Vertical dispersal of plant pathogens by splashing. Part I: the theoretical relationship between rainfall and upward rain splash

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Abstract
The theoretical relationship between rainfall intensity, raindrop size distribution and the upward transport of splash droplets is examined to establish a better understanding of the natural rainfall characteristics that can cause upward movement of plant pathogens in a crop. The theory suggests that splash transport is determined by the rain splash intensity index, which is defined as the intensity of the rainfall with raindrops greater than a threshold size. Ulbrich's (1983) empirical model of the size distribution of raindrops is used to calculate the relationship between rainfall intensity and rain splash intensity index. The calculations show that rainfall intensity is not a reliable indicator of the rain splash intensity index, particularly in convective showers. Therefore, a correlation between rainfall volume and upward disease progress is unlikely to provide a reliable basis for forecasting sudden disease outbreaks associated with short‐duration convective showers during the summer. Finally, we consider the instruments that have the capability to measure the rain splash intensity index.