Impact of Warmer Eastern Tropical Pacific SST on the March 2015 Atacama Floods

Abstract

Northern Chile hosts the driest place on Earth in the Atacama Desert. Nonetheless, an extreme precipitation event affected the region on 24-26 March 2015 with 1-day accumulated precipitation exceeding 40mm in several locations and hourly mean rainfall rates higher than 10mm h(-1), producing floods and resulting in casualties and significant damage. The event is analyzed using ERA-Interim, surface station data, sounding observations, and satellite-based radar. Two main conditions favorable for precipitation were present at the time of the event: (i) a cutoff low (COL) off the coast of northern Chile and (ii) positive sea surface temperature (SST) anomalies over the eastern tropical Pacific. The circulation driven by the COL was strong but not extraordinary. Regional Climate Model, version 4 (RegCM4), is used to test the sensitivity of precipitation to SST anomalies by removing the warm SST anomaly in the eastern tropical Pacific. The cooler simulation produced very similar COL dry dynamics to that simulated in a control run (with observed SST), but suppressed the precipitation by 60%-80% over northern Chile and 100% in parts of the Atacama Desert due to the decreased availability of precipitable water. The results indicate that the warm SST anomaly over the eastern Pacific, favored by the onset of El Nino 2015/16, was instrumental to the extreme precipitation event by providing an anomalous source of water vapor transported to Atacama by the circulation ahead of the COL.Fondo de Financiamiento de Centros de Investigacion en Areas Prioritarias (FONDAP)/Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) Chile 15110009-CR2 Fondo Nacional de Desarrollo Cientifico y Tecnologico (FONDECYT)-Chile 3150036 National Laboratory for High Performance Computing (NLHPC) ECM-0

Winter Snow Level Rise in the Northern Sierra Nevada from 2008 to 2017

“…As found in field studies [56] and modeling experiments [57], anomalous positive SSTs offshore of continents modify air masses by contributing upward heat flux and decreasing static stability, leading to increases in downstream precipitation. At longer (seasonal) timescales, we observe that the negative correlations between snow fraction and SSTs offshore of California (Figure 6a,b) are located near the primary region of storm track activity that is correlated with winter California precipitation [16].…”

The 2010–2015 megadrought in central Chile: impacts on regional hydroclimate and vegetation

“…S2). To the north of 32 • S positive anomalies during 2010 and 2015 were associated with cut-off lows crossing this arid region in early winter (Bozkurt et al, 2016). Precipitation in 2014 was also near normal -albeit mostly below average -to the south of 35 • S. In contrast, 2012 and 2013 featured annual rainfall deficits larger than 30 % across much of the region.…”

Modelación de Crecidas Aluvionales en la Cuenca del Río Copiapó, Chile

“…Los registros de CAP sobre las costas peruanas al momento del fenómeno hidrometeorológico se encontraban 20 mm arriba del normal climatológico (ver Barret et al, 2016). Además, valores de CAP sobre la media histórica también fueron registrados en Antofagasta (Bozkurt et al, 2016). Dichos fenómenos coincidieron con un calentamiento extremo de las temperaturas superficiales que se registró en el centro, sur y zona austral de Chile, incluso también alcanzando la Antártica Chilena (Barret et al, 2016).…”

“…Según registros de 13 estaciones pluviométricas, se acumularon en promedio más de 45 mm en la Cuenca del Río Copiapó durante el periodo de duración del evento. De acuerdo con Bozkurt et al (2016), en la región hiperárida del desierto de Atacama se registraron intensidades de lluvia de más de 10 (mm/h), lo que generó una importante crecida del caudal del Río Copiapó, la cual fue parcialmente contenida por el Embalse Lautaro, logrando minimizar el impacto en el sector de Tierra Amarilla. Sin embargo, aguas abajo en la misma subcuenca, la Quebrada Paipote que confluye al Río Copiapó y que bajo condiciones normales se encuentra seca, registró un aumento significativo de su caudal directo (más de 1500 m 3 /s), el cual arrastró a su paso un gigantesco volumen de arena, combinado con partículas de arcilla y limo (Izquierdo et al, 2016).…”