Survey on the applicability of different Evapotranspiration-calculating methods on the tree nursery in Schinznach

Besides the FAO56 method wich was discussed earlier in this blog, there exists a variety of methods to calculate and assess the evapotranspiration of a crop. In general, there are radiation-based, temperature-based and combination-based ways for calculating evapotranspiration (Kashyap & Panda, 2001). Listed below, three of these methods are compared to see if they are applicable with justifiable expenditure on the water-balance survey in Schinznach.

·      FAO56/Penman – Monteith (combination-based)

·      Priestly – Taylor (radiation-based)

·      Blaney - Criddle (temperature-based)

table 1: Comparision of three evapotranspiration-calculating methods.

	+	-	Applicability Schinznach?
FAO56/Penman - Monteith	·      High precision ·      Adaptable to different crops with changing Kc-values	·       Requires detailed weather-data ·      Realtively high effort	·       Applicable ·       uncertainities about weather data provided
Priestly - Taylor	·      No weather data needed ·      Less effort needed	·      Calculated evapotranspiration tends to be too high in sub-humid areas (Xu & Singh, 2002)	·       Applicable ·       Possible to do in one week
Blaney – Criddle	·      Distinguishes between different grow periods and vegetation types ·      No weather data needed except temperature data	·      low precision if consumptive coefficient k isn’t adjusted (Xu & Singh, 2002)	·       not to favour due to low precision

Now, therefore there is only a small time frame of one week to compile a water-balance model of the tree nursery, a justifiable expenditure is going to be the one key factor on choosing a method to calculate the evapotranspiration of the tree nursery area. If anyhow possible, the data that are going to be provided by the remote-sensing team should be integrated in the calculation, for example by distinguishing different vegetation stages and heights for the calculation. Combined with measurements on individual plants itself it should be possible to compile a replicable water balance. This leads to the following superior research question for the project week:

“In view of compiling a water-balance model, how can remote-sensing data be integrated in the calculation of the evapotranspiration of the tree nursery in Schinznach?”

References:

- Kashyap, P.S., Panda, R.K. (2001). Evaluation of evapotranspiration estimation methods and development of crop-coefficients for potato crop in a sub-humid region. Agric. Water Manag. 50, 9–25. 

- XU, C.-Y. & SINGH, V. P. (2002). Cross Comparison of Empirical Equations for Calculating Potential Evapotranspiration with Data from Switzerland. Water Resources Management, 16, 197–219.