What is spells analysis

When analysing annual time periods, it is necessary to know if we are in an event at the end of the time-period. The Spell Analysis Tool records this information and considers it for the start of the next period. The occurrence of the event is recorded for the period in which it began, however the length is recorded in whichever period it occurs.

If a spell starts in one period and ends in another e. It is therefore possible to have a year when the only spell is one that spans from the end of the preceding year, in this case there will be no spell in the year, but there will be a spell duration recorded for the year. The Spell Analysis Tool also compares independence criteria between analysis periods. That is the number of days between peaks or the end and start of spells can span the end of an analysis period without affecting the output.

In addition to the spell threshold, optional spell length and volume criteria can be defined. A high- or low-flow spell only occurs if the spell threshold, length and volume criteria are all met. The available length and volume criteria are:.

The Overview menu item Figure 1 summarises the high-flow, or low-flow, spells of the selected time series. The Spells menu item Figure 1 displays the time series of high-flow, or low-flow, spells.

Flows that do not meet the specified threshold, length and volume criteria are not plotted. The time series can be viewed as a graph or a table. The Day of Year menu item Figure 1 displays the time series of high-flow, or low-flow, spells in terms of the day of the water year in which they occur.

The Spell Start Date menu item Figure 1 displays cumulative exceedance percentiles for the annual spell start dates expressed as day of water year. The exceedance percentiles can be viewed as a graph or a table. The Spell End Date menu item Figure 1 displays cumulative exceedance percentiles for the annual spell end dates expressed as day of water year. The Spell Peak Date menu item Figure 1 displays cumulative exceedance percentiles for the date expressed as day of water year of the spell peaks for high-flow spells or minima for low-flow spells.

The Spell Peak Frequency menu item Figure 1 summarises the number of spell peaks for high-flow spells or minima for low-flow spells occurring each month. The frequencies can be viewed as a bar chart or a table. The Spell Duration menu item Figure 1 displays cumulative exceedance percentiles for the spell durations. Marsh, N. Note: This is documentation for version 4. For a different version of Source go to the Space Directory. Source User Guide 4.

In estimating the average timing and sd of timing of minimum flows, the function calculates the average DOY day of year of minimum flows in each year first, before calculating the average across years.

Circular functions are used to address the proximity between days toward the beginning and end of the year. Missing values are allowed for convenience NA's are removed and the time-series is concatenated before functions are applied , but of course may lead to biased results. For the purpose of the annual statistics years with fewer than days of available record are ignored. When used with ddply to compute outputs for multiple gauges or time periods simultaneously, results, icluding graphs are produced for each factor level, including graphs.

Note however that the funtion will return warnings if annual stats are calculated when year is used as a factor. Dataframe with date and discharge data in columns named "Date" and "Q" respectively.

If a third column exists then this is assumed to provide a vector of years for the purpose of calculating annual spell statistics based on a predetermined hydrologic year. A value of 0. A user supplied threshold for defining spells. This would typically be derived from hydraulic models or similar knowledge pertaining to a gauge site. In fact, mean values ranging between 6 and 8 days, and higher than 8 days have been detected on the Tyrrhenian and on the Ionian side, respectively.

The results regarding the maximum values of the lengths show much higher values of dry spells than the wet ones, and different temporal distributions throughout the year. In particular, with respect to dry spells, in autumn the maximum lengths reached values higher than days, while the longest wet spells have been identified in winter, with a maximum value of 44 consecutive days with rain. The outcomes of this study can be useful for both water resources with respect to the dry sequences and risk reduction regarding the wet spells management.

This is a preview of subscription content, access via your institution. Rent this article via DeepDyve. Theor Appl Climatol — Article Google Scholar. Clim Dyn — Sci Data Int J Climatol — Caloiero T, Coscarelli R, Ferrari E, Sirangelo B An analysis of the occurrence probabilities of wet and dry periods through a stochastic monthly rainfall model. Water J Hydrol —— Email required Address never made public. Name required. Follow Following. Sign me up. Already have a WordPress.

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