Subsurface storage drives drought propagation and recovery across climates and catchment properties

Abstract

<p>Extensive knowledge of hydrological processes occurring during droughts is required for a sustainable water resources management, especially in a changing climate. Large-sample analyses are particularly informative in this sense, because they allow us to extend the understanding beyond specific catchments. Data from experimental catchments and observatories showed that water stored within the catchment can sustain evapotranspiration and discharge during dry periods and previous multi-catchments studies on droughts highlighted the storage control on hydrological drought characteristics, through the quantification of hydrological signatures and catchment properties. However, few studies have explicitly quantified across different climates and catchment types the contribution of subsurface storage changes (ΔS) in the annual water balance, in drought propagation (from the meteorological to the hydrological one), and in drought recovery. Here, we assembled a dataset blending ground-based precipitation and discharge data, and remote-sensed actual evapotranspiration data to study drought propagation and recovery in a water-balance and data-based perspective for 102 catchments across various climatic and morphological properties in Italy. This region experienced severe drought years over the study period (hydrological years 2010 - 2019), as detected by the Standardised Precipitation Index for an accumulation period of 12 months. This large-sample analysis revealed that (i) subsurface storage is a non-negligible term in the annual water balance, as ΔS mean annual value represents on average the 11% of precipitation across the catchments, (ii) its depletion sustains discharge during drought years (median annual ΔS anomaly equal to -97 mm for catchments attenuating the hydrological drought with respect to the meteorological one), and (iii) it recovers from precipitation deficits over shorter time scales than evapotranspiration, but similar as those of discharge. These findings emphasize the need of explicitly considering subsurface storage in drought analyses to properly inform policy makers and water managers, as it is a key driver in drought propagation and recovery across climates and catchment properties.</p>

IT-SNOW: a snow reanalysis for Italy blending modeling, in-situ data, and satellite observations (2010–2021)

“…The second source of validation data considered here were in-situ data taken in Aosta Valley (north-western Italy, see Figure 5), Lombardia (northern Italy, see Figure 6), and Molise (central Italy, see Figure 7). These three areas present significantly different climates and thus snow types (Sturm and Liston, 2021) The third source of validation data were streamflow measurements for a selection of 102 basins in Italy for which long-term, serially complete, and quality-checked time-series of streamflow were available for the period 01/09/2010 through 31/08/2019 (Bruno et al, 2022). We used these data to compare annual peak SWE and annual cumulative streamflow at the closure section of these basins (both in Gm 3 ), as a proxy of the proportion of annual flow that was accumulated as snow.…”