Reconstructing phreatic palaeogroundwater levels: A methodological review

Abstract

Nature-based water management requires a clear understanding of baseline hydrological regimes. Reconstruction of Palaeogroundwater Level (PGWL) is emerging as an approach to determine past groundwater level as a mean to estimate ‘baseline’ or ‘pre-management’ conditions, thereby providing essential benchmarks to guide such interventions. However, methods for PGWL reconstruction remain fragmented across disciplines. This review synthesizes existing approaches of PGWL reconstruction across multiple disciplines, with a specific focus on phreatic groundwater systems, where water-table depth can be inferred from near-surface environmental archives and related proxies. Such aquifers are among the most vulnerable to depletion under global change. We present a range of reconstruction approaches grouped into three major categories: 1) Historical records provide direct evidence of hydrological condition from documented and measured sources; 2) Proxy methods rely on a combination of natural and anthropogenic geo-archives, including biological indicators, soils, sediment profiles, archaeological features, and geomorphological landforms; and 3) Model-based estimations use mathematical relationships to hindcast PGWLs. For each approach, we synthesize its theoretical foundations, evaluate its practical applicability and limitations, analyse its respective spatiotemporal scales, and illustrate its implementation with representative examples. By unifying scattered knowledge, we establish a critical guide for selecting appropriate reconstruction approaches tailored to specific contexts and objectives. We further propose an integration framework in which historical archives are used as evaluation and calibration datasets to strengthen proxy- and model-based reconstructions. This synthesis ultimately supports more resilient and nature-based water management strategies by providing robust methods for determining baseline conditions in unconfined groundwater systems.