Hydrological modelling of a closed lake (Laguna Mar Chiquita, Argentina) in the context of 20th century climatic changes
Résumé
A major hydroclimatic change occured in southeastern South America at the beginning of the 1970s. This change was recorded in Laguna Mar Chiquita (central Argentina), the terminal saline lake of a 127,000 km2 catchment as a dramatic rise in lake level larger than any observed over the past 230 years. Based on available continuous lake level monitoring since 1967, our study aimed to develop a lake water balance model for investigating the link between climate and lake level variations. Since un-gauged downstream surfaces represented approximately 80% of the catchment, the main challenge of the model development and implementation came from estimating the magnitude of catchment inputs from sparsely available gauge data. We determined a strongly negative water balance in the un-gauged part of the catchment that can be attributed to evapotranspiration in two large surface water hydrosystems. The chloride balance indicated that the lake is hydrologically closed, without significant groundwater outflows. Using contrasted hydroclimatic conditions, the robustness of the model calibration was evaluated with the model residual, and a short validation proposed for the 1998-2006 time period. Sensitivity analyses were performed in order to identify the main forcing factors of lake variations. We determined that the abrupt lake level rise in the early 1970s could be attributed to increased runoff in the upper northern sub-basin, suggesting a tropical climatic influence. Based on available hydroclimatic data, we propose a continuous lake level simulation for the 1926-2006 time period which could be used as a reference curve for better constraining paleohydrological reconstructions from sedimentary proxies.