Measurement of Measurement of Precipitation Using Rain Precipitation Using Rain

GaugesGauges

Jennifer AdamJennifer AdamDepartment of Civil and Department of Civil and

Environmental EngineeringEnvironmental EngineeringUniversity of WashingtonUniversity of Washington

OverviewOverview

Precipitation GaugesPrecipitation Gauges Types UsedTypes Used Gauge Networks in USA and CanadaGauge Networks in USA and Canada

Undercatch of Precipitation using GaugesUndercatch of Precipitation using Gauges Other Problems with Gauge-Measured Other Problems with Gauge-Measured

PrecipitationPrecipitation World Meteorological Precipitation Gauge World Meteorological Precipitation Gauge

IntercomparisonsIntercomparisons Available Precipitation Data SetsAvailable Precipitation Data Sets

Station DataStation Data Gridded DataGridded Data

Precipitation GaugesPrecipitation Gauges Non-Recording Gauges: Manually ObservedNon-Recording Gauges: Manually Observed

For 24-hour collection, a standard rain gauge is For 24-hour collection, a standard rain gauge is typically used. This is a hollow metal tube with an typically used. This is a hollow metal tube with an open top that collects precipitation. The observer uses open top that collects precipitation. The observer uses a ruler to measure the depth of the water in a small a ruler to measure the depth of the water in a small inner tube. In the winter, the small tube is taken out, inner tube. In the winter, the small tube is taken out, and snow falls directly into the large tube. Then, snow and snow falls directly into the large tube. Then, snow is melted down and poured into the small tube to be is melted down and poured into the small tube to be

measured.measured.

Precipitation GaugesPrecipitation Gauges

Recording Gauges:Recording Gauges: Tipping Bucket: Automatically tips when a certain Tipping Bucket: Automatically tips when a certain

amount of precipitation accumulates inside of it. Total amount of precipitation accumulates inside of it. Total precipitation is determined by the number of tips. precipitation is determined by the number of tips.

Weighing Gauge: Tall and typically cone-shaped. It Weighing Gauge: Tall and typically cone-shaped. It collects all types of precipitation continuously into a collects all types of precipitation continuously into a bucket. Its weight presses down on a scale, and every bucket. Its weight presses down on a scale, and every 15 minutes, a hole is punched in a ticker tape or a 15 minutes, a hole is punched in a ticker tape or a marking is made on paper by pen to record the bucket's marking is made on paper by pen to record the bucket's weight. This is useful for hourly collections. weight. This is useful for hourly collections.

Optical Gauge: Measures precipitation rate proportional Optical Gauge: Measures precipitation rate proportional to a disturbance to a beam between a light-emitting to a disturbance to a beam between a light-emitting diode and a sensor.diode and a sensor.

Precipitation Gauges of the Precipitation Gauges of the WorldWorld

~50 types of ~50 types of National National Standard Standard gauges gauges

(Sevruk et al., 1989)(Sevruk et al., 1989)

Shielded Nipher GaugeShielded Nipher Gauge

Used in Canada for Solid PrecipitationUsed in Canada for Solid Precipitation Small errorsSmall errors

Hellmann GaugeHellmann Gauge

Yugoslav Standard

Dannish Standard

German Unshielded

Nipher-Shielded

Various Designs: German, Polish, Danish, HungarianVarious Designs: German, Polish, Danish, Hungarian Standard in 30 countries: used 30,000 locations Standard in 30 countries: used 30,000 locations

world-wideworld-wide

Shielded Tretyakov GaugeShielded Tretyakov Gauge

Former USSR countries, North Korea, Former USSR countries, North Korea, Mongolia, FinlandMongolia, Finland

SMHI GaugeSMHI Gauge

SwedenSweden NorwayNorway

Finnish Standard GaugesFinnish Standard Gauges

1908-1981: Wild

1982-1991: Wild

Japanese Standard GaugesJapanese Standard Gauges

Unshielded Tipping Bucket – mostly in South

Shielded and Heated Tipping Bucket – mostly in North

The Canadian NetworkThe Canadian Network

• Unique Precipitation Gauge NetworkUnique Precipitation Gauge Network– Liquid Precipitation: AES Type B Liquid Precipitation: AES Type B

– non-recording gauge non-recording gauge – as of mid 1970’sas of mid 1970’s– at ~2500 AES stationsat ~2500 AES stations

– Solid Precipitation:Solid Precipitation:

~560 Nipher Gauges~560 Nipher Gauges

~1800 Snow Ruler Stations (assume a ~1800 Snow Ruler Stations (assume a density of 100 kg/mdensity of 100 kg/m33))

