Gross Evaporation Calculations and Database

Presentation at PPWB Prairie Hydrology WorkshopJanuary 29, 2013

Overview

• Why is gross evaporation data required by the PPWB?• How is Gross Evaporation Calculated?• The Meyer Formula• The Future?

Why is gross evaporation data required by the PPWB?

• Net evaporative losses from reservoirs are considered a consumptive use in calculating net depletion to natural flow for apportionment monitoring purposes

• Various methods are currently used:• Meyer Formula – Lake Diefenbaker, Reid Lake,

Tobin Lake, St. Mary Reservoir, Waterton Reservoir, Moosomin Reservoir, Pipestone Lake

• Morton’s Model – Glennifer Lake• Penman’s (recently replaced Evaporation Pan station) – Lodge,

Middle and Battle Creek basins• Various attempts over the years to assess the most appropriate

methodology for computing gross evaporation for operational needs• Discussion in PPWB Report No. 162 (Hopkinson, 2003)

How is Gross Evaporation Calculated?

• Mass Transfer• Energy Budget• Water Budget• Empirical Formulae (Meyer, Penman, etc.)• Direct Measurement (pan)

Use of the Meyer Formula on the Canadian Prairies

• 1962 study by McKay and Stichling on Weyburn Reservoir compared seven methods for evaporation determination including water budget, energy budget, pan and empirical formulae

• Recommended the Meyer Formula for operational purposes because of data availability and simplicity

• PPWB used the Meyer Formula to estimate gross evaporation for the period 1921 to 1950 at 15 locations (PPWB Report No. 5, 1952)

• SNBB used the Meyer Formula to calculate gross evaporation for the period 1912 to 1967 at 17 locations

• PFRA refined the Meyer Formula for Prairie conditions and published updated data (Hydrology Reports #113, 121, 133 and 143)• Data and maps are widely distributed and are used by federal and provincial

governments, consultants and academia in the Canadian Prairies

Meyer Formula

Requires only monthly:• Air Temperature• Wind Speed• Dew Point Temperature or Relative Humidity

Water temperature data is estimated from air temperature as:

TW = 0.60TA + Bwhere: TW = monthly mean surface water temperature, in oC,

TA = monthly mean air temperature, in oC, andB = intercept value corresponding to the month under

consideration and location

Meyer Formula

EG = CK(Vw - Va)(1 + 6.2139x10-2W)(1 + 3.28084x10-5A) ............................. (1)

where: EG = monthly gross evaporation, in millimetres, at the meteorological station, C = coefficient of 11 if saturated vapour pressure is based on two observations of relative

humidity per day; a coefficient of 10.1 if saturated vapour pressure is based on either two, four or 24 observations of dew point temperature per day; and a coefficient of 10.2 if saturated vapour pressure is based on three observations of dew point temperature per day,

K = metric conversion factor of 0.750062, Vw = saturated vapour pressure, in millibars, corresponding to the estimated monthly mean

water temperature at the surface of a hypothetical open body of water at the station site,

Va = actual monthly mean vapour pressure, in millibars, in the atmosphere at 7.62 metres above the ground level at the station,

W = monthly mean wind speed, in kilometres per hour, at 7.62 metres above the ground level at the station, and

A = elevation, in metres above mean sea level, of ground level at the station.

