Statistical downscaling of general circulation model outputs to precipitation-part 2 : Bias-correction and future projections
- Sachindra, Dhanapala, Huang, Fuchun, Barton, Andrew, Perera, Bimalka
- Authors: Sachindra, Dhanapala , Huang, Fuchun , Barton, Andrew , Perera, Bimalka
- Date: 2014
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 34, no. 11 (2014), p. 3282-3303
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- Reviewed:
- Description: This article is the second of a series of two articles. In the first article, two models were developed with National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis and HadCM3 outputs, for statistically downscaling these outputs to monthly precipitation at a site in north-western Victoria, Australia. In that study, it was seen that the downscaling model developed with NCEP/NCAR reanalysis outputs performs much better than the model developed with HadCM3 outputs. Furthermore, it was found that there is large bias in HadCM3 outputs which needs to be corrected. In this article, the downscaling model developed with NCEP/NCAR reanalysis outputs was used to downscale HadCM3 20th century climate experiment outputs to monthly precipitation over the period 1950-1999. In all four seasons, the precipitation downscaled with HadCM3 20th century outputs, displayed a large scatter and the majority of precipitation was overestimated. The precipitation downscaled with HadCM3 outputs was bias-corrected against the observed precipitation pertaining to the period 1950-1999, using three techniques: (1) equidistant quantile mapping (EDQM), (2) monthly bias-correction (MBC) and (3) nested bias-correction (NBC). Although all these bias-correction techniques were able to adequately correct the statistics of downscaled precipitation, the magnitude of the scatter of precipitation remained almost the same. Considering the performances and its ability to correct the cumulative distribution of precipitation, EDQM was selected for the bias-correction of future precipitation projections. HadCM3 outputs for the A2 and B1 greenhouse gas scenarios were introduced to the downscaling model and the downscaled precipitation for the period 2000-2099 was bias-corrected with the EDQM technique. Both A2 and B1 scenarios indicated a rise in the average of future precipitation in winter and a drop in it in summer and spring. These scenarios showed an increase in the maximum monthly precipitation in all seasons and an increase in percentage of months with zero precipitation in summer, autumn and spring. © 2014 Royal Meteorological Society
- Authors: Sachindra, Dhanapala , Huang, Fuchun , Barton, Andrew , Perera, Bimalka
- Date: 2014
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 34, no. 11 (2014), p. 3282-3303
- Full Text:
- Reviewed:
- Description: This article is the second of a series of two articles. In the first article, two models were developed with National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis and HadCM3 outputs, for statistically downscaling these outputs to monthly precipitation at a site in north-western Victoria, Australia. In that study, it was seen that the downscaling model developed with NCEP/NCAR reanalysis outputs performs much better than the model developed with HadCM3 outputs. Furthermore, it was found that there is large bias in HadCM3 outputs which needs to be corrected. In this article, the downscaling model developed with NCEP/NCAR reanalysis outputs was used to downscale HadCM3 20th century climate experiment outputs to monthly precipitation over the period 1950-1999. In all four seasons, the precipitation downscaled with HadCM3 20th century outputs, displayed a large scatter and the majority of precipitation was overestimated. The precipitation downscaled with HadCM3 outputs was bias-corrected against the observed precipitation pertaining to the period 1950-1999, using three techniques: (1) equidistant quantile mapping (EDQM), (2) monthly bias-correction (MBC) and (3) nested bias-correction (NBC). Although all these bias-correction techniques were able to adequately correct the statistics of downscaled precipitation, the magnitude of the scatter of precipitation remained almost the same. Considering the performances and its ability to correct the cumulative distribution of precipitation, EDQM was selected for the bias-correction of future precipitation projections. HadCM3 outputs for the A2 and B1 greenhouse gas scenarios were introduced to the downscaling model and the downscaled precipitation for the period 2000-2099 was bias-corrected with the EDQM technique. Both A2 and B1 scenarios indicated a rise in the average of future precipitation in winter and a drop in it in summer and spring. These scenarios showed an increase in the maximum monthly precipitation in all seasons and an increase in percentage of months with zero precipitation in summer, autumn and spring. © 2014 Royal Meteorological Society
- Sachindra, D. A., Huang, Fuchun, Barton, Andrew, Perera, Bimalka
- Authors: Sachindra, D. A. , Huang, Fuchun , Barton, Andrew , Perera, Bimalka
- Date: 2013
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 33, no. 5 (2013), p. 1087-1106
- Full Text: false
