Whether or not rainfall has a major 

 effect on marsh organisms depends in part 

 on tidal conditions and the degree 

 flooding. Rainfall during high tides may 

 have no effect, while a storm during 

 periods when tides rarely wet the middle 

 or upper marsh elevations may 

 substantially increase soil moisture, 

 decrease salinity, and improve plant 

 growing conditions. In contrast, lack of 

 rainfall at such times results in extreme 

 desiccation of marsh soils and soil algae, 

 as was documented for Tijuana Estuary in 

 April 1977 (Zedler 1980). 



Table 1 . Climate data for southern 

 California coastal weather stations (from 

 NOAA 1980). 



Station, 

 elevation (m) 

 and location 



Mean 



Daily 



Temp ( C) 



Mean 



Annual 



Ppt (cm) 



Chula Vista (2.7m) 

 32°36'N 117 06'W 



San Diego C^^O) 

 32°44'N 117 10'W 



Lone Beach (7.6) 

 33 ^g'N 118 09'W 



Los Angeles (29.6) 

 33°56'N, 118°24'W 



Santa Barbara (2.7) 

 34°26'N 119°50'W 



15.7 

 21.3 

 17. '4 

 20.7 

 14.9 



20.4 



24.0 



26.0 



29.4 



39.5 



Floods occur under a number of 

 conditions in southern California. Heavy 

 rainfall concentrated in a short period of 

 time is likely to cause flooding of 

 coastal wetlands. According to Climates 

 of the States (NOAA 1980, p. 66), 



"The maximum intensity of 

 precipitation for periods of 12 hours 

 or longer which might be expected at 

 intervals of 10 to 100 years is 

 greater in portions of the San 

 Gabriel and San Bernardino Mountains 



in Southern California than anywhere 

 else in the continental United 

 States." 



Twenty inches of rain in 24 hours is not 

 impossible! When one storm closely 

 follows another, watershed soils may 

 become supersaturated and result in 

 flooding sufficient to inundate coastal 

 marshes. Or, when water is released from 

 upstream reservoirs, the volume may be 

 sufficient to overflow the channels and 

 tidal creeks. 



Stream discharge data provide a 

 better measure of flooding in coastal 

 marshes than does annual rainfall along 

 the coast. For example, Tijuana Estuary 

 had severe flooding during 1980, even 

 though rainfall was not much greater than 

 in the previous two years. From 1978 to 

 1980, the coast had 1.5 to 2 times average 

 rainfall, yet winter discharges from the 

 Tijuana River ranged from average in 1979 

 to 28 times normal in 1980 (Table 2). At 

 least two factors interacted to make 1980 

 a year of severe flooding at Tijuana 

 Estuary — successive storm events in 

 January and February and release of water 

 from Rodriguez Dam upstream, as a flood 

 protective measure for the city of 

 Tijuana, Mexico. Reservoir releases can 

 change the stream discharges both by 

 altering peak flows (as at Tijuana River 

 in 1980) or by changing the period of 

 freshwater flow (as at San Diego River in 

 1980). 



Drought is also a common occurrence 

 in southern California, since evaporation 

 usually exceeds precipitation during the 

 summer and fall. Along the coast, the 

 tidal cycle is such that upper marsh 

 habitats are not inundated during the 

 periods of greatest drought stress (i.e. 

 late fall). The high spring tides, which 

 occur in January and June (Figure 4), are 

 primarily responsible for wetting the 

 highest marsh habitats. Their absence in 

 August and September leads to dry, cracked 

 soils in the upper marsh. Late fall is 

 also the time when hot, dry desert winds 

 displace the usual moist marine air mass. 

 The dry air, sometimes close to zero in 



