Sub-daily rainfall events in an arid environment with marked climate variability: Variation among wet and dry years at Fowlers Gap, New South Wales, Australia

Earth Surf Processes Landf

2014

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Laboratory rainfall simulation experiments using a small artificial olive tree are used to show that the fraction of rain falling at a constant intensity that becomes stemflow rises from 9% at 2.5 mm/h to 36.1% at 35 mm/h. Natural rainfall events commonly exhibit wide fluctuations of intensity. Simulated rainfall events each having a mean intensity of 10 mm/h, but containing short intensity peaks of 20 to 100 mm/h at varying intra-event positions, were used to explore the effect of varying intensity profiles. Results demonstrate that changes in rainfall event profile are associated with wide variation in stemflow flux, stemflow volume and stemflow fraction. When applied to an initially dry plant, rainfall events with a late intensity peak yielded an average peak stemflow flux up to 188% larger than events of contrasting profile, such as early peak events. The increase was smaller, up to 141%, when rain was applied to plants that were already partially wet, but was again found in events with a late intensity peak. Moreover, such events yielded a peak stemflow flux up to approximately seven times larger than comparable events of uniform intensity. Likewise, changing event profile with no change in rainfall depth was associated with a maximum stemflow fraction that was 31% larger than theminimum stemflow fraction, and a maximum stemflow volume that was nearly 37% larger than the minimum stemflow volume. These results suggest that rainfall event profile exerts a significant effect on all of the studied stemflow parameters. It is hypothesized that this is a consequence of the way in which intensity profile affects the rate of wetting-up of trickle pathways on the plant, and variation in the time taken for these pathways to become fully connected. Event profile must therefore be considered along with plant architecture in seeking to understand stemflow.

Section: Discussionmentioning

confidence: 99%

Section: The Influence Of Rainfall Intensity On Stemflow Yieldmentioning

confidence: 99%

Section: The Influence Of Rainfall Intensity On Stemflow Yieldmentioning

confidence: 99%

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Stemflow production and intrastorm rainfall intensity variation: an experimental analysis using laboratory rainfall simulation

Earth Surf Processes Landf

2014

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“…Annual rainfall amounts vary markedly from year to year, related to the El Niño–Southern Oscillation (ENSO) cycle of drought and wet years. Some aspects of the rainfall climatology of this site, including the nature of rainfall in wet and dry years and the intensity variations at intra‐event timescales, have been described previously (Dunkerley, ; ). FG is located ~950 km from the Australian east coast, and more than 450 km from the nearest coastline in Spencer Gulf, South Australia.…”

Section: Field Sites and Datamentioning

confidence: 99%

How does sub‐hourly rainfall intermittency bias the climatology of hourly and daily rainfalls? Examples from arid and wet tropical Australia

Intl Journal of Climatology

2018

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Statistical rainfall climatologies for application to problems in ecohydrology or urban flood hydrology employ indices such the average rainfall depth per rain day or rain hour, and the average daily or hourly rainfall intensity. These subsume finetemporal-scale aspects of rainfall arrival such as sub-hourly intermittency that vary among locations with different climatic conditions. Rainfall duration and intensity derived from data aggregated to hourly or daily level thus involve some bias, generally overestimating the duration of rainfall and underestimating rainfall rates, and this bias will vary with location. The magnitude of bias is documented for two Australian locations having rainfall records of high temporal resolution: one arid and one wet tropical. Rainfall data aggregated to hourly or daily level yield substantial overestimates of time raining, and underestimates of rainfall rates. The magnitude of bias is shown to differ between the two field locations where on average rain is only recorded during 3.6 hr (14.9%) of a rain day at the arid location, but 8.2 hr (34%) at the wet tropical site. Resulting bias in estimates of time raining and of rainfall intensities is worse at the arid location. The significance of intermittency in particular for the detection of the effects of climate change on temporal rainfall climatology is explored. If intermittency varies with climate change, but is concealed through the use temporally aggregated rainfall data, erroneous assessments of changes in rainfall intensities may result. The use of rainfall events rather than clock-period data appears to reduce some of these effects, but there is still a failure to reflect shortperiod, high-intensity rainfall that may be important to soil erosion and the loss of carbon, nutrients, and agrochemicals from agricultural land.

“…Intensity extremes are not straightforward to quantify, in part owing to the relative infrequency of observations toward the upper tail of the distribution of intensities. Pooling data from various observing sites and years in order to accumulate more data on intensity extremes would blur secular trends, the variation of intensity with drought, or associated with various teleconnections such as ENSO, which are known to affect the intensity distribution [77]. Likewise, the use of long records may hinder the detection of secular change in rainfall intensities.…”

Section: Data Availability and The Detection Of Intensity Extremesmentioning

confidence: 99%

Sub-Daily Rainfall Intensity Extremes: Evaluating Suitable Indices at Australian Arid and Wet Tropical Observing Sites

2019

Water

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Rainfall intensity extremes are relevant to many aspects of climatology, climate change, and landsurface processes. Intensity is described and analysed using a diversity of approaches, reflecting its importance in these diverse areas. The characteristics of short-interval intensity extremes, such as the maximum 5-min intensity, are explored here. It is shown that such indices may have marked diurnal cycles, as well as seasonal variability. Some indices of intensity, such as the SDII (simple daily intensity index), provide too little information for application to landsurface processes. Upper percentiles of the intensity distribution, such as the 95th and 99th percentiles (Q95 and Q99) are used as indices of extreme intensity, but problematically are affected by changes in intensity below the nominated threshold, as well as above it, making the detection of secular change, and application to sites with contrasting rainfall character, challenging. For application to landsurface processes, a new index is introduced. This index (R Q95 ), is that intensity or rainfall rate above which 5% of the total rainfall is delivered. This index better reflects intense rainfall than does Q95 of even 5-min accumulation duration (AD) rainfall depths. Such an index is helpful for detecting secular change at an observing station, but, like Q95, remains susceptible to the effects of change elsewhere in the distribution of intensities. For understanding impacts of climate and climate change on landsurface processes, it is argued that more inclusive indices of intensity are required, including fixed intensity criteria.