Abstract
Abstract. Downscaling of climate projections is the most adopted method to assess the impacts of climate change at regional and local scale. In the last decade, downscaling techniques which provide reasonable improvement to resolution of General Circulation Models' (GCMs) output are developed in notable manner. Most of these techniques are limited to spatial downscaling of GCMs' output and still there is a high demand to develop temporal downscaling approaches. As the main objective of this study, combined approach of spatial and temporal downscaling is developed to improve the resolution of rainfall predicted by GCMs. Canberra airport region is subjected to this study and the applicability of proposed downscaling approach is evaluated for Sydney, Melbourne, Brisbane, Adelaide, Perth and Darwin regions. Statistical Downscaling Model (SDSM) is used to spatial downscaling and numerical model based on scaling invariant concept is used to temporal downscaling of rainfalls. National Centre of Environmental Prediction (NCEP) data is used in SDSM model calibration and validation. Regression based bias correction function is used to improve the accuracy of downscaled annual maximum rainfalls using HadCM3-A2. By analysing the non-central moments of observed rainfalls, single time regime (from 30 min to 24 h) is identified which exist scaling behaviour and it is used to estimate the sub daily extreme rainfall depths from daily downscaled rainfalls. Finally, as the major output of this study, Intensity Duration Frequency (IDF) relations are developed for the future periods of 2020s, 2050s and 2080s in the context of climate change.
Highlights
Quantifying of the design storm magnitude is one of challenging steps of urban hydrology study
In Australia, existing Intensity Duration Frequency (IDF) relations have been developed by the Australian Bureau of Meteorology (BoM) are based on past rainfall records, and impacts of climate change has not been taken into account in the IDF development
This study develops an approach for spatial and temporal downscaling of regional rainfall data to develop IDF curves, which will assist hydrologists in estimating design storms in the future
Summary
Quantifying of the design storm magnitude is one of challenging steps of urban hydrology study. Once the impact of climate change need to be considered for sensitive hydrological studies, it becomes very complicated more than previous. Intensity Duration Frequency (IDF) curve is one of popular methods among the water engineers/hydrologists in estimating the magnitude of design storms. These IDF curves do not represent the impact of climate change as it has been developed decades ago using historical rainfall records. In Australia, existing IDF relations have been developed by the Australian Bureau of Meteorology (BoM) are based on past rainfall records, and impacts of climate change has not been taken into account in the IDF development. Urban development in most of Australian states need to evaluate the impacts of climate change on urban hydrologic processes. There is a great need to develop IDF curves under climate change scenarios to facilitate future catchment investigations
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