## 5 Discussion
### Climatic Trends at Maipo Basin  
The climate variability in Central Andes of Chile is partly driven by El Nino-Southern Oscillation (ENSO) events, characterized by irregular fluctuations between warm (El Nino) and cold (La Nina) phases with a periodicity of 2 to 7 years [64]. In the Central Andes El Nino and La Nina crucially determine the interannual variability in precipitation. The Pacific Decadal Oscillation (PDO) is a second driver, which is a pattern of climate variability, visible in the precipitation records over South America on a decadal to inter-decadal scale [64]. A relationship between ENSO and mass balance can be observed in the Echaurren Norte Glacier (Figure 5). The mechanisms controlling mass balance in this area are still a matter of debate. However, [PERSON] et al. [33] observed that the precipitation appears to be the main driver. Early comparisons by [PERSON] et al. [24] showed that glacier mass balance in Echaurren Norte Glacier between 1975 and 1991 was stronger correlated with precipitation than temperature. We observed the same for the period 1975-2015 with a high correlation between the precipitation and glacier mass balance (R\({}^{2}\) = 0.73), and a low correlation with temperature (R\({}^{2}\) = 0.26) (Figure 6). Previous studies indicated a temperature increase of +0.25 \({}^{\circ}\)C per decade (significant at the 95% level) in the period 1979-2006 for the Central Andes of Chile at the El Yeso Embalse weather station (247 m a.s.l.) [13]. However, a recent temperature reanalysis showed no significant annual warming between 1979 and 2015 (Figure S3, Table S1) [65], though a significant trend of +0.43 \({}^{\circ}\)C per decade was measured (21 th March-21 th June; Figure S4, Table S1).The Quinta Normal station, located in the central valley of Chile (Figure 1 and Figure S4), showed autumn warming as well of +0.26 \({}^{\circ}\)C per decade during the same period (significant at the 95% level) [65] (Table S1). In summer and spring, in the valley station mean temperature has been increasing at a rate of 0.15 and 0.18 \({}^{\circ}\)C per decade, respectively (Figure S4). The increase in the autumn temperature could extend the ablation period of the Echaurren Norte Glacier, leading to more negative glacier mass balances [65]. However, we did not observe a correlation between autumn temperature anomalies and glacier mass balance (Figure S5). In support of previous studies [24; 33], our results suggest that the glacier mass balance depended mainly on precipitation. Figure 6: (**a**) Correlation analysis between glacier mass balance of the Echaurren Norte Glacier with annual precipitation and (**b**) annual temperature anomalies [65]. It is noteworthy that a higher correlation between mass balance and precipitation is observed (meteorological data from El Yeso weather station, 2474 m a.s.l.). It is noteworthy that the ELA at the Echaurren Norte Glacier has not been reported in glaciological mass balance calculations [24; 33; 39]. In fact, the Echaurren Norte Glacier is currently located below the regional ELA, which was located at \(\sim\)4000 m a.s.l. at 33\({}^{\circ}\)S in the Central Andes of Chile in the year 2000 [14]. Therefore, at the end of the summer, ablation takes place over the whole glacier area, resulting in a negative annual mass balance. In addition to the well-known interannual precipitation variability [66], a drastic drought occurred in Central Chile 2010-2015 (Figure 5 and Figure S3) with an annual rainfall deficit between 25% and 45% [12]. This drought probably triggered the observed mass balance deficit of 1.2 m w.e. a\({}^{-1}\) on Echaurren Norte Glacier between 2009 and 2015. Comparing our results between the periods 2000-2009 and 2000-2013 (Figure 4a,b), thinning rates have increased coincident with the drought [12]. Similar trends have also been observed in other studies [33]. The atmospheric dynamics behind this dry period are not clear. However, the negative decrease on precipitation during 2009-2015 was unprecedented [12].