Development and Assessment of Sub-seasonal Cyanobacteria Abundance Forecasts in Lake Mendota, WI.

In recent decades, cultural eutrophication of coastal waters and inland lakes around the world has contributed to a rapid expansion of potentially toxic cyanobacteria. Currently, little information regarding xpected summertime cyanobacteria abundance is available prior to the season. With sufficient lead time, communicating the likelihood of elevated cyanobacteria abundance may be informative for proactively managing potential threats to lake and beach safety. Seasonal forecasts have been produced for summertime cyanobacteria abundance on Lake Mendota (Madison, WI) since 2015. The highest summertime abundances, however, have historically occurred in July and August. Therefore, selecting Lake Mendota as a case study, a sub-seasonal cyanobacteria abundance model conditioned on season-ahead (spring) and within-season (June) local and global scale predictors is constructed. A Nino Index Phase Analysis is performed to identify relevant predictors given the state of the local climate. The prediction model demonstrates good skill overall and outperforms a season-ahead forecast when cyanobacteria abundance conditions are above-normal. This warrants further investigation into the development of paired seasonal and sub-seasonal cyanobacteria forecast systems, and application to other eutrophic lakes.