PRECIS

An Introduction to the PRECIS system

PRECIS was developed in order to help generate high-resolution climate change information for as many regions of the world as possible. The intention is to make PRECIS freely available to groups of developing countries in order that they may develop climate change scenarios at national centres of excellence, simultaneously building capacity and drawing on local climatological expertise. These scenarios can be used in impact, vulnerability and adaptation studies, and to aid in the preparation of National Communications, as required under Articles 4.1 and 4.8 of the United Nations Framework Convention on Climate Change (UNFCCC).

Quick links:

Download the PRECIS handbook (PDF format, 2.0MB)
Generating High Resolution Climate Change Scenarios using PRECIS - April 2004.  This handbook was published jointly by the UNDP and the Hadley Centre following and extensive review process.

Download PRECIS -- Update 2002 brochure (PDF format, 1.0MB)
 This brochure, produced for the Conference of the Parties to the UNFCC (Cop8) meeting in Delhi in 2002, describes the PRECIS system and includes examples of its use.

Download the PRECIS brochure (PDF format, 1.3MB)
 This brochure, produced for the Conference of the Parties to the UNFCC (Cop7) meeting in Marrakech in 2001, introduces the PRECIS system.

Read more:

Why use a regional climate model?

Formulation of the PRECIS model

What hardware and operating system is required to run PRECIS?

How fast is PRECIS?

What output does PRECIS produce?

How are boundary conditions supplied?

Other Frequently Asked Questions:

Is a Windows version of PRECIS available?

Is a Macintosh version of PRECIS available?

Can we have the PRECIS source code?

Can PRECIS be parallelized/run on a cluster?

A regional climate model (RCM) is a downscaling tool that adds fine scale (high resolution) information to the large-scale projections of a global general circulation model (GCM). GCMs are typically run with horizontal scales of 300km; regional models can resolve features down to 50km or less. This makes for a more accurate representation of many surface features, such as complex mountain topographies and coastlines. It also allows small islands and peninsulae to be represented realistically, where in a global model their size (relative to the model gridbox) would mean their climate would be that of the surrounding ocean.

RCMs are full climate models, and as such are physically based. They represent most if not all of the processes, interactions and feedbacks between climate system components represented in GCMs. They produce a comprehensive set of output data over the model domain.

There are three types of technique for obtaining regional climate change projections: statistical, dynamical and hybrid (statistical-dynamical) techniques. RCMs fall into the dynamical category.

You can view a flyer from the Conference of the Parties to the UNFCCC (COP9) meeting (Italy 2003) which includes some general information about regional climate modelling and PRECIS.

Annexes I & II of the PRECIS handbook describes the (very similar) scientific formulations of the PRECIS regional model and HadAM3P, the model that provides the default lateral boundary conditions (LBCs).  Both are based on the atmospheric component of the Hadley Centre's current "operational" coupled climate model, HadCM3.

HadAM3P is a global atmosphere-only model with a resolution of order 150km, forced by surface boundary conditions (sea-surface temperature and sea-ice fraction) from HadCM3 and observations.  It has been run for two "time slices": 1960-1990 and 2070-2100.  These are the periods for which boundary conditions are available to the PRECIS system.  The Hadley Centre is running a suite of climate change experiments, sampling a range of scenarios from the IPCC Special Report on Emissions Scenarios (SRES), using HadAM3P.  See Obtaining Precis for more information about which experiments are available to drive PRECIS.

We are also developing software that will allow other modelling centres' data formats to be read and converted to LBC format, so that PRECIS can be driven by a variety of global models.  We expect boundary data from the Max Planck Institute ECHAM4 global climate model (Germany) and the National Centers for Environmental Protection (NCEP) re-analysis project (USA) to be available soon.

PRECIS has been developed to run on PCs under 32-bit Intel (x86) compatible Linux-based systems. No particular Linux flavour is recommended; several distributions of SuSE, RedHat and Mandrake/Mandriva have been tested successfully. (Dual-boot PCs can be used, but bear in mind that the Windows partition will be unavailable unless the experiment is interrupted and the machine re-booted.) PRECIS's control scripts require the public domain Korn shell (pdksh) to be installed, which is not always done as part of a default Linux installation; however, it isn't necessary to use the Korn shell as the interactive shell.

At least 512MB physical memory is required, and 768MB or more is recommended. The difference in performance is small, but the smaller memory imposes a (possibly undesirable) upper limit on the size of the domain that can be modelled.  Processor speeds of 2.0GHz or greater are recommended - in general, simulation speed is proportional to chip speed.

Depending on the output options chosen, a typical 30-year PRECIS experiment generates between 130 and 540GB of output data, whilst the  boundary conditions for a thirty-year experiment occupy 40GB. A hard disk size of at least 100GB is therefore recommended, although with careful data management by the user, smaller disks can be used. It is recommended that DLT or DAT tapes are used for back-up and permanent storage of the output data.  The preferred medium for supplying boundary data is via an IDE hard drive, typically 200GB.

The standard distribution of PRECIS, which includes sample boundary driving data, is on a dual layer DVD, so a DVD-ROM is required. 

If power supplies are unreliable, PRECIS can be shut down cleanly (ready for a re-start) given approximately half-an-hour's notice. If shut down without warning, the model can be re-started from the beginning of the model month in progress, which might involve repeating up to typically twelve (real) hours of simulation. A UPS (uninterruptible power supply) may therefore be appropriate if power outages are frequent.

For more information, please see Chapter 2 of the PRECIS technical manual - download PDF (2.0MB).

A typical experiment, covering a 100-by-100 gridbox domain and including a representation of the atmospheric sulphur-cycle, run on a 2.8GHz machine, takes 4.5 months to complete a 30-year simulation. The simulation is 33% faster if the sulphur cycle is not modelled.

A comprehensive set of variables has been chosen for PRECIS's default output - for a listing, please see Appendix C of the PRECIS technical manual (download PDF (2.0MB) ). The user can specify the levels on which upper-air variables are output. Variables are automatically output as "climate" means (monthly, seasonal, annual, decadal etc.). Daily and hourly means can be selected if required.

If a particular variable is not included in the standard list or an existing variable on a different timescale is require, it is easy (with help from the Hadley Centre) to reconfigure PRECIS so as to include it. Similarly, custom meaning periods or timeseries of instantaneous values may be available.

PRECIS has three possible output data formats: PP, GRIB and NetCDF. It is up to the user to decide which is most appropriate to their data analysis and visualisation software. PP format is a Met Office format, and various tools are supplied with PRECIS to process it. It can easily be converted into both GRIB and NetCDF formats, but not vice versa.  PP format is the recommended output data format.

Boundary condition data are supplied on an IDE hard drive of roughly 200GB (or possible a DLT tape). See Obtaining Precis for more information.

There are no plans to produce a Windows version of PRECIS.

Is a Macintosh version of PRECIS available? (back to top)

Though Macintosh OS X is Unix based, PRECIS has not been compiled to support anything other than Intel or AMD processors.  Thus, PRECIS is not supported on older Macintosh computers .  This includes any Linux distribution for PowerPC.  Now that Apple is using Intel processors, there's no reason why Precis wouldn't run on Linux running on an Intel Macintosh, although we haven't verified that it works.

The PRECIS source code is included with the standard distribution. Compilers will be required in order to produce new executables.

The current version of PRECIS runs on a single processor only, and there are no plans to make this version run on parallel processors.  We recommend that spare processing capacity be used to run separate experiments (e.g. baseline + climate change, or different ensemble members for a given scenario) simultaneously.  Version 2.0 of PRECIS will be multiprocessor only.