[ACG44-P06] Projections of the duration of low-precipitation season in the Chao Phraya river basin based on the output from CMIP5 GCMs
Keywords:Climate change, Precipitation, Chao Phraya river basin
The result of projection is significantly different between with and without applying bias correction method. For the average duration, an increase trend calculated without bias correction changes to a decrease trend after bias correction. It is well known that precipitation simulated by GCMs generally have considerable bias, thus it is common to correct bias before the application. This is true for the projections of the duration of low-precipitation season. To the best of our knowledge, there is no specific correction method for this purpose. Hence, we developed a method that correct the duration of low-precipitation season directly by changing threshold of precipitation for GCMs so that a duration of GCM low-precipitation season calculated by corrected threshold is agree to that of observation by original threshold in historical period. The developed method is different from common bias correction method in terms of the characteristic that not a precipitation itself but a threshold is corrected. This approach used in the correction of low-precipitation amount, which correct low-precipitation below a threshold as 0 considering the characteristic of GCM that there are significantly larger number of low-precipitation than observation.
It is important to understand the change of the duration of low-precipitation season because not only it has some impact on hydrology but also it affects the accuracy of bias correction for the amount of precipitation especially for pre- and post-monsoon season because many of bias correction methods adopt the approach that low-precipitation and others are separately corrected. Due to this reason, it is known that the error of bias correction generally large in these seasons. The results of this study can contribute to the improvement of bias correction as well as understanding the characteristics of the projections of precipitation among GCMs in monsoon regions.