Sivan et al. (2026) Evaluation of compound agrometeorological drought and hot events using a copula-based standardized index

Identification

• Journal: Irrigation Science
• Year: 2026
• Date: 2026-02-16
• Authors: Sruthi D. Sivan, S. K. Pramada
• DOI: 10.1007/s00271-026-01091-8

Research Groups

• Department of Civil Engineering, National Institute of Technology, Calicut, Kerala, India

Short Summary

This study introduces a novel Standardized Agrometeorological Drought and Hot Index (SADHI) based on a vine copula framework to analyze compound agrometeorological drought and hot events (CADHE) in Kerala, India, from 1955 to 2020, revealing a significant increase in their frequency and severity, particularly after 1980, with the 2016 event being the most widespread and extreme.

Objective

• Develop a novel index (SADHI) for analyzing Compound Agrometeorological Drought and Hot Events (CADHE) in Kerala using a vine copula framework that integrates the Standardized Precipitation Index (SPI), Standardized Soil moisture Index (SSI), and Standardized Temperature Index (STI).
• Compare the developed vine copula model with traditional copulas to evaluate its performance in capturing complex dependence structures.
• Identify regions in Kerala highly prone to CADHE.
• Evaluate the multivariate joint return period of CADHE using the developed index.

Study Configuration

• Spatial Scale: Kerala, a state in southwestern India, spanning 38,863 square kilometers, located between 8°15’N and 12°50’N parallels and 74°50’E and 77°30’E meridians, analyzed at 64 grid points (0.25° × 0.25° resolution).
• Temporal Scale: 66 years (1955–2020)

Methodology and Data

• Models used:
  • Standardized Agrometeorological Drought and Hot Index (SADHI)
  • Vine copula framework (specifically D-vine copula for index development, C-vine copula for return period analysis)
  • Standardized Precipitation Index (SPI)
  • Standardized Soil moisture Index (SSI)
  • Standardized Temperature Index (STI)
  • Modified Mann-Kendall (MMK) trend test
  • Sen’s slope method
  • Run theory
  • RStudio "VineCopula" and "copula" packages
• Data sources:
  • Monthly precipitation, soil moisture, and temperature data from the Global Land Data Assimilation System (GLDAS) Noah Land surface model (version 2.0 and 2.1) at 0.25° × 0.25° resolution, combining ground and satellite observations.

Main Results

• The D-vine copula provided the best fit for the joint distribution of SPI, SSI, and STI across all 64 grid points, with minimum Akaike Information Criteria (AIC) values ranging from –292.12 to –555.51 and Bayesian Information Criteria (BIC) values from -278.1 to -541.48, outperforming traditional copulas.
• SADHI exhibited strong positive correlations with SPI and SSI, and a strong negative correlation with STI, indicating its effective integration of all three component indices.
• Temporal analysis revealed a marked increase in the frequency of CADHE after 1980, with extreme events (SADHI < -2) notably occurring in 1983, 1988, 2002, 2012, 2016, and 2019.
• The 2016 event was identified as the most widespread and severe CADHE, with all grid points across Kerala exhibiting a SADHI value less than −2.
• Modified Mann-Kendall trend analysis showed a statistically significant decreasing trend in SADHI values across all 64 grid points (Z-statistic values from −3.49 to -18.01), confirming an increasing severity of CADHE in Kerala.
• Spatially, severe and extreme CADHE were more frequently observed in the northern districts (Kozhikode, Wayanad, Malappuram, and Palakkad).
• Maximum severity (ranging from -60 to -120) and duration (ranging from 55 to 90 months) of CADHE were recorded in the southern districts of Thiruvananthapuram and Kollam.
• Joint return period analysis indicated that the southern parts of Kerala consistently experience shorter return periods for CADHE across all exceedance scenarios (e.g., 50th percentile return periods of less than 2.5 years, and 75th percentile return periods ranging from 3 to 4.5 years), highlighting their high vulnerability.

Contributions

• Development of a novel Standardized Agrometeorological Drought and Hot Index (SADHI) using a flexible vine copula framework, which effectively integrates meteorological drought (SPI), agricultural drought (SSI), and hot events (STI) for a comprehensive assessment of compound extreme events.
• Demonstrated the superior performance of the vine copula model over traditional copulas in capturing complex, higher-dimensional dependencies for compound events.
• Provided detailed spatiotemporal analysis of CADHE in Kerala, identifying specific hotspot regions and years of extreme events, which was previously lacking for this region.
• Established a robust framework for evaluating multivariate joint return periods of CADHE characteristics (severity, duration, peak intensity), offering critical insights for regional drought management and early warning systems.

Funding

The authors did not receive support from any organization for the submitted work.

Citation

@article{Sivan2026Evaluation,
  author = {Sivan, Sruthi D. and Pramada, S. K.},
  title = {Evaluation of compound agrometeorological drought and hot events using a copula-based standardized index},
  journal = {Irrigation Science},
  year = {2026},
  doi = {10.1007/s00271-026-01091-8},
  url = {https://doi.org/10.1007/s00271-026-01091-8}
}