Dendrohydrology and water resources management in South-Central Chile: Lessons from the Río Imperial streamflow reconstruction

Abstract

Abstract. Streamflow in South-Central Chile (SCC, ∼35 o S-42 o S) is vital for agriculture, forestry production, hydroelectricity, and human consumption. Recent drought episodes have generated hydrological deficits with damaging effects on these activities. This region is projected to undergo major reductions in water availability, concomitant with projected increases in water demand. However, the lack of long-term records hampers the development of accurate estimations of natural variability and trends. In order to provide more information on long-term streamflow variability and trends in SCC, here we report findings 5 of an analysis of instrumental records and a 296-year tree-ring reconstruction of the summer streamflow of the Río Imperial (∼37 o 40'S-38 o 50'S). This is the first reconstruction in Chile targeted at this season. Results from the instrumental streamflow record (∼1940 onwards) indicated that the hydrological regime is fundamentally pluvial with a small snowmelt contribution during spring, and evidenced a decreasing trend, both for the summer and the full annual record. The reconstruction showed that streamflow below the average characterized the post-1980 period, with more frequent, but not more intense, drought episodes. 10We additionally found that the recent positive phase of the Southern Anular Mode has significantly influenced streamflow. These findings agree with previous studies, suggesting a robust regional signal and a shift to a new hydrological scenario. In this paper, we also discuss the implications of these results for water managers and stakeholders; we provide rationale and examples that support need for the incorporation of tree-ring reconstructions into water resources management.

Asymmetric emergence of low-to-no snow in the midlatitudes of the American Cordillera

“…Risks associated with markedly reduced runoff pose direct challenges to an already complex decision-making system 5,7,16,18 . These risks are heightened by centuries of infrastructure design and management strategies that have largely assumed climate stationarity and that do not agree with palaeoclimate records or future climate projections [58][59][60] . Further compounding these risks, the southern midlatitudes of the American Cordillera are projected to face low-to-no snow emergence nearly 20 years earlier than the northern midlatitudes.…”

Hydroclimatic variability in Santiago (Chile) since the 16th century

“…(2017, 2020), was associated with significant ecological and socioeconomic impacts over the territory. Throughout the period analysed, the duration and intensity of dry and wet events becomes progressively more muted, especially during the mid‐20th century, a phenomenon already documented (Le Quesne, 2006) and also reflected in streamflow reconstructions (Fernández et al ., 2018). When analysing hydroclimate signals at the 11‐year scale, however, this tendency disappears after the mid‐ 20th century, being replaced by two subsequent prolonged events of positive and negative anomalies, respectively.…”

Cross-continental hydroclimate proxies: Tree-rings in Central Chile reconstruct historical streamflow in Southeastern South American rivers

“…Model verification for the calibration period (1957–2009) was conducted using the R 2 and adjusted R 2 to evaluate explained variance between observed and predicted values, the latter adjusted for loss of degrees of freedom; the F statistic for testing the accuracy of the regression model; and the reduction of error (RE) statistic to account for the relationship between the actual value and the estimate. The robustness of the reconstruction was evaluated using the root mean square error (RMSE), the Reduction Error (RE), and the Durbin–Watson test (DW) (Fernández et al, 2018; Muñoz et al, 2020). We evaluated the linear correlation between the reconstruction and historical hydroclimate data from the Upper Negro River basin, including annual CRU 4.03 precipitation, CSIC 1-month SPEI, and the annual self-calibrated Palmer Drought Severity Index (scPDSI) available at the SADA Explorer (https://sada.cr2.cl/, Morales et al, 2020).…”

“…Ocean-atmosphere-land teleconnections among remote regions can permit the historical reconstruction of streamflow using multiple proxies. Tree-ring data in South America has been used to reconstruct streamflow of major rivers in South America (Fernández et al, 2018; Ferrero et al, 2015; Holmes et al, 1979; Mundo et al, 2012; Muñoz et al, 2016), as well as drought conditions from 1400-present in the Southern Cone (Morales et al, 2020). The positive response of tree growth to ENSO variability shown here is influenced by the relationship between ENSO and local hydroclimate variables in both Central Chile and SESA (Garreaud et al, 2009).…”

“…The 115-year reconstruction suggests major flooding events in 1930, 1959, 1966, and 1998, all of which could be potentially excluded from an estimation of environmental streamflow in the last two decades. In Chile, dendrohydrological reconstructions using tree-rings show that Q during the period used to legally determine water allocation was above the long-term mean (Fernández et al, 2018). As central Chile currently faces severe drought and a decline in tree growth in the past two decades (Garreaud et al, 2020; Miranda et al, 2020; Venegas-González et al, 2019), the allocation of water based on a surplus of discharge has had severe ecological and economic consequences.…”