Evapotranspiration Deposition Water Vapor Liquid Water Solar Radiation

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Evapotranspiration

Evapotranspiration

Deposition

Deposition

Water Vapor Liquid Water

Water Vapor Liquid Water

Solar Radiation Wind Evaporation Relative Humidity Temperature

Solar Radiation Wind Evaporation Relative Humidity Temperature

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

Evaporation

High Winds Low Relative Humidity High Evaporation High Solar Radiation High Temperature

High Winds Low Relative Humidity High Evaporation High Solar Radiation High Temperature

Mean Annual Lake Evaporation Mean Daily Solar Radiation (langleys) 200 -250 250 -300 300

Mean Annual Lake Evaporation Mean Daily Solar Radiation (langleys) 200 -250 250 -300 300 -350 350 -400 400 -450 450 -500 500 -550 Mean daily solar radiation in the United States and Puerto Rico. (Source: Data from the U. S. Department of Commerce, 1968). From Hanson 1991. Annual Lake Evaporation (inches) 10 -20 20 -30 30 -40 40 -50 50 -60 60 -70 70 -80 80+ Mean annual lake evaporation in the conterminous United States, 1946 -55. Data not available for Alaska, Hawaii, and Puerto Rico. (Source: Data from U. S. Department of Commerce, 1968). From Hanson 1991.

Evapotranspiratio n Evaporation from the land surface, including evaporation of soil moisture and transpiration

Evapotranspiratio n Evaporation from the land surface, including evaporation of soil moisture and transpiration from plants Figure by Mwtoews (Own work) [GFDL (http: //www. gnu. org/copyleft/fdl. html) or CC-BY 3. 0 (http: //creativecommons. org/licenses/by/3. 0)], via Wikimedia Commons

Transpiration Evaporation of water from plant leaves water vapor Water moves from the soil

Transpiration Evaporation of water from plant leaves water vapor Water moves from the soil into plant roots, through the plant, and finally out through the leaves Background image licensed under Creative Commons Attribution-Share Alike 3. 0 via Wikimedia Commons - http: //commons. wikimedia. org/wiki/File: Photosynthesis. gif#mediaviewer/File: Photosynthesis. gif

Transpiration Evaporation of water from plant leaves water vapor Background image licensed under Creative

Transpiration Evaporation of water from plant leaves water vapor Background image licensed under Creative Commons Attribution-Share Alike 3. 0 via Wikimedia Commons - http: //commons. wikimedia. org/wiki/File: Photosynthesis. gif#mediaviewer/File: Photosynthesis. gif Microscopic structure of a leaf, and the processes of photosynthesis and transpiration. Image credit nasa. gov

Transpiration is an evaporative process Same meteorological factors: solar radiation temperature wind humidity And

Transpiration is an evaporative process Same meteorological factors: solar radiation temperature wind humidity And more factors plant structure, age, health and other factors Image used with permission from http: //mesonet. k-state. edu/about/evapotranspiration/

Estimated Mean Annual Actual Evapotranspiration (ET) for the Period 1971 -2000 Estimates are based

Estimated Mean Annual Actual Evapotranspiration (ET) for the Period 1971 -2000 Estimates are based on a regression equation of ET⁄P that includes land cover multiplied by the mean annual precipitation from the PRISM climate data for the same period. Calculations of ET were made first at the 800 -m resolution of the PRISM climate data. The mean values for the counties (shown) were then calculated by averaging the 800 -m values within each county. Estimated Mean Annual Precipitation, for the Period 1971 to 2000 Data compiled from PRISM Climate Group, Oregon State University (Daly et al. , 2008), http: //www. prism. oregonstate. edu, accessed July 2009. From Sanford and Selnick 2012. Images Copyright (2012) Wiley. Used with permission from: Sanford, Ward E. and David L. Selnick, 2012. Estimation of Evapotranspiration Across the Conterminous United States Using a Regression with Climate and Land-Cover Data. Journal of the American Water Resources Association, John Wiley & Sons.

