Alafia River Minimum Flows and Levels - Southwest Florida Water ...

1) Upper Alafia River Hydrology
Sect. 2.3 of the draft report proposes that causal relationships exist between multi-
trends in the gaged flow of the Alafia River (measured at the Lithia gage) and
decadal
rainfall patterns that vary in response to changes in sea surface temperature (SST)
associated with the Atlantic Multidecadal Oscillation (AMO).
The proposed multi-decadal relationship between the AMO, rainfall, and river flow are
not analyzed in detail in the report itself. Instead, the reader is referred to a group of
other documents (e.g., Enfield et al. 2001, Basso and Schultz 2003, Kelly 2004) for a
more detailed explanation. Basso and Schultz (2003) explain the proposed relationship
as follows:
“A new study by scientists from the National Oceanic and Atmospheric
Administration (NOAA) the University of Miami, and the South Florida Water
Management District found statistically significant differences in rainfall between
the pre-1970 period versus the last 30 years... Their research attributed this shift
in the rainfall regime to the Atlantic Multidecadal Oscillation (AMO), a naturally
occurring variation in North Atlantic Ocean temperatures that occurs every 20 to
50 years.
Enfield and others (2001) indicate that warmer than average sea surface
temperature periods of the AMO lead to increased wet season rainfall while
cooler than average ocean temperatures decrease summer rainfall on the Florida
peninsula. During warmer ocean temperature periods, global atmospheric
circulation patterns shift to a more predominant southeasterly flow across the
Florida peninsula, which leads to increased afternoon convective-activity and
higher wet season rainfall. During cooler ocean temperature intervals, the upper
atmospheric pattern is interrupted more frequently by mid-latitude disturbances,
which generally results in less wet
season rainfall.”
A quick examination of the Enfield et al. (2001), Basso and Schultz (2003), Kelly
(2004), and draft Alafia River MFL documents leads to the following questions:
Question 1A. If other researchers wish to analyze multi-decadal variations in
rainfall and river flow patterns in west-central Florida, which time
periods should they designate as “warmer Atlantic SST/higher
rainfall” and which should they designate as “cooler Atlantic
SST/lower rainfall”?
The Enfield et al. (2001) report states that warmer SST conditions existed from 1860
through 1880, 1940 – 1960, and began once again in 1995. They indicate that cooler
SSTs were present from 1905 – 1925 and from 1970 – 1990.
Basso and Schultz (2003) define the warmer SST periods as1869 – 1893, 1926 through
1969, and post 1995. They indicate that cooler SST conditions were present during
1894 – 1925 and 1970 – 1994.
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