enso forcing of streamflow conditions in the pearl river basin
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ENSO Forcing of ENSO Forcing of Streamflow Conditions in Streamflow Conditions in
the Pearl River Basinthe Pearl River Basin
R. Jason Caldwell, LMRFCR. Jason Caldwell, LMRFCandand
Robert J. Ricks, WFO LIXRobert J. Ricks, WFO LIX
Regional HydrologyRegional Hydrology Pearl River BasinPearl River Basin
• Yockanookany RiverYockanookany River• Pearl RiverPearl River• Bogue Chitto RiverBogue Chitto River• Among others…Among others…
Yockanookany
Upper Pearl
Lower Pearl
Bogue Chitto
Streamflow EventsStreamflow Events Daily mean streamflow in cfsDaily mean streamflow in cfs 7575thth/25/25thth Percentile values from USGS Percentile values from USGS
used to denote above/below normal used to denote above/below normal streamflow daysstreamflow days
Monthly counts for high/low flow Monthly counts for high/low flow events calculatedevents calculated
Missing data were considered to be Missing data were considered to be non-events for conservative non-events for conservative estimates of actual event daysestimates of actual event days
ENSO Impacts on PrecipitationENSO Impacts on Precipitation
Dry winter across the north, wetter south
Transitions to wetter spring season
Dry winter with increasing moisture across north in
spring season
Near normal winter condition trends to dry
conditions in spring season
Composite Analysis MethodologyComposite Analysis Methodology ONI values and ENSO episode assigned to ONI values and ENSO episode assigned to
monthly streamflow event countsmonthly streamflow event counts Terciles computed to determine Terciles computed to determine
above/near/below normal conditionsabove/near/below normal conditions Counts for each ENSO episode-category Counts for each ENSO episode-category
performed (e.g. ENa, LNb, NUn)performed (e.g. ENa, LNb, NUn) Probabilities for each event define the Probabilities for each event define the
historical compositeshistorical composites Only statistically significant (90% Only statistically significant (90%
confidence) and at least half of sites confidence) and at least half of sites withing the Mainstem, Yockanookany, or withing the Mainstem, Yockanookany, or Bogue Chitto must indicate similar Bogue Chitto must indicate similar relationshipsrelationships
Cool Season Wet Tendency
Cool Season Wet Tendency
DRY AT COAST MIGRATES NORTH IN SPRING
DRY CONDITIONS NEARLY PREDOMINATE COOL SEASON
DRY CONDITIONS NEARLY PREDOMINATE COOL SEASON
MIXED SIGNALS IN THE SUMMERTIME
Cool Season Wet Tendency at Coast Migrates Northward in Spring
Cool Season Wet
Tendency at Coast
DRY NORTH EARLY IN COOL
SEASON
2525thth Percentile Composites Percentile Composites No signal in seasons: MAM, AMJ, JJA, No signal in seasons: MAM, AMJ, JJA,
JAS, SON, OND, and NDJJAS, SON, OND, and NDJ Increased/decreased probability of Increased/decreased probability of
below/above normal low flow days in below/above normal low flow days in Bogue Chitto during El NinoBogue Chitto during El Nino
Forecast VerificationForecast Verification 1982-2005 CPC Nino 3.4 SST Forecast 1982-2005 CPC Nino 3.4 SST Forecast
probabilities combined with historical probabilities combined with historical composites to produce hindcasts for each composites to produce hindcasts for each monthmonth
Only 0.5 month leads utilizedOnly 0.5 month leads utilized• Decreasing forecast accuracy with increasing Decreasing forecast accuracy with increasing
lead timelead time• 90-day outlooks for SFPO90-day outlooks for SFPO
Contingency tables used to compute Contingency tables used to compute statistical scoresstatistical scores
Heidke Skill ScoresHeidke Skill Scores
Least skill in Least skill in southernmost southernmost basinsbasins• BXAL1, TYTM6, BXAL1, TYTM6,
and BSHL1and BSHL1
Mainstem and Mainstem and Yockanookany Yockanookany ranged from ranged from 0.13 to 0.250.13 to 0.25
Heidke Skill Score 75th Percentile Flow Day Forecasts
Based on ENSO Composite Analysis(Perfect = 1, No Skill = 0)
0.13318
0.170668
0.216392
0.2475550.231548
0.094829
0.048804 0.053382
0
0.05
0.1
0.15
0.2
0.25
0.3
KSCM6 OFAM6 ENBM6 JACM6 MTCM6 BXAL1 TYTM6 BSHL1
Site ID
Heid
ke S
kill
Scor
e
Heidke
Skill relative to random chance
Ranked Probability ScoresRanked Probability Scores
Marginal Marginal skill skill indicated indicated with RPS with RPS of 0.40 to of 0.40 to 0.460.46
ENSO Composite Performance Using Ranked Probability Score(Perfect = 0, No Skill = 1)
0.417874 0.420369 0.407035 0.412881 0.436875 0.455066 0.436195 0.432091
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
KSCM6 OFAM6 ENBM6 JACM6 MTCM6 BXAL1 TYTM6 BSHL1
Site ID
RPS RPS
Skill in predicting the proper category
Ranked Probability Skill ScoreRanked Probability Skill Score
Limited Limited improvement improvement over climo in over climo in upper Pearl; upper Pearl; little or no little or no skill across skill across lower Pearllower Pearl
ENSO Composite Performance Using Ranked Probability Skill Score
(Perfect = 1, No Skill <=0)
0.046397
0.0766430.063382
0.005853 0.010495 0.019804
0.052056
-0.03231
-0.2
-0.1
0
0.1
0.2
KS
CM
6
OFA
M6
EN
BM
6
JAC
M6
MTC
M6
BX
AL1
TYTM
6
BS
HL1
Site ID
RPSS RPSS
Skill relative to climatology
ConclusionsConclusions Precipitation departures attributed to Precipitation departures attributed to
ENSO episode correlate well with ENSO episode correlate well with streamflow events streamflow events
Locations near the Gulf of Mexico exhibit Locations near the Gulf of Mexico exhibit least improvement over climatology least improvement over climatology (localized forcing)(localized forcing)
ENSO-based composites yield greatest ENSO-based composites yield greatest forecast improvement in upper Pearl River forecast improvement in upper Pearl River BasinBasin
Smaller basins can produce contradictory Smaller basins can produce contradictory signals compared to larger mainstem signals compared to larger mainstem basinsbasins
Future ResearchFuture Research Include lag-time response in Include lag-time response in
computationscomputations 2525thth percentile hindcast verification percentile hindcast verification Ensemble streamflow prediction and Ensemble streamflow prediction and
Spring Flood Potential Outlook Spring Flood Potential Outlook applicationsapplications
Web access to composites and Web access to composites and forecastsforecasts
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