115


trend for the past 15 yrs. Both wet season (June-Oct.) and

dry season (Nov.-May) moving averages (Figure 21) show the

decline, but the wet season drop is more precipitous. (The

increase near the end of the dry season plot reflects the

period of unseasonably intense rainfall in March, 1970).

 Total dry season rainfall averaged 18.74 inches (475

mm) and total wet season rainfall averaged 39.33 inches

(999 mm) for June-May periods from 1951 through 1975. Wet

season rainfall was less variable (coefficient of variation

= 0.309) than dry season rainfall (coefficient of variation

= 0.372).



Frequency Analysis

 Six important harmonics were found in the monthly

rainfall record of Ft. Myers. These corresponded to cycles

of 1 yr, 1.35 yr, 6 mo, 4 mo, and 3 mo, with relative

importance given in Table 5. A 6-mo cycle- is often

present in monthly rainfall data; and subharmonics, usually

those of 4, 3, and 2.4 mo, are also necessary to reproduce

most rainfall patterns (Roesner and Yevdjevich, 1966). The

obvious bimodality of the Ft. Myers pattern can be

reproduced by interacting 4 and 6 mo cycles.

 Except for the 1.35 -yr cycle, no important cycle

longer than one year was found in 36 yrs of monthly data.

A 9.6 -yr cycle was indicated by analysis of the 82-yr

record of annual rainfall at Ft. Myers.