Spatiotemporal Assessment of Aridity and Hydroclimatic Deficits in the Jabal Nafusa Region, Northwestern Libya (1994–2023)

This comprehensive assessment quantified the spatiotemporal gradients of aridity and climatic water deficits across the Jabal Nafusa mountain range in northwestern Libya, encompassing the municipalities of Nalut, Zintan, Gharyan, Tarhuna, and Msallata in the study area. Using the high-resolution (4 km) TerraClimate dataset for the climatological normal period of 1994–2023, we evaluated the shifting thermodynamic balance between the meteorological water supply, represented by precipitation (P), and atmospheric moisture demand, represented by the reference evapotranspiration (ET₀). Addressing persistent methodological gaps identified in regional hydroclimatology, this study explicitly integrates a modified trend analysis, specifically the Modified Mann–Kendall (MMK) test, utilizing the Hamed and Rao variance correction for temporal autocorrelation, and leverages recent literature-based quantitative validations of TerraClimate data for analogous Southern Mediterranean and North African contexts. Regional cross-validation metrics demonstrated that TerraClimate maintained robust temporal consistency, achieving correlation coefficients (R²) ranging from 0.65 to 0.80 and acceptable Root Mean Square Error (RMSE) margins when compared with local terrestrial station data and ERA5-Land reanalysis benchmarks. The analytical findings confirmed that the entire geographic domain of the Jabal Nafusa Plateau fell strictly within the arid climate classification. The modified United Nations Environment Programme (UNEP) Aridity Index (P/ET₀) exhibited a distinct spatial gradient, ranging from a severe 0.062 in the western extremity (Nalut) to 0.160 in the eastern transitional zone (Msallata). Trend analyses revealed a statistically significant escalating trajectory within the central municipalities of Zintan and Gharyan, coupled with a significant downward trend in precipitation at the western boundary of the study area. Consequently, the annual climatic water deficit (ET₀–P) exceeds 1,800 mm in the west, indicating a persistent and deteriorating hydrological baseline for this region. A clear west-to-east hydroclimatic gradient is evident, wherein the westernmost sites experience atmospheric demands that systematically exceed the annual precipitation by a factor of 15.1. By neutralizing historical statistical redundancies and systematically addressing the data uncertainties inherent in gridded climate products, these findings underscore the acute vulnerability of this region to anthropogenic climate change. The results establish a statistically robust, cross-validated climatological baseline that is fundamentally essential for future multi-scalar drought modeling, sustainable groundwater management, and agricultural adaptation within the hyper-arid fringes of NW of Libya.