ABNORMAL SUMMERS IN THE PERUVIAN COASTAL 



CURRENT 



By Erwin Schweigger 



Compania Adviinistradora del Gtuino 

 Lima, Peru 



The fact that the Peruvian Coast has a temperate and dry climate, 

 although geographically situated in tropical latitude, is known since 

 the Spanish conquest of Peru and northern Chile. The phenomenon 

 of rainless years, especially rainless summers is due to the effects of the 

 cool Peruvian Current which flows slowly along the greater part of the 

 Chilean and almost the whole length of the Peruvian coasts, in the 

 direction to the Equator. It was first explained by Alexander von 

 Humboldt, who believed that this current was derived from the cold 

 polar waters in the Antarctic. Modern investigation, however, proved 

 that the low surface temperatures along that part of the West coast of 

 South America are produced by "upwelling" of water from depths at 

 more or less 130 m. below the surface. (Schott, 1931; Gunther, 1936). 



In this zone, as in any other place, the most interesting phenomena 

 are brought forth by anomalies which in the Peruvian Current are also 

 observed from time to time. The basis of our knowledge regarding 

 these abnormalities is laid by the description of the occurrences in 1891 

 and 1925, made by Schott in 1931. They have their origin in changes 

 of the course of the Equatorial Countercurrent in combination with 

 the displacement of the zone of convergence of the trade-winds of the 

 northern and the southern hemisphere, and of the situation of the baro- 

 metric low-pressure-area. Although very little is known regarding the 

 mechanism which originates these changes, we are well informed of the 

 effects it has on the Peruvian Coast. Thunderstorms and heavy rain- 

 falls accompany the change of the hydrographic conditions as far as 

 about 9°S. Further south the coastal plain and the western slopes 

 of the Andes are soaked by rains producing great landslides and destruc- 

 tion of arable soil. Together with such meteorological and hydro- 

 graphic anomalies goes a deep change in the ecologic conditions in the 

 Peruvian Current which leads eventually to a complete destruction of 

 the habitual life in the current. 



The last of these great catastrophes occurred in 1925, and since 

 then the system of the current and life depending upon its normal con- 



801 



