UNIVERSITY OF READING - E-Library - WMO

uncertainty’. Another uncertainty comes from internal variability also termed as ‘climatenoise’ (Schneider & Kinter, 1994; Madden, 1976; Feldstein, 2000).5.2 Calibration approachesBased on the results from Chapter 4 summer and autumn daily mean temperature projectionsfor Wangdue and summer daily mean temperature projections for Wangdue-Shelganaaverage will be calibrated. This section outlines two approaches to perform the calibration.Further details on the related mathematical derivations can be found in Ho (2010, Chapter 5).The calibration of PRECIS daily mean temperatures involves three variables;i) Station observations (denoted by ) for the ‘present’ reference period (1990-2010).ii) PRECIS simulations for the grid box where the station is located for the samereference period (denoted by ).iii) PRECIS projection (denoted by ) for the ‘future’ period (2030-2050).a)Coi) Bias Correction (BC)obsmodeldelX oX mpresentCorrectionii) Change Factor (CF)X oX mfuturec)Cob)CoobsX oCorrectionX od)Comodel X mpresentX mfutureFigure 5-1 Schematic diagrams showing two approaches for calibrating climate modelprojections: i) bias correction and ii) change factor. (a,b) shows the approach of calibrationwhile (c,d) are examples of probability density functions (PDF) of the variables, which areassumed to have different mean and variance but same shape. The dashed orange line is thecalibrated PDF. Reproduced from Hawkins et al. (2012) (a,b) and Ho et al. (2012) (c,d).37