Ortenzi et al. (2026) Exploring groundwater-surface water interactions and recharge in fractured mountain systems: an integrated approach

Identification

• Journal: Hydrology and earth system sciences
• Year: 2026
• Date: 2026-03-31
• Authors: Sofia Ortenzi, Lucio Di Matteo, Daniela Valigi, Marco Donnini, Marco Dionigi, Davide Fronzi, Josie Geris, Fabio Guadagnano, Ivan Marchesini, Paolo Filippucci, Francesco Avanzi, Daniele Penna, Christian Massari
• DOI: 10.5194/hess-30-1755-2026

Research Groups

• Department of Physics and Geology, University of Perugia, Italy
• National Research Council, Research Institute for Geo-Hydrological Protection, Italy
• Department of Science and Matter Engineering, Environment, and Urban Planning, Marche Polytechnic University, Italy
• School of Geosciences, University of Aberdeen, UK
• CIMA Research Foundation, Italy
• Department of Agriculture, Food, Environment and Forestry, University of Florence, Italy
• Forest Engineering Resources and Management Department, Oregon State University, USA

Short Summary

This study developed an integrated approach to map groundwater-surface water interactions and quantify aquifer recharge in a fractured Mediterranean mountain catchment. By combining multi-source data, the research revealed significant groundwater contributions to streamflow, identified distinct hydrogeological sources, and quantified snowmelt's substantial role (approximately 18%) in aquifer recharge.

Objective

• To improve the quantification of groundwater inflow to streams and the delineation of recharge areas in fractured mountain systems by integrating Earth Observation (EO) data, in situ observations, and environmental tracers.
• To determine the role of snow accumulation and melt in controlling aquifer recharge and sustaining dry-season baseflow in Central Apennine carbonate catchments.

Study Configuration

• Spatial Scale: Ussita stream catchment (44 km²), Central Apennine Ridge, Italy. Mean altitude of 1315 m above sea level, ranging from 645 m to 2256 m above sea level.
• Temporal Scale: Hydrological data collected from 2019 to 2024 (streamflow), 2022 to 2025 (spot discharge), November 2023 to March 2025 (hydrochemical/isotopic), and January/July 2025 (thermal drone). Water budget analysis covered the 2019–2023 period.

Methodology and Data

• Models used:
  • One-parameter recursive digital filter (Lyne and Hollick, 1979) for baseflow separation.
  • Maillet equation for stream recession analysis.
  • Korkmaz (1990) method for estimating water storage changes (ΔS).
  • Thornthwaite-Mather (T-M) method for evapotranspiration (ET) estimation.
  • Water budget equations (Eqs. 3-7) for quantifying water balance components and recharge area.
  • Linear regression for Local Meteoric Water Line (LMWL) and δ¹⁸O–elevation relationship.
  • Stefan–Boltzmann equation for thermal drone data calibration.
• Data sources:
  • In-situ observations: Daily stream levels (S2, S5), spot discharge measurements (S1, S3, S4, S5) using OTT MF Pro flow meter, ground-based weather stations (temperature, rainfall, snow depth).
  • Hydrochemical and Isotopic analyses: Major soluble ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, SO₄²⁻, Cl⁻, HCO₃⁻) and stable water isotopes (δD, δ¹⁸O) from stream and precipitation samples.
  • Tracer tests: Instantaneous release of Sodium fluorescein (Na-Fluorescein) tracked by PME fluorometric probe.
  • Thermal drone surveys: DJI MAVIC 2 ENTERPRISE Dual drone with integrated thermal sensor for surface water temperature mapping.
  • Satellite-based meteorological datasets:
    • Precipitation (P): Modified Conditional Merging (MCM), European Reanalysis 5th generation (ERA5-Land), Multi-satellitE Retrievals for Global Precipitation Measurements (GPM IMERG) – Final run.
    • Snow Water Equivalent (SWE): IT-SNOW dataset.
    • Evapotranspiration (ET): MOD16A2 (MODIS), EUMETSAT LSA SAF, Global Land Evaporation Amsterdam Model (GLEAM), ECOSTRESS.
  • Regional hydrological dataset: BIGBANG 8.0 dataset for nationwide GIS-based hydrological budget.

