WATSON Wednesdays: James Kirchner

WATSON Wednesdays: James Kirchner

The first of many WATSON Wednesdays is scheduled for the 2 November at 12:30 CEST.

Our first speaker is Prof. James Kirchner, head of the Physics of Environmental Systems at the ETH in Zürich.

He will talk about “Partitioning precipitation between streamflow and evapotranspiration
using end-member splitting analysis

The terrestrial water cycle partitions precipitation between its two ultimate fates: “green water” that is evaporated or transpired back to the atmosphere, and “blue water” that is discharged to stream channels. Measuring this partitioning is difficult, particularly on seasonal timescales. End-member mixing analysis has been widely used to quantify streamflow as a mixture of isotopically distinct sources, but knowing
where streamwater comes from is not the same as knowing where precipitation goes, and this latter question is the one we seek to answer. Here I introduce “end-member splitting analysis”, which uses
isotopic tracers and water flux measurements to quantify how isotopically distinct inputs (such as summer vs. winter precipitation) are partitioned into different ultimate outputs (such as evapotranspiration and summer vs. winter streamflow). I illustrate this data-driven, model-independent approach with publicly available biweekly isotope time series from Hubbard Brook Watershed 3. This proof-of-concept study demonstrates that end-member mixing and splitting yield different, but complementary, insights into catchment-scale partitioning of precipitation into blue water and green water. It could thus help in gauging the vulnerability of both water resources and terrestrial ecosystems to changes in seasonal precipitation.

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