High-Resolution Modeling of ENSO-Induced Precipitation in the Tropical Andes: Implications for Proxy Interpretation

Abstract

Sediment records from Lake Pallcacocha, Ecuador, have been interpreted as proxies of El Niño–Southern Oscillation (ENSO) variability, owing to increased precipitation in the area during El Niño events. However, the lake's watershed receives precipitation from processes arising from both the eastern and western Andes, where ENSO has different impacts; this has led to ambiguity in observed regional ENSO signals and has consequently challenged the suitability of the lake's records as ENSO proxies. Here, a mesoscale weather prediction model is used to investigate the regional circulation dynamics and precipitation response during different ENSO events, namely, Eastern Pacific (EP), Central Pacific (CP), coastal El Niño (COA), and La Niña (LN). The region receives more accumulated precipitation during COA and LN compared to EP and CP events. However, during EP and COA events, the region is prone to extreme precipitation associated with convective bursts originating from the Pacific. During CP and LN, moisture originates from the Atlantic and may reach the area as broader-scale less-intense precipitation. Statistical analysis of modeled precipitation reveals consistency between the number of threshold-exceeding precipitation events in the high Andean elevations and the number of events identified in the late Holocene Pallcacocha record. These results illustrate the importance of considering ENSO flavors when interpreting paleoclimate proxies, highlight the role of COA events in understanding eastern Pacific proxy records, and support the hypothesis that Holocene changes in the number of events recorded in the lake sediment may indicate a change in the relative frequency of ENSO flavors.