Skip to content

indices based on annual climatology of percentiles

This is an overall issue aiming at splitting the "issue of percentile based indices" into more tangible and concrete sub-issues.

  1. Indices counting the number of occurrences (days) above/below a temporally and spatially variable threshold. I.e. for each point (gridcell) there is a threshold value for each day of the year (complication: leap days!). Example indices are `tn10p, tx10p, tg10p, tx90p, tg90p, txgt50p, txgt{PRC}p, tngt{PRC}p, tmgt{PRC}p, txlt{PRC}p, tnlt{PRC}p, tmlt{PRC}p. Cf. #196 (closed) (M 0.13)

  2. Same as for point 1, but the climatology of threshold values is based on days meeting a threshold condition. E.g. for r75p, r95p, r99p, r{PRC}p only "rainy days" (e.g. days with precipitation of at least X mm day-1) are included in the percentile calculation. Cf. #197 (closed).

  3. Indices giving the total precipitation, in mm day-1, above a percentile threshold as a percentage of total wet-day precipitation, e.g. r95ptot, r99ptot, r{PRC}ptot.

  4. Indices counting the total number of days belonging to temperature spells of length at least ND above/below a percentile-based threshold (as per details under 1). Example indices include wsdi, wsdi{ND}, csdi, csdi{ND}. In these indices the percentile threshold is fixed at 90 for wsdi and 10 for csdi, but this should be possible to specify as a parameter.

  5. A few other indices involving two input variables, each one with its own threshold array. Examples are txDtnD, ..., but let's leave them for now as they need further specification (as to whether it is all days or only the longest spell).

The threshold array is calculated as a daily climatology over a reference period, typically 30 years. For each day the percentile is calculated based all days in all years of the reference period and falling under a centred 5-day sliding window. This a bit involved as

  • the window should extend into the previous/next year (including extending outside the reference period)
  • handling of leap years
  • use the right percentile method, see wiki page
  • use bootstrapping as per Zhang et al, 2005

For thresholded data, e.g. indices based on "rainy days" include only RR >= 1 mm day-1 in percentile calculation.

Edited by Lars Bärring