The US NetworkThe US Network National Standard since 1870 National Standard since 1870

(inception of NWS): the NWS 8” non-(inception of NWS): the NWS 8” non-recording gaugerecording gauge

~7,500 locations in US ~7,500 locations in US (~1,340 elsewhere)(~1,340 elsewhere)

1940: Alter Shield 1940: Alter Shield Introduced – currently Introduced – currently about 200 shielded about 200 shielded gauges (Western US)gauges (Western US)

Unshielded gauge has Unshielded gauge has large wind-induced large wind-induced undercatchundercatch

US Recording GaugesUS Recording Gauges

~3,000 Recording gauges used in the US~3,000 Recording gauges used in the US Tipping Bucket GaugeTipping Bucket Gauge Weighing GaugeWeighing Gauge Fischer and Porter Gauge (also a type of Fischer and Porter Gauge (also a type of

weighing gauge) – gradually replacing WG as weighing gauge) – gradually replacing WG as predominate rain gauge since 1963.predominate rain gauge since 1963.

These gauges tend to have more These gauges tend to have more undercatch than the 8” gauge (especially undercatch than the 8” gauge (especially the TB)the TB)

National Weather ServiceNational Weather Service

278 primary stations (1278 primary stations (1stst order) order) Mainly at airportsMainly at airports Staffed on 24-hr basis by paid employeesStaffed on 24-hr basis by paid employees Hourly precipitation measured at 241 stations, Hourly precipitation measured at 241 stations,

the rest are dailythe rest are daily 8000 cooperative stations8000 cooperative stations

Staffed mainly by volunteersStaffed mainly by volunteers Hourly precipitation measured at ~2600 Hourly precipitation measured at ~2600

stations, the rest are dailystations, the rest are daily

Automated Surface Observing Automated Surface Observing System (ASOS)System (ASOS)

Introduced in 1990’s, joint program of NWS, Introduced in 1990’s, joint program of NWS, FAA, and DODFAA, and DOD

Serves as nation’s primary surface observing Serves as nation’s primary surface observing network – used at essentially all US sites on the network – used at essentially all US sites on the GTSGTS

Primarily located at airportsPrimarily located at airports >600 ASOS stations in the US, increasing >600 ASOS stations in the US, increasing

number every yearnumber every year Observations include temperature, pressure, Observations include temperature, pressure,

wind speed, and precipitation accumulationwind speed, and precipitation accumulation

ASOS Heated Tipping Bucket ASOS Heated Tipping Bucket (HTB) Gauge(HTB) Gauge

The HTB is The HTB is replacing many replacing many of the standard of the standard 8” gauges8” gauges

Increased Increased Inhomogeneity Inhomogeneity in time and in time and spacespace

Mid 1990’s is Mid 1990’s is period of period of greatest changegreatest change

Problems with US NetworkProblems with US Network

Gauge Type and Shielding Inhomogeneous in Gauge Type and Shielding Inhomogeneous in time and spacetime and space

Trend towards Recording Gauges Trend towards Recording Gauges Relocations frequently occurRelocations frequently occur 11stst order stations located mainly at airports order stations located mainly at airports Inhomogeneous in gauge density: low gauge Inhomogeneous in gauge density: low gauge

density in Western US and mountainous areas – density in Western US and mountainous areas – difficult to support higher resolution griddingdifficult to support higher resolution gridding

The unshielded 8” has large wind-induced The unshielded 8” has large wind-induced undercatch, especially for solid precipundercatch, especially for solid precip

Undercatch of Precipitation Using Undercatch of Precipitation Using Standard GaugesStandard Gauges

Wind-Induced Wind-Induced Undercatch Undercatch

Snow: 10 to >50%Snow: 10 to >50%

Rain: 2 to 10%Rain: 2 to 10%

Wetting LossesWetting Losses 2 to 10%2 to 10%

Evaporation LossesEvaporation Losses 0 to 4%0 to 4%

Treatment of Trace Treatment of Trace Precipitation as ZeroPrecipitation as Zero

Significant in Cold Arid Significant in Cold Arid RegionsRegions

Splash-out and splash-inSplash-out and splash-in 1 to 2%1 to 2%

Blowing and Drifting Blowing and Drifting SnowSnow ????

