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Anne Stoner, Katharine Hayhoe Texas Tech University Keith Dixon, John Lanzante, Aparna RadhakrishnanGFDL COMPARING STATISTICAL DOWNSCALING METHODS: FROM.

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Presentation on theme: "Anne Stoner, Katharine Hayhoe Texas Tech University Keith Dixon, John Lanzante, Aparna RadhakrishnanGFDL COMPARING STATISTICAL DOWNSCALING METHODS: FROM."— Presentation transcript:

1 Anne Stoner, Katharine Hayhoe Texas Tech University Keith Dixon, John Lanzante, Aparna RadhakrishnanGFDL COMPARING STATISTICAL DOWNSCALING METHODS: FROM SIMPLE TO COMPLEX

2 Goal: Evaluate and compare multiple statistical downscaling methods using the same framework Monthly and daily versions of Delta, Quantile Mapping, and Asynchronous Regional Regression Model Variables – Minimum, maximum daily 2m temperature Daily accumulative precipitation Input: GFDL-HiRES experimental model as both model and observations OBS: 25km GFDL-HiRES ( ) Model: 200km coarsened GFDL-HiRES ( , ) Output: Daily 25km downscaled Tmin, Tmax, Prcp ( ) APPROACH

3 Calculates average difference between present and future GCM simulations, then adds that difference to the observed time series for the point of interest Here: individually for each high-resolution grid cell METHOD 1: DELTA CHANGE Assumptions – GCMs are more successful at simulating changes in climate rather than actual local values Stationarity in local climate variability

4 Projects PDFs for monthly or daily simulated GCM variables onto historical observations METHOD 2: QUANTILE MAPPING (e.g. BCSD) Changes the shape of the simulated PDF to appear more like the observed PDF, but allowing the mean and variance of the GCM to change in accordance with GCM future simulations

5 Asynchronous Regional Regression Model METHOD 3: QUANTILE REGRESSION (e.g. ARRM) Daily quantile regression using piecewise linear segments to improve fit for the training period Individual monthly models allows for different distributions throughout the year

6 COMPARISON The shape of the resulting downscaled distribution depends highly on the downscaling method used Delta Quantile Mapping ARRM Colorado National Monument, CO

7 MAXIMUM TEMPERATURE

8 MINIMUM TEMPERATURE

9 PRECIPITATION

10

11 MAXIMUM TEMPERATURE

12 MINIMUM TEMPERATURE

13 PRECIPITATION

14

15 DAILY DOWNSCALED TMAX

16 MONTHLY DOWNSCALED TMAX

17 Comparing multiple downscaling methods in a standardized framework gives us useful information If someone has already used a certain downscaling method they can correctly interpret the biases If someone is trying to decide which method to use, this can help their decision, because theres no perfect method Simple methods can be fine for studying monthly/annual means, daily output for low latitudes More complex methods are required when studying climate extremes and high latitudes CONCLUSIONS

18 Downscale relative humidity Figure out physical causes of the biases were seeing Explore the influence of different predictors Incorporate more downscaling techniques NEXT STEPS


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