Use of disdrometer data to evaluate the relationship of rainfall kinetic energy and intensity (KE-I)

Determination of rainfall kinetic energy (n) is required to calculate erosivity, the ability of rainfall to detach soil particles and initiate erosion. Disdrometers can measure rainfall IC by measuring raindrop size and velocity. In the absence of such devices, KE is usually estimated with empirical equations that derive KE from measured rainfall intensity (I). We evaluated the performance of 14 different KE-I equations to estimate the 1 min KE and event total ICE, and compared these results with 821 observed rainfall events recorded by an optical clisdrometer in the inner Ebro Basin, NE Spain. We also evaluated two sources of bias when using such relationships: bias from use of theoretical raindrop terminal velocities instead of measured values; and bias from time aggregation (recording rainfall intensity every 5, 10,15, 30, and 60 min). Empirical relationships performed well when complete events were considered (R-2 > 0.90), but performed poorly for within-event variation (1 min resolution). Also, several of the KE4 equations had large systematic biases. When raindrop size is known, estimation of terminal velocities by empirical laws led to overestimates of raindrop velocity and IKE. Time aggregation led to large under-estimates of ICE, although linear scaling successfully corrected for this bias. (C) 2016 Elsevier B.V. All rights reserved.