The hyperarid Atacama Desert coast receives scarce moisture inputs mainly from the Pacific Ocean in the form of marine advective fog. The collected moisture supports highly specialized ecosystems, where the bromeliad Tillandsia landbeckii is the dominant species. The fog and low clouds (FLCs) on which these ecosystems depend are affected in their interannual variability and spatial distribution by global phenomena, such as ENSO. Yet, there is a lack of understanding of how ENSO influences recent FLCs spatial changes and their interconnections and how these variations can affect existing Tillandsia stands. In this study, we analyze FLCs occurrence, its trends and the influence of ENSO on the interannual variations of FLCs presence by processing GOES satellite images (1995–2017). Our results show that ENSO exerts a significant influence over FLCs interannual variability in the Atacama at ~ 20°S. Linear regression analyses reveal a relation between ENSO3.4 anomalies and FLCs with opposite seasonal effects depending on the ENSO phase. During summer (winter), the ENSO warm phase is associated with an increase (decrease) of the FLCs occurrence, whereas the opposite occurs during ENSO cool phases. In addition, the ONI Index explains up to ~ 50 and ~ 60% variance of the interannual FLCs presence in the T. landbeckii site during summer and winter, respectively. Finally, weak negative (positive) trends of FLCs presence are observed above (below) 1000 m a. s. l. These results have direct implications for understanding the present and past distribution of Tillandsia ecosystems under the extreme conditions characterizing our study area.

We investigate the influence of regional atmospheric circulation on the evaporation of a saline lake in the Altiplano (also known as the Andean Plateau) region of the Atacama Desert. For that, we conducted a field experiment in the Salar del Huasco (SDH) basin (135 km east of the Pacific Ocean), in November 2018. The measurements were based on surface energy balance (SEB) stations and airborne observations. Additionally, we simulate the meteorological conditions on a regional scale using the Weather Research and Forecasting Model. Our findings show two evaporation regimes: (1) a morning regime controlled by local conditions, in which SEB is dominated by the ground heat flux (∼0.5 of net radiation), very low evaporation (L_vE<30 W m⁻²) and wind speed <1 m s⁻¹; and (2) an afternoon regime controlled by regional-scale forcing that leads to a sudden increase in wind speed (>15 m s⁻¹) and a jump in evaporation to >500 W m⁻². While in the morning evaporation is limited by very low turbulence ($u^{*}\sim \mathrm{0.1}$ m s⁻¹), in the afternoon strong winds ($u^{*}\sim \mathrm{0.65}$ m s⁻¹) enhance mechanical turbulence, increasing evaporation. We find that the strong winds in addition to the locally available radiative energy are the principal drivers of evaporation. These winds are the result of a diurnal cyclic circulation between the Pacific Ocean and the Atacama Desert. Finally, we quantify the advection and entrainment of free-tropospheric air masses driven by boundary layer development. Our research contributes to untangling and linking local- and regional-scale processes driving evaporation across confined saline lakes in arid regions.

We investigate how evaporation changes depending on the scales in the Altiplano region of the Atacama Desert. More specifically, we focus on the temporal evolution from the climatological to the sub-diurnal scales on a high-altitude saline lake ecosystem. We analyze the evaporation trends over 70 years (1950–2020) at a high-spatial resolution. The method is based on the downscaling of 30 km ERA5 reanalysis data at hourly resolution to 0.1 km spatial resolution data, using artificial neural networks to analyze the main drivers of evaporation. To this end, we use the Penman open-water evaporation equation, modified to compensate for the energy balance non-closure and the ice cover formation on the lake during the night. Our estimation of the hourly climatology of evaporation shows a consistent agreement with eddy-covariance (EC) measurements and reveals that evaporation is controlled by different drivers depending on the time scale. At the sub-diurnal scale, mechanical turbulence is the primary driver of evaporation, and at this scale, it is not radiation-limited. At the seasonal scale, more than 70 % of the evaporation variability is explained by the radiative contribution term. At the same scale, and using a large-scale moisture tracking model, we identify the main sources of moisture to the Chilean Altiplano. In all cases, our regime of precipitation is controlled by large-scale weather patterns closely linked to climatological fluctuations. Moreover, seasonal evaporation significantly influences the saline lake surface spatial changes. From an interannual scale perspective, evaporation increased by 2.1 mm yr⁻¹ during the entire study period, according to global temperature increases. Finally, we find that yearly evaporation depends on the El Niño–Southern Oscillation (ENSO), where warm and cool ENSO phases are associated with higher evaporation and precipitation rates, respectively. Our results show that warm ENSO phases increase evaporation rates by 15 %, whereas cold phases decrease it by 2 %.

