Forest Carbon Management

Water is central to the region’s productivity. Projected increases in winter and spring precipitation in the Southern Plains may benefit productivity by increasing water availability through soil moisture reserves during the early growing season. The Southern Plains will remain vulnerable to periodic drought because much of the projected increase in precipitation is expected to occur in the cooler months while increasing temperatures will result in additional evapotranspiration.

The freeze-free season is defined as the period of time between the last spring frost (daily minimum temperature below 32 degrees F) and the first fall frost. The length of the annual freeze-free season has been increasing since the 1980s, and all climate models agree that it will continue to increase in the future. The largest increases are projected for southeastern Texas, where the freeze-free season could be 30 days longer.

By mid-century, summer precipitation is expected to decrease by 5-15% for much of Kansas, Oklahoma, and northern Texas, and increase by as much as 15% in central Texas. The means of several climate models indicate that winter and spring precipitation may increase by up to 10% percent by mid-century across most of the region, although southwest Texas may see decreases during these seasons. Under mild climate scenarios, changes are generally smaller than in more extreme climate scenarios.

The frequency and intensity of heavy precipitation events are anticipated to continue to increase, particularly under higher scenarios and later in the century. Most of the Southern Great Plains region is projected to experience 0 to 30% more days each year with more than an inch of precipitation by the middle of the century. Days with more than 2 inches, 3 inches, and 4 inches of precipitation are also expected to occur more regularly. Rare events, such as 100-year floods, may also become more common.

There is uncertainty between different climate scenarios for future precipitation projections in the Southern Great Plains. Overall annual changes in precipitation are expected to be small through mid-century, with slight decreases projected from Texas to Kansas. The largest decreases in annual precipitation are expected in Texas, which may see 6-12% less annual rainfall by late-century.

Different modeling approaches generally conclude that future climate conditions will increase the risk of wildfire across the Great Plains. In the Southern Great Plains, increased wildfire activity is linked to periods of abundant precipitation followed by high temperatures and drought. Annual fire probability, calculated solely with climate data and physical principles, is projected to increase by 20% to 1200% across the region by the end of the century. Fire probability may decrease in Texas, however.

The Southern Great Plains region can expect increased dryness and aridity in the future, as hotter temperatures increase evapotranspiration and deplete soil moisture. Some of the negative effects of drying may be offset by the increased atmospheric concentrations of carbon dioxide, which can stimulate plant growth and increase water-use efficiency. Decreases in available surface water may lead to an increased demand for groundwater. Model simulations predict conditions to possibly become drier than at any time during at least the last 1,000 years.

The largest decreases in cold days are expected in Kansas. The smallest decrease in cold days is expected in Oklahoma and Texas, where these kinds of cold days rarely occur. Similarly, the region is expected to have up to 30 fewer days with a minimum temperature below 32 degrees by the middle of the century, particularly on the western edges of Kansas, Oklahoma, and Texas.

For an average of seven days per year, maximum temperatures reach more than 100° F in the Southern Plains. By mid-century, the frequency of very hot days (with maximum temperatures above 100°F) could possibly double. By late century, Central Texas north to Kansas may experience an increase of 60-80 more hot days per year. South Texas is projected to see 90-100 additional hot days by the end of the century, according to a range of climate scenarios. The smallest increase in days over 100°F will occur in Kansas, with 40-60 additional hot days.

All climate models agree that temperatures are projected to increase over the 21st century across the Southern Great Plains, with almost uniform temperature increases across the entire region. Summer shows the largest amount of warming, with a localized maximum in western Kansas. Springtime warming is generally smaller than other seasons, with the largest increases occuring in southwest Texas.