Modelling of rain splash trajectories and prediction of rain splash height

Rain splash is the most important factor in the spread of epidemics of many plant pathogens. Splash height is highly dependent on the kinetic energy of impacting drops. However, direct measurements of rain such as the duration, the amount or the intensity are not related to splash height. We derive a mechanistic model that describes the trajectory of the splashing droplets in terms of the kinetic energy. Experimental data from controlled indoor experiments were used to estimate model parameters and predict the whole distribution of splashes given the kinetic energy of impacting drops. A separate data set from 21 natural rain events was used to verify the model. The maximum splash height was well estimated and the overall splash distribution was well predicted except for lower heights. Three reasons for these differences are discussed: they may be due to (1) ‘secondary’ splashes, (2) the distance between the drop impacting point and the centre of the ‘Precipitation Impact Sensor’ and (3) sampling differences. Different impacting surfaces may have an effect on the model; its robustness is, therefore, discussed. As a first approximation, this model could be used for droplets splashing from leaves within a crop if the structure of the model can be assumed to remain unchanged for different impacting surfaces.