Abstract
The coastal regions of South Ecuador and Peru belong to the areas experiencing the strongest impact of the El Niño Southern Oscillation phenomenon. However, the impact and dynamic development of weather patterns during those events are not well understood, due to the sparse observational networks. In spite of neutral to cold conditions after the decaying 2015/16 El Niño in the central Pacific, the coastal region was hit by torrential rainfall in 2017 causing floods, erosion and landslides with many fatalities and significant damages to infrastructure. A new network of X-band weather radar systems in South Ecuador and North Peru allowed, for the first time, the spatio-temporally high-resolution monitoring of rainfall dynamics, also covering the 2017 event. Here, we compare this episode to the period 2014–2018 to point out the specific atmospheric process dynamics of this event. We found that isolated warming of the Niño 1 and 2 region sea surface temperature was the initial driver of the strong rainfall, but local weather patterns were modified by topography interacting with the synoptic situation. The high resolution radar data, for the first time, allowed to monitor previously unknown local spots of heavy rainfall during ENSO-related extreme events, associated with dynamic flow convergence initiated by low-level thermal breezes. Altogether, the coastal El Niño of 2017, at the same time, caused positive rainfall anomalies in the coastal plain and on the eastern slopes of the Andes, the latter normally associated only with La Niña events. Thus, the 2017 event must be attributed to the La Niña Modoki type.
Highlights
A common conception about tropical regions is the abundance of water supply
To put the radar results into a larger context, additional analyses are supplied as Supplementary Material, partially referring to the additional analyses are supplied as Supplementary Material, partially referring to the larger larger RNP-domain covered by the ERA5 products and long-term monitoring (1998–2018)
Spatial differences of interannual variability could be mapped in detail and process dynamics of extreme events unraveled
Summary
A common conception about tropical regions is the abundance of water supply. large parts of the tropical South American Pacific coast are characterized by aridity and a strong inter-annual variability of rainfall.Ecuador is located in a transition zone between one of the wettest spots on earth and the coastal deserts of Peru. Large parts of the tropical South American Pacific coast are characterized by aridity and a strong inter-annual variability of rainfall. In Colombia, close to the northern border of Ecuador, several places are exceeding 10,000 mm of rainfall per year [1]. In North Peru, annual amounts go down to less than 20 mm [2]. In addition to this zonal gradient, a strong meridional rainfall gradient is present in South Ecuador and Peru: The entire Amazonian (eastern) parts of Ecuador and Peru are permanently humid all year long, while the south-western parts of Ecuador and the coast of Peru are fully arid
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