Elias et al. (2025) Drought feature assessment unravels how temperature increase has enhanced earlier and more severe drought in Lebanon over the last 60 years

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2025
• Date: 2025-11-13
• Authors: Georgie Elias, Georgia Majdalani, Ghaleb Faour, Florent Mouillot
• DOI: 10.1016/j.ejrh.2025.102930

Research Groups

• CEFE, Univ Montpellier, CNRS, EPHE, IRD, Montpellier, France
• National Center for Remote Sensing, National Council for Scientific Research (CNRS), Beirut, Lebanon

Short Summary

This study investigated how climate change from 1960 to 2020 affected various drought facets in Lebanon using the DFEAT tool, which analyzes daily soil moisture. It revealed a significant shift towards drier conditions, characterized by an earlier drought onset (up to 17 days) and a delayed offset (up to 5 days), primarily driven by rising temperatures despite stable annual precipitation.

Objective

• To investigate recent spatiotemporal trends in seven key drought features (onset, offset, duration, drying rate, peak drought timing and severity, and mean rainfall pulses intensity) from 1960 to 2020 across Lebanon.
• To explore how regional trends in climatic variables (air temperature and precipitation) differentially affect seasonal drought aspects, thereby revisiting previous assessments based solely on precipitation or standard anomalies.

Study Configuration

• Spatial Scale: Lebanon, Middle-East, at a 9 km pixel resolution.
• Temporal Scale: 1960–2020 (60 hydrological years), with sub-periods of 1960–1989 and 1990–2019 for breakpoint analysis.

Methodology and Data

• Models used: DFEAT (Drought FEature Assessment Tool), Keetch-Byram Drought Index (KBDI, Mediterranean-adapted version), Mann-Kendall test, Theil-Sen slope estimator.
• Data sources: ERA5-Land datasets for daily air temperature at 2 m and total precipitation.

Main Results

• A gradual shift toward drier conditions was observed across Lebanon from 1960 to 2020.
• Drought onset occurred significantly earlier, by 7 to 17 days in coastal and western mountainous areas, and by 40 to 150 days in eastern arid regions.
• Drought offset showed a slight delay of approximately 5 days along the coastal line, becoming more pronounced in some eastern arid parts (up to 45-360 days in 1990-2019 sub-period).
• Drought duration increased by approximately 15 days in coastal areas and by 50 to 135 days in eastern arid regions.
• Peak drought severity increased by around 3 mm in coastal areas and up to 15 mm in eastern arid parts.
• Soil moisture drying rates marginally increased, notably by +0.0016 mm·day⁻¹ per year in the humid western mountains.
• The intensity of autumnal rainfall pulses decreased by approximately 10 mm in southern coastal areas.
• Annual precipitation showed a non-significant decreasing trend (up to -70 mm in coastal areas), while annual mean air temperature significantly increased across all climatic zones (by +0.7 °C to +1.2 °C over 60 years).
• A regime shift in drought dynamics was identified around 1990, with a pronounced intensification of drought conditions during the 1990–2019 period.

Contributions

• First application of the DFEAT tool for operational drought trend monitoring, providing a multifaceted assessment of drought features.
• Offers novel insights into spatiotemporal drought trends in Mediterranean conditions by analyzing daily soil water content, overcoming limitations of traditional monthly-aggregated indices.
• Demonstrates that rising temperatures are the primary driver of drought intensification in Lebanon, even in the absence of statistically significant precipitation trends.
• Reveals specific climate change signals (e.g., earlier onset, increased drying rates, altered rainfall pulse intensity) that were previously obscured by coarser temporal resolution indices.
• Provides a more nuanced understanding of drought dynamics, which can inform adaptive management strategies for Lebanon's agro-environmental sectors.

Funding

• MENAFFIS specific action from IRD (granted to Florent Mouillot).
• Doctoral fellowship to Georgie Elias from the National Council for Scientific Research of Lebanon (CNRS-L), the French Embassy in Lebanon, and Campus France (SAFAR program).

Citation

@article{Elias2025Drought,
  author = {Elias, Georgie and Majdalani, Georgia and Faour, Ghaleb and Mouillot, Florent},
  title = {Drought feature assessment unravels how temperature increase has enhanced earlier and more severe drought in Lebanon over the last 60 years},
  journal = {Journal of Hydrology Regional Studies},
  year = {2025},
  doi = {10.1016/j.ejrh.2025.102930},
  url = {https://doi.org/10.1016/j.ejrh.2025.102930}
}

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