High-resolution regional climate modeling of coastal jets and their future evolution in the Peruvian Upwelling System

Coastal jets, characterized by wind maxima at low atmospheric levels, are a prominent feature of Eastern Boundary Upwelling Systems (EBUS) and play a crucial role in regional ocean dynamics and climate. These jets significantly affect environmental processes and human activities, particularly in marine ecosystems and fisheries. Despite their importance, the coastal jet in the Peruvian Upwelling System remains one of the least studied phenomena within EBUS.

This study employs high-resolution (7 km) regional climate simulations using the Weather Research and Forecasting (WRF) model to analyze the characteristics of coastal jets off the coast of Peru. We performed a retrospective simulation for the period 1994–2003, driven by NCEP2 reanalysis data, to characterize the baseline conditions of coastal jets in terms of their frequency of occurrence, intensity, vertical structure, and directional patterns. The identification of coastal jets was based on a detailed analysis of vertical wind and temperature profiles, focusing on wind speed maxima at low atmospheric levels and their association with upwelling events and coastal features. The vertical profiles of wind and temperature were examined at multiple altitudes (from 10 m to 1000 m a.s.l.) to determine the spatial distribution, intensity, and vertical extent of these jets.

In addition to the retrospective analysis, we conducted future climate projections for the period 2086–2095 under the RCP8.5 climate change scenario. The future simulations were forced with climate change signals derived from the CMIP5 ensemble, which includes the differences between monthly mean climatologies for the periods 2080–2100 and 1989–2009. These climate change forcings were added to the NCEP2 reanalysis data to simulate future atmospheric conditions. The future projections focus on the potential changes in the frequency, intensity, and altitude of coastal jets, as well as shifts in their seasonal patterns and directional tendencies.

Results indicate that coastal jets occur year-round, with variations in frequency and spatial distribution. In summer, jets are more frequent and concentrated near the coastline, with intensities between 8 and 10 m.s⁻¹ and altitudes ranging from 200 to 300 m a.s.l. In contrast, winter coastal jets are less frequent but cover larger areas, with intensities between 9 and 11 m.s⁻¹ and altitudes of 400–500 m a.s.l. The predominant direction of the jets is south-southeast, parallel to the coastline, throughout the year, except in winter when significant occurrences are also observed from the southeast.

Under the climate change scenario, the frequency of coastal jets is projected to increase, particularly along the northern and central coasts of Peru. A notable increase of up to 20% in frequency is expected during June, July, August, September, and October, especially north of the Paracas Peninsula (14°S). While the intensity of the jets remains largely unchanged, the vertical distribution of coastal jets is expected to shift, with a tendency towards lower altitudes in future projections.