Summary Statistics of Rainfall Data for Sites in West-Central Florida

In the Southwest Florida Water Management District, located in west-central Florida, relatively small changes in rainfall can result in relatively large changes in recharge, since recharge represents what remains of rainfall after evapotranspiration (which varies little year-to-year) and runoff. Many long-term rainfall and flow patterns observed in the District from 1940 to the present can be explained, in large part, by climatic cycles such as the AMO and ENSO, plus the frequency of tropical cyclone landfalls in the District. Comparing the current AMO warm phase to the last AMO warm phase, fewer tropical cyclone landfalls in the District, more La Nina months, and fewer El Nino months have led to decreased annual rainfall at most long-term stations. Thus, high flows that characterized the 1960s were unusually high as a function of higher rainfall caused by more El Nino months, fewer La Nina months, and more tropical cyclone strikes (on top of the warm AMO phase). Comparing the current warm phase to the last cool phase, wet season rainfall has generally increased, aligning with predictions of how the AMO impacts peninsular Florida rainfall. As a result of this increased wet season rainfall, most southern District stations have now exceeded their cool phase annual totals. At the same time, an increase in La Nina months and a simultaneous decrease in El Nino months have led to lower dry season rainfall at most stations. In the northern District, these ENSO-driven dry season decreases have completely cancelled out AMO-related wet season increases such that the current warm phase has experienced lower annual rainfall than the preceding cool phase. This reduced dry season rainfall in the northern District largely explains more recent low aquifer water levels, river, and spring flows that haven't recovered to those of the preceding warm AMO period prior to 1970.