Rain event properties in nature and in rainfall simulation experiments: a comparative review with recommendations for increasingly systematic study and reporting

Abstract

Abstract:In hydrology and geomorphology, less attention has been paid to rain event properties such as duration, mean and peak rain rate than to rain properties such as drop size or kinetic energy. A literature review shows a lack of correspondence between natural and simulated rain events. For example, 26 studies that report event statistics from substantial records of natural rain reveal a mean rain rate of just 3Ð47 mm h 1 (s.d. 2Ð38 mm h 1 ). In 17 comparable studies dealing with extreme rain rates including events in cyclonic, tropical convective, and typhoon conditions, a mean maximum rain rate (either hourly or mean event rain rate) of 86Ð3 mm h 1 (s.d. 57Ð7 mm h 1 ) is demonstrated. However, 49 studies using rainfall simulation involve a mean maximum rain rate of 103Ð1 mm h 1 (s.d. 81Ð3 mm h 1 ), often sustained for >1 h, exceeding even than of extreme rain events, and nearly 30 times the mean rain rate in ordinary, non-exceptional, rain events. Thus rainfall simulation is often biased toward high rain rates, and many of the rates employed (in several instances exceeding 150 mm h 1 ) appear to have limited relevance to ordinary field conditions. Generally, simulations should resemble natural rain events in each study region. Attention is also drawn to the raindrop arrival rate at the surface. In natural rain, this is known to vary from <100 m 2 s 1 to >5000 m 2 s 1 . Arrival rate may need to be added to the list of parameters that must be reproduced realistically in rainfall simulation studies.

Data-driven clustering of rain events: microphysics information derived from macro-scale observations

“…In the present study it was decided to set the MIT to 30 min. This is in agreement with the value used by Coutinho et al (2014), Haile et al (2011), Dunkerley (2008a, Balme et al (2006) and Cosgrove and Garstang (1995).…”

“…The choice of MIT thus has a direct impact on the macrophysical characteristics that are ultimately determined by the analysis. Other researchers have proposed to use MIT values of 20 min, 1 h or even 1 day (see Dunkerley, 2008a, for a detailed list). In the present study it was decided to set the MIT to 30 min.…”

Rainfall timing and runoff: The influence of the criterion for rain event separation

“…These periods allow water to evaporate from the canopy and, thus, tend to increase the rate of interception during the event. Additionally, allowing for partial deep infiltration of ground water, these periods make the soil stores available to be filled when rainfall resumes, which has an effect on runoff (Aryal et al, 2007;Dunkerley, 2008a). Therefore, the longer the MIT and the larger independence there is between events, the greater the independence between the parts of an event.…”

“…However, by defining rain events, additional information can be obtained, such as the effects of rain intensity or the effect of antecedent rain. More research on the properties of rain events is necessary and justified by changes in precipitation that may be experienced due to global environmental change (Dunkerley, 2008a).…”

Estimating rainfall erosivity from daily precipitation records: A comparison among methods using data from the Ebro Basin (NE Spain)

“…for comparison with simulated rain, are scarce (Dunkerley 2008). This has encouraged studies 50 relating more conventional rainfall indices, such as the maximum intensity during a period of 51 time, to overall rainfall energy or directly to soil detachment rates.…”