Case Studies

At the culmination of this project, a case study report will be published for each study region, consisting of:

  • A review of historical management practices within each basin, along with an overview of present needs and future management challenges.
  • A review of the meteorology and hydrology of the study region, including features and processes with the greatest impact on these regions.
  • A description of stakeholder and water manager needs and outcome-oriented metrics.
  • An assessment of relevant regional climate datasets, and the skill of these datasets at representing relevant features, processes and outcomes.
  • The development of new high-quality regional climate data that is specifically targeted to support stakeholder needs, including future projections of stakeholder-relevant outcomes over the next 40 years.
  • An assessment of uncertainties in each outcome that arise due to uncertainties, biases and variability in the regional climate models.
  • A case study narrative, written in broadly accessible language that summarizes the above.

The four case study regions that have been selected include the Colorado headwaters, Kissimmee River in South Florida, the Sacramento-San Joaquin River System in California's Central Valley and the Susquehanna River in the Northeast. Future case studies will build on the success of our work in these regions and provide more comprehensive coverage of the continental US, including the Missouri River in the Northern Great Plains and the Columbia River in the Northwest.

Colorado River Headwaters: In the Colorado River Basin, water supply is largely controlled by climatic factors. Nonetheless, the accuracy of climate predictions in this region has been poor, which has prevented effective resource management and strategic planning activities. The most recent projections of the Colorado River water supply provided by the Bureau of Reclamation are clouded by large uncertainties in the climate model ensembles, which fail to capture the marked decadal variability experienced in the past. Climate variability in this region is strongly attuned with several interconnected climatological features. Decadal climate oscillations in Colorado River water supply and across much of the Great Basin are associated with fluctuations of the Great Salt Lake (GSL) level. Colorado streamflow is also strongly modulated by winter snowpack, which has been recently impacted by increasing spring temperatures. During the wet phases of the climate cycle, rapid snowmelt and subsequent flooding is possible; in April 2011 line convection caused widespread wind damage and urban flooding around the GSL. This type of fast-moving MCS was found to increase in frequency during spring. (Lead: Sara Rauscher)

Photo: Horseshoe Bend on the Colorado River by Luca Galuzzi [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

Kissimmee River and South Florida: The rivers of southern Florida, such as the Kissimmee, the Caloosahatchee, and the tributaries of Tampa Bay provide the water supply for a large share of Florida's population and maintain important ecological services. Tampa Bay Water derives nearly 60% of its water supplies from local rivers and Tampa Bay, making the region more susceptible to the effects of climate variability. The Kissimmee river is a key headwater basin to the Florida Everglades, which are part of the largest ecological restoration project in the country's history. Many of these rivers are also connected to the Biscayne Aquifer of South Florida's lower east coast, which serves as the primary fresh water source. So while South Florida has relatively abundant rainfall, meteorological variability and threat from rising sea levels, saline aquifers, and changing environmental and management objectives -- for instance, the Everglades and Lake Okeechobee operations -- makes this a critical region to understand climate variability and change. This region is also a focus for assessing tropical cyclones (TCs), which account for half of the extreme precipitation events that occur in this region, and sea breeze, which is key for local rainwater generation and energy budgets. (Lead: David Yates)

Sacramento-San Joaquin Watershed: The Sacramento and San Joaquin rivers are the two principal river systems of California's Central Valley, a major agricultural region that produces more than 50% of the nation's fruit, vegetable, and nut crops. The two rivers are connected through the Sacramento-San Joaquin Delta, a region of great ecological significance complicated by a network of aqueducts, pumping stations, and reservoirs. More than 25 million people (~60% of the state population) rely on the State Water Project for drinking water, and this number is expected to double in the coming decades. Periodic and lengthened drought conditions have worsened the groundwater depletion. The lowlands of the Central Valley are also prone to flooding, including much of the city of Sacramento.

Water storage is critical in California given its dry summers. High-amplitude interannual precipitation can often be traced to only a few extreme events, with atmospheric rivers accounting for 30-40% of seasonal snowpack accumulation. Currently the Sierra Nevada snowpack accounts for approximately half of the water storage in the state, while man-made reservoirs account for the other half. Warmer temperatures will decrease the accumulation of snowpack, shift the seasonality of streamflow, and enhance evapotranspiration from vegetated landscapes, thereby increasing irrigation demands.

Regional climate simulations over California have exposed the need for high spatial and temporal resolution to better address regional climate and extreme events, where complex topography drives large climatological gradients. There is also significant disagreement among global climate models regarding changes in the magnitude and distribution of precipitation. This uncertainty stems largely from the degree to which simulated storm tracks will shift under climate change. (Lead: Andrew Jones)

Photo: Sacramento-San Joaquin by worldislandinfo.com. [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

Susquehanna River: The Susquehanna River Basin (SRB) (New York, Pennsylvania and Maryland) is one of the nation's most flood-prone watersheds, experiencing on average tens of millions of dollars of damage each year, and a major flooding on mainstem rivers on average once every 14 years. In September 2011 the remnants of Tropical Storm Lee ruined bridges and roads, killed 10 people, displaced 100,000 others and caused an estimated 1.6 billion in damages. Nonetheless, the 2011 flood is only the 5th most damaging flood in the SRB (the Johnstown flood in 1889 killed 2,209 people). The disheartening damages are a result of not only extreme rainfalls, but also antecedent moisture conditions, shallow bedrock geology, limited channel hydraulic conveyance capacity, and human activities in the floodplain.

The SRB is also a major contributor of sediment and nitrogen pollution to the Chesapeake Bay. Sediment and pollution inputs to the Bay are heightened during extreme events, echoing concerns in other regions. The Conowingo dam near the mouth of the river is a major hydroelectric plant, drinking water source, cooling water source for the Peach Bottom nuclear power plant, and a major regulator of sediment to the Bay. During droughts that occur approximately once every five years, there is competition for water between energy production, ecological flows for the Bay and cooling water needs. Therefore, predicting both high and low flows are important for the energy-water-land nexus. (Lead: Chaopeng Shen)

Photo: Susquehanna River by Nicholas A. Tonelli from Pennsylvania, USA (Hyner View State Park) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons