measurement of precipitation using rain gauges
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Measurement of Precipitation Using Rain Gauges. Jennifer Adam Department of Civil and Environmental Engineering University of Washington. Overview. Precipitation Gauges Types Used Gauge Networks in USA and Canada Undercatch of Precipitation using Gauges - PowerPoint PPT PresentationTRANSCRIPT
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