Time series transformation tool: description of the program to generate time series consistent with the KNMI'06 climate scenarios

Parallel to the development of the KNMI’06 climate scenarios in 2006 a tool was developed to generate temperature and precipitation time series for the future (http://climexp.knmi.nl/Scenarios_monthly/). These time series are often needed for climate impact and adaptation models. The aim of this time series transformation tool is to adjust a historical precipitation or temperature time series (on a daily basis) in such a way that the newly generated time series for the future is consistent with one of the four KNMI’06 climate scenarios for a selected time horizon.

Until now, no official report was available with a description of all aspects of the KNMI transformation tool, although there are an elaborate user online guide and some popular-scientific publications (e.g. Bakker and Bessembinder, 2007). Within the COM28-project (“Climate data”) this transformation tool was used regularly. As part of this project, the present background report is written, that gives a description of the tool together with an overview of its development and the analyses performed by KNMI to determine its limitations and advantages.

After the first release on internet in 2006, the transformation tool was further developed and improved. In Chapter 2 an extensive description is given of the functioning of the current and previous versions of the transformation tool. Chapter 3 gives an overview of the differences between the various versions of the temperature and precipitation transformation tool. Chapter 4 explores the characteristics of the various versions of the transformation tool. It describes e.g. the effect of changing the method to remove and add wet days and the effect of using other reference periods than the standard period of 1976-2005.

Chapter 5 describes the advantages and limitations of the current time series transformation tool and it gives information on alternative methods for generating time series for the future. The chapter indicates on which points the transformation tool could be improved or extended and whether it is useful to develop (further) other methods to generate time series for the future. Desired points for improvement and extension are closely linked to user requirements, which are also discussed shortly. Several projects are ongoing or will start that include already several of the desired and possible developments. A few examples are: “Theme 6: Climate projections” of the Knowledge for Climate programme, the project “Kritische Zone” of the National Model and Data Centre, and the activities for the next generation of the KNMI climate scenarios.