Kabe et al. (2025) Impact of hydrogeological regime changes on the Bakhtegan-Tashk lake system under groundwater overextraction

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2025
• Date: 2025-11-20
• Authors: Marzieh Kabe, Mohsen Rezaei
• DOI: 10.1016/j.ejrh.2025.102953

Research Groups

• Department of Earth Sciences, School of Science, Shiraz University, Shiraz, Iran

Short Summary

This study investigated the impact of human-induced hydrogeological regime changes on the desiccation of the Bakhtegan-Tashk Lake (BTL) system in southern Iran. It revealed a reversal in the natural groundwater-surface water flow, with the lake now losing approximately 10.5 million cubic meters of water annually to overexploited adjacent aquifers, accelerating its desiccation.

Objective

• To assess the impacts of hydrogeological regime changes and groundwater–surface water interactions on the desiccation of the Bakhtegan-Tashk Lake (BTL) system, while also considering the influence of rainfall and other climatological factors.

Study Configuration

• Spatial Scale: Bakhtegan-Tashk Lake (BTL) system and its seven adjacent aquifers in the Bakhtegan and Tashk Basin, Fars Province, southern Iran, covering approximately 31,451.8 square kilometers.
• Temporal Scale: Primary analysis period from 2009 to 2020, with satellite imagery analysis extending from 1990 to 2020.

Methodology and Data

• Models used: Not applicable (statistical analysis and remote sensing techniques were employed, not process-based hydrological models).
• Data sources:
  • Observation well data (87 wells): Groundwater levels, well depth, and discharge (2009–2020) from the Fars Regional Water Authority.
  • Satellite imagery: Landsat 5 TM (1990–2011), Landsat 7 ETM+ (1999–2013), and Landsat 8 OLI (2013–2020) for lake water body detection via Normalized Difference Water Index (NDWI) processed on Google Earth Engine (GEE).
  • Climatological data: Precipitation, temperature, evaporation, and river discharge.
  • Statistical analysis: Lagged Cross-Correlation Function (CCF) computed using SPSS software.

Main Results

• The natural groundwater-surface water (GW-SW) flow regime has reversed, with the Bakhtegan-Tashk Lake (BTL) now losing approximately 10.47 million cubic meters (MCM) of water annually to adjacent aquifers, while receiving only 1.01 MCM from them.
• Groundwater levels in adjacent aquifers declined by approximately 2 meters between 2010 and 2020, despite continuous precipitation, due to overexploitation.
• Water budget analysis revealed a reservoir deficit of -69.85 MCM per year across all adjacent aquifers, with groundwater extraction identified as the most significant output component.
• Evaporation rates are high (1843.5 millimeters per year for Bakhtegan Lake, 1813.5 millimeters per year for Tashk Lake), consuming nearly all precipitation and surface water inflows, highlighting groundwater's critical role in lake sustainability.
• Cross-correlation analysis showed a strong positive correlation between groundwater levels and lake water bodies, with a peak correlation observed at a 3-month lag, indicating that groundwater changes significantly influence lake levels.
• The hydraulic connection between the lake and aquifers weakened significantly from 2009–2014 to 2014–2020, with a clear shift from groundwater recharging the lake to the lake recharging the aquifers (inverse flow).
• By 2020, Bakhtegan Lake was completely desiccated, and Tashk Lake retained only about 35 square kilometers of residual water.

Contributions

• Quantifies the temporal relationship and lagged responses (up to 3 months) between lake water bodies and adjacent groundwater levels using cross-correlation analysis across 87 observation wells, a factor largely unexplored in previous studies for the BTL system.
• Demonstrates the reversal of the natural groundwater-surface water flow regime, showing the lake now acts as a "losing" system to overexploited aquifers, providing new insights into the primary driver of desiccation.
• Enhances understanding of groundwater-lake interactions in semi-arid regions, offering crucial insights for improved groundwater-surface water modeling and sustainable water management strategies in the BTL basin and similar environments.

Funding

• This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Citation

@article{Kabe2025Impact,
  author = {Kabe, Marzieh and Rezaei, Mohsen},
  title = {Impact of hydrogeological regime changes on the Bakhtegan-Tashk lake system under groundwater overextraction},
  journal = {Journal of Hydrology Regional Studies},
  year = {2025},
  doi = {10.1016/j.ejrh.2025.102953},
  url = {https://doi.org/10.1016/j.ejrh.2025.102953}
}

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