Abstract
Ratios of stable oxygen isotopes in tree rings (δ18O) are a valuable proxy for reconstructing past climates. Such reconstructions allow us to gain better knowledge of climate dynamics under different (eg warmer) environmental conditions, which also forms the basis for effective risk management. The latter aspect is particularly relevant for our study site on the western flanks of the Andes in Southern Ecuador, since the region is frequently affected by droughts and heavy precipitation events during the rainy season (January to April), leading to enormous social and economic losses. In particular, we focus on precipitation amounts and moisture source regions as they are known to influence the δ18O signature of tree rings. Moisture source regions are based on 240 h backward trajectories that were calculated with the trajectory model LAGRANTO for the rainy seasons 2008 to 2017. A moisture source diagnostic was applied to the air parcel pathways. The resulting moisture source regions were analyzed by calculating composites based on precipitation amounts, season, and calendar year. The precipitation amounts were derived from data of a local Automatic Weather Station (AWS). The analysis confirms that our study site receives its moisture both, from the Atlantic and the Pacific Oceans. Heavy precipitation events are linked to higher moisture contributions from the Pacific, and local SST anomalies along the coast of Ecuador are of higher importance than those off the coast toward the central Pacific. Moreover, we identified increasing moisture contributions from the Pacific over the course of the rainy season. This change and also rain amount effects are detectable in preliminary data of δ18O variations in tree rings of Bursera graveolens. These signatures can be a starting point for investigating atmospheric and hydroclimatic processes, which trigger δ18O variations in tree rings, more extensively in future studies.
Highlights
Ecuador and in particular its share of the western flanks of the tropical Andes are prone to heavy rain events and floods that occur with a high interannual variability (Endlicher et al, 1989; Bendix, 2000; Bendix et al, 2003; Bendix and Bendix, 2006; Takahashi and Martinez, 2019)
We evaluate the influence of different precipitation events and their moisture source regions on the oxygen isotopic signature of Bursera graveolens tree rings in southwestern Ecuador during the rainy season on interannual and intra-annual time scales
We considered the performance of ERA5, focusing on precipitation variability
Summary
Ecuador and in particular its share of the western flanks of the tropical Andes are prone to heavy rain events and floods that occur with a high interannual variability (Endlicher et al, 1989; Bendix, 2000; Bendix et al, 2003; Bendix and Bendix, 2006; Takahashi and Martinez, 2019). We evaluate the influence of different precipitation events and their moisture source regions on the oxygen isotopic signature of Bursera graveolens tree rings in southwestern Ecuador during the rainy season on interannual and intra-annual time scales. For this purpose, the two main goals are (1) to investigate local precipitation events and (2) to identify moisture source regions based on trajectories for different composites (precipitation events, each month and each calendar year). To put the two goals in a wider context and future perspective, we discuss a possible relationship between precipitation as well as moisture source regions and the isotopic signatures in Bursera graveolens tree rings
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