Analysis of Blue Mesa Inflow Forecast Errors

Analysis of Blue Mesa Inflow Forecast ErrorsTom Pagano,

[email protected] 503 414 3010

aka: “Wha’ happa’???”

Performance of 2008 forecasts

NRCS daily forecasts

Official coordinated

forecasts

Daily forecast skill

Observed

http://www.wcc.nrcs.usda.gov/wsf/daily_forecasts.html

2008

OfficialhistoricalpublishedoutlooksissuedApril 1

Blue Mesa + Taylor Park Reservoir Storage

Kac

ft

FullAug 1

Jan 1

Forecasts and storage have come up short since 2000

2008 obs

Historical NRCS “End of season”

daily forecast skill

This takes into account

all available dataincluding

spring/summer precipitation.

Even then, this yearstill falls out as a big anomaly

(major over-forecast)

April-July 2008 Blue Mesa Inflow Forecast Comparison

Forecast issue date

official1971-00 norm

Apr

il-Ju

ly in

flow

kac

-ft

NRCS dailyforecastsbased on:

Precip/Snow

obs


Forecast issue date

official1971-00 norm

Apr

il-Ju

ly in

flow

kac

-ft

NRCS dailyforecastsbased on:Snow only

Precip/Snow

Precip onlyobs


Forecast issue date

official

NWS ESP

1971-00 norm

Apr

il-Ju

ly in

flow

kac

-ft

NRCS dailyforecastsbased on:Snow only

Precip/Snow

Precip onlyobs

NRCS Daily Forecasts for Apr-Jul Blue Mesa Inflowusing snow information available by April 11

Forecast too high

Forecast too low

2008 snowpack composite well beyond

recent historical variability

Daily forecast input is a composite of 7 snotel sites:North lost trail, butte, park cone, brumley, independence pass, porphyry creek, slumgullion

2008

Historical range1981-2007

Park Cone Historical April 1 Snow DataS

no

w w

ater

eq

uiv

alen

t (i

n)

2008…2nd biggest

in last 42 years

6th biggestin last 72 years

End of season wyprecipEnd of season snow

Apr 11 snow Apr 11 wyprecip

Sources of predictability 1950-99 VIC model skill(University of Washington)Explained variance in predicting Apr-July runoff

Blue – SnowpackGreen – Soil MoistureRed – El Nino

Darker colors- more important

(courtesy of M Dettinger, Scripps)

What basin processes are important?How have they been behaving recently?

(using actual and model data)

How is runoff driven by:

snow and precipitationsoil moisture

evaporation/temperature

Note: Model is not necessarily reality

snow and precipitation

Snow and precipitation are easily the dominant factor

R2

(% var expl)

1.0 = perfect

better

worse

Blue Mesa April-July Inflow Forecast Skill 1979-2007

Model swe + precip versus Model runoff

Univ Washingtonmodel Snow + Precip

NRCS Daily Forecasts

Real world SNOTEL vs Real world runoff

Issue date of forecast

Snow/precipitation explain upwards of 90% of

the year to year variability in runoff

Gunnison BasinApril-June Precipitation

1920-2008

Per

cent

of

1971

-200

0 av

erag

e

Data from WESTMAP: http://www.cefa.dri.edu/Westmap/

200872%

200230%

1995206%

2000-08 avg:75% norm

Precipitation after April 1 is important

Spring precipitation, especially the sequencing with snowmelt is also important

Runoff

Snowmelt Rainfall

Rainfall mixed with snowmelt“normal”

April July


Runoff

Snowmelt Rainfall


Rainfall boosting snowmeltLarger volumes

Snowmelt and rainfall separateNot enough “momentum” to produce big volumes

All these complex interactions are tough to “cartoonize”;Simulation models can handle this… but still it’s tough to predict beyond 1-2 weeks.

April July


April July

Runoff

Snowmelt Rainfall


Rainfall boosting snowmeltLarger volumes

Snowmelt and rainfall separateNot enough “momentum” to produce big volumes

Even then, however,high heat and no rain

can lead to “pouring sunshine”

All these complex interactions are tough to “cartoonize”;Simulation models can handle this… but still it’s tough to predict beyond 1-2 weeks.

2008

Runoff

Blu

e M

esa

nat

ura

l in

flo

wka

c-ft

/day

Total:Independ PassSnowmeltRainfall

SchofieldSnowmeltRainfall

(inches)

Many fits and starts to snowmelt…Almost no spring rainfall

2008

Runoff

Blu

e M

esa

nat

ura

l in

flo

wka

c-ft

/day



(inches)

1999

Good mix of rainand snowmelt

1993

2008

Runoff

Blu

e M

esa

nat

ura

l in

flo

wka

c-ft

/day



(inches)

1999

Snowpack poor, but “perfect storm”

for runoff efficiency

Soil moisture/GroundwaterAre we still feeling the effects of 2002?

Blue Mesa Basin Soil Moisture 2001-2008(According to the Univ Washington Model- top 2 layers)


(According to Park Cone Snotel- ~0-30” depth)

Snotel does poorly in frozen soils, so that has been censored

Model resembles snotel, but also remember we’re comparing basin average with point measurement


(According to Park Cone Snotel- ~0-30” depth)

Snotel does poorly in frozen soils, so that has been censored

Univ Washington Model “deep” soil moisture layer

Colorado Active Well Level Network

Only one Colorado USGS groundwater station

in realtime (Pueblo)

Gunnison:Period of record 2003-2008 + 1996

Measured 1x/year

Crested Butte

8/1996

Taken inMid-may

What influence humans?Does it matter?

Blue Mesa

For each site, all measurements Jan-Jun, Jul-Dec are averaged by year. Station half-year data then converted into standardized anomaly (o-avg(o))/std(o) vs

period of record for the half year. Multiple stations are then averaged.

