In the coming decades, droughts may be less frequent in Florida according to a new study by scientists that links slow, multi-decadal changes in North Atlantic Ocean temperatures to North American rainfall and river flows.

Scientists from the Commerce Department's Atlantic Oceanographic and Meteorological Laboratory and Florida's South Florida Water Management District have known for years that short-term climate patterns such as El Niño greatly affect yearly rainfall. But this study, slated for publication in the May issue of the journal Geophysical Research Letters, looks at North Atlantic sea surface temperature shifts between warm and cool phases that last two to four decades each.

According to the scientists, central and south Florida receive more rainfall during multi-year periods when the North Atlantic is warm. For example, a 10-year average inflow to Lake Okeechobee during warm phases is 40 percent greater than for cool phases. For most of the past 30 years the North Atlantic has been cool and Florida has had less rainfall. Current data suggest that a transition to warm conditions is under way. The result may be less frequent droughts in Florida, but more frequent flooding.

By adapting water management strategies to this North Atlantic climate pattern, water managers hope to better meet the competing objectives of flood control, water supply and environmental enhancement.

"Southern Florida's natural ecosystems benefit greatly from this newly found relationship," said Paul Trimble with the Hydrologic Systems Modeling Department at the SFWMD. "Climate variability affects the evolution and needs of the natural systems that depend on water availability. Understanding these climate factors will allow us to make operating decisions on flood protection and water supply sooner and less abruptly. This will help us manage south Florida's precious natural ecosystems in a less intrusive, more friendly manner."

"As North Atlantic temperatures rise, the increased rainfall may take the form of fewer droughts and/or more frequent flooding, although occasional droughts may still occur. Such extreme events can be likened to the effects of occasional large waves that alternately crash on a beach at different phases of the tide," said David Enfield of AOML. "Storm waves are less likely to produce damage during low tide than during high tide, but some damage will still occur."

The observed link between temperatures and wet and dry cycles is but a general indicator and does not take into consideration issues such as global warming or changing land use. As Enfield warns, "We can only make these projections based on a natural cycle observed in the past when land use and development pressures were much less. We may now be entering an era so affected by human changes that the natural cycle will be swamped."

This climate research is being done in cooperation with the South Florida Water Management District. Research scientists at AOML are learning about the role that climate variability plays in regional water management decisions and the potential benefits possible from improved seasonal to multi-seasonal climate forecasts. This new perspective of the application of climate forecasts will allow the results of research to be used more effectively on future water management strategies.

NOAA's mission is to describe and predict changes in the Earth's environment, and to protect, conserve and sustain the nation's coastal and marine resources.

For more information about the Atlantic Oceanographic and Meteorological Laboratory, visit: http://www.aoml.noaa.gov

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