Measurement uncertainty in rainfall kinetic energy and intensity relationships for soil erosion studies: An evaluation using PARSIVEL disdrometers in the Southern Appalachian Mountains

- The study quantifies measurement uncertainty of rain drop size distributions (DSDs).
- Number of drops for each instrument varies with rainfall regime and microphysics.
- Uncertainty in counting small and midsize drops impacts kinetic energy estimation.
- Kinetic energy estimates between Parsivel1 and Parsivel2 differ by 40%.
- Spatial variability in rainfall and microphysics explains spatial uncertainty in KE.

The increased use of observations of rainfall microphysics from disdrometers to produce more accurate rainfall kinetic energy estimates requires closer analysis of measurement uncertainty, and in particular how the type of sensor influences rainfall kinetic energy estimates in different hydrometeorological regimes. This study evaluates the performance of Parsivel1 (P1) and Parsivel2 (P2) in measuring rainfall DSDs (drop size distributions) in terms of rain depth (P), rain rate (I), and kinetic energy (KE) at three locations in the Southern Appalachian Mountains for warm season rainfall. For the same storm system, there is large spatial variability of rainfall DSDs between ridges and valleys, and between exposed upwind ridges and the inner region. Parsivel1 measures underestimate the number of small drops, while all rainfall variables are overestimated for DSDs with a large number of drops in the midsize range (1-2 mm in diameter) for both P1 and P2. Overall, results show differences of 40% in KE estimates when P1 is used compared with the more recent P2. The uncertainty analysis clearly illustrates the dependence on hydrometeorological regime and the instrument proper. Relationships between rainfall KE and intensity (I) need to account for the instrumental influence towards better characterization of the rainfall erosion potential locally; and regional scale studies must include spatially distributed observations to capture the dominant hydrometeorological regimes, especially in regions of complex topography where the spatial variability of rainfall is very high.