Drought and Coastal Ecosystems State of Knowledge Report

1. Tools and Research to Improve the Characterization of Drought and Understanding of Impacts on Water and Ecological Resources Ashley Brosius, Climate Outreach Specialist Carolinas Integrated Sciences & Assessments, University of South Carolina Assessing the Impact of Salt-Water Intrusion in the Carolinas Under Future Climatic and Sea-Level Conditions Drought and Coastal Ecosystems State of Knowledge Report Introduction Carolinas Integrated Sciences and Assessments (CISA) is part of the NOAA Regional Integrated Sciences and Assessments (RISA) program. CISA conducts research in collaboration with water and coastal stakeholders across the Carolinas to produce usable, useful, and accessible climate information for decision making. The potential users of this information cover a broad range of interests including municipal water supply planners, natural area/refuge managers, regulatory staff involved in mitigation or restoration activities, and coastal emergency planning staff. Focus areas include drought, watershed and climate modeling, coastal climate, health, and adaptation. CISA’s drought work seeks to improve monitoring methods, to develop a more comprehensive understanding of regional impacts, and to assess drought planning and early warning needs. CISA has initiated several projects to advance regional and local capacity to cope with drought and to improve understanding of drought impacts on social and environmental systems. This poster highlights three projects. First, the Dynamic Drought Index Tool (DDIT) provides a web based drought mapping tool that displays multiple drought indices for different time scales and across user-specified regions. Second, with other scientists and water suppliers in the Carolinas, CISA developed a decision support tool that allows resource managers to assess the effects of salinity intrusion on surface water resources in coastal areas. Third, we are investigating drought impacts on coastal environments, an area currently under-represented in regional drought assessments. CISA produced a state of knowledge report that synthesizes and analyzes the peer reviewed literature regarding drought impacts on coastal ecosystems in the Carolinas. Findings from this report will help inform CISA’s collaboration with the National Integrated Drought Information System (NIDIS) to develop a drought early warning system pilot project in the Carolinas. Background The ability of water-resource managers to adapt to future climatic change is especially challenging in coastal regions of the world. There are many municipal water intakes along the South Atlantic coast that are proximal to the saltwater-freshwater interface of tidal rivers. An increase in the extent of saltwater intrusion along the coast due to climate changes could threaten freshwater intakes for several major cities along the coast. Water-resource managers need estimates of the change in the frequency, duration, and magnitude of salinity intrusion near their water intakes that may occur as a result of climate change. Background This “State of Knowledge” Report provides a synthesis and analysis of the peer-reviewed literature for the state of knowledge of drought impacts on coastal ecosystems in the Carolinas. Its objective is to expand current, limited understanding of drought impacts on coastal ecosystems, to identify critical gaps, to inform future research efforts, and to suggest measures to facilitate drought adaptation for ecosystems. The report focuses on coastal ecosystems of North and South Carolina and concentrates on the portion bordered inland by the extent of tidal freshwater. Because there is significant ecological continuity between extreme southeastern Virginia and northeastern North Carolina and between coastal Georgia and the south coast of South Carolina, work done in those parts of Virginia and Georgia was included in the report. Methods Salinity intrusion results from the interaction of three different forces: streamflow, mean tidal water levels, and tidal range. To analyze, model, and simulate hydrodynamic behaviors at critical coastal gage locations along the Atlantic Intracoastal Waterway and Waccamaw River near Myrtle Beach, SC, data-mining techniques were applied to over twenty years of hourly streamflow, coastal water-quality, and water-level data. Artificial neural network (ANN) models were trained to learn the specific variable interactions that cause salinity intrusions. Streamflows into the estuarine systems are input to the models as time-delayed variables and accumulated tributary inflows. Tidal inputs to the models were obtained by decomposing tidal water-level data into a “periodic” signal of tidal range and a “chaotic” signal of mean water levels. The ANN models were able to convincingly reproduce historical salinity dynamic behaviors in both systems. User-defined hydrologic and coastal water-level inputs from down-scaling of regional climate models can be simulated in the salinity intrusion models to evaluate various climate-change scenarios. • Review of Findings The research reviewed for this report indicates that drought is discussed primarily in terms of the hydrology-related impacts that affect coastal ecosystems, such as changes to river discharge, freshwater inflows, water level, and water table depth. The severity of these effects depends upon the longevity and