Sevruk, 1982

Wind-Induced UndercatchWind-Induced Undercatch

Influencing Influencing Factors:Factors: Wind speedWind speed TemperatureTemperature Gauge typeGauge type Gauge heightGauge height WindshieldWindshield ExposureExposure

Nespor and Sevruk, 1999

Wetting LossesWetting Losses

• Influencing Influencing Factors:Factors:– Gauge typeGauge type– ClimateClimate– MeasuremenMeasuremen

t t MethodologyMethodology

Evaporation LossesEvaporation Losses

• Influencing Influencing Factors:Factors:– Gauge typeGauge type– ClimateClimate– MeasuremeMeasureme

nt nt MethodologMethodologyy

Other Sources of ErrorsOther Sources of Errors Obstruction (ideally in a clearing surrounded by trees)Obstruction (ideally in a clearing surrounded by trees) Occult Precipitation: fog drip and rimeOccult Precipitation: fog drip and rime Observer Errors: random, systematic, and grossObserver Errors: random, systematic, and gross Errors due to differences in observation time (ideally Errors due to differences in observation time (ideally

midnight)midnight) Instrument MalfunctionInstrument Malfunction Specific to Recording Gauges – bad calibration…Specific to Recording Gauges – bad calibration… Tampering / VandalismTampering / Vandalism Observation Record Inhomogeneity – changes in Observation Record Inhomogeneity – changes in

instrumentation, site, and local environmentinstrumentation, site, and local environment

World Meteorological Organization World Meteorological Organization (WMO) Precipitation Measurement (WMO) Precipitation Measurement

IntercomparisonsIntercomparisons

1960 through 1975: 11960 through 1975: 1stst Intercomparison Intercomparison

1972 through 1976: 21972 through 1976: 2ndnd Intercomparison – Intercomparison – Liquid Precipitation Liquid Precipitation

1986 through 1993: 31986 through 1993: 3rdrd Intercomparison – Intercomparison – Solid PrecipitationSolid Precipitation

Goals:Goals: To determine reduction coefficients relating the catch To determine reduction coefficients relating the catch

efficiency of different gauge typesefficiency of different gauge types

Reference Gauge: IPRGReference Gauge: IPRG Snowdown Gauge withSnowdown Gauge with

Alter ShieldAlter Shield

Results: Inconclusive –Results: Inconclusive –

poor reference gaugepoor reference gauge

11stst WMO Intercomparison WMO Intercomparison

Goals:Goals: Evaluate wind corrections factors for rainfallEvaluate wind corrections factors for rainfall Correct systematic errors in different parts of the worldCorrect systematic errors in different parts of the world

60 gauge sites in 22 countries60 gauge sites in 22 countries Reference Gauge: PitReference Gauge: Pit

Snowdon Gauge Snowdon Gauge Negligible wind lossesNegligible wind losses

Results: Errors as a Results: Errors as a

function of wind speedfunction of wind speed

and precipitation intensityand precipitation intensity

22ndnd WMO Intercomparison WMO Intercomparison

Goals:Goals: Introduce reference method for gauge calibrationIntroduce reference method for gauge calibration Derive standard method to adjust for wind-induced Derive standard method to adjust for wind-induced

solid precipitation undercatchsolid precipitation undercatch

Reference Gauge:Reference Gauge: DFIRDFIR

33rdrd WMO Intercomparison WMO Intercomparison (Goodison et al. 1998)(Goodison et al. 1998)

Double-Fenced International Double-Fenced International Reference (DFIR)Reference (DFIR)

Encloses Encloses the the Shielded Shielded Tretyakov Tretyakov GaugeGauge

UCAR

Catches 92 to 96% of bush gauge Catches 92 to 96% of bush gauge snowfallsnowfall

Participating CountriesParticipating Countries

Canada, China, Croatia, Denmark, Canada, China, Croatia, Denmark, Finland, Germany, Iceland, India, Japan, Finland, Germany, Iceland, India, Japan, Norway, Romania, Russia, Slovakia, Norway, Romania, Russia, Slovakia, Sweden, Switzerland, UK, USA.Sweden, Switzerland, UK, USA.

DFIR operated at 19 stations in 10 DFIR operated at 19 stations in 10 countries during the study.countries during the study.

ResultsResults

CATCH RATIO (CR) = Measured PrecipitationCATCH RATIO (CR) = Measured Precipitation

True PrecipitationTrue Precipitation

Smaller-Scale StudiesSmaller-Scale Studies Mississippi: Lisa Sieck, Steve BurgesMississippi: Lisa Sieck, Steve Burges

Austrialian Hydrologic Services Gauge (TB3) Agricultural

Research Service (ARS)

Buried TB3

Belfort with Weighing Mechanism

Smaller-Scale StudiesSmaller-Scale Studies Urban Horticulture Center Gauges: Steve Urban Horticulture Center Gauges: Steve

BurgesBurgesTipping Bucket Gauge

Belfort with Weighing Mechanism

Novalynx Collector

Some Available Precipitation Data Some Available Precipitation Data Sets: Station DataSets: Station Data

