Climate Variability Impacts on Water Supply

Climate Variability


Impacts on Water Supply


Understanding the impacts of climate variability is essential for Florida's public water supply utilities, which are among the United States' most vulnerable to sea-level change, storm surges and salt water intrusion into aquifers.

As the largest wholesale water utility in the southeastern United States, Tampa Bay Water continually grapples with seasonal water availability issues and periodic droughts, which will likely be exacerbated by climate change and variability conditions.

Nearly 40 percent of Tampa Bay Water’s water supply comes from local rivers and Tampa Bay. Using surface water sources adds uncertainty to Tampa Bay Water’s operations. This makes the Tampa Bay region more susceptible to the effects of climate variability. Because of these changes, Tampa Bay Water is involved in several research studies to find answers to the following questions:

  • How will the earth’s changing climate affect our local rainfall? 
  • Will rainfall be less predictable in the future? 
  • Will river flows be less predictable? 
  • How good will our estimates be and what can we rely on for future water supplies?

Florida Water and Climate Alliance

Tampa Bay Water is working with the Florida Water and Climate Alliance, whose members include the University of Florida Water Institute, Florida State University, three water management districts and six major public water supply utilities, to better understand how varying weather affects the reliability of our water supplies. Our engineers and scientists will use this information to better manage our water supply system under whatever conditions Mother Nature may provide in the future.

Water Utility Climate Alliance

Tampa Bay Water is also collaborating with other large water providers through the Water Utility Climate Alliance, 12 of the nation's largest water providers that collectively supply drinking water for more than 50 million people throughout the United States. Together, these utilities are collecting data, examining modeling tools and holding forums to exchange information with the goal to better understand the impact of changing weather patterns on the world's drinking water resources.

Climate Science Advisory Panel

Tampa Bay Water is also a member of the local Climate Science Advisory Panel. Members include local scientists, policy makers and stakeholders collaborating on understanding the impact of sea level rise and climate change/variability on the region’s infrastructure. In 2016, the group released a guiding document on sea level rise for regional planning councils and stakeholders and currently working on updating those guidelines. The group is also an adviser for Tampa Bay Regional Resiliency Coalition.

Application of Climate Variability Data

El Niño and La Niña

One condition that affects Florida climate occurs far from home, known as the El Niño-Southern Oscillation (ENSO). Across the world, this condition has the strongest effect on year-to-year climate variation.

The El Niño condition occurs when the temperature is above normal in the eastern Pacific Ocean near the equator. When the temperature is lower than normal, the La Niña condition occurs. When the temperature is normal, the condition is called Neutral. During fall and winter, El Niño normally brings 30-40 percent more rainfall. La Niña brings less rainfall during fall and winter. El Niño brings cooler temperatures during fall and winter; La Niña is warmer. Florida also gets few Atlantic hurricane landfalls during El Niño years. During the last century, 11 out of 12 major freezes in central Florida occurred during Neutral phases.

The El Niño or La Niña condition seems to return in the range of two to seven years. The tropical Pacific is Neutral at least half of the time. El Niño or La Niña each occur about a quarter of the time. Each El Niño, La Niña, or Neutral year begins in October and ends in the following September. Knowing the sea surface temperature in the tropical Pacific Ocean can help predict the climate conditions for the coming year.

Tampa Bay Water uses these climate outlooks to guide its river flow forecast and seasonal demand projections as part of its seasonal source allocation decision support tools. Since 2009, Tampa Bay Water has been collaborating with the University of Florida's Water Institute and Center for Ocean-Atmosphere Prediction Studies (COAPS) of Florida State University to understand how changes in rainfall and temperature can affect water supply sources and drinking water demands.

Atlantic Multidecadal Oscillation

The AMO is an ongoing series of long-duration changes in the sea surface temperature of the North Atlantic Ocean, with cool and warm phases that may last for 20-40 years at a time. These changes are natural and have been occurring for at least the last 1,000 years. Right now, since the mid-1990s, we are in a warm phase.

Historical information shows that the AMO affects temperatures and rainfall in both North America and Europe. These affects include occurrence of droughts and hurricanes.

During warm phases of AMO, Florida seems to have more rainfall especially in the central and southern parts of the state. Also, the number of tropical storms that form into major hurricanes is increased. During the cool phase, droughts and wildfires are more frequent.

Our research work with the University of Florida’s Water Institute and the Southeast Climate Consortium includes statistical analysis and computer modeling of AMO cycles and rainfall effects. Our effort concentrates on West Central Florida and the Tampa Bay area, related to predictions of river flows over multiple years.

Once this research is complete, Tampa Bay Water hopes to better understand factors that affect water source availability (especially rainfall and river flows). Results can help determine the reliability of our water supply. We can then use management strategies that adapt to changing conditions as they occur. The outcome will be a more reliable and more sustainable drinking water supply in the future. This knowledge will benefit the region as Tampa Bay Water looks toward new supplies, and cost-effective approaches, in the coming decades.