1054 Estimation of Reference Evapotranspiration Using Meteorological Data from Czech Republic

Wednesday, 25 January 2017
4E (Washington State Convention Center )
Michael Opare Asare, WMO, Prague, Czech Republic

Evapotranspiration (ET) is an important component of the hydrological cycle, and thus a key input to groundwater models. Meteorological data offers great opportunities for acquiring data on environmental variables for large and remote areas, and different methods have been developed for using this data to estimate ET. This project seeks to address how efficient the Penman-monteith formular is used to estimate reference evapotranspiration with or without missing data.
According to Dingman (2002), evapotranspiration (ET) can be defined as a collective term for all the processes by which water at or near the land surface becomes atmospheric water vapor. The word is composed of the term evaporation, referring to water vapor coming from liquid water such as rivers, lakes, bare soil and vegetation surfaces, and the term transpiration, referring to the water vapor originating from within the leaves of plants. Evaporation and transpiration are different processes governed by different rules, but since the earth’s surface is often covered by a mixture of open water, soil and vegetation, it can be difficult to distinguish between the two fluxes, and for operational purposes they are often treated as one. ETref is a measure of the evaporative demand of the atmosphere independent of crop type, crop development and management practices. Only climatic factors affect ETref. Consequently, ETref is a climatic parameter and can be computed from meteorological data . Different categories of methods have been developed in attempts to model ETref, including (Xu and Singh, 2002): (1) water budget (e.g., Guitjens, 1982), (2) mass-transfer (e.g., Harbeck, 1962), (3) combination (e.g.,Penman, 1948). The Standardized Penman–Monteith (P–M) method is recommended by FAO as the sole method to calculate reference evapotranspiration wherever the required input data are available and was applied to Nemicine catchment area in the Czech Republic. To study the physical process of reference evaportranspiration and its interactions with the surrounding environment, an elaborate evaporation experiment was carried out by means of meteorological method, in which 5 minutes evaporation variables were measured for 12 months. The standardized FAO56 Penman–Monteith model, which has been the most reasonable method in both humid and arid climatic conditions, provides reference crop evapotranspiration (ETo) estimates for planning and efficient use of agricultural water resources. Daily time steps, maximum and minimum air temperature, air humidity, soil temperatures, soil moistures and solar radiation are the meteorological inputs as well as basic information about the soil properties and vegetation cover. To check the accuracy of the approach used in estimation ETo models were estimated with coefficient of determination and root mean square error which was finally be compared with eddy-covariance with a special R code.
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