Presenter: Claudia Tebaldi

Title: Estimating mean and variability of temperature and precipitation extremes from initial condition ensembles: how many members do we need?

Abstract:

I will present some highlights from a recently published paper (available from https://doi.org/10.5194/esd-12-1427-2021). We use two existing large initial condition (IC) ensembles (CESM and CanESM) to study the effect of ensemble size on estimating mean and variability of several metrics of extreme daily temperatures and precipitation. We show that we can use a small IC ensemble (5 members) to guide a-priori the choice of the size of a large IC ensemble to be run, depending on the precision we demand of our estimates. Of course, the answer to the question of how many ensemble members are needed will always depend on the quantities of interest, and what precise means for us. For this application, we target a range of metrics and two fairly common ESM resolutions (~1 degree and ~2 degrees), and we want to characterize changes in mean and variability under RCP8.5 over the 21st century. We show that a size of 20-25 members appears sufficient to accurately estimate the signal of change in these metrics over the course of the century, with additional members contributing only marginal gains (We use the full ensembles of 40 and 50 members as our truth). In addition, the same size ensemble is sufficient to accurately estimate internal variability and its changes over the course of the 21st century, in fact in most cases a much smaller size is sufficient for this purpose.

Date

12 May 2022

Time

PT: 8:30 am
ET: 11:30 am

Call Info

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Attendees:

Time	Title	Presenter	Presentation	Recording	Notes
30 min	Estimating mean and variability of temperature and precipitation extremes from initial condition ensembles: how many members do we need?	Claudia Tebaldi	E3SMAllHandsMay2022_Tebaldi_final.pdf	MP4 Movie (on the E3SM YouTube Channel)

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