Joint bias correction of temperature and precipitation in climate model simulations

Monday, 15 December 2014: 11:50 AM
Chao Li1, Anna M Michalak1,2, Eva Sinha1,2, Daniel E Horton2 and Noah S Diffenbaugh2, (1)Carnegie Institution for Science, Stanford, CA, United States, (2)Stanford Earth Sciences, Environmental Earth System Science, Stanford, CA, United States
Bias correction of meteorological variables from climate model simulations is a routine strategy for circumventing known limitations of state-of-the-art general circulation models. Although the assessment of climate change impacts often depends on the joint variability of multiple variables, commonly used bias correction methodologies treat each variable independently, and do not consider the relationship among variables. Independent bias correction can therefore produce non-physical corrections and may fail to capture important multivariate relationships. Here, we introduce a joint bias correction methodology (JBC) and apply it to precipitation (P) and temperature (T) fields from the CMIP5 model ensemble. This approach is based on a general bivariate distribution of P-T, and can be seen as a multivariate extension of the commonly used univariate quantile mapping method. It proceeds by correcting either P or T first and then correcting the other variable conditional upon the first one, both following the concept of the univariate quantile mapping. JBC is shown to reduce model-simulated biases in P-T correlation fields, as well as biases in the mean and variance of P and T. In addition, it overcomes a noted problem with an existing joint P-T correction method, namely that this earlier approach did not yield appreciable improvements in P-T correlation coefficients. JBC, using methods such as the one presented here, thus represents an important step in impacts-based research as it explicitly accounts for inter-variable relationships as part of the bias correction procedure, thereby improving not only the individual distributions of P and T, but critically, their joint distribution.