In the endorheic basins of the Altiplano, water is crucial for sustaining unique ecological habitats. Here, the wetlands act as highly localized evaporative environments, and little is known about the processes that control evaporation. Understanding evaporation in the Altiplano is challenging because these environments are immersed in a complex topography surrounded by desert and are affected by atmospheric circulations at various spatial scales. Also, these environments may be subject to evaporation enhancement events as the result of dry air advection. To better characterize evaporation processes in the Altiplano, the novel Evaporation caused by Dry Air Transport over the Atacama Desert (E-DATA) field campaign was designed and tested at the Salar del Huasco, Chile. The E-DATA combines surface and airborne measurements to understand the evaporation dynamics over heterogeneous surfaces, with the main emphasis on the open water evaporation. The weather and research forecasting model was used for planning the instruments installation strategy to understand how large-scale air flow affects evaporation. Instrumentation deployed included: meteorological stations, eddy covariance systems, scintillometers, radiosondes and an unmanned aerial vehicle, and fiber-optic distributed temperature sensing. Additional water quality and CO₂ fluxes measurements were carried out to identify the link between meteorological conditions and the biochemical dynamics of Salar del Huasco. Our first results show that, in the study site, evaporation is driven by processes occurring at multiple spatial and temporal scales and that, even in the case of available water and energy, evaporation is triggered by mechanical turbulence induced by wind.

Estimating lake evaporation is a challenge due to both practical considerations and theoretical assumptions embedded in indirect methods. For the first time, we evaluated measurements from an optical microwave scintillometer (OMS) system over an open water body under arid conditions. The OMS is a line-of-sight remote sensing technique that can be used to measure the sensible- and latent heat fluxes over horizontal areas with path lengths ranging from 0.5-10 km. We installed an OMS at a saline lake surrounded by a wet-salt crust in the Salar del Huasco, a heterogeneous desert landscape in the Atacama Desert. As a reference, we used Eddy Covariance systems installed over the two main surfaces in the OMS footprint. We performed a footprint analysis to reconstruct the surface contribution to the OMS measured fluxes (80% water and 20% wet-salt). Furthermore, we investigated the applicability of the Monin-Obukhov Similarity Theory (MOST) which was needed to infer fluxes from the OMS-derived structure parameters to the fluxes. The OMS structure parameters and MOST were compromised, which We mitigated by fitting MOST coefficients to the site conditions. We argue that the MOST deviation from values found in the literature due to the effects of the surface heterogeneity and the non-local processes induced by regional circulation. With the available data set we were not able to rule out instrument issues, such as additional fluctuations to the scintillation signal due to absorption or the effect of vibration in high wind conditions. The adjusted MOST coefficients lowered by a factor of 1.64 compared to using standard MOST coefficients. For H and L _v E, we obtained zero-intercept linear regressions with correlations, R², of 0.92 and 0.96, respectively. We conclude that advances in MOST are needed to successfully apply the OMS method in landscapes characterized by complex heterogeneity such as the Salar del Huasco. Estimating lake evaporation is a challenge due to both practical considerations and theoretical assumptions embedded in indirect methods. For the first time, we evaluated measurements from an optical microwave scintillometer (OMS) system over an open water body under arid conditions. The OMS is a line-of-sight remote sensing technique that can be used to measure the sensible- and latent heat fluxes over horizontal areas with path lengths ranging from 0.5-10 km. We installed an OMS at a saline lake surrounded by a wet-salt crust in the Salar del Huasco, a heterogeneous desert landscape in the Atacama Desert. As a reference, we used Eddy Covariance systems installed over the two main surfaces in the OMS footprint. We performed a footprint analysis to reconstruct the surface contribution to the OMS measured fluxes (80% water and 20% wet-salt). Furthermore, we investigated the applicability of the Monin-Obukhov Similarity Theory (MOST) which was needed to infer fluxes from the OMS-derived structure parameters to the fluxes. The OMS structure parameters and MOST were compromised, which We mitigated by fitting MOST coefficients to the site conditions. We argue that the MOST deviation from values found in the literature due to the effects of the surface heterogeneity and the non-local processes induced by regional circulation. With the available data set we were not able to rule out instrument issues, such as additional fluctuations to the scintillation signal due to absorption or the effect of vibration in high wind conditions. The adjusted MOST coefficients lowered by a factor of 1.64 compared to using standard MOST coefficients. For H and L _v E, we obtained zero-intercept linear regressions with correlations, R², of 0.92 and 0.96, respectively. We conclude that advances in MOST are needed to successfully apply the OMS method in landscapes characterized by complex heterogeneity such as the Salar del Huasco.