Limitations of Rain Gauges Doug Lundquist with Excerpt

Limitations of Rain Gauges Doug Lundquist with Excerpt from: Measurement of Precipitation Using Rain Gauges Jennifer Adam Department of Civil and Environmental Engineering University of Washington http: //www. hydro. washington. edu/Lettenmaier/Presentations/2003/adam_gauges_precipclass_apr_2003. ppt

Undercatch of Precipitation Using Standard Gauges Wind-Induced Undercatch Snow: 10 to >50% Rain: 2 to 10% Wetting Losses 2 to 10% Evaporation Losses 0 to 4% Treatment of Trace Precipitation as Zero Significant in Cold Arid Regions Splash-out and splash-in Blowing and Drifting Snow Sevruk, 1982 1 to 2% ? ?

Wind-Induced Undercatch Ø Influencing Factors: l l l Nespor and Sevruk, 1999 Wind speed Temperature Gauge type Gauge height Windshield Exposure

Wetting Losses • Influencing Factors: – Gauge type – Climate – Measurement Methodology

Evaporation Losses • Influencing Factors: – – – Gauge type Climate Measurement Methodology

Other Sources of Errors Obstruction (ideally in a clearing surrounded by trees) Ø Occult Precipitation: fog drip and rime Ø Observer Errors: random, systematic, and gross Ø Errors due to differences in observation time (ideally midnight) Ø Instrument Malfunction Ø Specific to Recording Gauges – bad calibration… Ø Tampering / Vandalism Ø Observation Record Inhomogeneity – changes in instrumentation, site, and local environment Ø

Example of Snow Melt Ø Following data from Wednesday January 07 2009 Ø Ø Ø Ø Ø CHAP SA 1000 AUTO 9 M M/0/0/MMMM/M/0390 RMK PCPN 3. 0 MM PAST HR CLIMATE 39 MM/6 CM/88 CM (ALLISON PASS/1340 m) [22 MM]= CHAP SA 1100 AUTO 9 M M/0/0/MMMM/M/0420 RMK PCPN 3. 0 MM PAST HR CLIMATE 42 MM/7 CM/88 CM (ALLISON PASS/1340 m) [22 MM]= CHAP SA 1200 AUTO 9 M M/0/0/MMMM/M/0440 RMK PCPN 2. 0 MM PAST HR CLIMATE 44 MM/8 CM/89 CM (ALLISON PASS/1340 m) [22 MM]= CHAP SA 1300 AUTO 9 M M/0/0/MMMM/M/0490 RMK PCPN 5. 0 MM PAST HR CLIMATE 49 MM/9 CM/90 CM (ALLISON PASS/1340 m) [22 MM]= CHAP SA 1400 AUTO 9 M M/0/0/MMMM/M/0510 RMK PCPN 2. 0 MM PAST HR CLIMATE 51 MM/10 CM/91 CM (ALLISON PASS/1340 m) [22 MM]= CHAP SA 1500 AUTO 9 M M/0/0/MMMM/M/0020 RMK PCPN 2. 0 MM PAST HR CLIMATE 2 MM/M/90 CM (ALLISON PASS/1340 m) [22 MM]= CHAP SA 1600 AUTO 9 M M/0/0/MMMM/M/0040 RMK PCPN 2. 0 MM PAST HR CLIMATE 4 MM/2 CM/92 CM (ALLISON PASS/1340 m) [22 MM]= CHAP SA 1700 AUTO 9 M M/0/0/MMMM/M/0070 RMK PCPN 3. 0 MM PAST HR CLIMATE 7 MM/2 CM/92 CM (ALLISON PASS/1340 m) [22 MM]= CHAP SA 1800 AUTO 9 M M/0/0/MMMM/M/0130 RMK PCPN 6. 0 MM PAST HR CLIMATE 13 MM/2 CM/92 CM (ALLISON PASS/1340 m) [22 MM]= CHAP SA 1900 AUTO 9 M M/0/0/MMMM/M/0150 RMK PCPN 2. 0 MM PAST HR CLIMATE 15 MM/2 CM/92 CM (ALLISON PASS/1340 m) [33 MM]= CHAP SA 2000 AUTO 9 M M/0/0/MMMM/M/0190 RMK PCPN 4. 0 MM PAST HR CLIMATE 19 MM/4 CM/93 CM (ALLISON PASS/1340 m) [44 MM]= CHAP SA 2100 AUTO 9 M M/1/1/MMMM/M/0300 RMK PCPN 11. 0 MM PAST HR CLIMATE 30 MM/4 CM/93 CM (ALLISON PASS/1340 m) [55 MM]= CHAP SA 2200 AUTO 9 M M/0/0/MMMM/M/0320 RMK PCPN 2. 0 MM PAST HR CLIMATE 32 MM/5 CM/94 CM (ALLISON PASS/1340 m) [33 MM]= CHAP SA 2300 AUTO 9 M M/0/0/MMMM/M/0340 RMK PCPN 2. 0 MM PAST HR CLIMATE 34 MM/5 CM/93 CM (ALLISON PASS/1340 m) [33 MM]= Ø Following data from Thursday January 08 2009 Ø Ø CHAP SA 0000 AUTO 9 M M/0/0/MMMM/M/0360 RMK PCPN 2. 0 MM PAST HR CLIMATE 36 MM/6 CM/95 CM (ALLISON PASS/1340 m) [22 MM]= CHAP SA 0100 AUTO 9 M M/0/0/MMMM/M/0370 RMK PCPN 1. 0 MM PAST HR CLIMATE 37 MM/7 CM/94 CM (ALLISON PASS/1340 m) [22 MM]= CHAP SA 0200 AUTO 9 M M/0/0/MMMM/M/0390 RMK PCPN 2. 0 MM PAST HR CLIMATE Ø Ø Ø

The Orographic Effect on Precipitation

References Ø Dennis Lettenmaier l University of Washington Ø Jennifer Adam l University of Washington