United Slates 



Mexico 



300 



225- 



150- 



Morena Dam 162/52 = 3 1 



| 225 



150 



o 75- 



Barrett Dam 163/45 = 3 6 



evaporation —  * 



rainfall » • * 



Annual evaporation and 



rainfall data and their 



V» ratio are given as, e.g., 



* 162 cm evaporation/52 



cm rainfall = 3.1 



JFMAMJJASOND 



300 -i 



225- 



150 



Lower Otay Dam 146/28 = 5 2 





I i I I "I I 

 JFMAMJJASOND 



Month 



J FMAMJJ ASOND 

 300 1 Valle Redondo 183/37 = 5.1 



150 





 300 



i-^— t— r^ — i — i i i 

 J FMAMJ J ASOND 



Rodriguez Dam 177/22 = 79 



225 



150 



75- 



•» 



T— I— 1—^ 1 I I 



J FMAMJ J ASOND 

 Month 



Figure 2.4. Monthly averages of evaporation and rainfall at six Tijuana River watershed locations 

 in the U.S. and Mexico (see map, Figure 1.1, and elevations, Table 2.1; data from IBWC 1983). 



and 1983. Rainfall patterns differed greatly 

 for each of those years. In some years, there 

 were summer storms (5 cm of rain fell at 

 Chula Vista in August 1977); in some years 

 there were winter droughts (almost no rain 

 fell from late December 1983 through 

 summer of 1984). Again, the factors most 

 important to the estuary are not necessarily 



annual rainfall totals. Rather, from recent 

 studies of estuarine dynamics, the amounts 

 and times of rainfall and streamflow within 

 the entire Tijuana River watershed appear to 

 be critical. The extremes of wet and dry 

 years are apparent in the frequency 

 histogram for rainfall years (Figure 2.5) and 

 in the high coefficient of variation (438%). 



13 



