Intercomparison of moisture tracking methods simulating sources of extreme precipitation events

To better understand the mechanisms behind precipitation extremes, one can determine the origin of the precipitation, i.e. its moisture sources. The time and spatial distribution of these sources provide insights into the importance of land-ocean–atmosphere interactions and moisture recycling and the synoptic situation of an extreme event. This allows for better prediction and improved disaster preparedness.

However, the moisture sources of extreme precipitation cannot be measured directly. Therefore, a variety of moisture tracking methods have been developed over recent decades, but the uncertainties associated with these methods remain poorly quantified. Here, we present the IdentificatioN of Sources of Precipitation through an International Research Effort (INSPIRE), a coordinated intercomparison of moisture tracking methods. Within this initiative, the moisture tracking community gathered to compare moisture sources of three extreme precipitation events across 14 different methods. The events occurred under different meteorological conditions: monsoon precipitation in Pakistan, convective precipitation in Australia, and atmospheric river-associated precipitation over Scotland. Our findings show that, in all cases, the different moisture tracking methods qualitatively agree on moisture source patterns, although there are regional and quantitative differences. For example, for the Pakistan case, the recycling ratio shows a multi-method spread of 2–20%.  We also find that groups of methods behaved similarly across events. This study provides a first quantitative benchmark of inter-method uncertainty and establishes a reference framework for future moisture tracking studies.