The Southern Great Plains encompasses diverse ecoregions (areas where ecosystems are generally similar) stretching from the High Plains to the Edwards Plateau and from the Tamaulipan Brushlands to the Gulf Coast Prairie.118 The region is prone to periods of drought punctuated by heavy rainfall events, with evidence that these events are occurring more frequently.10 These precipitation patterns influence water availability and aquatic habitats such as lakes, rivers, springs, and streams. Freshwater inflows from rivers flowing to coastal estuaries provide important nutrients and sediments while moderating salinities to create and maintain productive estuarine ecosystems.
Species Distribution and Habitats
Climate plays a key role in the distribution of species (Ch. 7: Ecosystems). Species’ response to climate change is complex and variable.119 As temperatures increase, the geographic distribution of some species tends to shift to areas with temperature ranges where a given species can survive. A notable species of concern in the region is the lesser prairie‐chicken, which was listed as threatened under the U.S. Endangered Species Act in May 2014. Currently, the lesser prairie‐chicken habitats include Kansas, Texas, and Oklahoma (as well as Colorado and New Mexico) with 70% of the population in Kansas.120 At this time, it is not clear whether climate change will influence the lesser prairie-chicken in positive or negative ways.121,122 Rising temperatures are also causing changes to growing seasons and migration patterns of birds and butterflies.123 In Texas, white-wing doves, originally confined to the Lower Rio Grande valley, have been expanding northward124 and are now common across Oklahoma. Other factors such as habitat loss also influence species distributions, making it difficult to pinpoint a single cause for these distribution changes.
While it is unclear how climate change will affect species directly, the effects of increased aridity will likely have negative impacts. In addition, ecosystem services—the materials and processes that ecosystems produce that benefit people—will also be affected.123 In general, drought forces wildlife to travel farther to locate food, water, and shelter, which can deplete body condition going into winter or spring migration, when food sources are typically scarcer, making them more vulnerable to other stresses. The highly endangered Houston toad was negatively impacted during the 2011 drought and devastating wildfire in Bastrop County, Texas. Whooping crane numbers, which depend on sufficient freshwater inflows for a reliable food source (primarily blue crabs), were also reduced. In addition, a lack of freshwater can force whooping cranes to fly to uplands to drink, using more energy and exposing birds to more threats from predators and other mortality factors.
Aridification exacerbates stress in highly isolated habitats and fragmented lands, diminishing the ability for species to persist if they cannot move to better conditions. Migratory birds are better able to move to areas with better habitat conditions but could be in a weakened condition to do so. Migratory waterfowl can also be negatively impacted by reductions in wetland habitat areas due to aridification. Loss of irrigated rice fields in Texas contributed to significant declines in wintering waterfowl along the Gulf Coast. The most significant decline was documented for snow geese, with a 71% decline for 2011–2014 as compared to the long-term average.125 Playa lakes in the High Plains serve as important habitat for migrating waterfowl, but during the drought these wetlands were virtually nonexistent.
Plant community changes are also occurring, possibly due to climate change and other factors, and these changes in turn affect fish and wildlife. In the Southern Great Plains region, winters are warmer and spring is arriving earlier. Along the Texas coast, black mangroves, which are sensitive to cold, are expanding northward along the coast, and red mangroves, formerly not found in Texas, are now appearing there.126 Warmer winters with fewer freezes are also conducive to pests and diseases. Woody shrubs invading prairie grasslands are favored by increases in concentrations of carbon dioxide (CO2), changes in soil moisture cycles, fire suppression activities, and soil disturbances.125 The 2011 drought produced a direct and indirect tree mortality rate of over 6%—many times the normal rate.127
Climate change impacts to aquatic ecosystems include higher water temperatures in lakes, wetlands, rivers, and estuaries that can result in lower dissolved oxygen, leading to more fish kills. Impacts to reservoirs include fluctuating lake levels, loss of habitat, loss of recreational access, increase in harmful algal blooms, and disconnectedness from upstream and downstream riverine habitats.128 Localized declines in fish populations have been documented in rivers due to lack of water or water confined to increasingly narrow pools; in some cases, these declines prompted biologists to capture and relocate some endangered species to fish hatcheries.129 Aridification (a gradual change to a drier climate) can have a number of negative impacts on freshwater mussel populations, including increased predation pressures, hypoxia (low oxygen conditions), increasing water temperature, and, ultimately, anoxia (no dissolved oxygen in water) or emersion (stranding the organism out of water and exposing it to air).
