Regional Controls on Climate and Weather Variability on the Southwest Coast of Peru

Abstract

Southwestern Peru has an arid climate typical of subtropical west coasts bordering cold ocean currents. Mountain runoff is barely able to sustain urban needs and motivates this research. Using high-resolution satellite reanalysis products, the meso-scale climate and weather variability are explored via point-to-field regression. A time series spanning 1970–2022 of Tacna area (18 S, 70.2 W, 570 m) rainfall, potential evaporation, wind, and weather parameters were evaluated for thermodynamic and kinematic features. Although sea breezes draw marine air inland, they simultaneously generate low-level divergence and subsidence aloft. Potential evaporation in early summer causes water deficits that are rarely offset by late summer runoff from the Andes Mountains. Winter (May–September) showers from passing cold fronts are more frequent during El Niño. Warming of the tropical east Pacific accelerates subtropical westerly winds that lift over the coastal plains. Quasi-stationary Rossby wave patterns amplify transient troughs at 70 W, but the winter showers rarely exceed 4 mm/day due to low-level stability from negative heat fluxes over cool seawater offshore. Two winter wet spells were studied using satellite and surface data (July 2002, July 2009). Light showers were prominent in elevations from 400 to 900 m. An early summer dry spell was considered (November 2020), wherein southeast winds, coastal upwelling, and low dewpoint temperatures coincided with La Niña conditions. A rain-gauge transect showed that summer convection stays east of the Andes escarpment and seldom benefits the coastal plains. Thus, water resources in Tacna are strained beyond the carrying capacity.