csa symposium 2016 - shanice bedward day 1 session 2
TRANSCRIPT
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“Assessing the Skill of Seasonal Rainfall Forecast for Jamaica and Exploring Methods to Improve Existing
Skill”
Author: Sheldon GrantPresenter: Shanice Bedward
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Content
IntroductionMethodology
ResultsThe way forward
LimitationsConclusion
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Objectives
1. To use seasonal forecast verification as an approach to identifying strengths and weakness in the current forecast methodologies
2. To examine the influence of local, regional and global scale climate phenomena on Jamaica’s rainfall and to identify those that may be useful towards improving the skill of current forecast models
3. To create new predictive models for select seasons
Introduction
Methodology
Results
Way Forward
Limitations
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Purpose of Study
Improving Forecasting
Skill
Inform Public
Early Warning
Planning
Capacity Building
Introduction
Methodology
Results
Way Forward
Limitations
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Seasonal Forecast
http://jamaicaclimate.net
JFM FMA MAM AMJ MJJ JJA JAS SON OND NDJ DJF
January-February-March
Introduction
Methodology
Results
Way Forward
Limitations
Conclusion
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Climate Predictability Tool (CPT)
Statistical tool currently providing the seasonal rainfall forecasts for Jamaica - Climate Predictability Tool (CPT).CPT offers the option of selecting an area over a predictor data set which correlates well with seasonal rainfall over the target region.
Introduction
Methodology
Results
Way Forward
Limitations
Conclusion
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Is this “SKILL”?Introduction
Methodology
Results
Way Forward
Limitations
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Validation
• What is a Skill Score?– Heidke Skill Score (HSS)– Ranked Probability Skill Score (RPSS)– Relative Operating Characteristic (ROC)
• Four Seasons Selected– JFM– AMJ– JAS– SON
Introduction
Methodology
Results
Way Forward
Limitations
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Heidke Skill Score (HSS)
HSS = (H-E) / (N-E) ____Eq 1H is the number or categorically correct forecastsN is the number of forecasts issuedE is the number of forecast expected to occur by chance
NB:• Negative values indicate that the chance forecast is better;• 0 means no skill;• A perfect forecast obtains a HSS of 1.
Introduction
Methodology
Results
Way Forward
Limitations
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Preliminary Results 1
• Skill of forecasts derived using CPT varies by season and by year.• JJA and OND show reasonable skill for 2013-2015.• MJJ shows poor skill. MJJ represents our early rainfall season.
Introduction
Methodology
Results
Way Forward
Limitations
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1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
-0.30-0.20-0.100.000.100.200.300.400.500.600.70
Heidke Skill Score - AMJ
Years
Scor
es
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
-0.40
-0.20
0.00
0.20
0.40
0.60
0.80
Heidke Skill Score - JAS
Years
Scor
es
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Ranked Probability Skill Score (RPSS)
RPS = ∑ (PF(cum) – PO(cum))2 ___Eq 2
RPS is the ranked probability score for the forecastPF(cum) is the cumulative forecast probability
PO(cum) is the cumulative observation probability
RPSS = 1 – RPSfct/RPScli _______ Eq 3
RPSfct is the RPS for the forecast RPScli is the RPS climatology forecasts
Introduction
Methodology
Results
Way Forward
Limitations
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Ranked Probability Skill Score (RPSS)
RPS = ∑ (PF(cum) – PO(cum))2 ___Eq 2
RPS is the ranked probability score for the forecastPF(cum) is the cumulative forecast probability
PO(cum) is the cumulative observation probability
RPSS = 1 – RPSfct/RPScli _______ Eq 3
RPSfct is the RPS for the forecast RPScli is the RPS climatology forecasts
NB:• Negative values indicate that the forecast is less accurate than the
standard forecast.• A perfect forecast obtains a RPSS of 1
Introduction
Methodology
Results
Way Forward
Limitations
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JFM AMJ JAS SON
-1.2-1
-0.8-0.6-0.4-0.2
00.20.40.60.8
Manley - RPSS
2012201320142015
Seasons
Scor
es
JFM AMJ JAS SON
-0.60-0.40-0.200.000.200.400.600.801.001.20
Serge Island - RPSS
201320142015
Seasons
Scor
es JFM AMJ JAS SON
-1.5
-1
-0.5
0
0.5
1
Savanna-la-mar - RPSS
2012201320142015
Seasons
Scor
es
JFM AMJ JAS SON
-2
-1.5
-1
-0.5
0
0.5
1
Sangster - RPSS
2012201320142015
Seasons
Scor
es
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Relative Operating Characteristic (ROC)
• It is a plot of the true positive rate (Hit rate) against the false positive rate (False alarm rate)
NB:An area of 1 represents a perfect test; an area of 0.5 represents a worthless test
Introduction
Methodology
Results
Way Forward
Limitations
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0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
ROC JFM
ROC Below.ROC ABOVE
False Alarm
Hit R
ate
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0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
ROC JAS
ROC Below.ROC ABOVE
False Alarm
Hit R
ate
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0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
ROC SON
ROC Below.ROC ABOVE
False Alarm
Hit R
ate
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What Next?• Based on preliminary results, skill of models created in
CPT vary by year, season and location.
• Questions arising:– Are different seasons and different areas of the island
influenced by different sections of the ocean?– What are the other significant drivers on all scales? (Global,
Regional, Local)– Do local factors such as topography, influence rainfall on a
large scale?
Introduction
Methodology
Results
Way Forward
Limitations
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Methodology and Datasets 2
• Identify the local, regional and global scale drivers that influence Jamaica’s Rainfall.– Analysis will include correlations,
canonical correlation analysis, composite maps, EOF’s
• Create and validate statistical models based motivated by drivers identified.– Analysis will include the use of backward
regression and cross-validation analyses
Rainfall data from the (Met Office).
SST’s and other identified parameters from various global institutions
Atmospheric Temperatures from atmospheric soundings done locally (Met Office)
Introduction
Methodology
Results
Way Forward
Limitations
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Limitations
• Missing Data
• Relatively new for Jamaica
– Limited research on drivers other than ENSO especially small scale and local drivers for Jamaica
Introduction
Methodology
Results
Way Forward
Limitations
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The End