finding 17.3 : decreased-water-availability-impacts

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.

This finding is from chapter 17 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: A central component of the process was the Southeast Regional Climate Assessment Workshop that was held on September 26-27, 2011, in Atlanta, with approximately 75 attendees. This workshop began the process leading to a foundational Technical Input Report (TIR). That 344-page foundational “Southeast Region Technical Report to the National Climate Assessment”4739fda9-9431-4cb3-8572-5f992fd61519 comprised 14 chapters from over 100 authors, including all levels of government, non-governmental organizations, and business. The writing team held a 2-day meeting in April 2012 in Ft. Lauderdale, engaged in multiple teleconference and webinar technical discussions, which included careful review of the foundational TIR,4739fda9-9431-4cb3-8572-5f992fd61519 nearly 60 additional technical inputs provided by the public, and other published literature and professional judgment. Discussions were followed by expert deliberation of draft key messages by the authors, and targeted consultation with additional experts by the Southeast chapter writing team and lead author of each key message.

Description of evidence base: The key message and supporting text summarize extensive evidence documented in the Southeast Technical Input Report (TIR).4739fda9-9431-4cb3-8572-5f992fd61519 Technical inputs (57) on a wide range of topics were also received and reviewed as part of the Federal Register Notice solicitation for public input. Chapter 2, Our Changing Climate, describes evidence for drought and precipitation in its key messages. Numerous salient studies support the key message of decreased water availability, as summarized for the Southeast in the TIR.4739fda9-9431-4cb3-8572-5f992fd61519 Evidence for the impacts on the region’s economy and unique ecosystems is also detailed in the TIR4739fda9-9431-4cb3-8572-5f992fd61519 and the broader literature surveyed by the authors.55e8faf4-e85e-4338-bbbd-b4f57d17b249

New information and remaining uncertainties: Many studies have been published since 2007 documenting increasing demands for water in the Southeast due to increases in populations and irrigated agriculture, in addition to water shortages due to extensive droughts.4739fda9-9431-4cb3-8572-5f992fd61519 b50d0bc7-8731-41e7-861c-b88b678f51d0 There is also new evidence of losses in fresh water wells near coastlines due to saltwater intrusiond0797088-3f92-4cfc-be8d-15027a28378e c95237bc-7d04-4c92-bb83-4a9d8ac3eaed and of continuing conflicts among states for water use, particularly during drought periods.4739fda9-9431-4cb3-8572-5f992fd61519 47f6b2ff-a48f-4b48-899d-a901424bf5b2 It is a virtual certainty that population growth in the Southeast will continue in the future and will be accompanied by a significant change in patterns of land use, which is projected to include a larger fraction of urbanized areas, reduced agricultural areas, and reduced forest cover.74461848-086f-4ea7-b3b3-e1693e3a21d8 With increasing population and human demand, competition for water among the agriculture, urban, and environment sectors is projected to continue to increase. However, the projected population increases for the lower (B1) versus higher (A2) emissions scenarios differ significantly (33% versus 151%).b50d0bc7-8731-41e7-861c-b88b678f51d0 Consequently, the effect of climate change on urban water demand for the lower emissions scenario is projected to be much lower than for that of the higher emissions scenario. Land-use change will also alter the regional hydrology significantly. Unless measures are adopted to increase water storage, availability of freshwater during dry periods will decrease, partly due to drainage and other human activities. Projected increase in temperature will increase evaporation, and in areas (the western part of the region619bdb75-3568-4791-85ae-fcbafbcb18fc) where precipitation is projected to decrease in response to climate change, the net amount of water supply for human and environmental uses may decrease significantly. Along the coastline of the Southeast, accelerated intrusion of saltwater due to sea level rise will impact both freshwater well fields and potentially freshwater intakes in rivers and streams connected to the ocean. Although sea level rise (SLR) corresponding to the higher emissions scenario is much higher (twice as much), even the SLR for the lower emissions scenario will increasingly impact water supply availability in low-lying areas of the region, as these areas are already being impacted by SLR and land subsidence. Projections of specific spatial and temporal changes in precipitation in the Southeast remain highly uncertain and it is important to know with a reasonable confidence the sign and the magnitude of this change in various parts of the large Southeast region. For the Southeast, there are no reliable projections of evapotranspiration, another major factor that determines water yield. This adds to uncertainty about water availability. There are inadequate regional studies at basin scales to determine the future competition for water supply among sectors (urban, agriculture, and environment). There is a need for more accurate information on future changes in drought magnitude and frequency.

Assessment of confidence based on evidence: There is high confidence in each aspect of the key message: it is virtually certain that the water demand for human consumption in the Southeast will increase as a result of population growth. The past evidence of impacts during droughts and the projected changes in drivers (land-use change, population growth, and climate change) suggest that there is a high confidence of the above assessment of future water availability. However, without additional studies, the resilience and the adaptive capacity of the socioeconomic and environmental systems are not known. Water supply is critical for sustainability of the region, particularly in view of increasing population and land-use changes. Climate models’ precipitation projections are uncertain. Nonetheless, the combined effects of possible decreases in precipitation, increasing evaporation losses due to warming, and increasing demands for water due to higher populations (under either lower [B1] or higher [A2] emissions scenarios) will have a significant impact on water availability for all sectors.

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