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Abstract. Potential impacts of global climate changes on the groundwater are largely unknown, especially for densely populated areas where groundwater is heavily exploited for public and industrial supply. Hence, to better plan and manage the 10 groundwater resources, medium-long term numerical modelling of groundwater flow, which takes into account climate change, population growth, and industrial and agricultural activities, is needed. The objective of this paper is to tackle three main issues: (1) the development of a robust hydro-stratigraphic model of a multi-aquifer system from a well logs database by means of a novel multi-dimensional approach which includes a hierarchical classification of the lithologies, the interpretation of crosssections, and the interpolation of aquifer boundary surfaces; (2) the parametrization and calibration of both a steady state and 15 a transient groundwater flow model, starting from empirical relationships (for unconfined aquifer) and step-drawdown and well tests (for semi-confined and confined aquifers) to define equivalent homogenous sub-units; and (3)

A comprehensive and reliable water balance of snow‐dominated alpine catchments is required for a holistic analysis of the hydrological and hydrogeological processes. A major limitation to the elaboration of this balance in alpine terrain is the difficulty of data acquisition as well as the limited presence of meteorological stations. Remotely sensed data can provide valuable information for the water balance assessment on a regional scale. We exploited Sentinel‐satellite data to estimate the groundwater storage for one hydrologic year in an extensive Alpine catchment located in northern Italy by means of the residual water balance approach. In particular, Evapotranspiration (ET) and Snow Water Equivalent were estimated with the combined use of Sentinel data, at a spatial resolution of 20 and 30 m, respectively. The results show that the adopted satellite‐based methods allow obtaining consistent and physically realistic values to describe the groundwater storage dynamics. In the period 2018–2020, a positive storage occurred only during the snowmelt period and the overall storage was negative, leading to a net lowering of the groundwater level in the floodplain. In addition, the influence of physiographic parameters (altitude, slope, and aspect) and seasonality on the estimates of ET and snow‐depth were investigated.

<p>The recognized evidence of global warming demands assessment of the present and future water cycle in Europe and worldwide. Recently, evidence of modified hydrological regime in the Alps under climate change has been documented. In particular, several studies (e.g. Bocchiola, 2014; Soncini et al. 2016) indicated an increase in hydrological flows in autumn and winter in response to snowfall trading with intense rainfall, shorter snow cover during winter, as well as decreased flows during dry spring and summer and large shrinking of glaciers at high altitude. However, according to the IPCC Fifth Assessment Report, it is still necessary to deepen our understanding of the impact of climate change and land use on groundwater recharge and levels in the alpine catchment areas (Cochand et al. 2019).</p><p>For this purpose, a water balance of the last three hydrogeological years (March 2017 - March 2020) was carried out on the Valtellina catchment (northern Italy, Central Italian Alps). This basin is a perfect case study for its wide unconfined aquifer in the floodplain, which makes it highly sensitive to this type of change. Moreover, the management of the water resource is of considerable importance, being crucial in a wide range of sectors (tourism, irrigation, domestic use, energy and industry).</p><p>Due to the extensive and diversified study area (26,000 km<sup>2</sup>) and the low ground data density (7 meteorological stations, 4 surface-water monitoring points, and 9 groundwater monitoring points), the water balance terms were estimated by exploiting and combining Earth Observation data products with ground data, also taking into account the geological and geomorphological characteristics of the basin. In particular, the evapotranspiration and the snow cover were provided, by MOD16A2 (MODIS/Terra Evapotranspiration 8-Day Level-4 Global 500m SIN Grid) and MOD10A2 (MODIS/Terra Snow Cover 8-Day L3 Global 500m SIN Grid, Version 6) satellite data, respectively.</p><p>As a result, the groundwater storage of a wet hydrogeological year compared with the groundwater storage of a dry hydrogeological year allowed analysing the sensitivity of groundwater resources to climate change.</p><p> </p><p>Bocchiola, D.: Long term (1921–2011) Hydrological regime of Alpine catchments in Northern Italy. Advances in Water Resources, 70, 51-64, 2014.</p><p>Cochand, M., Christe, P., Ornstein, P., & Hunkeler, D.: Groundwater storage in high alpine catchments and its contribution to streamflow. Water Resources Research, 55(4), 2613-2630, 2019.</p><p>Soncini, A., Bocchiola, D., Confortola, G., Minora, U., Vuillermoz, E., Salerno, F., Viviano, G., Shrestha, D., Senese, A., Smiraglia, C. and Diolaiuti, G.A.: Future hydrological regimes and glacier cover in the Everest region: The case study of the upper Dudh Koshi basin. Science of the Total Environment, 565, 1084-1101, 2016.</p>

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