CLIMATE OF THE SANTA CATALINA MOUNTAINS. 



49 



the summer months is almost negligible on the Pacific Coast and grad- 

 ually increases on passing eastward until it reaches 50 per cent at Tucson. 

 Between Tucson and the Rio Grande it remains at about 50 per cent, but 

 from the basin of the Rio Grande eastward the rainfall seasons of the 

 Tucson region cease to be a natural division of the year (see table 1). 



Table 1. — Percentages of summer rainfall and of winter rainfall to the annual rainfall for 

 a series of stations stretching from the Pacific coast to the Rio Grande River, through 

 southern Arizona. 



In figure 3 are given curves showing the percentages of the annual 

 rainfall which are formed by summer rains and by winter rains for a 

 chain of 13 stations stretching from Los Angeles to Mesilla Park, New 

 Mexico, on the Rio Grande River. 



Table 2. — The total annual rainfall, the summer rainfall, and the percentage of the latter to 

 the former for very wet and very dry years at Tucson. 



The fall of approximately half the annual precipitation in the humid 

 mid-summer is by no means a constant occurrence at Tucson. In 

 1881 the summer rainfall was 80.3 per cent of the annual, and in 1884 



