Perched aquifers and springs are common in the Levant, where they facilitated the existence of local historical societies in semiarid climates. In recent decades, however, spring discharge rates in the Jerusalem Mountains have declined significantly, with some drying up entirely. In order to investigate the combined effects of afforestation, urbanization, and changing precipitation patterns on the springs, a calibrated numerical flow model of a defined basin within the Jerusalem mountains was employed.
Analysis of aerial photographs and maps revealed extensive urbanization in the eastern part of the basin over seven decades, covering up to 26% of the total area by 2020. Meanwhile, intensive afforestation, primarily with pine trees, transformed the northern and western parts of the basin, covering 31% of its total area. These land cover changes, along with forest fires and reforestation, were integrated into the model as key factors influencing recharge to the perched aquifers. The model confirmed that the drying up of approximately half the basin's springs during the 1990s was primarily a result of these development processes rather than climatic variability alone.
Assessing spring response times, defined as the delay between rainfall and discharge fluctuations, proved complex. Some springs exhibited a rapid response lasting a few years due to fast flow paths, while others displayed a long-term "memory effect," with substantial discharge changes occurring up to a decade after heavy rainfall due to slow matrix flow. Additionally, the thickness of the unsaturated zone and the drainage basin’s internal structure played a crucial role in spring response and recovery after exceptionally dry years.
Future scenario simulations indicate that ongoing urbanization and afforestation will significantly alter the perched aquifers' flow field, potentially reducing groundwater availability and even shifting flow directions. These changes pose a considerable threat to the sustainability of perched aquifers and springs amid increasing anthropogenic pressures.