Clarifying the Role of ENSO on Easter Island Precipitation Changes: Potential Environmental Implications for the Last Millennium

Abstract

El Niño Southern Oscillation (ENSO) events yield precipitation deficits and ensuing droughts, often damaging regional forests, in many parts of the world. The relative roles of ENSO, other natural climate changes, and anthropogenic factors on the forest clearing of Easter Island over the last millennium are still debated. Here, we analyze Easter Island precipitation changes using in situ, satellite‐derived and reanalysis products spanning the last 4–7 decades, and 46 monthly 156‐year‐long (1850–2014) simulations derived from 25 CMIP5 and 21 CMIP6 (Coupled Model Intercomparison Project phases 5 and 6) General Circulation Models. Our analysis shows that La Niña events, the cold phases of ENSO, cause precipitation deficits of −0.2 to −0.3 standard deviation (relative to long‐term mean) in all analyzed data types. ENSO‐like events are further examined over the last millennium (850–1981). A new multiproxy reconstruction of the NINO3.4 index based on proxy records from the Past Global Changes 2k database and Random Forest method is produced. Our reconstruction reveals unusual high recurrences of La Niña‐like situations during the fifteenth to seventeenth centuries, which likely induced significant precipitation deficits on the island. These situations are compared to published vegetation reconstructions based on pollen analyses derived from sedimentary cores collected in three island sites. We conclude the environmental consequences of cumulative precipitation deficits over long‐lasting La Niña‐like situations reconstructed here over the fifteenth to seventeenth centuries were likely favoring drought and forest flammability. La Niña events should be better accounted for among the causes of forest clearing on Easter Island.

The Rapa Nui Little Ice Age drought: Evidence, potential causes and socioecological impact

“…According to Delcroix et al. (2022), the timing of these arid events is remarkably coherent with anthropogenic deforestation and geochemical aridity proxies, as quoted above (Roman et al., 2021; Rull et al., 2015; Seco et al., 2019). These authors emphasize that, although deforestation was primarily anthropogenic, aridity could have affected forest flammability, as formerly proposed by Rull (2021).…”

“…These authors modelled the ENSO variability over the last millennium (850-1851 CE) using a new reconstruction using the SST-NINO3.4 ENSO index, and observed remarkably high recurrences of La Niña events during the 15th to 17th centuries, as the potential causes for relevant precipitation deficits on Rapa Nui. According to Delcroix et al (2022), the timing of these arid events is remarkably coherent with anthropogenic deforestation and geochemical aridity proxies, as quoted above (Roman et al, 2021;Rull et al, 2015;Seco et al, 2019). These authors emphasize that, although deforestation was primarily anthropogenic, aridity could have affected forest flammability, as formerly proposed by Rull (2021).…”

“…(b) Elemental ratios demonstrating the desiccation of the Aroi mire (Roman et al., 2021). (c) El Niño Southern Oscillation (ENSO) variability reconstruction using the normalized SST‐NINO3.4 index (Delcroix et al., 2022).…”

“…More recently, Delcroix et al. (2022) have suggested that the El Niño Southern Oscillation (ENSO) variability could be an important driver of the Rapa Nui climate, especially in relation to the occurrence of century‐scale aridity phases. This statement is based on the observation that, during the last 4–7 decades, the colder ENSO phases known as the La Niña events have caused significant precipitation deficits, as measured instrumentally (Mataverí weather station).…”

“…The cause of these events may be a combination of atmospheric rivers, cold fronts, cut-off lows and other kinds of low-pressure systems, with some influence of the South Pacific subtropical anticyclone dynamics. Delcroix et al (2022) pointed out that a single weather station cannot represent the precipitation of the whole island due to relevant topographic gradients, as emphasized by Stevenson et al (2015). Therefore, the combined use of the Mataverí time series and GCM simulations provides a more reliable picture of Rapa Nui precipitation over time.…”