A moisture tracking intercomparison study - Addressing the uncertainty in modelling the origins of precipitation

To understand the mechanisms behind precipitation extremes, one can determine the origin of this precipitation, i.e. its moisture sources. The temporal and spatial distribution of these sources provide insights into the synoptic situation of the extreme event, and the importance of land-atmosphere interactions and moisture recycling. To determine moisture sources, moisture tracking models are used and forced with gridded atmospheric data to track water vapour in the atmosphere backward in time to its origin. Moisture tracking models have become an increasingly popular tool in scientific studies in recent years, but diversify in their underlying assumptions. Validation of tracking models is difficult due to the scarcity of isotope measurements as a benchmark. Further, structured intercomparisons among different models are lacking.Here, we present our efforts to coordinate a moisture tracking intercomparison study. Therefore, we reached out to many members of the moisture tracking community, and asked them to run their own moisture tracking model for three selected extreme precipitation events that occurred in 2022. Those three selected events cover different precipitation mechanisms: a monsoon event in Pakistan, a convective precipitation case in Australia, and an atmospheric river driven precipitation case over Scotland. We aim to compare the sources for the three cases among the different models during a one-week workshop in May 2024 in Leiden, The Netherlands. To this date, this intercomparison study covers about eight different moisture tracking models, allowing us to address and quantify the uncertainty in the moisture sources. At the EMS Annual meeting, we will present our approach and preliminary results of this intercomparison. This coordinated model intercomparison facilitates the explanation and quantification of uncertainty, acting as a point of reference for future work and literature on moisture tracking.