Climate Assessment Report Implications for the Mississippi River Basin

Tuesday saw the release of a National Climate Assessment ("NCA") report (the third since 2000) by a 44-member advisory committee established by the U.S. Department of Commerce to integrate federal research on environmental change and its implications for society.  The national implications of climate change on the environment, human health and the economy that were highlighted in the NCA report have received widespread media coverage.  In this article, we review the implications of climate change for the three main U.S. regions that make up the Mississippi River Basin: the Midwest, Southeast and Great Plains.

Midwest

In general, the report finds, climate change will tend to amplify existing climate-related risks to people, ecosystems, and infrastructure in the Midwest, which should see more heat waves, higher humidity, and declining air and water quality as a result of climate change.  The report  notes that the eight Midwestern states have already felt the effects of a changing climate pattern, exhibiting increased average temperatures in recent years.  Annual temperatures in the Midwest have generally been well above the 1901-1960 average since the late 1990s, with the decade of the 2000s being the warmest on record. 

A regional summary projects that "direct effects of increased heat stress, flooding, drought, and late spring freezes on natural and managed ecosystems may be multiplied by changes in pests and disease prevalence, increased competition from non-native or opportunistic native species, ecosystem disturbances, land-use change, landscape fragmentation, atmospheric pollutants, and economic shocks such as crop failures or reduced yields due to extreme weather events."

Projected average air temperature changes - Midwest

The region, an area that provides up to 65 percent of the country's corn and soybean production, may at first see increasing crop yields, as a result of rising atmospheric carbon dioxide levels and longer growing seasons. However, eventually, climate change's negative impacts such as extreme weather events, should outweigh the positives, according to Donald Wuebbles, a professor at the University of Illinois and member of the NCA advisory committee.  Wuebbles notes that "increased yields will be offset progressively by extreme weather events and precipitation events, and insect and disease threats," and adds that "though adaptation options can reduce some of the detrimental effects, in the long term, the combined stresses associated with climate change are expected to decrease agricultural productivity."

In addition to the above-noted Midwestern climate change scenarios, the report predicts that 

• The composition of the region’s forests will change as rising temperatures drive habitats for many tree species northward; and
• Extreme rainfall events and flooding should continue, causing erosion, declining water quality, and negative impacts on transportation, agriculture, human health, and infrastructure

Southeast

Key NCA report findings for the region are that sea level rises in conjunction with land subsidence will  result in "widespread and continuing threats to both natural and built environments and to the regional economy," and that "increasing temperatures and the associated increase in frequency, intensity, and duration of extreme heat events will affect public health, natural and built environments, energy, agriculture,

and forestry." Additionally, the report finds, "decreased water availability, exacerbated by population growth and land-use change, will continue to increase competition for water and affect the region’s economy and unique ecosystems."  Coastal Alabama, Mississippi, Louisiana, and Texas already face significant economic losses that annually average $14 billion from hurricane winds, land subsidence, and sea level rise.

In coastal Louisiana, since the 1930s, a combination of human and natural factors has resulted in 1,880 square miles of land being lost.  The NCA report regional analysis notes that "Four Native communities in Southeastern Louisiana  have already experienced significant land loss" (the Grand Bayou Village, Grand Caillou/Dulac, Isle de Jean Charles, and Pointe-au-Chien communities).

Among the reports other findings for the region are:

• Agricultural areas in southern Louisiana with shallow groundwater tables are at risk of increased inundation and future loss of cropland; and 
• Forest disturbances caused by insects and pathogens will be altered by climate changes due to factors such as increased tree stress, shifting phenology, and altered insect and pathogen life cycles; however, adaptation strategies are limited, except through post-epidemic management responses

Great Plains

The report found that the Great Plains are facing increasingly extreme periods of wetness and dryness due to climate change and experiencing depleted groundwater resources due to unsustainable agricultural usage patterns. The report authors observe that rising temperatures in the Great Plains region have contributed to an increased demand for water and energy, and that this trend is expected to continue, constraining development, stressing natural resources, and increasing competition for dwindling water among the region's communities, agriculture, energy production and ecological needs.  "We have been depending for water on underground aquifers, but they are running out. So we are now increasingly dependent on rainfall precisely at the time that the climate is changing those rainfall patterns," notes Katherine Hayhoe, an atmospheric scientist and associate professor of political science at Texas Tech University.

Significant Great Plains climate-related challenges are expected to include "1) resolving increasing competition among land, water, and energy resources; 2) developing and maintaining sustainable agricultural systems; 3) conserving vibrant and diverse ecological systems; and 4) enhancing the resilience of the region’s people to the impacts of climate extremes."  Great Plains communities that are already vulnerable to weather and climate extremes will be stressed even further by more frequent extreme events occurring within an already highly variable climate system, according to the report.

Other climate change implications for the Great Plains region predicted by the report include:

• Landscape fragmentation is increasing, and such a highly-fragmented landscape will hinder adaptation of species when climate change alters habitat composition and timing of plant development cycles;
• Changes to crop growth cycles due to warming winters and alterations in the timing and magnitude of rainfall events will continue, creating the need for new agriculture and livestock management practices; and 
• Existing adaptation and planning efforts are inadequate to respond to projected climate change impacts, since the magnitude of expected changes will exceed those experienced in the last century.