- Description: This study employed least square support vector machine regression (LS-SVM-R) and multi-linear regression (MLR) for statistically downscaling monthly general circulation model (GCM) outputs directly to monthly catchment streamflows. The scope of the study was limited to calibration and validation of the downscaling models. The methodology was demonstrated by its application to a streamflow site in the Grampian water supply system in northwestern Victoria, Australia. Probable predictors for the study were selected from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data set based on the past literature and hydrology. Probable variables that displayed the best significant correlations, consistently with the streamflows over the entire period of the study (1950-2010) and under three 20-year time slices (1950-1969, 1970-1989 and 1990-2010) were selected as potential predictors. To better capture seasonal variations of streamflows, downscaling models were developed for each calendar month. The standardized potential predictors were introduced to the LS-SVM-R and MLR models, starting from the best correlated three and then, others one by one, based on their correlations with the streamflows, until the model performance in validation was maximized. This stepwise model development enabled the identification of the optimum number of potential variables for each month. The model calibration was performed over the period 1950-1989 and validation was done for 1990-2010. LS-SVM-R model parameter optimization was achieved using simplex algorithm and leave-one-out cross-validation. The MLR models were optimized by minimizing the sum of squared errors. In both modelling techniques, validation was performed as an independent simulation. In calibration, LS-SVM-R and MLR models displayed equally good performances with a trend of under-predicting high flows. During validation, LS-SVM-R outperformed MLR, though both techniques over-predicted most of the streamflows. It was concluded that LS-SVM-R is a better technique for statistically downscaling GCM outputs to streamflows than MLR, but still MLR is a potential technique for the same task. Copyright © 2012 Royal Meteorological Society.
Statistical downscaling of general circulation model outputs to precipitation
- Sachindra, Dhanapala, Huang, Fuchun, Barton, Andrew, Perera, Bimalka
- Authors: Sachindra, Dhanapala , Huang, Fuchun , Barton, Andrew , Perera, Bimalka
- Date: 2012
- Type: Text , Conference paper
- Relation: 34th Hydrology and Water Resources Symposium, HWRS 2012 p. 595-602
- Full Text: false
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- Description: Victoria suffered a severe drought over the period 1998-2007, when the annual average precipitation plunged by about 13% from the long term average. Precipitation is directly related to the availability of water resources in a catchment. Therefore it is useful to predict precipitation, particularly in light of any future climate change, which will help in the management of water resources at the catchment level. General Circulation Models (GCMs) are considered to be the most advanced tools available for simulating the future climate. Due to the coarse spatial resolution, however, GCM outputs cannot be used directly at the catchment scale. To overcome this problem statistical and dynamic downscaling techniques have been developed. Downscaling techniques link the coarse GCM outputs to catchment scale hydroclimatic variables. The present research has focussed on statistically downscaling monthly NCEP/NCAR reanalysis outputs to monthly precipitation at the catchment level. A precipitation station in the operational area of the Grampians Wimmera Mallee Water Corporation (GWMWater) in northwestern Victoria was considered as the case study. Multi-linear regression was used in the development of the downscaling models. This research employed separate downscaling models for each calendar month, with the intention of better capturing the seasonal variations of precipitation. A set of probable predictors were selected following the past literature and hydrology. Data for the probable predictors and precipitation were split into three 20 year time slices; 1950-1969, 1970-1989 and 1990-2010. The probable predictors which displayed the best statistically significant correlations consistently with precipitation over the three time slices and the whole period of the study were selected as potential predictors, for each calendar month. These potential predictors were introduced to the downscaling model one at a time based on the strength of the correlation, over the whole period of the study, until the model performance, in terms of Nash-Sutcliffe Efficiency (NSE), was maximised. This approach ensured the identification of the best potential predictor for each calendar month. In calibration and validation, the model displayed good performances with NSEs of 0.74 and 0.70 respectively. In calibration, the average precipitation was perfectly reproduced by the model and in validation it was slightly over-predicted. However, both in calibration and validation, the model tended to under-predict high precipitations and over-predict near-zero precipitations. A graphical comparison of observed precipitation, downscaling model reproduced precipitation and the Hadley Centre Coupled Model version 3 GCM (HadCM 3) simulated raw precipitation output, revealed that there is large bias in the HadCM 3 precipitation outputs. Therefore, before producing any future precipitation projections with the downscaling model, a bias correction to GCM outputs is prescribed.