National Climatic Data Center (NCDC):National Climatic Data Center (NCDC): 15 minute, hourly, daily, monthly precipitation 15 minute, hourly, daily, monthly precipitation

(also other surface observations)(also other surface observations) ~6,000 precipitation stations with daily data~6,000 precipitation stations with daily data Mainly US but some non-USMainly US but some non-US No gauge undercatch correctionsNo gauge undercatch corrections Gridding of this data without prior corrections Gridding of this data without prior corrections

will cause time and space inhomogeneitieswill cause time and space inhomogeneities

Some Available Precipitation Some Available Precipitation Data Sets: Station DataData Sets: Station Data

NCEP CPC Global Summary of Day (GSOD) NCEP CPC Global Summary of Day (GSOD) data archivedata archive ~15,000 stations worldwide with daily precipitation, ~15,000 stations worldwide with daily precipitation,

wind speed, temperature, …wind speed, temperature, … 1979 through 20011979 through 2001 Archived at NCARArchived at NCAR Exchanged on the Global Telecommunications Exchanged on the Global Telecommunications

System (GTS)System (GTS)• Incomplete records, reporting errors, incorrect time interval Incomplete records, reporting errors, incorrect time interval

reports, unrealistically large reports…reports, unrealistically large reports…• Inhomogeneous in time and space even within each countryInhomogeneous in time and space even within each country• Inhomogeneous gauge densityInhomogeneous gauge density• Some Former USSR reports include corrections for wetting Some Former USSR reports include corrections for wetting

losses (although done incorrectly)losses (although done incorrectly)

Some Available Precipitation Some Available Precipitation Data Sets: Station DataData Sets: Station Data

Global Historical Climatology Network Global Historical Climatology Network (GHCN)(GHCN) ~7,500 stations worldwide with monthly ~7,500 stations worldwide with monthly

precipitation (also temperature data available)precipitation (also temperature data available) Through 1990Through 1990 Created from 15 data sourcesCreated from 15 data sources Extensive QA/QC and adjustments for station Extensive QA/QC and adjustments for station

inhomogeneities based on metadata inhomogeneities based on metadata informationinformation

No gauge undercatch correctionsNo gauge undercatch corrections

6,692 stations, through 19906,692 stations, through 1990 Wetting, wind-induced Wetting, wind-induced

undercatchundercatch Assumed CR = 90%Assumed CR = 90%

495 stations, through 1999495 stations, through 1999 Wetting, wind-induced, Wetting, wind-induced,

trace undercatchtrace undercatch Utilized WMO ResultsUtilized WMO Results

Canadian Gauge-Corrected Canadian Gauge-Corrected Data (Monthly Station Data)Data (Monthly Station Data)

Groisman ÷ Mekis and Hogg Groisman ÷ Mekis and Hogg (1979 – 1990)(1979 – 1990)

Gridded DataGridded Data

• Spatial Interpolation of Gauge Measurements over Land Areas

Problems with Gridded DataProblems with Gridded Data

Uniformity of Station DensityUniformity of Station Density Global precipitation – higher density in more Global precipitation – higher density in more

developed countriesdeveloped countries

Gauge Type UniformityGauge Type Uniformity If not uniform, station data should be first be corrected If not uniform, station data should be first be corrected

for undercatch – specific to each gauge typefor undercatch – specific to each gauge type

Station Representation – Do the stations used Station Representation – Do the stations used for gridding adequately represent the for gridding adequately represent the precipitation spatial patterns?precipitation spatial patterns? US stations mainly at airportsUS stations mainly at airports Stations located in valleys – orographic effectsStations located in valleys – orographic effects

The Orographic Effect on The Orographic Effect on PrecipitationPrecipitation

Interpolation from Valley Interpolation from Valley GaugesGauges

*

Selecting a Gridded Data Set: What Selecting a Gridded Data Set: What to be Aware ofto be Aware of

Source of data: station data, QA/QC of Source of data: station data, QA/QC of station data, was the station data station data, was the station data corrected for gauge undercatch? How corrected for gauge undercatch? How homogeneous is the station data?homogeneous is the station data?

Interpolation Methodology: does this take Interpolation Methodology: does this take into account orographic effects?into account orographic effects?

Spatial resolution and domainSpatial resolution and domain Temporal resolution and periodTemporal resolution and period AccessibilityAccessibility

Some Available Precipitation Some Available Precipitation Data Sets: Global Gridded DataData Sets: Global Gridded Data

LegatesLegates

19871987

Willmott Willmott and and MatsuuraMatsuura

20012001

CRU 0.5CRU 0.5

20002000

GPCC GPCC 19941994

GPCP GPCP 19971997

(Merged (Merged data)data)

½ degree½ degree ½ degree½ degree ½ degree½ degree 1 degree1 degree 1 degree /1 degree /

2½ degree2½ degree

monthlymonthly

Climatol.Climatol.

