Evaluating the Benefits of the New ‘State of the Art’ Multi-Year El Nino-Southern Oscillation (ENSO) Forecasts for Improving the Operational Proficiency for Lake Okeechobee and the Regional Hydrologic System of south-central Florida

Abstract:

El Nino-Southern Oscillation (ENSO) is a major driver of interannual global climate variability. Significant efforts have been dedicated to predicting the evolution of ENSO because of its extensive global impacts. South-central Florida’s climate is most influenced by ENSO events the during dry season months of November through May. Strong El Nino events have the potential to produce unusually large rainfall and inflow into Lake Okeechobee during the winter months leading to a reversal of the natural dry season recession. While such large dry season inflows may be considered natural occurrences, the anthropogenic modifications to the regional hydrologic system amplify the impacts to the natural system. The South Florida Water Management District (SFWMD) and the United States Army Corp of Engineers (USACE) adopted a “dynamic” flood control regulation schedule for Lake Okeechobee in July 2000 to attempt to lessen these impacts. This schedule considered both seasonal water levels and climate-based seasonal hydrologic inflow outlooks (Trimble et al, 2005). While these climate-based rules were considered successful, the degree of success was limited by the Spring ENSO Prediction Barrier (SEPB) in the ENSO operational forecast models.

Petrova et al (2020) reported on a new generation of ENSO model that skillfully predicts ENSO events through SEPB and up to 2.5 years in advance. ENSO (Niño-3.4) hindcasts were made for the period 1970-2016. This research illustrated that the hindcasts were of much greater skill after the completion of the Tropical Ocean-Global Atmosphere (TOGA) observing system in 1994. A preliminary assessment of the value of these multi-year ENSO forecasts for water management in south-central Florida is made. This is accomplished by considering historical meteorological and hydrologic conditions from 1995 to 2016 and the 24-month ENSO hindcast provided by Petrova et al in their report. These forecasts allow for additional low-flow Lake releases during drier periods prior to an El Nino event that would be of great benefit to the natural systems of the Lake littoral zone, the Caloosahatchee and St. Lucie estuaries and the Everglades and lessen the need for large harmful discharges through the estuaries and prolonged stressful high-water levels for the Lake littoral zone during the El Nino event.