These data were obtained from a weather station located In 

 the heart of well-established agricultural areas. Average 

 maximum temperatures are higher and minimum temperatures are 

 lower in these areas than on the large alluvial fans adjacent 

 to the foothills where irrigation is limited. According to 

 studies (9) conducted by the Department of Water Resources, 

 topography appears to influence air temperature extremes 

 more strongly than does agricultural environment . 



Evapotranspiration and 

 evaporation reach their ' 

 upper limits during July 

 and August. Irrigation 

 in the Valley increases 

 rather consistently with i 

 rising temperature. ! 

 Figure 7 shows monthly | 

 average ten^jeratures at | 

 Los Banos for 1968. 



Precipitation 



JAN F"EB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN 



1983 



FIGURE 7- MONTHLY AVERAGE TEMPERATURE AT LOS BANGS 



Less than a quarter inch 

 of precipitation falls 

 along the west side 



between the months of June and September; consequently, 

 relative humidity remains low during these months. High 

 temperatures and prevailing northwest winds combine to 

 produce very high rates of evaporation and evapotranspira- 

 tion, which means most crops need intensive irrigation. 



Precipitation is somewhat irregular from Tracy-Carbona in 

 the north to Corcoran in the south. T^e amount of precipi- 

 tation decreases to the north and to the south from Gustine. 

 Influence from coastal storms can be seen in the data 

 presented in Table 4. According to the data, for the period 

 of study, precipitation as far north as Tracy has not 

 greatly exceeded that recorded at Corcoran. 



Although the data show higher precipitation toward the 

 trough of the Valley, rainfall seldom exceeds 6 inches over 

 much of the area adjacent to the foothills of the Diablo 

 Range . 



Agriculture and Agricultural Practices 



The types of agriculture practiced in an area may influence 

 the quantity and quality of tile drainage. For instance, 

 tiled areas that sire devoted mainly to dairy farming receive 



27 



