From graphical methods to geochemical and isotope hydrology tools: Understanding baseflow mechanisms in mountainous Mediterranean watersheds

Most of the Mediterranean basin coasts are bordered by high mountain ranges (Atlas, Taurus, Alps and Balkans e.g.). As a result, most of the coastal socio-economic activities are highly dependent on the availability of water from mountainous catchment areas. However, these resources are increasingly vulnerable to climate change, population growth and agricultural development. Given the high seasonality of rainfall, groundwater covers a large part of the withdrawals and appears to be essential to maintain river flows during dry periods. One of the most important knowledge gaps remains in the characterization and quantification of the watershed contributors supplying river flow through time and space. This is especially the case for groundwater and snow contributions. Due to its location in the western Mediterranean basin as well as its diversity in catchment morphologies, Corsica is an excellent observatory of any mountainous hydrological processes. The first step of our research consists in characterizing baseflow contribution through a full hydrological year for several representative selected watersheds (contrasted lithology, area, resilience e.g.). In this purpose, different promising tools rarely used in the Mediterranean context are available to perform baseflow analysis. On one hand, the non-tracer-based methods, including several technics ranging from an empirical to physical basis. On the other hand, the more accurate tracer-based methods including the utilization of water stable isotopes and hydrogeochemical tracers. Our works allowed to test and highlight the high potential of isotope and hydrogeochemical tools in the Mediterranean mountainous context in many ways:

-        By correlating and calibrating some of the non-tracer-based methods for Mediterranean use (such as the BFI index for Eckhardt’s recursive digital filter)

-        By clearly highlithing that baseflow is mainly due to groundwater contribution during dry periods

Our next steps consist in going further using environmental tracers to provide conceptual models describing all components of the hydrological cycle which contribute to baseflow. At the end, this will serve as indicators for stakeholders in order to perform sustainable management and to assess the resilience of water resources facing global climate change, not only in Corsica, but for any similar regions.