GROSS EVAPORATION(MILLIMETRES)--- WINNIPEG

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC TOTAL

1911 0.0 0.0 0.0 31.4 120.5 110.6 141.8 104.0 81.7 26.4 0.0 0.0 6171912 0.0 0.0 0.0 41.4 132.8 175.4 145.0 122.3 82.8 43.9 0.0 0.0 7441913 0.0 0.0 0.0 44.6 130.8 184.7 164.6 119.1 69.9 34.7 0.0 0.0 7491914 0.0 0.0 0.0 45.0 150.9 188.4 172.8 150.8 96.7 20.2 0.0 0.0 8251915 0.0 0.0 0.0 43.8 144.9 149.3 172.2 160.8 76.5 43.3 0.0 0.0 7911916 0.0 0.0 0.0 41.2 118.9 120.7 132.0 123.1 104.3 43.6 0.0 0.0 6841917 0.0 0.0 0.0 50.8 163.2 179.5 161.7 156.4 71.3 43.2 0.0 0.0 8261918 0.0 0.0 0.0 52.9 127.7 159.0 157.1 136.8 92.2 44.9 0.0 0.0 7701919 0.0 0.0 0.0 22.5 101.1 95.0 147.6 107.9 91.9 45.2 0.0 0.0 6111920 0.0 0.0 0.0 40.6 120.9 127.7 168.2 137.0 78.6 48.2 0.0 0.0 7211921 0.0 0.0 0.0 37.7 129.4 141.1 151.6 126.9 55.9 19.1 0.0 0.0 6621922 0.0 0.0 0.0 37.8 116.5 158.8 160.7 109.2 68.6 35.2 0.0 0.0 6871923 0.0 0.0 0.0 45.3 144.7 159.2 149.6 159.7 119.3 54.8 0.0 0.0 8331924 0.0 0.0 0.0 41.3 135.9 162.7 180.3 157.6 101.3 49.9 0.0 0.0 8291925 0.0 0.0 0.0 47.8 136.6 129.0 180.4 149.8 81.8 43.6 0.0 0.0 7691926 0.0 0.0 0.0 45.1 153.3 168.6 173.7 146.9 100.1 43.4 0.0 0.0 8311927 0.0 0.0 0.0 59.9 127.3 153.0 145.7 162.1 97.2 41.1 0.0 0.0 7861928 0.0 0.0 0.0 38.5 130.6 127.7 118.9 125.3 96.0 48.2 0.0 0.0 6851929 0.0 0.0 0.0 47.6 140.4 164.9 181.0 186.2 104.5 41.2 0.0 0.0 8661930 0.0 0.0 0.0 38.5 119.3 134.4 142.3 130.9 101.6 40.3 0.0 0.0 7071931 0.0 0.0 0.0 54.1 126.3 160.5 172.8 161.4 80.0 37.6 0.0 0.0 7931932 0.0 0.0 0.0 39.3 159.5 133.1 158.2 157.7 118.2 47.3 0.0 0.0 8131933 0.0 0.0 0.0 52.3 144.9 184.5 184.7 191.0 110.6 50.7 0.0 0.0 9191934 0.0 0.0 0.0 58.4 170.3 159.5 193.8 175.2 105.0 48.0 0.0 0.0 9101935 0.0 0.0 0.0 43.0 140.5 157.9 151.9 159.8 104.2 59.6 0.0 0.0 8171936 0.0 0.0 0.0 51.8 151.3 165.0 185.8 168.4 109.6 62.1 0.0 0.0 8941937 0.0 0.0 0.0 42.8 144.2 168.5 175.0 169.3 103.2 53.6 0.0 0.0 8571938 0.0 0.0 0.0 56.9 134.2 172.5 153.2 193.2 133.3 62.4 0.0 0.0 9061939 0.0 0.0 0.0 53.5 137.5 140.9 205.1 159.1 101.4 50.1 0.0 0.0 8481940 0.0 0.0 0.0 50.1 134.1 156.0 170.8 168.0 105.0 47.9 0.0 0.0 8321941 0.0 0.0 0.0 33.7 124.5 124.8 143.0 143.3 94.8 46.7 0.0 0.0 7111942 0.0 0.0 0.0 42.1 123.6 143.7 159.2 143.1 106.3 56.2 0.0 0.0 7741943 0.0 0.0 0.0 61.6 127.3 128.0 160.1 155.8 120.3 64.9 0.0 0.0 8181944 0.0 0.0 0.0 54.5 119.5 118.7 167.9 157.9 79.6 47.5 0.0 0.0 7461945 0.0 0.0 0.0 41.9 115.9 145.6 151.7 161.7 103.7 51.5 0.0 0.0 7721946 0.0 0.0 0.0 64.0 136.9 157.6 175.6 172.7 115.9 51.3 0.0 0.0 8741947 0.0 0.0 0.0 44.7 126.5 148.3 161.8 137.0 111.6 55.2 0.0 0.0 7851948 0.0 0.0 0.0 38.9 138.4 147.1 152.7 145.9 134.6 66.6 0.0 0.0 8241949 0.0 0.0 0.0 48.4 131.8 158.1 175.2 159.7 110.5 52.3 0.0 0.0 8361950 0.0 0.0 0.0 42.3 101.5 156.2 142.7 143.5 98.7 49.4 0.0 0.0 7341951 0.0 0.0 0.0 50.1 156.2 155.3 180.3 142.1 91.3 46.1 0.0 0.0 8211952 0.0 0.0 0.0 76.8 143.3 163.7 164.5 167.1 125.5 64.6 0.0 0.0 9051953 0.0 0.0 0.0 54.7 124.9 134.9 165.8 156.7 101.0 50.6 0.0 0.0 7891954 0.0 0.0 0.0 48.1 131.7 144.7 145.5 134.7 96.9 54.7 0.0 0.0 7561955 0.0 0.0 0.0 52.2 147.6 143.6 167.4 190.7 122.8 58.4 0.0 0.0 8831956 0.0 0.0 0.0 45.5 126.8 174.8 142.7 149.5 104.6 59.0 0.0 0.0 8031957 0.0 0.0 0.0 46.5 164.3 141.8 171.1 155.1 100.6 51.1 0.0 0.0 8301958 0.0 0.0 0.0 71.8 173.2 179.6 163.9 170.2 123.0 54.3 0.0 0.0 9361959 0.0 0.0 0.0 57.9 141.2 158.7 182.7 176.3 104.3 44.3 0.0 0.0 8661960 0.0 