QUINN and NEAL: LONG-TERM VARIATIONS IN SOUTHERN OSCILLATION 



times, register these Southern Oscillation-related 

 changes, but to a lesser degree. 



Additional Considerations 



Although a decrease in frequency of occurrence of 

 moderate/strong El Ninos might be expected to have 

 some affect on average annual rainfall, the rainfall 

 records for recent decades show a sizeable decrease 

 in amounts for El Nino, anti-El Nino, and inter- 

 mediate years as well for subtropical Chile. Rainfall 

 data (table 5 in Quinn et al. 1981 and Table 1 here) 

 show that a significant decrease in average annual 

 rainfall at Santiago and Valparaiso occurs after 1944. 

 Table 6 shows large negative departures from the 

 long-term averages at La Serena, Santiago, and 

 Valparaiso for 1945-80. This climatic change, which 

 is also primarily noted over subtropical Chile, in- 

 dicates another source for change. It appears that the 

 desert conditions that have prevailed over northern 

 Chile have been spreading further southward into 

 subtropical Chile for several decades. Discussions 

 with Chilean scientists confirm that this is occur- 

 ring. 



This decrease in rainfall over the arid region be- 

 tween the west coast and the westernmost ranges of 

 the high Andes also appears to be affecting western 

 Peru. Santiago E. Antunez 2 stated that his 70-yr 

 regression analysis of river runoff in western Peru 

 showed that a very serious decrease in runoff was oc- 

 curring. The extremely arid zone between the west 

 coast of South America and the westernmost ranges 

 of the high Andes and extending from about lat. 30° S 

 almost to the Equator (as described in Lettau and 

 Lettau 1978) appears to be becoming increasingly 

 arid and slowly extending southward. 



Obviously the heavy rainfall that occasionally oc- 

 curs over the usually arid coastal lowlands of Peru 

 during significant El Ninos cannot be directly related 

 to the heavy rainfall occurrences over subtropical 

 Chile, although a superficial overview of statistics 

 from year-to-year rainfall records might so indicate. 

 Rainfall sources for these two areas, and times of year 

 the rainfall occurs in each, differ. The association 

 between these occurrences is indirect; the weakening 

 of the southeast Pacific subtropical high (as rep- 

 resented by low Southern Oscillation indices) with a 

 resulting slackening in the southeast trades facil- 

 itates both developments. 



Abnormal southward advances of the intertropical 



2 Santiago E. Antunez, Universidad Mayor de San Marcos at Lima, 

 Peru, pers. commun. 14 August 1978. 



convergence zone over the invading warm El Nino 

 surface waters along the coasts of southern Ecuador 

 and northern Peru cause the heavy rainfall over the 

 usually dry coastal lowlands. This El Nino-related 

 rainfall occurs during the Southern Hemisphere 

 summer and/or fall, a time when the regular annual 

 weakening of the trades augments this irregular in- 

 terannual slackening (Caviedes 1975). 



Years of abnormally heavy rainfall in subtropical 

 Chile result when storms of the westerly belt pene- 

 trate further to the north than usual into subtropical 

 Chile during the Southern Hemisphere winter (some- 

 times including late fall and/or early spring) months, 

 as a result of degeneration of the southeast Pacific 

 high and/ or displacement of the weakened high cen- 

 ter. This is similar to what happens north of the 

 Equator when the northeast Pacific subtropical high 

 breaks down, and we get unusually heavy rainfall 

 down into the southwestern United States and 

 northwestern Mexico during the Northern Hemi- 

 sphere winter. 



RECENT CHANGES IN THE PERU- 

 VIAN AND NORTHERN CHILEAN 

 ANCHOVETA FISHERIES 



Up through a little beyond the first half of this cen- 

 tury, the principal drain on the Peruvian anchoveta 

 fishery at shallow depths was the heavy consumption 

 by guano birds, on which Peru's guano industry 

 depends. Demands of the fishermen over these 

 earlier years were quite modest, and their catches ex- 

 tended to depths to which the birds could not reach. 

 During significant El Ninos the anchoveta were no 

 longer abundant at shallow depths, and large num- 

 bers of guano birds died of starvation along the Peru- 

 vian coast while others left the affected area. Yet, 

 limited demands of fishermen at that time and the 

 great reduction and slow recovery in bird populations 

 following El Ninos permitted a suitable recovery of 

 the fishery during the subsequent anti-El Nino 

 periods. However, by the late 1950's the growing 

 fishmeal industry was placing increasingly large 

 demands on the anchoveta fishery to meet fishmeal 

 production quotas. The anchovy fishery made Peru 

 the leading fish-producing nation from the late 

 1960's through 1971 (Idyll 1973). The record catches 

 of 1970-71 followed by the strong 1972-73 El Nino 

 led to a precipitous drop in fishmeal production 

 through 1973 (Fig. 3), from which there has never 

 be en a significant recovery. In 1972 and 1976, fishing 

 continued through the principal fishing season 

 (March-May) without taking into account the El 

 Ninos already underway. In retrospect, for these 



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