Table 2.2. Mean temperature (°C) and 

 electrical conductivity (mmho/cm) at 

 Winfield's (1980) tidal creek sampling 

 stations in Tijuana Estuary. Conductivity is a 

 measure of salinity; sea water is approx. 50 

 mmhos/cm). Data from two stations are 

 averaged. 



.ill 



£20 



in- 



 i I I I I I I I I I . m , 



5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 

 Annual Rainfall (cm) 



Figure 2.5. Histogram of annual rainfall for 

 San Diego (Lindbergh Field) 1880-1984. 

 Mean annual rainfall for this period = 25.87 

 cm (n = 105). 



Rainfall data for San Diego's Lindbergh 

 Field were recently re-examined to evaluate 

 the concept of "normal rainfall.". The issue 

 arose when the Environmental Protection 

 Agency proposed new criteria for wetland 

 delineation, which required that measure- 

 ments of hydrology be conducted during "years 

 of normal rainfall and normal monthly 

 distribution." The data base included 140.5 

 years, from 1850 through mid 1990. 

 Analyzing the calendar years (January 

 through December), and considering "normal" 

 as ±10% of the mean, both for annual and 

 monthly data, the high variability of the 

 region's rainfall became even clearer. 



Few years had 90-110% of the annual 

 rainfall in this long-term record; only 21 

 years, or 15% of the historic record, 

 qualified as being within 10% of the mean. To 

 assess monthly distributions, the data were 

 examined for successive months, beginning in 

 January. Only 11 years (8% of the record) 

 had January rainfall that fell within 10% of 

 the 141 -year average. Of these 11 years, 

 only 5 had February rainfall that was within 

 10% of the mean. Of these 5 years, none had 

 March rainfall that was within 10% of the 

 141 -year average. Thus, not one of the 141 

 years qualified as having "normal monthly 

 distribution." 



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