Ioniță et al. (2025) Multi-Indicator Drought Variability in Europe (1766–2018)

Identification

• Journal: Forests
• Year: 2025
• Date: 2025-11-18
• Authors: Monica Ioniță, Patrick Scholz, Viorica Nagavciuc
• DOI: 10.3390/f16111739

Research Groups

• Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany.
• Forest Biometrics Laboratory, Faculty of Forestry, “Stefan cel Mare” University of Suceava, Romania.
• Helmholtz Association (Changing Earth—Sustaining our Future program).
• Helmholtz Climate Initiative REKLIM.

Short Summary

This study compares three long-term European drought reconstructions (PDSI, SPEI, and SMI) from 1766 to 2018, finding that the identification of "extreme" drought years and decades varies significantly depending on the indicator used. While the 2015–2018 event was exceptional in several metrics, its "unprecedented" status is indicator- and region-dependent, though all indicators consistently link drought to large-scale atmospheric blocking.

Objective

• To perform a cross-validated analytical characterization of short-term and multi-year drought events in Europe using three independent reconstructions.
• To identify similarities and discrepancies between drought indicators (PDSI, SPEI, and SMI) in capturing the magnitude and spatial extent of extreme events.
• To determine the large-scale atmospheric circulation patterns (e.g., geopotential height at 500 hPa) associated with European drought variability.

Study Configuration

• Spatial Scale: European continent (0.5° × 0.5° grid resolution), with regional focus on the Mediterranean (MED), Central Europe (CEU), and Northern Europe (NEU).
• Temporal Scale: Primary common period of 1766–2018; extended analyses for PDSI (1401–2018) and SPEI (1601–2018).

Methodology and Data

• Models used:
  • mHM (mesoscale Hydrologic Model): Used to simulate root-zone soil moisture for the SMI reconstruction.
  • Principal Components Regression (PCR): Used for the PDSI reconstruction (Old World Drought Atlas).
  • Point-by-Point Regression (PPR): Used for the SPEI reconstruction based on tree-ring isotopes.
• Data sources:
  • Tree-ring width: Old World Drought Atlas (OWDA) for PDSI.
  • Stable isotopes: $\delta^{18}O$ and $\delta^{13}C$ from tree rings for SPEI.
  • Climate Data: CRU TS v4.07, E-OBS v21 (precipitation and temperature).
  • Reanalysis: EKF400v2 (paleoclimate reanalysis for geopotential height at 500 hPa).

Main Results

• Interannual Extremes: The driest years differ by indicator: 1874 for PDSI (Magnitude [M] = −1.97; Area [A] = 64.4%), 2003 for SPEI (M = −1.16; A = 90.1%), and 1868 for SMI (M = 0.21; A = 83.4%).
• Decadal Extremes: The driest decades diverge: PDSI identifies 1941–1950 (M = −0.82; A = 42.1%), SPEI highlights 2011–2018 (M = −0.36; A = 46.6%), and SMI points to 1781–1790.
• Trends: A significant European-scale increase in drought-affected area was found for SMI (+0.52% per decade, $p < 0.05$). Regional increases in drought area were noted for the Mediterranean in SMI (~+1.1% per decade) and Central Europe in both SPEI (+0.42% per decade) and SMI (+0.6% per decade).
• Atmospheric Drivers: Canonical Correlation Analysis (CCA) shows a strong link ($r = 0.82, p < 0.001$) between summer drought and 500 hPa geopotential height (Z500), specifically associating drought with atmospheric blocking patterns.

Contributions

• This is the first study to simultaneously analyze and cross-validate three distinct long-term drought reconstructions (meteorological, agricultural, and hydrological) over a common multi-century period in Europe.
• It reconciles conflicting literature regarding the "unprecedented" nature of recent droughts (e.g., 2015–2018) by demonstrating how physical sensitivities (such as SPEI’s sensitivity to potential evapotranspiration) and proxy types influence drought rankings.
• The research underscores the necessity of a multi-indicator framework for climate-resilient water management and historical climate assessment.

Funding

• Ministry of Research, Innovation and Digitization (Romania), National Recovery and Resilience Plan, project "Compound extreme events from a long-term perspective and their impact on forest growth dynamics (CExForD)" (number 760074/23.05.2023, code 287/30.11.2022).
• Helmholtz Association (Changing Earth—Sustaining our Future program).
• Helmholtz Climate Initiative REKLIM.

Citation

@article{Ioniță2025MultiIndicator,
  author = {Ioniță, Monica and Scholz, Patrick and Nagavciuc, Viorica},
  title = {Multi-Indicator Drought Variability in Europe (1766–2018)},
  journal = {Forests},
  year = {2025},
  doi = {10.3390/f16111739},
  url = {https://doi.org/10.3390/f16111739}
}

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