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, with the highest annual rainfall totals from June through September.

While the total amount of rainfall recorded so far this year was average, an unusually dry 'dry season' has resulted in water levels falling quite quickly. 

This Year's Rainfall

• Corkscrew Swamp Sanctuary received 60.6 inches of rain from June 1, 2024, through April 30, 2025.
• We recorded above-average rainfall from 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, conditions have been very dry. We recorded 4.72 inches of rain from November 1, 2024, through April 30, 2025. This is only about one-third of our average total rainfall for these months (the average is 13.2 inches). 
• This year was the fourth-lowest November-through-April rainfall total since we began recording rainfall in 1959 (the lowest was in 2008-2009 at 2.71 inches).
• This is a stark contrast from last year, when we received more dry season rainfall than typical (last year’s November -through-April rainfall was 18.17 inches).

What Does This Mean For the Swamp?

One of the ways we measure water levels long-term at Corkscrew is by 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 the hydrologic disruption Audubon detected around 2005, this gauge reaches zero most years, with water staying below ground at the gauge for an average of 2.5 months.

The date this gauge reaches zero can help tell us how quickly the swamp is drying each year. Since 2000, that gauge has typically reached zero in mid-April. This year, the staff gauge reached zero in early April (right on time). In 2008, the 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). So, while this spring is very dry, we've had several recent years that were drier from a rainfall perspective.

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 water — not just for drinking, but also for watering lawns and filling pools.

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 season”). This has resulted in water levels in the swamp falling unusually fast, but not getting unusually low.

Our wildlife is adapted for a dynamic ecosystem, but water levels falling too quickly can stress a lot of species as they have to adapt quickly to the dry conditions. Impacts of repeated "unusually dry" years also cause stress for wildlife.  "Dry" dry seasons like this year’s can cause nest failure for species like Wood Storks, as nests can become vulnerable to terrestrial predators and food supply can be low. While long-lived species like Wood Storks can overcome infrequent bad years, 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 them 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.