1920-19801920-1980

monthlymonthly

SeriesSeries

1950-19991950-1999

monthlymonthly

SeriesSeries

1901-19981901-1998

monthlymonthly

SeriesSeries

1986-19991986-1999

1dd -daily1dd -daily

1997-20001997-2000

v2 -monthlyv2 -monthly

1979-20001979-2000

Bias-Bias-AdjustedAdjusted

NANA NANA In progressIn progress Bias-Bias-AdjustedAdjusted

CRU / Willmott ComparisonCRU / Willmott Comparison

CRU / Willmott ComparisonCRU / Willmott Comparison

PRISMPRISM((PParameter-elevation arameter-elevation RRegressions on egressions on

IIndependent ndependent SSlopes lopes MModel)odel)

• 2.5 minute

• 1961-1990 clim

• Topographic facets

• Regresses P against elevation on each facet

• All 50 states, Puerto Rico, Mainland China, Taiwan, and Mongolia

UW-Created Data SetsUW-Created Data Sets

LDAS ForcingsLDAS Forcings 1/81/8thth degree over US and parts of Canada and degree over US and parts of Canada and

MexicoMexico Daily from 1950 through 1999Daily from 1950 through 1999 Gridded from NCDC station dataGridded from NCDC station data Climatology scaled to match PRISM (US only)Climatology scaled to match PRISM (US only) No gauge undercatch adjustmentsNo gauge undercatch adjustments

UW-Created Data SetsUW-Created Data Sets

Gauge-Corrected Global PrecipitationGauge-Corrected Global Precipitation Wind-induced and wetting losses for snow (in Wind-induced and wetting losses for snow (in

Northern countries) and rain (globally)Northern countries) and rain (globally) Half degree over terrestrial areas (excluding Half degree over terrestrial areas (excluding

Antarctica)Antarctica) Monthly from 1979 through 1999 (daily variability can Monthly from 1979 through 1999 (daily variability can

be determined)be determined) Gridded catch ratios applied to Willmott et al. (1999) Gridded catch ratios applied to Willmott et al. (1999)

global gridded precipitation time-seriesglobal gridded precipitation time-series Catch ratios gridded from monthly climatologies of Catch ratios gridded from monthly climatologies of

adjusted global (GTS) station dataadjusted global (GTS) station data Orographic adjustments not yet appliedOrographic adjustments not yet applied

Gridded Catch RatiosGridded Catch Ratios

Catch Ratio (%)

Adjusted Gridded PrecipitationAdjusted Gridded Precipitation

Catch Ratios Applied to Willmott and Matsuura (2001) Catch Ratios Applied to Willmott and Matsuura (2001) Monthly Time-Series from 1979 through 1998Monthly Time-Series from 1979 through 1998

Precipitation (mm/month)

Adjustment EffectsAdjustment Effects Global Global

Mean Mean Annual Annual Increase Increase of of 11.2%11.2%

All Adjustments

Wind-Induced SnowUndercatch

Wetting LossesWind-Induced Rain Undercatch

Methodology LimitationsMethodology Limitations Gauge RepresentationGauge Representation

Gauge type or shield uniform over countryGauge type or shield uniform over country Gauge height uniform, wind sensor height at 10 Gauge height uniform, wind sensor height at 10

mm Regression Equation ApplicationRegression Equation Application

N and rN and r22

Equation developed for what gauge?Equation developed for what gauge? InterpolationInterpolation

Station density and uniformityStation density and uniformity Are selected stations representative of network?Are selected stations representative of network?

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Scoring System – Solid Scoring System – Solid PrecipitationPrecipitation

CR Sensitivity: Unshielded 8”CR Sensitivity: Unshielded 8”

Sensitive to Sensitive to changes in changes in gauge height gauge height and snow depthand snow depth

Less-sensitive Less-sensitive to anemometer to anemometer heightheight

Legates Legates higher: higher: June – June – Sep.Sep.

Legates Legates lower: lower: Oct. - Oct. - MayMay

Mean Monthly PrecipitationMean Monthly Precipitation

Mean Annual Precipitation Vs. LatitudeMean Annual Precipitation Vs. Latitude

Legates up to 10% Legates up to 10% lower above 30° lower above 30° NorthNorth

Legates higher over Legates higher over Eurasia at some Eurasia at some latitudeslatitudes