Investigating the feasibility of using precipitation measurements from weather radar to estimate recharge in regional aquifers: the Majella massif case study in central Italy

The measurement of precipitation, based on traditional rain gauges, exhibits many limitations due to the spatial and temporal high variability of atmospheric precipitation. In the past decades, the use of ground-based microwave weather radar has greatly improved the quantitative rainfall estimation by providing spatially continuous estimates of rainfall, at high temporal (i.e., few minutes) and spatial resolution (i.e., hundreds of meters). Furthermore, weather radar data have also proved to be relatively reliable in mountainous areas (Vulpiani et al., 2012). These paramount features of radar-derived precipitation data could definitely improve the estimation of recharge of aquifers, which generally rely on geospatializations (e.g., Thiessen polygons) of rainfall data, collected by a sparse rain gauge network. In regional aquifers, the rain gauge network is often lacking at high altitude (i.e., recharge areas), introducing additional uncertainty in the inflow volumes. Indeed, weather radar rainfall estimation is also affected by various sources of error, comprehensively discussed in literature (Collier, 1996), that can be reduced by proper post-processing; however, uncertainties still remain, especially for surface rain rate estimations. Based on these considerations, this study is aimed at evaluating the feasibility of using radar-based precipitation data to estimate aquifer recharge and calculate a detailed water balance in the areas characterized by high elevations, such as the Majella massif (Nanni and Rusi, 2003). To address this objective, the Majella aquifer water balance has been calculated in the 2017-2018 period using both radar-based precipitation data and rain gauge data as well as adopting different methods (i.e., Turc, and Thornthwaite). Although intrinsically uncertain, the radar-based precipitation data provided robust results, pointed out by the comparison with water balance, obtained by rain gauge data, and the Majella aquifer total discharge. This interdisciplinary work may pave the way for continuous monitoring of aquifer recharge at very high temporal and spatial resolution.