Modelling runoff with statistically downscaled daily site, gridded and catchment rainfall series

- Statistical downscaling has been first time used for catchment and grid daily rainfall.
- Downscaling results from three techniques have been compared.
- Hydrological implications, rather than rainfall statistics, from statistical downscaling results have been explored.

SummaryStatistical downscaling has mainly been used for site (point) scales to provide daily rainfall series for climate change impact studies. The objectives of this study are to compare three methods of applying statistical downscaling to catchment rainfall and evaluating their hydrological response with a hydrological model: (a) statistically downscaling to sites and then interpolating to gridded rainfall which is accumulated to catchment average rainfall; (b) statistically downscaling to catchment average rainfall directly; and (c) statistical downscaling to grid cells and then accumulating to catchment average rainfall. Results indicate that statistical downscaling can be successfully applied at catchment average and grid cell scales. All three methods of application performed similarly for a range of rainfall characteristics, with directly downscaled catchment average rainfall producing a relatively better result for extreme daily rainfall indices. However, hydrological simulation indicated that the direct downscaling of catchment average rainfall did not have any advantages over the other two downscaling application methods in terms of the runoff statistics evaluated. In addition, all three methods of downscaling application could simulate the spatial correlation of daily and annual runoff across the nine focus catchments investigated. The advantages and limitations of applying statistical downscaling to the assessment of hydrological response to climate change are also discussed.