Coastal Areas, Bays, and Estuaries
The Texas coast, with 6.5 million people contributing over $37 billion to the region's economy, relies on its natural features, bays, and estuaries that serve as storm barriers to protect coastal infrastructure, and on its climate amenities to spur ecosystem services, such as fishing, ecotourism, and the ocean economy. These coastal ecosystems provide protection not only for people but also for 25% of the Nation's refining capacity, four crucial ports, much of the strategic petroleum reserves, and strategic military deployment and distribution installations. This protection was clearly on display with the recent impacts of Hurricane Harvey, where it has been estimated that natural coastal habitats protected about $2.4 billion worth of property in Texas and thousands of lives, with the suggestion that these habitats are potentially our first lines of defense.130
A rising sea level impacts more than 74% of Gulf-facing beaches in the upper Texas coast. The average rate of beach erosion is almost 10 feet per year.131 Sea level rise means more frequent and longer-lasting flooding of marshes that eventually could be permanently flooded, becoming open water.126,132 Higher tides and storm surges cause inundation of freshwater areas and beach erosion, leading to a potential decrease or loss of barrier islands and coastal habitats, including nesting habitats and submerged habitat such as seagrass beds affected by changes in water quality and changing water depths. A significant percentage of fishery species in the Gulf of Mexico are dependent upon estuaries for some portion of their life cycle.133
The warming of bay waters on the Texas coast has been documented for at least 35 years. This mostly reflects warmer winters, not warmer summers. The increase in water temperature directly affects water quality, leading to the higher potential for low levels of dissolved oxygen, or hypoxia. Hypoxic events and harmful algal blooms have caused fish kills, leading to lower productivity and diversity of estuarine ecosystems.126
Freshwater inflows are critical to both aquatic ecosystems and wetlands in the Southern Great Plains. Both surface and groundwater depletion have led to dramatic changes of the aquatic and wetland communities in Kansas134 that not only impact inland species but have a dramatic effect on coastal species relying on the freshwater inflow to ensure the integrity of the coastal ecosystem. Whooping crane and many other migratory species flying through this region during both spring and fall are impacted.135 Climate change and human use have impacted these aquatic systems and wetlands and, ultimately, the vital flow of freshwater to the coastal marshes and estuaries.
Changes to freshwater inflows to estuaries lead to changes in salinity and inflows of nutrients and sediment, resulting in impacts to oysters and other sensitive estuarine species. In addition, harmful algal blooms have become more frequent, more intense, and more widespread.123 Reduced freshwater inflows during 2011 led to record high salinities in Texas estuaries that contributed to a coast-wide “red tide” harmful algal bloom event. Red tides, a type of harmful algal bloom, most commonly occur during drought years, as the organism that causes red tide does not tolerate low salinity. Red tide blooms cause fish kills and contaminate oysters. In addition, oysters and other shellfish can accumulate red tide toxins in their tissues. People who eat oysters or other shellfish containing red tide toxins become seriously ill with neurotoxic shellfish poisoning. Once a red tide appears to be over, toxins can remain in the oysters for weeks to months. The 2011 bloom started in September and lasted into 2012. Fish mortality was estimated at 4.4 million. The commercial oyster season was closed and disaster declarations issued. The total economic loss was estimated at $7.5 million (dollar year not reported).136
Gray snapper have been ranging farther north since the 1990s; once found only in the lower Laguna Madre and off the extreme southern shore of Texas, they are now migrating northward along the upper Texas Coast. Conversely, flounder abundance has been declining due to the warmer winters,137,138 since sex ratios (the number of males versus females) are influenced by temperature during flounder development and increases in temperature produce increasingly male-dominated sex ratios in southern flounder from Texas (See Figure 23.9).
Existing Options for Managing Risk
The National Fish, Wildlife, and Plants Climate Adaptation Strategy123 was developed to provide natural resource managers and decision-makers the strategies and tools to address climate change impacts. The Strategy offers a guide for actions that can be taken in spite of remaining uncertainties over how climate change will impact living resources.
The Texas Edwards Aquifer Recovery Implementation Program Habitat Conservation Plan78 balances water pumping and use of the aquifer with protection of eight federally listed threatened and endangered species that depend on San Marcos Springs and Comal Springs, two of the largest springs in the southwestern United States. These springs are the headwaters of the San Marcos and Comal Rivers and provide important water flow, especially during drought, to the Guadalupe River and Estuary.
Environmental flows—instream flows and freshwater inflows to bays and estuaries—are critical for sustaining aquatic ecosystems. In 2007, the Texas Legislature passed Senate Bill 3, which established a comprehensive, statewide process to protect environmental flows.136 The process relies upon input from local stakeholder groups, composed of balanced interests ranging from agricultural water users to commercial anglers. The Texas Commission on Environmental Quality has adopted environmental flow standards intended to protect flow regimes that will help ensure healthy rivers, streams, and estuaries for Texas. The focus now is on adaptive management to refine standards, address research needs, and identify voluntary strategies to meet environmental flow standards.
The Texas Coastal Resiliency Master Plan139 promotes coastal resilience, defined as the ability of coastal resources and coastal infrastructure to withstand natural or human-induced disturbances and quickly rebound from coastal hazards. This definition encompasses the two dimensions of resilience: 1) taking actions to eliminate or reduce significant adverse impacts from natural and human-induced disturbances, and 2) responding effectively in instances when such adverse impacts cannot be avoided. To keep pace with the dynamic Texas coastline, the Plan will be updated regularly to allow the state to continually assess changing coastal conditions and needs and to determine the most suitable way to implement the appropriate coastal protection solutions.