Nawaz et al. (2026) Integrating Meteorological and GRACE-Based Indices to Assess Groundwater Drought Under Climate Change in Data-Scarce Mediterranean Basins

Identification

Journal: Earth Systems and Environment
Year: 2026
Date: 2026-02-21
Authors: Ayesha Nawaz, Maria Rosaria Alfio, M. Casarci, Gaetano DanieleFiorese, Hussein Hoteit, Gabriella Balacco
DOI: 10.1007/s41748-026-01085-8

Research Groups

Department of Civil, Environmental, Land, Construction and Chemistry (DICATECh), Polytechnic University of Bari, Bari 70125, Italy
ICU Istituto per la Cooperazione Universitaria HQ Nexus Dept, Roma, Italy
Department of Soil, Plant and Food Sciences (DISSPA), University of Bari Aldo Moro, Bari 70125, Italy
ICU Istituto per la Cooperazione Universitaria, Beiruth, Lebanon

Short Summary

This study integrates satellite-derived data (CHIRPS, CHIRTS-ERA5, GRACE) to investigate the relationship between meteorological (SPI, SPEI) and hydrogeological (GGDI) drought indicators in Lebanon, particularly the Al Assi River Basin, under climate change scenarios, revealing a projected increase in groundwater drought severity by the late 21st century.

Objective

To investigate the relationship between the Standardized Precipitation Index (SPI) and the Standardized Precipitation and Evapotranspiration Index (SPEI), derived from CHIRPS precipitation and CHIRTS air temperature datasets, and the Groundwater Drought Index (GGDI) from GRACE/GRACE-FO.
To assess the potential of these satellite-based products as tools for drought monitoring and water resource management under climate change conditions.
To provide initial insights into the hydrogeological dynamics of the Al Assi River Basin.

Study Configuration

Spatial Scale: Lebanon, with emphasis on the Al Assi River Basin (ARB, 2022 km²). Data harmonized/downscaled to a 10 km resolution.
Temporal Scale:
- Historical: CHIRPS (1991–2025), CHIRTS-ERA5 (1991–2024), GRACE (April 2002–June 2017). Baseline for SPI/SPEI (1991–2025/2024), for GGDI (2002-04 to 2017-06). RCM historical (1981–2005).
- Future Projections: 2006–2100, divided into short-term (2030–2050), mid-term (2060–2080), and long-term (2080–2100).

Methodology and Data

Models used:
- Standardized Precipitation Index (SPI)
- Standardized Precipitation and Evapotranspiration Index (SPEI) (Thornthwaite method for PET)
- Groundwater Drought Index (GGDI)
- Random Forest (RF) for GRACE downscaling
- CNRM-ALADIN53 Regional Climate Model (RCM) from EUR-CORDEX framework
- Quantile Delta Mapping (QDM) for bias correction
Data sources:
- Satellite/Observation:
  - CHIRPS (Climate Hazards Group Infrared Precipitation with Stations) for precipitation (0.05° resolution).
  - CHIRTS-ERA5 (Climate Hazards Center InfraRed Temperature with Stations ERA5) for temperature (0.05° resolution).
  - GRACE and GRACE Follow-On (GRACE-FO) for Terrestrial Water Storage Anomaly (TWSA) (55.5 km resolution).
  - MOD21C3.061 Terra for Land Temperature (1000 m).
  - MOD13A2.061 Terra for NDVI (1000 m).
- Reanalysis/Land Surface Models (for TWSA decomposition and RF predictors):
  - FLDAS Noah v01 (Famine Early Warning System Network Land Data Assimilation System) for Soil Moisture Storage Anomaly (SMSA), Snow Water Equivalent Anomaly (SWEA), Surface Water Storage Anomaly (SWSA) (10 km resolution).
  - GLDAS-2.1 (NASA Global Land Data Assimilation System) for Canopy Water Storage Anomaly (CWSA) (27 km resolution, resampled to 10 km).
  - ERA5-Land for precipitation, evaporation, runoff, air temperature (11.132 km resolution).

Main Results

SPEI at 18-month accumulation (SPEI-18) exhibits the highest correlation with GGDI (Pearson R ≈ 0.70) at zero lag in the ARB, reflecting the response of the multi-layered aquifer system. Nationally, R ≈ 0.60–0.67.
The maximum percentage area of ARB with a correlation coefficient greater than 0.6 is 96.7% for SPEI-18 at zero lag.
Future projections under RCP 4.5 and RCP 8.5 scenarios indicate a progressive increase in drought-affected areas and severity.
Average temperatures in the ARB are projected to increase by 1.4 °C (RCP 4.5) and 2.1 °C (RCP 8.5) by 2100.
Precipitation in the ARB is projected to decline by 1.3% (RCP 4.5) and 14.1% (RCP 8.5) by 2100, compared to the historical period (1981–2005).
Under RCP 8.5, extreme drought conditions for SPEI-18 are projected to reach 6% in the 2080–2100 period, with wet period classes disappearing.
For GGDI, mild drought increases from 12% to 30% under RCP 4.5 and from 19.8% to 31.8% under RCP 8.5 by 2100. Moderate drought increases from 4.8% to 9.9% (RCP 4.5) and from 4.4% to 15.8% (RCP 8.5). Severe drought reaches 4.0% under RCP 8.5 by 2100.
The percentage of drought-affected areas (SPEI-18) ranges from 23.3% (RCP 4.5) to 25.8% (RCP 8.5) for 2030–2100. For GGDI, it ranges from 11.8% (RCP 4.5) to 13.1% (RCP 8.5) for the same period.

Contributions

Demonstrates the effectiveness of integrating satellite-derived data (CHIRPS, CHIRTS-ERA5, GRACE) and drought indices (SPI, SPEI, GGDI) for robust climate-water assessment in data-scarce Mediterranean regions like Lebanon.
Provides initial insights into the hydrogeological dynamics of the Al Assi River Basin by characterizing the relationship and lag between meteorological and groundwater droughts.
Highlights SPEI-18 as the most robust proxy for GRACE-based groundwater drought (GGDI) in the multi-layered ARB aquifer system.
Generates future projections of groundwater drought under climate change scenarios (RCP 4.5 and 8.5) for Lebanon, underscoring the urgent need for integrated water resource management.
Offers a valuable framework for monitoring groundwater stress and informing climate-responsive water management strategies in regions with limited in-situ observational networks.

Funding

WATER4MED Project (https://water4med.com/)
PRIMA Programme (Partnership for Research and Innovation in the Mediterranean Area)
National funding agencies of MIUR (Italian Ministry of University and Research)
Politecnico di Bari (Open access funding within the CRUI-CARE Agreement)

Citation

@article{Nawaz2026Integrating,
  author = {Nawaz, Ayesha and Alfio, Maria Rosaria and Casarci, M. and DanieleFiorese, Gaetano and Hoteit, Hussein and Balacco, Gabriella},
  title = {Integrating Meteorological and GRACE-Based Indices to Assess Groundwater Drought Under Climate Change in Data-Scarce Mediterranean Basins},
  journal = {Earth Systems and Environment},
  year = {2026},
  doi = {10.1007/s41748-026-01085-8},
  url = {https://doi.org/10.1007/s41748-026-01085-8}
}

Original Source: https://doi.org/10.1007/s41748-026-01085-8