0.0 0.0 47.3 152.1 166.4 217.2 174.1 122.5 67.1 0.0 0.0 9471961 0.0 0.0 0.0 52.3 159.5 226.2 181.8 216.9 108.3 63.8 0.0 0.0 10091962 0.0 0.0 0.0 42.8 119.1 151.1 159.7 150.8 119.3 49.1 0.0 0.0 7921963 0.0 0.0 0.0 49.3 129.3 146.8 174.0 157.2 119.0 71.5 0.0 0.0 8471964 0.0 0.0 0.0 54.8 156.1 153.4 161.7 191.5 129.6 70.9 0.0 0.0 9181965 0.0 0.0 0.0 47.9 147.7 197.5 164.3 157.1 99.4 64.0 0.0 0.0 8781966 0.0 0.0 0.0 49.8 133.4 163.9 158.4 154.7 120.8 53.2 0.0 0.0 8341967 0.0 0.0 0.0 47.1 140.1 171.5 176.1 181.7 158.4 49.7 0.0 0.0 9251968 0.0 0.0 0.0 59.1 135.8 171.8 169.6 139.6 103.6 51.0 0.0 0.0 8301969 0.0 0.0 0.0 56.7 131.5 148.2 146.3 163.0 96.7 44.6 0.0 0.0 7871970 0.0 0.0 0.0 43.7 124.5 153.2 180.5 187.5 103.5 57.5 0.0 0.0 8501971 0.0 0.0 0.0 50.2 147.9 128.8 157.0 166.9 114.4 43.9 0.0 0.0 8091972 0.0 0.0 0.0 43.5 136.7 169.3 151.7 150.8 117.1 55.8 0.0 0.0 8251973 0.0 0.0 0.0 62.5 146.0 147.4 161.9 144.6 111.9 44.7 0.0 0.0 8191974 0.0 0.0 0.0 39.4 112.9 185.7 208.0 163.7 105.4 63.6 0.0 0.0 8791975 0.0 0.0 0.0 49.9 131.7 132.9 173.0 137.3 108.3 54.9 0.0 0.0 7881976 0.0 0.0 0.0 56.1 146.9 155.9 197.5 179.0 144.0 67.7 0.0 0.0 9471977 0.0 0.0 0.0 93.0 167.5 144.6 170.8 143.6 91.2 65.0 0.0 0.0 8761978 0.0 0.0 0.0 62.1 166.8 153.8 154.6 163.5 117.7 56.1 0.0 0.0 8741979 0.0 0.0 0.0 42.5 118.0 171.4 179.3 150.7 114.5 57.0 0.0 0.0 8331980 0.0 0.0 0.0 81.4 192.2 194.3 202.8 135.2 107.0 54.6 0.0 0.0 9671981 0.0 0.0 0.0 64.9 156.9 151.3 171.8 148.1 112.4 58.3 0.0 0.0 8641982 0.0 0.0 0.0 63.3 148.3 164.4 162.7 163.9 124.2 43.3 0.0 0.0 8701983 0.0 0.0 0.0 54.9 143.6 149.8 169.6 174.6 118.4 46.7 0.0 0.0 8581984 0.0 0.0 0.0 70.1 148.3 134.1 155.4 175.4 104.1 46.3 0.0 0.0 8341985 0.0 0.0 0.0 55.5 131.1 143.2 154.4 127.8 94.3 56.2 0.0 0.0 7621986 0.0 0.0 0.0 51.9 126.5 150.4 140.5 153.2 90.8 50.2 0.0 0.0 7631987 0.0 0.0 0.0 63.5 151.4 152.5 135.8 141.3 100.5 52.9 0.0 0.0 7981988 0.0 0.0 0.0 78.1 158.5 190.4 184.5 182.8 119.8 57.4 0.0 0.0 9721989 0.0 0.0 0.0 54.3 160.5 142.8 156.0 164.5 120.6 59.0 0.0 0.0 8581990 0.0 0.0 0.0 56.5 135.4 122.6 149.0 184.4 118.8 64.9 0.0 0.0 8321991 0.0 0.0 0.0 63.0 133.7 157.0 168.3 194.8 134.6 60.0 0.0 0.0 9111992 0.0 0.0 0.0 47.8 160.9 141.2 134.0 146.7 115.3 55.1 0.0 0.0 8011993 0.0 0.0 0.0 56.0 139.7 161.5 135.4 128.6 103.4 57.5 0.0 0.0 7821994 0.0 0.0 0.0 69.4 144.8 141.7 143.0 132.2 94.1 47.6 0.0 0.0 7731995 0.0 0.0 0.0 44.5 124.1 164.9 164.5 167.2 101.6 39.9 0.0 0.0 8071996 0.0 0.0 0.0 40.7 120.1 163.1 143.9 138.9 93.8 55.4 0.0 0.0 7561997 0.0 0.0 0.0 45.4 140.8 175.3 153.3 146.9 115.9 50.1 0.0 0.0 8281998 0.0 0.0 0.0 65.4 120.9 114.3 140.7 156.0 107.2 40.2 0.0 0.0 7451999 0.0 0.0 0.0 66.7 134.7 133.7 141.3 144.0 95.9 54.5 0.0 0.0 7712000 0.0 0.0 0.0 68.9 138.2 135.0 142.2 156.8 105.7 61.6 0.0 0.0 8082001 0.0 0.0 0.0 52.2 129.3 133.9 138.0 155.5 106.6 64.5 0.0 0.0 7802002 0.0 0.0 0.0 54.2 158.5 150.3 165.9 143.6 101.1 51.3 0.0 0.0 8252003 0.0 0.0 0.0 77.0 155.2 127.6 153.8 187.6 103.3 49.9 0.0 0.0 8542004 0.0 0.0 0.0 56.2 123.4 155.7 142.0 128.3 81.1 46.5 0.0 0.0 7332005 0.0 0.0 0.0 53.8 120.8 125.2 153.1 154.7 104.4 41.9 0.0 0.0 7542006 0.0 0.0 0.0 58.4 120.0 151.0 195.7 185.8 112.1 60.9 0.0 0.0 8842007 0.0 0.0 0.0 72.4 133.2 132.3 160.1 165.7 112.5 43.9 0.0 0.0 8202008 0.0 0.0 0.0 65.4 134.9 141.6 154.2 164.1 95.3 48.6 0.0 0.0 8042009 0 0 0 44.1 132.2 145.9 144.3 118.1 96.1 35.7 0 0 7162010 0 0 0 76.8 124.5 109.4 141.9 130.9 93.6 52 0 0 729

