Veysi et al. (2026) Spatiotemporal dynamics of single and compound drought–heatwave extremes impacts on water productivity

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2026
• Date: 2026-04-02
• Authors: Shadman Veysi, Milad Nouri
• DOI: 10.1016/j.ejrh.2026.103370

Research Groups

Soil and Water Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran

Short Summary

This study investigated the spatiotemporal impacts of single and compound drought-heatwave extremes on agricultural water productivity (WP) in Iran over 30 years, revealing that Compound Drought–Heatwave Extremes (CDHEs) pose the most significant threat, causing substantial WP declines (13.5% in irrigated and 27.4% in rainfed systems).

Objective

• To identify the most suitable drought indicator for capturing agricultural water productivity (WP) variability in Iran.
• To evaluate the spatial and temporal trends of single (drought, heatwave) and compound (drought-heatwave) climate extremes.
• To assess the differential impact of these extremes on WP across various agricultural land-use types (irrigated, rainfed, fallow).

Study Configuration

• Spatial Scale: Entire territory of Iran (approximately 1,650,000 square kilometers), analyzed on a 0.1 degree (approximately 11 kilometers) grid.
• Temporal Scale: Data analyzed for two periods: 1995–2024 (30 years) and 2010–2024 (15 years).

Methodology and Data

• Models used:
  • Standardized Precipitation Evapotranspiration Index (SPEI-6) for drought conditions.
  • FAO-56 Penman–Monteith formulation for calculating reference evapotranspiration (ET₀).
  • Log-logistic probability distribution for SPEI standardization.
  • Coefficient of determination (R²) for vulnerability assessment.
  • Sen’s slope trend analysis for spatiotemporal trends.
  • One-way Analysis of Variance (ANOVA) for statistical significance.
• Data sources:
  • ERA5-Land reanalysis (daily meteorological variables: precipitation, maximum/minimum temperature).
  • FAO’s WaPOR platform (annual water productivity (WP) data, Land Use/Land Cover (LULC) data v2).
  • Copernicus Global Land Service land cover map (basis for LULC data).

Main Results

• The Standardized Precipitation Evapotranspiration Index at a 6-month timescale (SPEI-6) was identified as the most robust indicator for capturing agricultural water productivity (WP) variability in Iran's arid agroecosystems.
• Drought, heatwave, and compound drought–heatwave extreme (CDHE) frequencies intensified significantly over the past 15 years (2010–2024), with emerging hotspots in central Iran and the Zagros Mountains.
• Irrigation effectively buffers croplands against meteorological drought, maintaining WP near normal levels (0.8% anomaly under severe drought), whereas rainfed systems experience severe WP losses (21.4% decline under severe drought).
• Heatwaves alone present a complex stressor; mild heat can lead to a positive WP anomaly in irrigated systems (+9.4%), but very high heat probability results in slight negative anomalies for irrigated systems (-0.3%) and significant declines for rainfed systems (-13.5%).
• Compound Drought–Heatwave Extremes (CDHEs) create a synergistic stress, causing substantial WP declines: 13.5% in irrigated zones and a catastrophic 27.4% in rainfed systems.
• Fallow land exhibited the highest normalized frequency of CDHEs, while irrigated areas experienced some of the most intense singular heatwaves.
• Annual WP anomalies showed a significant increasing trend for irrigated agriculture (+2.084% year⁻¹) and a moderate upward trend for rainfed systems (+1.403% year⁻¹), primarily driven by water availability limitations rather than enhanced management. Fallow areas showed a negative, non-significant trend (-1.257% year⁻¹).

Contributions

• Provides a systematic and integrated evaluation of the impacts of single and compound climate extremes on agricultural water productivity in Iran.
• Establishes SPEI-6 as a highly effective indicator for WP variability in arid agroecosystems, moving beyond precipitation-based drought monitoring.
• Offers a high-resolution diagnosis of shifting compound extreme hotspots and identifies the differential vulnerability of irrigated versus rainfed agricultural systems.
• Quantifies the synergistic and disproportionate impact of CDHEs, demonstrating they pose a greater threat to water security than individual extremes, even for irrigated systems.
• Delivers a practical diagnostic tool to prioritize location-specific adaptation and water-management interventions for enhancing drought resilience.

Funding

This research was conducted under the Research and Technology Operational Program of the Soil and Water Research Institute (SWRI).

Citation

@article{Veysi2026Spatiotemporal,
  author = {Veysi, Shadman and Nouri, Milad},
  title = {Spatiotemporal dynamics of single and compound drought–heatwave extremes impacts on water productivity},
  journal = {Journal of Hydrology Regional Studies},
  year = {2026},
  doi = {10.1016/j.ejrh.2026.103370},
  url = {https://doi.org/10.1016/j.ejrh.2026.103370}
}