Understanding high-resolution rainfall dynamics and variability in the Galápagos archipelago: Installation of an automatic weather stations network.

In the Intergovernmental Panel on Climate Change report (IPCC), “Climate Change 2022: Impacts, Adaptation and Vulnerability” it is stated that more frequent and intense extreme events due to climate change have a significant impact on the loss and damage of nature and people, which particularly holds for precipitation.

In the Galápagos archipelago, the primary source of water supply is rainfall, hence rainfall plays an important role for biodiversity and people in this iconic but remote region. The main assumption for Galapagos is that water supply is dominated by the cool season’s light Garúa rainfall originating from the Pacific stratus, which will significantly decrease under global warming conditions. At the same time, rainfall in the warm season shows large variability, particularly during extreme ENSO (El Niño-Southern Oscillation) events. While in the current decade, a decrease of strong El Niño rainfall events was observed in the eastern tropical Pacific, most (but not all) climate model projections of the CMIP6 ensemble reveal stronger El Niño rainfall under future warming.

To date, short and long-term rainfall dynamics in the Galápagos are not well understood, largely due to a lack of consistent spatially-time series of meteorological in-situ observations. The research project DARWIN ("Dynamics of precipitation in transition: The water source for the Galápagos Archipelago under climate change") has recently established 11 Automatic weather stations (AWS) covering a W-E and luff-lee transects over three islands (Isabela, S. Cruz, S. Cristóbal). The location of the stations is to consider different local and regional precipitation formation mechanisms. We seek to resolve influences of  the Equatorial Counter Current and the Humboldt Current, as well as the topographic exposition towards the main airstream. Furthermore, the altitudinal gradients concerning vertical dynamics of the trade inversion are considered. One main goal of the DARWIN project is to produce area-wide rainfall information by satellite retrievals and WRF dynamical downscaling. 

While warm-season rainfall is mainly driven by intense convection events, cool-season Garúa is assumed to be more in the drizzle intensity range. The area-wide techniques must thus properly model the very different types of occurring rain intensities in the cool and warm seasons. Hence, the observations from the AWS used as test and training data must be as accurate as possible. Beyond standard meteorology, we focus on different advanced observation principles (light, optical, radar, gauge) and their intercomparison, and warrant high-resolution measurements (up to one minute) including a vertical profiling of rainfall. The AWS stations in the Garúa zone are additionally equipped by a harp-type fog collector.         

The poster will present the overall structure of the project and some first results of the AWS network, with a focus  on temporally high-resolution rainfall dynamics during  different weather situations and precipitation types along the transects.