Ali et al. (2026) Threshold analysis of rainfall and groundwater recharge in mitigating drought risks in overexploited groundwater regions

Identification

• Journal: PLoS ONE
• Year: 2026
• Date: 2026-02-04
• Authors: Uneeb Ur Rehman Ali, Jinfeng Du, Muhammad Azram, Hassan Mujtaba Nawaz Saleem, Muhammad Hassan Raza
• DOI: 10.1371/journal.pone.0341713

Research Groups

• School of Public Policy and Administration, Xi’an Jiaotong University, Xi’an, Shaanxi, China
• Institute of Business Management & Administrative Sciences, The Islamia University of Bahawalpur, Bahawalpur, Pakistan
• Human Settlements and Architectural Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi, China

Short Summary

This study quantifies the thresholds of rainfall and groundwater recharge required to mitigate drought risks in the world's top ten groundwater-overexploited regions, finding that specific levels of precipitation (614.41 mm) and groundwater recharge (–0.0039 standard deviations) are critical for drought resilience.

Objective

• To examine the nature and magnitude of the rate to which rainfall and groundwater recharge affects drought.
• To investigate the thresholds policy effect of rainfall and groundwater recharge capable of mitigating the effect of drought.
• To determine the countries at risk of drought with respect to the level of rainfall and groundwater recharge.
• To uncover the theoretical argument about the specific direction of the causation of groundwater recharge in relation to drought.

Study Configuration

• Spatial Scale: Global sample of the top ten countries with significant underground water overexploitation: India, China, Pakistan, Iran, Indonesia, Bangladesh, Saudi Arabia, Turkey, the USA, and Mexico.
• Temporal Scale: 1961 to 2022.

Methodology and Data

• Models used: Dynamic Panel Threshold Regression (DPThR) model (Diallo, 2020), Juodis, Karavias, and Sarafidis (2021) Panel Non-causality Test. Groundwater recharge was calculated using nine empirical equations (Chaturvedi, Modified Chaturvedi, Sehgal, Krishina, Kirchner, Bredenkamp, Bhattacharjee, Kumar, Maxey and Eakin), then indexed via Principal Component Analysis (PCA).
• Data sources: Standardized Precipitation-Evapotranspiration Index (SPEI) from the Global SPEI database; rainfall (average precipitation in depth), temperature (temperature change per year in degrees Celsius), and CO₂ emissions (CO₂ emissions per capita in metric tons) from World Development Indicators (WDI), Climate Change Knowledge Portal (CCKP), India Environment Portal, and Gapminder.

Main Results

• A 1 millimeter increase in rainfall improves the Standardized Precipitation Evapotranspiration Index (SPEI) by 0.003 units, thereby reducing drought likelihood.
• The threshold for mitigating drought effects is identified at 614.41 millimeters of annual rainfall. Pakistan, Iran, and Saudi Arabia are most at risk when rainfall falls below this level.
• A one-standard-deviation increase in groundwater recharge enhances the SPEI by 5.06 units, indicating a substantial reduction in drought incidence.
• The threshold for mitigating drought effects is identified at –0.0039 standard deviations of groundwater recharge. China, Iran, Mexico, Pakistan, Saudi Arabia, Turkey, and the United States are most drought-prone when recharge falls below this level.
• Temperature exerts a consistently negative and highly significant effect on SPEI, indicating that warming intensifies drought through evapotranspiration and soil moisture depletion.
• CO₂ emissions show no significant direct impact on SPEI in the panel analysis, though some country-specific variations exist.
• Unidirectional causality runs from rainfall, groundwater recharge, temperature, and CO₂ emissions to drought conditions in the panel analysis, reinforcing the dominance of hydro-climatic forces.

Contributions

• Provides a comprehensive analysis of rainfall and groundwater recharge thresholds required to mitigate drought in the world’s most overexploited groundwater regions.
• Clarifies the direction of causality between drought and groundwater recharge, an area of ongoing debate in the literature.
• Offers a more nuanced understanding of the interactions between climate variables and drought by incorporating advanced modeling techniques (DPThR and JKS Panel Non-causality Test).

Funding

• Chinese Scholarship Council (CSC)

Citation

@article{Ali2026Threshold,
  author = {Ali, Uneeb Ur Rehman and Du, Jinfeng and Azram, Muhammad and Saleem, Hassan Mujtaba Nawaz and Raza, Muhammad Hassan},
  title = {Threshold analysis of rainfall and groundwater recharge in mitigating drought risks in overexploited groundwater regions},
  journal = {PLoS ONE},
  year = {2026},
  doi = {10.1371/journal.pone.0341713},
  url = {https://doi.org/10.1371/journal.pone.0341713}
}