The C/Q method has been proposed to explore the underlying mechanisms that explain the evolution of water quality in rivers. To complete this approach, I suggest exploring the drivers of water quantity or availability changes in the watersheds.

The idea is to apply the same time series analysis on the discharge data of the various watersheds included in the ABRESO project. The objective is to assess the possible correlation between annual hydrological indexes evolution and land use changes evidence. These evidence could be qualitative or descriptive data which are available at punctual dates, such as the percent of the watershed that is covered by forest, but also quantitative indexes such as Leaf Area Index or NDVI (normalized difference vegetation index) which are available at a regular step thanks to remote sensing. The hydrological signatures that could support this study are for example Base Flow Index and low water level indexes (such as the mean monthly annual minimum discharge).

In addition, the discharge (or piezometric levels) time series will be explored through statistical tests to detect trends and Sen’s slope discontinuities, and through spectral and wavelet analysis to identify possible changes in the functioning of the hydrosystem. Correlation between these results and land use metrics will then have to be evaluated. Of course, the contribution of climate change on the hydrosystem changes will have to be taken into account in the results analysis.

These methods need daily time series for discharge (and piezometric data), precipitation and temperature, covering at least a period of 10 years and if possible more than 30 years to detect climate change effects.

In short: Using stream discharge across our sites to infer critical zone controls on water availability:

• Long-term records of stream flow (average daily); perhaps same as C-Q watersheds
• Dr. Lanini will assess R code to determine base flow index or other hydrologic parameters
• If successful with French sites, method can be applied to sites with different land use trajectory, vegetation dynamics (LAI, NDVI), or climate over time

Proposed Timeline and Contact Person:

• Meeting (zoom) of potential working group members in early/mid January 2023
• Assessment of R code by January/February (Dr. Lanini)
• Plan for how to move forward spring 2023