water supply

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 affect 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 is working with the University of Florida's Water Institute to understand how changes in rainfall and temperature can affect water supply sources and drinking water demands. This work uses a computer model (MM5) to study climate based on physical features of our region. The research team includes the Southeast Climate Consortium who develops tools that guide decision making for water resource management. The research includes statistical analysis relating changes in rainfall across our region to the El Niño and La Niña conditions.

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.