MIN 0.0 0.0 0.0 22.5 101.1 95.0 118.9 104.0 55.9 19.1 0.0 0.0 611MAX 0.0 0.0 0.0 93.0 192.2 226.2 217.2 216.9 158.4 71.5 0.0 0.0 1009MEAN 0.0 0.0 0.0 52.5 137.9 152.1 162.1 155.1 104.8 51.1 0.0 0.0 816

mean 1981-2010 0.0 0.0 0.0 59.7 138.3 145.4 153.2 155.4 105.9 51.7 0.0 0.0 810

Mean Annual Gross Evaporation for the Standard 30-Year Period 1971-2000 at Selected Locations in the Canadian Prairies

LOCATION

1971-2000

MEAN ANNUAL GROSS

EVAPORATION (mm)

LOCATION

1971-2000

MEAN ANNUAL GROSS

EVAPORATION (mm)

BRITISH COLUMBIA

Fort Nelson Fort St. John

ALBERTA

Calgary Cold Lake Coronation Edmonton International Edmonton Municipal Edson Fort McMurray Grande Prairie High Level Jasper Lethbridge Lloydminster* Medicine Hat Peace River Pincher Creek Red Deer Rocky Mountain House Slave Lake* Whitecourt

SASKATCHEWAN

Broadview Buffalo Narrows

419 805

898 733 863 734 828 628 458 786 415 657 1071 787 1014 778 1083 765 618 712 619

817 452

Cree Lake* Estevan Kindersley La Ronge Meadow Lake Moose Jaw Nipawin* North Battleford Prince Albert Regina Saskatoon Swift Current Wynyard Yorkton

MANITOBA

Brandon Churchill Dauphin Flin Flon Gillam Gimli Island Lake Lynn Lake Norway House Pilot Mound* Portage La Prairie The Pas Thompson Winnipeg

453 946 947 465 699 983 763 852 769 989 913 1026 828 810

791 440 803 466 475 660 433 480 444 767 790 487 432 834

What Does the Future Hold?• Report with monthly gross evaporation data

updated to 2010 and new 30-year average maps (1980 to 2010) for gross evaporation and precipitation will be completed soon.

• ??????? – PFRA no longer exists, and there is no mandate in the current organization to continue gross evaporation updates.