Climatology

DARWIN

Project researchers

DynAmics of pRecipitation in transition: The Water source for the Galápagos ArchIpelago under climate ChaNge

The Galápagos archipelago is known for its unique and high endemic biodiversity. It is listed as a UNESCO’s World Heritage site, World Heritage in Danger (2007), as ‘most irreplaceable protected areas’ and a ‘flagship’ area for conservation and as a ‘Priority Ecoregion for Global Conservation’. Climatologically, Galápagos is of great interest because its location in the centre of the ENSO (El Niño - Southern Oscillation) phenomenon, affecting the archipelago with strong quasi-periodic oscillations in precipitation, sea surface (SST) and air temperatures. Thus, it is not surprising that many biological studies evaluated the relation of vegetation and fauna to the strong climate variability. They found a general relation of vegetation and their traits with rainfall, but also strong erosion with partly removals of vegetation during heavy El Niños (EN). Strong EN with enhanced SSTs are reducing food availability for the fauna: Galápagos penguins starve with population decrease of up to ca. 70 %, with contrary developments during La Niña cold events. During strong ENs Galápagos pinnipeds undergo almost complete losses of the four youngest generations and severe diebacks of females and nonterritorial males.

A significant reduction in the algal forage leads to starvation of marine iguanas. Extreme EN rainfall is causing increased lagoon water levels, resulting in a decline of flamingos. Modern climate change on the islands appears to cause ecosystem changes: unprecedented levels of upslope transport of pollen from the lowlands within the last 30 years are detected, which suggest increased convection consistent with a warming of hot season temperatures. A future extension of EN frequency in the scope of climate change could threaten vulnerable populations and, in the longer term, trigger microevolutionary changes in plants and animals.

There is, however, a knowledge deficit about the threats posed by changes in the atmospheric water cycle (precipitation) under climate change. This is problematic because of its crucial role for ecosystems, potable water supply of increasing population and agricultural production. Any database on climate and especially on precipitation of Galápagos is lacking. In the entire archipelago comprising more than 113 islands, with a total area of 98555 ha, data from only a few weather stations are available. In previous work, it was shown that the archipelago’s climates are governed by different phenomena of several scales, i.e., the seasonal shift of the Intertropical Convergence Zone (ITCZ) and the South Pacific Anticyclone (SPA), a well-developed land-sea breeze system and the quasi-periodic ENSO phenomenon. During January to May, the so-called hot season is characterized by above-normal SST and highly variable rainfall from orographic convection caused by the ITCZ passage. The cold season is dominated by subsidence from the SPA, accompanied by low stratus clouds with continuous drizzle rainfall (Garúa) in higher and drought conditions in lower areas. While the Garúa including occult precipitation seems to have major importance for water supply, its spatio-temporal occurrence and water potential is completely unknown.

With this program, we are gathering much needed spatio-temporal data of the atmospheric water cycle of this archipelago area with this complex interplay of topography, SST and cross-scale atmospheric circulation patterns. We aim to broaden our knowledge of the role of the Garúa in this system, it’s water potential and potential changes under a more extreme climate. The other focus point of this program is the warm season convective rainfall, the other major source of precipitation, and it’s sensitivity to climate change. We work with our partners at the University of Marburg, the Charles Darwin Foundation of Santa Crúz, Rolando Celleri of the University of Cuenca and Daniela Ballari of the Universidad del Azuay to combine field surveys with satellite remote sensing and dynamical downscaling of global reanalysis data to grids of very high spatial resolution, to provide explicit rainfall maps and disentangle the interplay of local breeze systems, SST development and synoptic weather situations in order to understand the spatiotemporal character of rainfall formation processes.

Prof. Dr.

Dieter Scherer

M.Sc.

Benjamin Schmidt

Area of Investigation

Publications

2023

Zander, Samira; Bendix, Jörg; Turini, Nazli; Schmidt, Benjamin; Ballari, Daniela; Bayas López, Steve Darwin; Celleri, Rolando; Delgado Maldonado, Byron; Orellana-Alvear, Johanna; Scherer, Dieter
The Spatio-Temporal Cloud Frequency Distribution in the Galapagos Archipelago as Seen from MODIS Cloud Mask Data
Atmosphere, 14 (8) :1225
July 2023
ISSN: 2073-4433