Spatiotemporal patterns of ENSO‐precipitation relationships in the tropical Andes of southern Peru and Bolivia

Abstract

Precipitation is vital in the outer tropical Andes, regulating freshwater availability, flooding, glacier mass balance, and droughts. Precipitation in the region, however, is highly seasonal and exhibits considerable interannual variability. The primary driver in interannual variability is the El Niño Southern Oscillation (ENSO), with most investigations reporting that the El Niño (La Niña) results in negative (positive) precipitation anomalies across the region. Recent investigations, however, have identified substantial spatiotemporal differences in ENSO-precipitation relationships. Motivated by the dissimilarity of these findings, this study examines a carefully selected dataset (≥ 90% completeness) of ground-based precipitation observations from 75 high-elevation (≥ 2,500 m asl) meteorological stations in the tropical Andes of southern Peru and Bolivia to identify distinct groups and associated variability in precipitation characteristics (e.g., total seasonal precipitation, wet season onset, and wet season length). Using no spatial constraints, the K-Means algorithm optimally grouped stations into five easily identifiable groups. Groups 3, 4, and 5 farthest from the Amazon basin had significant positive (negative) precipitation anomalies (p < .05) during La v Niña (El Niño), aligning with the traditional view of ENSO-precipitation relationships while Groups 1 and 2 closest to the Amazon had opposite relationships. Additionally, though studies have reported delays in the wet season, years characterized by El Niño had an earlier wet season onset in all five groups. These findings may aid in improving seasonal climate prediction and managing water resources, and could also allow for improved interpretation of tropical Andean ice cores. vi ix Dedication I dedicate this thesis to my loving and beautiful wife Jenna Rose, our baby John Casimir, and any other future children with which God may bless our family.

The Energy and Mass Balance of Peruvian Glaciers

“…Fluctuations in ENSO between warm (El Niño) and cold (La Niña) phases are the main drivers of interannual precipitation and air temperature variability across South America (Garreaud et al, 2009). However, the influence of ENSO on precipitation in Peru varies between the north and south of the country, with distance from the Amazon and according to the El Niño regime (Jonaitis et al, 2021;Lavado-Casimiro & Espinoza, 2014;Sanabria et al, 2018). At Shallap, Maussion et al (2015) found a strong anticorrelation between glacier mass balance and ENSO, with El Niño years associated with reduced snowfall and increased net shortwave radiation, which generally agrees with the results for Artesonraju (Section 5.5).…”

“…El Niño (La Niña) episodes are characterized by anomalously warm (cold) temperatures, which increase (decrease) ablation across the tropical Andes (Francou et al., 2004; Maussion et al., 2015; Thompson et al., 2017). However, the effect of ENSO fluctuations on precipitation is spatially variable across Peru, with the sign of precipitation change varying with latitude, El Niño regime, and in southern Peru, with distance to the Amazon (Jonaitis et al., 2021; Lavado‐Casimiro & Espinoza, 2014; Sanabria et al., 2018)…”

“…El Niño (La Niña) episodes are characterized by anomalously warm (cold) temperatures, which increase (decrease) ablation across the tropical Andes (Francou et al, 2004; Maussion Thompson et al, 2017). However, the effect of ENSO fluctuations on precipitation is spatially variable across Peru, with the sign of precipitation change varying with latitude, El Niño regime, and in southern Peru, with distance to the Amazon (Jonaitis et al, 2021;Lavado-Casimiro & Espinoza, 2014;Sanabria et al, 2018) There is strong evidence that air temperatures in the tropical Andes will increase in the future, with a warming of 4.5-5°C predicted by the end of the 21st century under the SRES A2 scenario, which will be enhanced over the Cordillera Blanca (Urrutia & Vuille, 2009;Vuille, Francou, et al, 2008). Yarleque et al (2018) projected a warming over the Quelccaya Ice Cap of 2.4°C under RCP 5.4 and 5.4°C under RCP 8.5 by the end of the 21st century.…”

Evaluation of Reanalysis Temperature and Precipitation for the Andean Altiplano and Adjacent Cordilleras

“…As described in the Introduction, the ENSO is a dominant teleconnection to central Andean climate with a complex response over the high terrain of the Altiplano (e.g., Jonaitis et al., 2021; Vuille et al., 2000). Below we map ENSO correlations from each reanalysis to the large‐scale South America domain using two approaches.…”

“…For example, Jonaitis et al. (2021) show from 75 observational records above 2,500 m a.s.l. that El Niño (La Niña) elicits wet‐season (December–February) precipitation deficits (surpluses) across the eastern and northeastern Altiplano, while El Niño or ENSO‐neutral conditions bring precipitation surpluses to the west.…”