pool_ic: Pooling Procedures of Low Flow Events
In lfstat: Calculation of Low Flow Statistics for Daily Stream Flow Data

Description Usage Arguments Details Value See Also Examples

Several pooling procedures can be applied to reduce the number of dependent droughts.

pool_ic(x, tmin = 5, ratio = 0.1)
pool_it(x, tmin = 5)
pool_ma(x, n = 10)
pool_sp(x)

`x`	an object of class `deficit`, e.g. as produced by `find_droughts`.
`tmin`	numeric vector of length one interpreted as the number of days between two droughts to be considered independent events. Two droughts are pooled if their inter-event time is less than `tmin`.
`ratio`	numeric vector of length. Specifies the minimum ratio of inter-event volume and precedent drought volume. Two droughts are pooled if the critical `ratio` is deceeded.
`n`	numeric vector of length one determining the width of the smoothing window

The inter-event criterion (pool_ic) pools subsequent drought events if the inter-event time is less than tmin and the ratio of the drought volume and the inter-event volume is less than a given ratio. The function pool_it is simply a wrapper around pool_ic(..., ratio = Inf).

Pooling by a moving average (pool_ma) simply smooths the time series before finding drought events.

Using the Sequent Peak algorithm (pool_sp), a drought lasts until its cumulative deficit volume is zero again.

an object of class deficit (inherited from xts), with an additional column event.orig.

find_droughts, summary.deficit

data(ngaruroro)
ng <- as.xts(ngaruroro)
ng <- ng["1986::1990", ]

drought <- find_droughts(ng)


ic <- pool_ic(drought)
summary(ic)

ma <- pool_ma(drought)
summary(ma)

sp <- pool_sp(drought)
summary(sp)
plot(sp)

Loading required package: xts
Loading required package: zoo

Attaching package: ‘zoo’

The following objects are masked from ‘package:base’:

    as.Date, as.Date.numeric

Loading required package: lmom
Loading required package: lattice
Warning message:
3% of the discharges (54 observations) are NA values. NAs always terminate a drought event. 
Summary of pooled droughts
River: Ngaruroro at Kuripapango
Pooling: IC, 0 were pooled
Units: volumes in m³, duration in days

Filtered 2 minor events of 9 total. 
Only droughts with volume >= 5930.712 m³ and duration >= 5 days are reported.

  event.no      start       time        end    volume duration dbt  qmin
1        1 1986-04-12 1986-04-27 1986-04-27  770999.0       16  16 3.969
2        2 1986-05-07 1986-05-13 1986-05-13  267209.3        7   7 4.189
4        4 1987-01-15 1987-01-20 1987-01-20  221840.6        6   6 4.196
5        5 1988-01-27 1988-02-04 1988-02-04  204759.4        9   9 4.279
6        6 1989-04-05 1989-04-29 1989-04-29 1186142.4       25  25 3.900
7        7 1990-02-26 1990-03-09 1990-03-09  497076.5       12  12 4.031
8        8 1990-04-14 1990-04-24 1990-04-24  255061.4       11  11 4.309
       tqmin
1 1986-04-26
2 1986-05-13
4 1987-01-20
5 1988-02-03
6 1989-04-29
7 1990-03-09
8 1990-04-23
Warning message:
4.4% of the discharges (81 observations) are NA values. NAs always terminate a drought event. 
Summary of pooled droughts
River: Ngaruroro at Kuripapango
Pooling: Moving Average, 3 were pooled
Units: volumes in m³, duration in days

Filtered 1 minor events of 6 total. 
Only droughts with volume >= 4348.426 m³ and duration >= 5 days are reported.

  event.no      start       time        end    volume duration dbt   qmin
1        1 1986-04-12 1986-04-23 1986-04-23 479684.16       12  12 4.0951
2        2 1986-05-07 1986-05-12 1986-05-12 101684.16        6   6 4.5387
4        4 1989-04-05 1989-04-25 1989-04-25 869685.12       21  21 4.0561
5        5 1990-02-26 1990-03-04 1990-03-04 193484.16        7   7 4.2898
6        6 1990-04-15 1990-04-19 1990-04-19  80706.24        5   5 4.5496
       tqmin
1 1986-04-22
2 1986-05-12
4 1989-04-24
5 1990-03-04
6 1990-04-19
Warning message:
In pool_sp(drought) :
  Time series ended before recovery of drought. (event number: 8)
Summary of pooled droughts
River: Ngaruroro at Kuripapango
Pooling: Sequent Peak, 1 were pooled
Units: volumes in m³, duration in days

Filtered 1 minor events of 8 total. 
Only droughts with volume >= 5930.712 m³ and duration >= 5 days are reported.

  event.no      start       time        end    volume duration dbt  qmin
1        1 1986-04-12 1986-04-27 1986-04-29  770999.0       16  16 3.969
2        2 1986-05-07 1986-05-13 1986-05-17  267209.3        7   9 4.189
3        3 1987-01-15 1987-01-20 1987-01-21  221840.6        6   6 4.196
4        4 1988-01-27 1988-02-04 1988-02-05  204759.4        9   9 4.279
5        5 1989-04-05 1989-04-29 1989-05-01 1186142.4       25  25 3.900
6        6 1990-02-26 1990-03-09 1990-03-09  497076.5       12  12 4.031
7        7 1990-04-14 1990-04-24 1990-04-24  255061.4       11  11 4.309
       tqmin
1 1986-04-26
2 1986-05-13
3 1987-01-20
4 1988-02-03
5 1989-04-29
6 1990-03-09
7 1990-04-23