Abstract
Abstract. The El Niño and La Niña impacts on the hydrology of Peru were assessed based on discharge data (1968–2006) of 20 river catchments distributed over three drainage regions in Peru: 14 in the Pacific Coast (PC), 3 in the Lake Titicaca (TL) region, and 3 in the Amazonas (AM). To classify the El Niño and La Niña events, we used the Southern Oscillation Index (SOI) based on hydrological years (September to August). Using the SOI values, the events were re-classified as strong El Niño (SEN), moderate El Niño (MEN), normal years (N), moderate La Niña (MLN) and strong La Niña (SLN). On average during the SEN years, sharp increases occurred in the discharges in the north central area of the PC and decreases in the remaining discharge stations that were analyzed, while in the years of MEN events, these changes show different responses than those of the SEN. During the years classified as La Niña, positive changes are mostly observed in the majority of the stations in the rivers located in the center of Peru's Pacific Coast. Another important result of this work is that the Ilave River (south of the Titicaca watershed) shows higher positive (negative) impacts during La Niña (El Niño) years, a fact that is not clearly seen in the rivers of the northern part of the Titicaca watershed (Ramis and Huancane rivers).
Highlights
Introduction climatic anomalies arounGd teheowsocrilednAtifciocmplete analysis by Chiew andMMocMdaehol nD(2e0v0e2)loinpdimcateesnat clear relation-M ship between ENSO and river discharges: regionally signifi-Strong El Nino Southern Oscillation (ENSO) events like cant and consistent teleconnections between ENSO and dis-1982–1983 and 1997–1998 have induced the greatest im- charges are identified in Australia and New Zealand, South pacts on the Peruvian economy as a result of the disasters and Central America, aHndymdordoerlaoteglyysiagnnifidcant signals are caused by the floods and droughts
Nina events on the hydrology of Peru has been carried out 12 using 20 discharge stations distributed in three drainages regions of Peru: 14 in the Pacific Coast (PC), 3 in the Lake Titicaca (TL) and 3 in the Amazonas (AM)
– It can be clearly observed that during strong El Nino (SEN) years, there are sharp increases in the river discharges in the northern part of the PC, as previously reported in the literature (Waylen and Caviedes, 1986; Wells, 1987; Waylen and Poveda, 2002 and others). We show that such relationship between river discharge and ENSO is altered during moderate El Nino (MEN) years; in particular, the discharges are reduced during MEN years in the southern part of the PC, the Titicaca Lake (TL) and AM being these anomalies, similar to MEN years in the southern PC and in the southern TL (Ilave River) during El Nino years
Summary
Watersheds across the Peruvian territory are distinguished due to the presence of the Andes Cordillera. The rivers that drain into the Pacific Ocean are characterized by steep slopes, they are not very long, and their rainfall and discharge peaks occur simultaneously. 20 stations with discharge data at monthly step were used: 14 stations at rivers flowing into the Pacific Coast (PC), 3 into the Titicaca Lake (TL) and 3 into the Amazonas (AM). This information was provided by the SENAMHI, except for the information from the Tabatinga station (AQ-3), which is from the National Wat2er Agency of Brazil (www.ana.gov.br). SOI values higher than 10 and moderate La Nina (MLN) years (MLN 1974/75, 1998/99, 1999/00 and 2000/01) for values between 5 and 10
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