Precipitation event characteristics influence its partitioning into evapotranspiration and streamflow regardless of the season

The partitioning of precipitation into streamflow (Q) and evapotranspiration (ET ) is a fundamental aspect of the terrestrial
water cycle. Gaining insights into the mechanisms governing precipitation partitioning is critical for nutrient transport in
surface and subsurface water fluxes, ensuring plant water supply and maintaining atmospheric water dynamics. While previous
studies have highlighted the role of seasonal variability in precipitation partitioning, the influence of event characteristics
on precipitation partitioning has received less attention. In this study, we used hydrometeorological and tracer data from a
forested headwater catchment (Wüstebach, DE, 38.5 ha ) and a tracer-aided model based on StorAge Selection (SAS) functions
to quantify precipitation partitioning across different event types (mild, moderate and intense) and seasons after a period
of one year. Similar to previous studies, we showed seasonal precipitation input variability affects its partitioning.
Roughly about 82 % of spring season precipitation is released back into the atmosphere after one year, while this rate decreased
to 41 % for autumn season precipitation. Different season’s precipitation showed variation in partitioning to streamflow as
well. Approximately 11 % of autumn season precipitation ended in streamflow after one year, while this rate decreased to
3 % for spring season precipitation. However, within the same season, event characteristics showed stronger variation in
the partitioning of precipitation to ET and Q. Independent of in which season the precipitation fell, from mild to intense
events, ET partitioning decreased, and Q partitioning increased. Particularly for autumn precipitation, event types showed the
greatest variation in partitioning to ET and Q. ET partitioning for autumn precipitation declined roughly by 30%, Q partitioning
increased by 2%, and the fraction of precipitation remaining in the storage increased by 30% from mild to intense events. For
winter, ET decreased by 20 %, and Q and storage both increased by 6% and 15%, respectively. These patterns were consistent
across all seasons, indicating that precipitation event characteristics exerted a strong influence on the long-term partitioning
of precipitation. Thus, while seasonal variability remains important for precipitation partitioning, our results highlight which
type of precipitation returns to the atmosphere, contributes to discharge, or persists within catchment storage. These findings
emphasize the need to consider event-level precipitation dynamics under changing climatic conditions, given their potential
to alter water availability, contaminant transport, and flood mitigation strategies.