’s. They have since become some of the most invasive plants in Northwest Arkansas.
Impacts to Our Ozark Forests
Kessler Mountain in Fayetteville, Arkansas.
As the observed changes in plant hardiness zones indicate, plant species historically found in South Arkansas are advancing northward. The degree of change we will experience in Northwest Arkansas varies based on carbon emission/reduction scenarios and how well we do on that front.
Scientists have analyzed tree ring samples from specific tree species in the Ozark Highlands to estimate how trees have responded to past temperature fluctuations and drought conditions by comparing tree growth to historical climate data. This research provides insight into which tree species are more likely to thrive over time in a warming Ozark climate.
Preliminary data suggests drought-adapted post oaks could expand in range, where black walnuts would be less adaptable because they require more moisture. The recent drought in 2012 killed large populations of white and red oak in the Ozarks, indicating they may also be more vulnerable to the predicted increased periods of intense drought in Northwest Arkansas. The loss of walnut, white oak, red oak and other native Ozark hardwood tree species would have an economic and ecological impact on our region.
In addition, the increased proliferation of invasive plant species, as mentioned above, already threatens to overtake our Ozark understory trees, such as Redbuds and Dogwoods, and shades the wildflowers and other plants characteristic of our Ozark woodlands in early spring.
Impacts to Our Aquatic Ecosystems and Water Quality
Increased temperatures and varying precipitation levels have a direct impact the health of vulnerable aquatic habitats in Northwest Arkansas.
When water temperatures increase with increasing air temperature, the amount of available dissolved oxygen in the water decreases. Aquatic fish, insects, bacteria, and plants require a specific range of dissolved oxygen to survive. Warmer temperatures can also lead to an overgrowth of algae, which negatively impacts water quality, including consumption of available dissolved oxygen.
Extreme rainfall events increase the runoff of pollution into our waterways, including sediment, nitrogen-rich fertilizers and agricultural waste, further degrading water quality. These pollutants already impact our waterways negatively, and problems will predictably intensify with increased flood events.
Largemouth bass in an Ozark stream.
According to the Arkansas Wildlife Action Plan, fish species that rely on shallow pools and streams would be most impacted by altered flows and drier conditions associated with climate change. Like terrestrial animals, fish can move in search of new habitats with more favorable conditions, but man-made barriers such as dams and changes in hydrology often prohibit their ability to relocate. Rising water temperatures could also impact local sport fishing and tourism revenue. As an example to consider, a U.S. Forest Service study found that between 53 and 97 percent of natural trout populations in the Southern Appalachian region of the U.S. could disappear with warmer temperatures predicted by global climate change models.
Impacts on Livestock Farming
Agriculture is an important economic driver in Northwest Arkansas and an important part of our cultural heritage. According to the Washington and Benton County profile reports, farm income from 2010 livestock and product sales was estimated at $834 million in Benton and Washington counties. Temperature and precipitation predictions could have a direct economic impact on farmers in Northwest Arkansas.
Protein production is an economic driver in our region.
Research by the University of Arkansas Extension office reports that in the state of Arkansas, the 2012 drought resulted in an estimated $128 million loss in the cow-calf sector. The average loss for the for cow-calf producer was $141 per bred cow.
Warmer temperatures also impact milk productivity. As temperatures rise from 90° to 100°F and humidity remains in the 50 to 90 percent range, dairy cattle consume less and in turn milk production usually decreases by greater than 25 percent.
Impacts on Crop Farming
Some studies suggest that increases in atmospheric carbon dioxide levels could increase production of certain crops, but higher temperatures and increased drought also amplify crop heat stress, irrigation requirements, and susceptibility to pests. Many weeds and pests also flourish in warmer climates, and new ones introduced, posing additional ongoing difficulties for farmers. The nutritional value of crops may also be impacted. According to the EPA’s Climate Change Impacts Agriculture report, higher CO2 levels have been associated with a reduction in protein and nitrogen content of alfalfa and soybean plants, degrading the quality of these crops.