Assessing the long-term trend of spring discharge in a climate change hotspot area.

Global warming affects atmospheric and oceanic energy budgets, modifying the Earth's water cycle. The Mediterranean region is a critical zone for climate change due to a decrease in recharge and an increase in the frequency and severity of droughts over recent decades. While the impacts of possible emissions scenarios on surface water have been extensively studied, the effects on groundwater discharge remain uncertain at both global and local scales. The primary objective of this study is to predict the long-term effects of climate change on the discharge of two springs with extensive discharge records, located in distinctly different hydrogeological settings within the Mediterranean climate zone. Through multivariate statistical analyses on secular time-series, correlation factors were identified between the springs' historical discharge and recharge-related parameters representative of their catchment. Future climate projections from a Regional Circulation Model were used to estimate long-term discharge trends of the springs for the 2040-2070 period. The results indicate that the discharge of both springs, on a multi-decadal trend scale, could decrease by 9 % to 11 % by 2040-2070 compared to that of the past few decades. The consistent negative trends observed across the two different hydrogeological settings suggest that the multi-decadal decline in spring discharge is more influenced by climatic factors than by specific hydrogeological features. This leads to the speculation that similar trends could be expected in other springs within Mediterranean-type climates worldwide. Future water shortages will significantly impact the hydrogeological contexts within these climates. Therefore, the long-term outcomes of this study are crucial for assisting water utility agencies in the sustainable management of groundwater resources, providing them with adequate time to plan and implement large-scale infrastructure projects over the coming decades.