Main Results

• Streamflow analysis revealed a significant increase in baseflow between sections S3 and S5, with mean groundwater inflow estimated at approximately 650 L/s (OTT MF Pro) to 695 L/s (tracer test).
• The Base Flow Index (BFI) increased from approximately 0.80 in the upper catchment (S2) to 0.90 at the catchment outlet (S5), indicating a dominant and increasing groundwater contribution downstream.
• Thermal drone surveys identified groundwater inflows as warmer anomalies (1–2 °C) entering the stream from specific points (I1, I2) and diffuse sources, particularly evident during winter.
• Hydrochemical and isotopic analyses distinguished two main groundwater sources: the Maiolica Complex (EC ≈ 210 µS/cm, SO₄ ≈ 2.5 mg/L) feeding the upper stream, and the Basal Limestone Complex (EC ≈ 310 µS/cm, SO₄ ≈ 18.7 mg/L) interacting with underlying Evaporites Complex, contributing to the lower stream.
• Stream water samples showed generally positive line-conditioned excess (mean 2.75 ‰), indicating rapid infiltration and minimal evaporative fractionation.
• Isotope Recharge Elevation (CIRE) estimates ranged from 1672–1855 m above sea level for the upper stream (S1) to 1960–2193 m above sea level for the catchment outlet (S5), consistent with recharge in high-altitude areas.
• Multi-source water budget analysis (2019–2023) without snowmelt indicated a potential hydrogeological catchment area of 51.98 ± 4.08 km², larger than the topographic catchment (44.06 km²), with approximately 22% of stream discharge originating from outside groundwater inflow.
• When snowmelt was explicitly included in the water budget, the estimated hydrogeological catchment area (42.97 ± 4.09 km²) was similar to the topographic catchment, implying negligible net groundwater exchanges with external systems.
• Snowmelt contributed approximately 18% to aquifer recharge during the 2019–2023 period.
• The specific groundwater discharge for the Ussita catchment was estimated at approximately 22 L s⁻¹ km⁻².

Contributions

• Developed and demonstrated a novel integrated methodological framework combining remote sensing, in situ hydrometeorological monitoring, streamflow observations, and environmental tracers to quantify groundwater inflow and delineate recharge areas in data-scarce fractured mountain carbonate regions.
• Provided a detailed spatial mapping of groundwater-surface water interaction zones, including those obscured by vegetation, which are difficult to identify with traditional methods.
• Quantified the significant contribution of snowmelt (approximately 18%) to aquifer recharge in a Mediterranean mountain environment, addressing a knowledge gap in such regions.
• Constrained the water budget closure and recharge area extent by explicitly accounting for both rainfall and snowmelt contributions using an ensemble of multi-source datasets.
• Offered a transferable workflow that can guide and optimize field campaigns in similar data-scarce mountainous carbonate catchments facing increasing drought stress, supporting water resource management and climate-related risk mitigation.

Funding

• Resilience and vulnerability of water resources under drought conditions – new insights from integrated in-situ and remote sensing approaches revolution (REVULUTION, 2023–2025), Joint Bilateral Agreement CNR/Royal Society of London (UK) Biennial Programme 2023–2025 (IEC/R2/232027)
• Hydrological Controls on Carbonate-mediated CO2 Consumption – Hydro4C (code 2022PFNNRSPE10PRIN2022, Protocol 2022PFNNRS), funded by the European Union – Next Generation EU (CUP J53D23002840006, Protocollo 2022PFNNRS)
• Unravelling interactions between WATER and carbon cycles during drought and their impact on water resources and forest and grassland ecosySTEMs in the Mediterranean climate – WATERSTEM (PRIN2020, code: 20202WF53Z), funded by the Italian Ministry of University and Research (MUR)
• Analisi dei processi idrogeologici ed idromorfologici nel contesto dei cambiamenti climatici ed antropici (grant number RICATENEO2024DIMATTEO)

Citation

@article{Ortenzi2026Exploring,
  author = {Ortenzi, Sofia and Matteo, Lucio Di and Valigi, Daniela and Donnini, Marco and Dionigi, Marco and Fronzi, Davide and Geris, Josie and Guadagnano, Fabio and Marchesini, Ivan and Filippucci, Paolo and Avanzi, Francesco and Penna, Daniele and Massari, Christian},
  title = {Exploring groundwater-surface water interactions and recharge in fractured mountain systems: an integrated approach},
  journal = {Hydrology and earth system sciences},
  year = {2026},
  doi = {10.5194/hess-30-1755-2026},
  url = {https://doi.org/10.5194/hess-30-1755-2026}
}