Alternative approach to establishing a local meteoric water line in data-limited regions

The linear relationships between stable water isotopes (δ¹⁸O and δ²H) in precipitation are the cornerstone of isotope hydrology. These relationships underpin investigations of groundwater and surface water provenance, recharge, and hydrological processes across spatiotemporal scales. While these defined relationships namely the global meteoric water line (GMWL) is well-established, local meteoric water lines (LMWL) are dependent on local climate and geography. In data- and resource-scarce regions, where regular continuous precipitation isotope monitoring networks are absent, the construction of reliable LMWLs at basin and regional scales remains a significant challenge. To bridge this gap, we proposed an applied statistical methodology of random-effects meta-analysis (REM) to integrate spatiotemporally fragmented linear δ¹⁸O - δ²H equations from legacy independent hydrological studies. We tested the method on LMWLs constructed at twenty-two independent study locations across Ghana between 1986 and 2016. Using the DerSimonian-Laird estimator, we derived a pooled regression equation δ²H = 7.31 ± 0.08·δ¹⁸O + 7.12 ± 0.59‰, which closely matched the LMWL, δ²H = 7.31 ± 0.07·δ¹⁸O + 7.24 ± 0.31‰, obtained from eight regularly monitored precipitation isotopes stations across Ghana. Wald statistical tests indicated no statistically significant differences in slope (|Z| ≤ 1.76, p ≥ 0.08) and intercept (|Z| ≤ 1.49, p ≥ 0.14) between the REM, standard Ordinary Least Squares Regression (OLSR) and Precipitation-Weighted Least Squares Regression (PWLSR) of the regular continuous isotopes in precipitation data, confirming overall consistency across estimation approaches. The meta-regression demonstrates latitude and elevation alone are poor predictors of the spatial variability in Ghanaian LMWLs. The study presented a scalable, cost-effective framework for constructing LMWLs in data-limited regions, where substantial fragmented legacy precipitation isotopes data exist, for enhanced regional isotope hydrology and hydroclimatic assessments.