Statistical downscaling of general circulation model outputs to precipitation—part 1: calibration and validation
- Sachindra, Dhanapala, Huang, Fuchun, Barton, Andrew, Perera, Bimalka
- Authors: Sachindra, Dhanapala , Huang, Fuchun , Barton, Andrew , Perera, Bimalka
- Date: 2014
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 34, no. 11 (2014), p. 3264-3281
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- Description: This article is the first of two companion articles providing details of the development of two separate models for statistically downscaling monthly precipitation. The first model was developed with National Centers for Environmental Prediction/National Center for Atmospheric Research (/) reanalysis outputs and the second model was built using the outputs of Hadley Centre Coupled Model version 3 (). Both models were based on the multi‐linear regression () technique and were built for a precipitation station located in Victoria, Australia. Probable predictors were selected based on the past literature and hydrology. Potential predictors were selected for each calendar month separately from the / reanalysis data, considering the correlations that they maintained with observed precipitation. Based on the strength of the correlations, these potential predictors were introduced to the downscaling model until its performance in validation, in terms of Nash–Sutcliffe Efficiency (), was maximized. In this manner, for each calendar month, the final sets of potential predictors and the best downscaling models with / reanalysis data were identified. The 20th century climate experiment data corresponding to these final sets of potential predictors were used to calibrate and validate the second model. In calibration and validation, the model developed with / reanalysis data displayed of 0.74 and 0.70, respectively. The model built with outputs showed of 0.44 and 0.17 during the calibration and validation periods, respectively. Both models tended to under‐predict high precipitation values and over‐predict near‐zero precipitation values, during both calibration and validation. However, this prediction characteristic was more pronounced by the model developed with outputs. A graphical comparison of observed precipitation, the precipitation reproduced by the two downscaling models and the raw precipitation output of , showed that there is large bias in the precipitation output of . This indicated the need of a bias‐correction, which is detailed in the second companion article.
- Authors: Sachindra, Dhanapala , Huang, Fuchun , Barton, Andrew , Perera, Bimalka
- Date: 2014
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 34, no. 11 (2014), p. 3264-3281
- Full Text:
- Reviewed:
- Description: This article is the first of two companion articles providing details of the development of two separate models for statistically downscaling monthly precipitation. The first model was developed with National Centers for Environmental Prediction/National Center for Atmospheric Research (/) reanalysis outputs and the second model was built using the outputs of Hadley Centre Coupled Model version 3 (). Both models were based on the multi‐linear regression () technique and were built for a precipitation station located in Victoria, Australia. Probable predictors were selected based on the past literature and hydrology. Potential predictors were selected for each calendar month separately from the / reanalysis data, considering the correlations that they maintained with observed precipitation. Based on the strength of the correlations, these potential predictors were introduced to the downscaling model until its performance in validation, in terms of Nash–Sutcliffe Efficiency (), was maximized. In this manner, for each calendar month, the final sets of potential predictors and the best downscaling models with / reanalysis data were identified. The 20th century climate experiment data corresponding to these final sets of potential predictors were used to calibrate and validate the second model. In calibration and validation, the model developed with / reanalysis data displayed of 0.74 and 0.70, respectively. The model built with outputs showed of 0.44 and 0.17 during the calibration and validation periods, respectively. Both models tended to under‐predict high precipitation values and over‐predict near‐zero precipitation values, during both calibration and validation. However, this prediction characteristic was more pronounced by the model developed with outputs. A graphical comparison of observed precipitation, the precipitation reproduced by the two downscaling models and the raw precipitation output of , showed that there is large bias in the precipitation output of . This indicated the need of a bias‐correction, which is detailed in the second companion article.
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