Univ Washington model Blue Mesa inflow basin total soil moisture (mm)

January 1 1920-2008

Start of

2008

Evapotranspiration/sublimation

Butte SNOTEL sublimation (as modeled by NOHRSC)

Wat

er y

ear

to d

ate

cum

ulat

ive

subl

imat

ion

(inch

es)

Oct-Jul SublYear Precip Prcp2004 19.3” 30%2003 19.6” 29%

2005 24.5” 15%2006 22.7” 16%2007 18.1” 18%2008 29.3” 10%

Long-term averageevaporation + transpiration + sublimation = 73% of annual precipitation

Gunnison BasinMarch-May Average Temperature

1920-2008D

epar

ture

fro

m 1

971-

2000

Data from WESTMAP: http://www.cefa.dri.edu/Westmap/

Warm spring temps recently

exceptlastyear

How good are forecasts in general?

“Perfect forecasts are all alike;

Every bad forecast is bad in its own way.”

“Published Official”-Subjective (based on objective guidance)-Humans actively involved-Coordinated by NRCS+NWS

“NRCS Daily”-Objective-Statistical model-based-Highly automated-Only uses SNOTEL snow+wytd precip

http://www.wcc.nrcs.usda.gov/wsf/daily_forecasts.html

http://www.hydro.washington.edu/forecast/westwide/sflow/index.shtml

University of Washington-Objective-Simulation model-based-Highly automated-Research grade

NWS ESP-Objective-Simulation model-based-Human controlled/vetted (in realtime)

Sources

Natural flow: (1968-2008)http://www.usbr.gov/uc/crsp/GetSiteInfoBlue Mesa outflow – Taylor Park change in storage

Published official: (1971-2008)ftp://ftp.wcc.nrcs.usda.gov/data/water/forecast/With gaps filled in from other sources

NWS ESP: (1981-2002)http://www.nwrfc.noaa.gov/westernwater/database/index.php?id=BMDC2#forecasts

University of Washington: (1971-2008)http://www.hydro.washington.edu/forecast/hepex/esp_cmpr/NRCS Daily: (1979-2008)

http://www.wcc.nrcs.usda.gov/wsf/daily_forecasts.htmlAll reforecasts available internally, some available online


RMSE as % 1971-2000

Normal

0 = perfect

worse

better Published officialNRCS Daily

Issue Month of Forecast(e.g. January 1)

RMSE = sqrt(avg(f-o)2)

Period common to all datasets


RMSE as % 1971-2000

Normal

0 = perfect

worse


NRCS Daily (residual)



ModelForecast

Observed

Model Simulated

Forecasting runoff from a start date in June…

ModelForecast

Observed

Model Simulated

Forecasting runoff from a start date in June…

Is your April-July “forecast” your 1. observed + future only forecast or is it2. simulated + future only forecast?

Forecasting “residuals” (1.) is more accurate but is an “open book” exam


RMSE as % 1971-2000

Normal

0 = perfect

worse






RMSE as % 1971-2000

Normal

0 = perfect

worse



University of Washington




RMSE as % 1971-2000

Normal

0 = perfect

worse




NWS ESP




R2

(% var expl)

100 = perfect

better

worse

Published officialNRCS Daily



NWS ESP


What’s different: This does not

penalize for bias

Blue Mesa April-July Inflow Forecast Bias 1981-2002

ForecastBias as %1971-2000

Normal

Forecasts too high

Forecaststoo low


Published officialNRCS DailyUniversity of Washington

NWS ESP

Bias = avg(f) – avg(o)

Blue Mesa April-July Inflow Forecast Bias 2000-2007

ForecastBias as %1971-2000

Normal

Forecasts too high

Forecaststoo low


Published officialNRCS Daily


NWS ESP(not available)

Bias = avg(f) – avg(o)

Note:2000-2007 were dry years.

Comparatively, the 71-00 normal had a “bias” of +36% (!)

Conclusions

From a snow perspective, 2008 was an epic bust.Water year precipitation matched runoff however.

Lack of spring precip and sequencing of snowmelt important

All existing models have comparable skill.30% normal error is typical Jan 1, 20-25% error on April 1

Snow, rainfall, evap, soil moisture important to runoff. Some easier to quantify than others.

Recommendations

Have local/anecdotal observationsfeed quantitative historical analyses

to build appropriate models.

Collect the right data to support creation of objective operational guidance, tempered by reason.

Recognize the unknowable versus the unknown.

Remember too that higher accuracy is not the only way to improve forecasts

Snow sublimation (inches/day)

Snow sublimation (inches/day)

Daily average wind speed (mph)

Daily average relative humidity (%)

Butte SNOTEL Site

Data fromNOHRSC model

Nov 2002-Aug 2008www.nohrsc.nws.gov

Note that winds don’t vary from year to year in most hydrologic models

(e.g. NWS and UWashington)

Blue Mesa Basin Evaporation Losses by Month(according to the Univ Washington Model)

Monthly average temperatures (deg F)

Eva

po-t

rans

pira

tion

(kaf

/mon

th) April-June:

temperatures and ETrelated

July-September: ET moisture driven

November-March: ET constant, small

jan feb

mar

apr

may

jun jul

aug

sep

oct

novdec

Blue Mesa Basin Water Year Water Balance(according to the Univ Washington Model)

Kac

-ft/

year

Long-term average Evapotransporation (ET)/Precipitation = 73%

ET doesn’t vary much from year to year. Even then, 65% of its variability depends annual precipitation

(at least in the model’s reality…)

PrecipitationRunoff

Evapotranspiration

Analysis of Blue Mesa Inflow Forecast Errors

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