With this circular, we are sending you some important information on the following topics:
1) Changes in bias correction method, replacement of input data
2) Status of precipitation and snowfall data
3) New email archive on website
4) New tools and auxiliary files available on website
5) Timeline for data upload
1) Changes in bias correction method, replacement of input data
What’s the problem?
In pre-processing the ISI-MIP climate input data, we have so far been
using an existing bias correction method (used e.g. in the WaterMIP
project), which we believe is well suited particularly for studies
focusing on periods of relatively stable climate. However, we have
recently become aware of some drawbacks of this method when it comes to
future climate projections.
Most importantly, projected
long-term trends (relative precipitation and absolute temperature
change) are not preserved by the current bias-correction algorithm in
all cases. In particular, monthly global mean temperatures calculated
using future daily temperature values can be rendered incompatible with
the uncorrected global monthly means. Since a principal aim of ISI-MIP
is the quantification of uncertainties at different levels of global
warming, it is essential that the time series of global mean temperature
change is consistent. Therefore, we are currently revising the bias
correction method. We will provide corrected temperature data, that
preserves the monthly temperature averages, except for an offset. This
unfortunately means that we will have to replace the temperature data.
In addition, we are working on a modified version of the precipitation
code to ensure that the relative change in precipitation is preserved.
What to expect?
At the moment we are testing the revised bias correction method, and
are putting all our efforts towards completing the revision of the data
as quickly as possible.
In the best case we will provide a completely new data set for all variables, that preserves the absolute or relative trend of the original GCM data.
At the very least we will provide revised temperature data, that preserves the trend, while the other variables are still corrected based on the WaterMIP method.
In any case we will provide a complete set of bias corrected historical and RCP8.5 climate data for the HadGEM2-ES model by 1 May, so that you can start model production runs by that date; and we will of course continue processing additional data as fast as we can after that date.
We will of course notify you of any changes in data availability, and kindly ask for your patience.
How to proceed?
If you have already done model runs using the currently available input
data, this work remains useful. To minimise delay, it will be extremely
helpful if you have already tested and prepared your model and
routines, so that once the revised data is available, production runs
can start immediately.
We will provide you with a detailed
explanation of the revised bias correction method as soon as possible.
We would also like to thank everybody who pointed out to us specific
problems with the currently available input data! We are confident that
we can address these problems with a revised bias correction method, and
that the revised data will be much improved.
We are genuinely
sorry for the inconvenience that this procedure is causing. After
considering all aspects of the problem, we came to the conclusion that
only by revising the data we can ensure that the research objectives in
ISI-MIP can be met and high-quality scientific results achieved. We
sincerely hope that you understand our motivation, and we apologize for
the additional work that this decision may cause you.
2) Status of precipitation and snowfall data
As reported in the two previous circulars, unrealistically high
monthly-mean precipitation (pr) and snowfall (prsn) values were found in
some input data files. We have identified the source of the problem and
resolved it. The revised data set (see above) will contain corrected pr
and prsn data, and we will notify you when it is available.
3) New email archive on website
To make sure that all the information and updates we are communicating
to you are permanently accessible independent of people's email clients,
we have set up an email archive on the website which will be frequently
updated. Visit www.isimip.org, then click "E-mail archive".
4a) Regridding tools available on website for HadGEM2-ES grid under "Input data"
As indicated in the simulation protocol, ISI-MIP input data is provided
on a 0.5 x 0.5 degree grid, and ISI-MIP participants are asked to run
their models at 0.5 x 0.5 degree horizontal resolution where possible.
Nonetheless, some participants will need to run at a coarser resolution
in order to be able to cover at least the minimal scenario set-up.
The JULES model team has kindly provided some tools that can be used to
interpolate the data to the 1.875 x 1.25 degree grid of the HadGEM2-ES
climate model. You may use these if you choose to regrid to this
resolution. Visit the ISI-MIP website www.isimip.org and click "Input data", then "Regridding to coarser resolution" or simply follow the link:
http://www.pik-potsdam.de/research/climate-impacts-and-vulnerabilities/projects/Externally_RD2/isimip/input-data-1/regridding-to-coarser-resolution
4b) WFD lat-lon file available on website under "Input data"
The WATCH Forcing data files come without latitude-longitude information. On the website www.isimip.org
under "Input data" you will find a NetCDF file that contains that
information and can be used to map the WATCH data to the
latitude-longitude grid.
4c) Land-cover data on website under "Input data"
Harmonizing land cover and land-use data is not intended within the
ISI-MIP Fast Track. However, if you need data for your model runs and do
not have your own set-up you may use the data listed on www.isimip.org.
Go to "Input data", then click "Land-cover and topographic data" . For
references please see the simulation protocol (section 4.3).
5) Timeline for data upload
Because of the delay caused by the revision of the input data (see 1)),
we need to relax the May 1st deadline for submitting a first output
data set for testing. We now simply ask you to provide us with a first
piece of output data for testing purposes as soon as you have completed
your first model production run. A web platform will be made available
where you can upload output data, and we will inform you about the
details as soon as they are sorted out.
Please do not hesitate to contact us if you have any questions or comments.
