3 Geomorphological, Hydrologic, and Geothermal investigations of basin aquifers in Baja California Sur (BCS), Mexico

The session will explore BCS basins, focusing on groundwater storage, evaporation, runoff and transport mechanisms, featuring experts on thermal and shallow groundwater interactions, soil mapping for hydrological planning, geomorphology, and human impacts on water balance.

Wednesday, 22 April 2026
8:00 AM - 12:00 PM
LMH, Isla Carmen

Isotopic Characterization (δ¹⁸O and δ²H) of the Hydrological Cycle in the Semi-Arid South of the Baja California Peninsula: Influence of Tropical Cyclones and Hydrogeological Processes

Paper number: 3-2
Program: Technical Sessions
Time: 8:20 AM – 8:35 AM

Authors

  • Jobst Wurl Presenting Author
    Universidad Autonoma de Baja California Sur, La Paz, Baja California Sur
  • Mabilia Urquidi Gaume
    Autonomous University of Baja California Sur (UABCS), La Paz, BCS, Mexico, La Paz, Baja California Sur
  • Loic Peiffer
    de Investigación Científica y de Educación Superior de Ensenada (CICESE) , La Paz, Baja California Sur
  • Miguel Imaz-Lamadrid
    Autonomous University of (UABCS), La Paz, Baja California Sur
  • Pablo Hernández Morales
    Autonomous University of Baja California Sur (UABCS), La Paz, Baja California Sur

Abstract

The isotopic composition of precipitation, surface water, and groundwater was analyzed in a critical recharge area of the La Paz basin, specifically the Sierra El Novillo–San Pedro region. A total of 38 water samples were collected to characterize isotopic variations associated with tropical cyclones, seasonal rainfall, and recharge processes. Rainfall samples were obtained during and after tropical cyclone events and other significant precipitation episodes to capture source-related variability.

The results demonstrate that rainfall from tropical cyclones is isotopically depleted relative to seasonal (summer/winter) precipitation. This distinct signature enables the identification of cyclones' disproportionate contribution to aquifer recharge. Mean isotopic values in shallow groundwater are significantly more negative than the weighted average of local rainfall, robustly confirming the dominant role of these episodic cyclonic events in modern recharge dynamics.

Synthesizing these findings with prior studies reveals that groundwater originating from the Sierra El Novillo exhibits progressive depletion in ¹⁸O and ²H along its subsurface flow path. This trend is attributed to kinetic and equilibrium isotopic fractionation during prolonged water-rock interactions within the aquifer matrix. Furthermore, a consistent vertical isotopic gradient is observed, with the most depleted signatures found in the deepest groundwater zones of the central La Paz basin.

In the coastal zone, this inland isotopic framework is fundamentally altered. The primary process is mixing with seawater, which results in heavier  (δ¹⁸O and δ²H) values in the mixed fluid. Additionally, the potential upwelling of deep-seated thermal waters may further modify the final isotopic composition of the coastal hydrogeological system. This work underscores the critical importance of tropical cyclones as a primary recharge mechanism in semi-arid regions and establishes an isotopic framework for delineating complex groundwater flow paths, recharge sources, and degradation processes such as saline intrusion.

 

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410933

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