Groundwater is an important resource in semi-arid Chile to meet local social, economic and environmental water demands. Historical ground water level (GWL) data (1986–2014) in the Coquimbo Region were analysed to characterize short and long-term alluvial aquifer dynamics. Long-term trends were assessed using a seasonal Mann-Kendall trend test, which indicated that more than 80% of the time series exhibit a negative trend. Short-term analysis using cross-correlation provided information on recharge origin and its spatial pattern. Runoff and GWL are highly correlated depending on elevation, signifying that stream to aquifer flow is an important recharge process at higher altitudes. Long-term recharge behaviour was characterized using time-frequency wavelet power spectra. The results show significant amplitude of the 5-year recharge period for GWL, which is driven by a 5-year El Niño index periodicity. Such results provide key information of the spatiotemporal functioning of aquifers.

High-altitude peatlands in the Andes, i.e., bofedales, play an essential role in alpine ecosystems, regulating the local water balance and supporting biodiversity. This is particularly true in semiarid Chile, where bofedales develop near the altitudinal and hydrological limits of plant life. The subterranean geometry and stratigraphy of one peatland was characterized in north-central Chile using Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR) and core extraction. Two sounding locations, two transversal and one longitudinal profile allowed a 3D interpretation of the bofedal’s internal structure. A conceptual model of the current bofedal system is proposed. Geophysical results combined with porosity measurements were used to estimate the bofedal water storage capacity. Using hydrological data at the watershed scale, implications regarding the hydrological role of bofedales in the semiarid Andes were then briefly assessed. At the catchment scale, bofedal water storage capacity, evapotranspiration losses and annual streamflow are on the same order of magnitude. High-altitude peatlands are therefore storing a significant amount of water and their impact on basin hydrology should be investigated further.

Estimating subsurface hydraulic properties using the groundwater (GW) response to Earth tides (ET) and atmospheric pressure is an alternative approach to pumping or slug tests (passive vs. active methods). Yet testing the applicability of models under different subsurface conditions and comparing results with traditional hydraulic methods are lacking. We first review the assumptions of analytical models used to evaluate the GW response to ET and their applicability in unconfined to confined conditions. Second, we develop a robust approach to select the right model based on amplitude and phase pattern of the diurnal and semi‐diurnal tides. Third, based on earlier works we develop an approach to derive the hydraulic conductivity of the screened interval using the GW response to atmospheric tides, here named “atmospheric slug test” (AST). We estimate transmissivity and storativity at three shallow aquifers in Cambodia and compare the results with subsurface properties derived from pumping tests (PT). Transmissivity values from AST and PT are in good agreement. However, we show that storativity values derived from ET show large discrepancies if borehole skin effects are ignored. Further, the GW response to ET exhibits a strong decay in amplitude with frequency while maintaining close to zero and positive phase shifts. When supplemented with the calculated transmissivity values, none of the analytical models was able to reproduce this frequency dependent behavior. Our work emphasizes the need for evaluating passive methods robustness under different subsurface conditions. Further work is required to understand the frequency dependent GW response to natural or artificial forces.

In semi-arid Chile, rock glaciers cover more surface area than glaciers and are potentially important water reserves. To understand their current and future hydrological role, it is necessary to characterize their internal structure (e.g. internal boundaries and ice, air, water and rock content). In this study, we present the results and interpretations of profiles of electrical resistivity and refraction seismic tomography collected on two contrasting rock glaciers in the Chilean Andes located at the headwaters of the Elqui River within the Estero Derecho nature reserve. These geophysical measurements are interpreted both independently and jointly through a scheme of petrophysical four-phase inversion. These first in situ measurements in Estero Derecho confirm that El Ternero (intact rock glacier) contains a significant volume of ground ice, while El Jote contains little to no ice (relict rock glacier). Within our study, we highlight the strong differences in the geophysical responses between intact and relict rock glaciers and propose a diagnostic model that differentiates between them.

Semiarid Andean headwaters are key components of the hydrological system of north-central Chile as this is the main source of runoff which supports ecosystems and population located downstream. This study develops a conceptual hydrological model of the Chilean semiarid Andes headwaters, based on an integrative critical analysis of the current state of published research in the region. We combine a plethora of literature focused on isolated hydrological units including extensive literature on glacier and snowpack hydrological processes and less abundant literature on permafrost landforms, groundwater dynamics and other hydrological features. Among others, we identify important knowledge gaps related to the hydrogeomorphological understanding of permafrost area and its interaction with groundwater, as well as deep aquifer recharge and circulation. These two research topics are necessary next steps to better constrain model predictions of catchment response to future climatic scenarios associated with decreasing water contribution from glaciers and precipitation.