Motamedi et al. (2026) Hydrometeorological and hydrogeological trends and drought dynamics in a cold-humid, coastal region

Identification

• Journal: Journal of Hydrology
• Year: 2026
• Date: 2026-10-01
• Authors: A. Motamedi, Nicole K. LeRoux, A.M.R. Hill, R.C. Jamieson, Lauren Somers, Barret L. Kurylyk
• DOI: 10.1016/j.jhydrol.2026.136507

Research Groups

• Department of Civil and Resource Engineering and Centre for Water Resources Studies, Dalhousie University, Nova Scotia, Canada

Short Summary

This study investigated hydrometeorological and hydrogeological drought dynamics in Nova Scotia, Canada, revealing that the fall season exhibits the most significant drying trends across the hydrological cycle, with droughts becoming more frequent and spatially extensive since 2016. Groundwater systems generally show rapid, strong correlations with meteorological and baseflow conditions but exhibit longer and more variable recovery times from drought events.

Objective

• To investigate hydrometeorological and hydrogeological drought using a paired approach linking groundwater level fluctuations to meteorological and hydrological (baseflow) conditions in a cold, humid, coastal climate.
• To analyze spatiotemporal trends in meteorological, hydrogeological, and hydrological variables and standardized indices.
• To explore how drought signals propagate across the atmosphere-aquifer-stream continuum, assess the strength and timing of cross-system relationships, and investigate the duration of drought events and recovery periods.
• To examine changing spatiotemporal drought patterns through geospatial layer analysis.

Study Configuration

• Spatial Scale: Province-wide in Nova Scotia, Canada, utilizing data from 32 observation wells, 15 climate stations, and 15 hydrometric stations.
• Temporal Scale: Primary analysis period of 17 years (2009-2025) with daily data; complementary long-term meteorological analysis for 41 years (1985-2025 water years).

Methodology and Data

• Models used:
  • Penman-Monteith equation (for Potential Evapotranspiration, PET)
  • Recursive filter method (Lyne and Hollick, 1979) for baseflow separation
  • Mann-Kendall trend test (with trend-free pre-whitening) and Sen’s slope
  • Standardized Groundwater Index (SGI), Standardized Precipitation Evapotranspiration Index (SPEI), Standardized Base Flow Index (SBFI)
  • Kernel density estimation
  • Two-sample Kolmogorov-Smirnov tests
  • Levene test
  • Pettitt test (for change point detection)
  • Cross-correlation analysis
• Data sources:
  • Daily groundwater level data: Nova Scotia Groundwater Observation Well Network (32 wells).
  • Daily precipitation, maximum/minimum air temperatures: Environment and Climate Change Canada (ECCC) climate stations (15 stations).
  • Relative humidity, wind speed, solar radiation: NASA POWER database.
  • Daily streamflow data: Water Survey of Canada HYDAT database (15 hydrometric stations).
  • Historical drought areas: Canadian Drought Monitor geospatial layers by Agriculture and Agri-Food Canada (AAFC).

Main Results

• The fall season exhibited the most significant and persistent negative trends across the hydrological cycle (net precipitation, baseflow, and groundwater level) from 2009-2025.
• Significant negative fall trends were identified in 67% of net precipitation records (mean Sen’s slope = -0.098 mm/yr), 60% of streamflow records, 40% of baseflow records (province-wide Sen’s slope = -0.10 m³/s/yr), and 25% of groundwater level records (mostly < 0.1 m/yr).
• Geospatial drought layer analysis revealed that more intensive droughts (D2, D3, D4 categories) are becoming more frequent and spatially extensive, particularly since 2016. D3 and D4 categories collectively covered over 50% of the province in September 2025.
• Kernel density analyses for summer and fall indicated significant shifts toward drier SPEI, SGI, and SBFI distributions (p < 0.05) after 2016, with increased variance.
• SGI exhibited strong correlations with SBFI (average > 0.6 for 50% of wells) and SPEI (average > 0.5 for 37% of wells).
• Most groundwater systems showed short lag times (< 1 month) for drought signal propagation across the atmosphere-aquifer-stream continuum (over 85% of observation wells).
• Drought durations were generally consistent across indices (1 to 10 months, mostly < 3 months), but groundwater recovery durations showed greater variability (coefficient of variation = 123%), with 66% of wells exceeding the 95th percentile (6.0 months) for SGI recovery.

Contributions

• Provides a comprehensive, integrated analysis of meteorological, hydrogeological, and hydrological drought dynamics in a cold, humid, coastal region (Nova Scotia), addressing a critical knowledge gap for such environments.
• Quantifies the propagation of drought signals and recovery dynamics across the atmosphere-aquifer-stream continuum, highlighting rapid responses but prolonged groundwater recovery.
• Identifies the fall season as a period of increasing drought risk and significant drying trends across the hydrological cycle, which is crucial for water management in cold regions.
• Demonstrates the increasing frequency and spatial extent of severe droughts in the region since 2016, offering insights into ongoing climate change impacts.
• Offers practical implications for water resource management, conservation practices, and climate adaptation strategies, particularly for groundwater-dependent communities and vulnerable aquifer types (e.g., shallow surficial aquifers).

Funding

• Sustainable Communities Challenge Fund (Nova Scotia Federation of Municipalities on behalf of the Province of Nova Scotia)
• Nova Scotia Department of Environment and Climate Change
• Natural Sciences and Engineering Research Council Alliance program (ALLRP 591830)
• Nova Scotia Graduate Scholarship program (A. Motamedi)
• Killam Trust (A. Motamedi)
• Canada Research Chairs Program (B. Kurylyk)
• NSERC Discovery Grant (RGPN-2018-05420 to B. Kurylyk)

Citation

@article{Motamedi2026Hydrometeorological,
  author = {Motamedi, A. and LeRoux, Nicole K. and Hill, A.M.R. and Jamieson, R.C. and Somers, Lauren and Kurylyk, Barret L.},
  title = {Hydrometeorological and hydrogeological trends and drought dynamics in a cold-humid, coastal region},
  journal = {Journal of Hydrology},
  year = {2026},
  doi = {10.1016/j.jhydrol.2026.136507},
  url = {https://doi.org/10.1016/j.jhydrol.2026.136507}
}