The Mexican Type. 51. 



Chihuahua, and now later data shows the great probabiHty that 

 it dominates far the greater part of Mexico ; hence it is now called 

 the " Mexican " type. 



The characteristics of the Mexican type are VQvy heavy pre- 

 cipitation after the summer solstice and a very dry period after 

 the vernal equinox. August is the month of greatest rainfall 

 and, with July and September, furnishes over 75 per cent of the 

 year's precipitation at Mazatlan, about 87 per cent at Topolo- 

 bampo, 58 per cent at El Paso, Texas, fort Davis, Texas, and 

 fort Union, New Mexico. On the other hand, the months of 

 February, March and April are marked by an almost entire 

 absence of precipitation, aggregating for this period only 1 to 2 

 per cent of the year's rain on the western coast of Mexico, and 

 about 8 per cent at Chihuahua, Mexico, the city of Mexico, 

 El Paso, Texas, fort Davis, Texas, and fort Union, New Mexico 

 (34 years). 



This type dominates New Mexico, save the small drainage 

 basins of the Gila and San Juan, the trans-Pecos region of Texas, 

 and probably all of Mexico, except the eastern coast and possibly 

 the southern part of that country. The proof of its prevalence 

 in Mexico rests on about ten years' observations at the city of 

 Mexico, ten at Pueblo (where, however, the type is composite and 

 the maximum falls in July, conforming to the rainfall regime of 

 Vera Cruz as given by Loomis;, six years at Mazatlan, seven 

 at Leon de Aldemas, five at Chihuahua and four at Topolo- 

 bampo. 



While the Mexican type of rainfall does not absolutely obtain 

 in Arizona, yet, taken as a whole, its influence is more potent 

 than that of the Pacific type. The Arizona rainfall is of a com- 

 posite type, the result of interference between the Pacific and 

 Mexican. The primary maximum, closely following the Mexi- 

 can type, occurs from July to August, while most generally the 

 second maximum falls with the Pacific type in December. 

 Interference of the types, however, brings about the principal 

 minimum in October and the secondary minimum in May or 

 June. 



The following shows the departures from the daily normal 

 rainfall of .028 inch at fort McDowell, deduced from the longest 

 record (24 years) in Arizona : January, .006 inch ; Februar}^, 

 .015 ; March, — .004 ; April, — .010 ; May, — .024 ; June, — .024 ; 

 July,— .012; August, .019; September, .003 ; October, — .014 ; 



