The Effect of This Year’s Drought on Corkscrew Swamp

Background

Audubon has collected monthly rainfall data from Corkscrew Swamp Sanctuary since November 1959. Corkscrew’s average annual rainfall is 60.0 inches. The hydrologic year is measured from June 1 through May 30.

This year, while the total amount of rainfall recorded this year was average, a drier dry season resulted in water levels falling unusually fast. 

2024-25 Rainy Season through April

• Corkscrew Swamp Sanctuary received 60.6 inches of rain from June 1, 2024 to April 30, 2025.
• We recorded above average rainfall June through October (a total of 55.9 inches). This means that we got 93% of our annual rainfall in those five months. Typically, we get about 70% of our annual rainfall in those five months.
• Since November 1, however, conditions have been very dry. We recorded only 4.72 inches of rain from November 1, 2024 to April 30, 2025. Our average total rainfall for these months is 13.2 inches. We recorded about one-third of the amount of rain we usually get during these dry season months.
• Since 1959, this year was the fourth lowest November through April rainfall on record, with the lowest being in 2008-2009 (2.71 inches).
• This is a stark contrast from last year, when we received more dry season rainfall than typical (last year’s Nov-Apr rainfall was 18.17 inches).
• We’ve had eight years with more than 20 inches of rain Nov-Apr, with 30.88 inches recorded in 2009-2010. 

What does this mean for the swamp?

One of the ways we measure water levels long-term at Corkscrew is using a staff gauge that is located along the boardwalk at the Lettuce Lakes. Prior to the mid-2000s, water levels at this gauge only reached zero about once every five years. Since Audubon staff first observed hydrologic changes at Corkscrew around the year 2000, this gauge reaches zero most years.

The date this gauge reaches zero can help tell us how quickly the swamp is drying. On average since 2000, that gauge has reached zero in mid-April. This year the staff gauge reached zero in early-April (so right about on-time). In 2008 that gauge reached zero in February, and we’ve had seven years where it’s reached zero in March (2001, 2007, 2009, 2012, 2013, 2017, 2023).

Without adequate rain, water levels below ground continue to fall through the dry season, so the earlier we dry down often the lower ground water ultimately gets. Water levels always fall increasingly faster in the spring when the air temperature is warm and plants are growing. This is also the time of year that people are using more water, and with more people moving to Southwest Florida, there is a greater need for watering lawns, filling pools, etc.

What’s particularly interesting about this year is that we had typical annual rainfall through April, but the distribution of rainfall across the year was unusual. We had more rain in the rainy season (a “wetter wet season”) and little rain in the dry season (a “drier dry”). This has resulted in water levels in the swamp falling unusually fast, but not getting unusually low.

Our wildlife are adapted for a dynamic ecosystem, but water levels falling too fast can stress a lot of species as they have to adapt quickly to the dry conditions.

"Dry" dry seasons like this year’s can cause nest failure for species like Wood Storks. This is a long-lived species so nest failure every once in a while is ok, but the cumulative effect of stressors (less food available, loss of foraging habitat, impacts to nesting sites, etc.) and stress year-after-year (the same stressor or different stressors) is difficult for species like Wood Storks to overcome.

Overall, the biggest risk with these dry conditions is wildfire which is why habitat management (prescribed fire) and wetland/water conservation are so important.