Actual ET – varies with climate and plant type Reference ET = ETo Wellwatered

Actual ET – varies with climate and plant type Reference ET = ETo Wellwatered standard grass

Reference ET, or ETo Reference ET standard height and stage of growth factors vary

Reference ET, or ETo Reference ET standard height and stage of growth factors vary with location and climate Image modified from FAO, 'Guidelines for computing crop water requirements' Chapter 1. [http: //www. fao. org/docrep/x 0490 e 04. htm]). This is an adaptation of an original work by FAO. Views and opinions expressed in the adaptation are the sole responsibility of the author or authors of the adaptation and are not

Landscape ET = ETL plant factor PF reference ET (well-watered grass) landscape area L

Landscape ET = ETL plant factor PF reference ET (well-watered grass) landscape area L landscape ET Image modified from FAO, 'Guidelines for computing crop water requirements' Chapter 1. [http: //www. fao. org/docrep/x 0490 e 04. htm]). This is an adaptation of an original work by FAO. Views and opinions expressed in the adaptation are the sole responsibility of the author or authors of the adaptation and are not

Measuring ET and estimating irrigation Atmometer – measures reference ET Image from etgage. com

Measuring ET and estimating irrigation Atmometer – measures reference ET Image from etgage. com Precipitation gauge Image from Co. Rahs. org

Measuring ET and estimating irrigation Water surplus Water Deficit

Measuring ET and estimating irrigation Water surplus Water Deficit

Landscape water needs Sprinkler efficiency 70% Very Low Water Demand, PF = 0. 2

Landscape water needs Sprinkler efficiency 70% Very Low Water Demand, PF = 0. 2 Image from Detweiler et al. 2005 Image from Hattendorf 2012 High Water Demand, PF = 0. 8

Landscape water needs sprinkler efficiency ETL = ETo x PF Irrigation = (ETL –

Landscape water needs sprinkler efficiency ETL = ETo x PF Irrigation = (ETL – P) / 0. 7 Very Low Water Demand, PF = 0. 2 Image from Hattendorf 2012 For example, If ETo = 1 in, and P = 0. 1 in, for July For Yucca, PF = 0. 2 ETL = 1 in x 0. 2 = 0. 2 in Irrigation = (0. 2 in – 0. 1 in) / 0. 7 = 0. 14 in For Turf, PF = 0. 8 ETL = 1 in x 0. 8 = 0. 8 in Irrigation = (0. 8 in – 0. 1 in) / 0. 7 = 1. 0 in High Water Demand, PF = 0. 8

Summary Evapotranspiration = soil evaporation + plant transpiration • Meteorological factors • Solar radiation,

Summary Evapotranspiration = soil evaporation + plant transpiration • Meteorological factors • Solar radiation, temperature, wind, humidity • Plant factors • Age, health, season, structure and others Estimating ET • Landscape ET, ETL = ET from different plants • Reference ET, ETo = ET from well-watered grass (varies with meteorological factors) • Plant Factor, PF = plant dependent factor used to estimate ET of a particular plant ET = ET PF

Summary Landscape Water Needs = ETL - Precipitation • If ETL > P, then

Summary Landscape Water Needs = ETL - Precipitation • If ETL > P, then irrigation is necessary • Must consider sprinkler efficiency ( 0. 7) when estimating irrigation rates Irrigation = (ETL – P) / 0. 7

References Allen, R. G. , L. S. Pereira, D. Raes and M. Smith, 1998,

References Allen, R. G. , L. S. Pereira, D. Raes and M. Smith, 1998, Crop evapotranspiration - Guidelines for computing crop water requirements – FAO Irrigation and drainage paper 56, Food and Agriculture Organization of the United Nations, Rome, Italy, http: //www. fao. org/docrep/x 0490 e 00. htm. Detweiler, A. J. P. Griffiths, and R. Olson, 2005. An Introduction to xeriscaping in the High Desert And Pictorial Plant Guide for Central & Eastern Oregon, Oregon State University Extension Service. http: //extension. oregonstate. edu/yamhill/sites/default/files/an_introduction_to_xeriscaping. pdf Hanson, R. L. , 1991, Evapotranspiration and Droughts, in Paulson, R. W. , Chase, E. B. , Roberts, R. S. , and Moody, D. W. , Compilers, National Water Summary 1988 -89–Hydrologic Events and Floods and Droughts: U. S. Geological Survey Water-Supply Paper 2375, p. 99 -104. http: //geochange. er. usgs. gov/sw/changes/natural/et/ Hattendorf, M. J. 2012. Northern Water Irrigation Management – Xeriscape Irrigation Recommendations, https: //www. northernwater. org/docs/Water. Conservation/Conservation. Gardens/Xeriscape. Recom mendations. pdf Sanford, W. E. and D. L. Selnick, 2012. Estimation of Evapotranspiration Across the Conterminous United States Using a Regression with Climate and Land-Cover Data. Journal of the American Water Resources Association (JAWRA) 1 -14. DOI: 10. 1111/jawr. 12010