recurrence interval of drought event(s) and may be compounded by other anthropogenic stressors on the system. In addition, some drought-related research considers how sea level interacts with freshwater precipitation and runoff to influence the salinity levels experiences by these systems. The review indicated that some ecoregions and locations have been better studied and researched than others. Examples include: • Droughts represent an important stressor of estuarine ecosystem functioning through their potential to reduce freshwater delivery to estuaries. Effects may include changes in nutrient loading, phytoplankton dynamics and primary productivity, resultant changes in secondary production, food web dynamics, water quality, and fish habitat. • Although the literature is not conclusive about drought as the single cause of salt marsh dieback in all localities, it has been strongly implicated in concert with other stressors. There is a clear relationship between decreased marsh productivity and high pore water salinity to which drought can contribute. • Numerous authors reported on studies showing the adverse effects of salinity intrusion into tidal freshwater forests. There appears to be a consensus that any extended periods of chronic or elevated exposure to saltwater intrusion without freshwater recharge will ultimately lead to tree death and forest dieback. • Hydrology in non-alluvial wetland systems is largely driven by rainwater making them particularly vulnerable to extended droughts. Impacts include vegetation community shifts and invasion by upland species. Results Artificial Neural Network models were trained to learn the variable interactions that cause these salinity events. Model results from Pawleys Island stream gage (USGS station 02110125), near a municipal freshwater intake, indicate that 1 foot (30 cm) of SLR would double the number of days the municipal intake is unavailable to 400 days and a 2-ft rise increases the unavailability to nearly 2 years (700 days). (Conrads et al. 2010). Changes in precipitation patterns due to changes in the climate have the potential of decreasing streamflow to the coast. Salinity intrusion in coastal rivers during low streamflow periods and a decrease in streamflow combined with a sea-level rise could increase the duration of salinity intrusion along the coast. A 1-ft sea-level rise combined with a 25-percent decrease in historical streamflow would increase the days the intake is unavailable to over 700 days. Water-resource managers can use this information to plan mitigation efforts to adapt to potential effects from climate change. The project team developed a new, web-based Decision Support System (DSS) PRISM2 (Pee Dee River and Atlantic Intracoastal Waterway Salinity Intrusion Model) for stakeholder and government agency use in evaluating potential changes in the hydrologic system of the Pee Dee River under different climatic regimes. In December 2011 the CISA team conducted a workshop in Georgetown, SC, with resource managers, water/utility managers, and applied researchers to provide information about the PRISM2 DSS and to gather feedback about the potential impacts of sea level rise and salinity intrusion on existing ecological and infrastructure systems and about the model’s applicability for decision making. Insights from the workshop will be used to enhance the DSS. Reference Conrads, P. et al. 2010. Estimating Salinity Intrusion Effects Due to Climate Change Along the Grand Strand of the South Carolina Coast. In: Proceedings Paper for the 4th Federal Interagency Hydrologic Modeling Conference. June 27- July 1, Las Vegas, Nevada.. Literature Gaps and Research Needs The most critical needs include examining drought impacts in ecosystems not studied by existing research, implementing long term studies to identify and examine causal relationships, and developing a set of indicators with which to monitor ecological change and impacts. More research and information is needed regarding drought impacts on groundwater resources, the significance of drought during different seasons, the longevity of droughts in relation to long-term impacts and/or length of recovery, and responses to potential future changes in salinity regimes. AZ NM Next Steps CISA is partnering with the National Integrated Drought Information System (NIDIS, www.drought.gov) to develop a Carolinas pilot project in 2012, with a focus on coastal ecosystems. Possible projects might include assessment of the most appropriate and relevant drought indices for coastal ecosystems, collaboration with resource managers to develop relevant drought information for decision making, building – or improving existing – regional communication networks to disseminate drought data and information, or research to fill science gaps. CISA TEAM Co-Pis: Greg Carbone, Kirstin Dow, Chip Konrad (Southeast Regional Climate Center), Daniel Tufford, Jessica Whitehead (SC Sea Grant Extension and NC Sea Grant) Research Associates: Kirsten Lackstrom, Jinyoung Rhee Climate Outreach Specialist: Ashley Brosius Research Assistants: Amanda Brennan, Ben Haywood, Peng Gao, Nate Kettle, Aashka Patel Collaborators: Ryan Boyles (NC State Climatologist), Paul Conrads (USGS), Art DeGaetano (NERCC), Hope Mizzell (SC State Climatologist) , Edwin Roehl and Ruby Daamen (Advanced Data Mining International) For more information about CISA’s projects, contact cisa@sc.edu