Abstract
Abstract. In agricultural ecosystems the use of evapotranspiration (ET) to improve irrigation water management is generally widespread. Commonly, the crop ET (ETc) is estimated by multiplying the reference crop evapotranspiration (ETo) by a crop coefficient (Kc). Accurate estimation of ETo is critical because it is the main factor affecting the calculation of crop water use and water management. The ETo is generally estimated from recorded meteorological variables at reference weather stations. The main objective of this paper was assessing the effect of the uncertainty due to random noise in the sensors used for measurement of meteorological variables on the estimation of ETo, crop ET and net irrigation requirements of grain corn and alfalfa in three irrigation districts of the middle Ebro River basin. Five scenarios were simulated, four of them individually considering each recorded meteorological variable (temperature, relative humidity, solar radiation and wind speed) and a fifth scenario combining together the uncertainty of all sensors. The uncertainty in relative humidity for irrigation districts Riegos del Alto Aragón (RAA) and Bardenas (BAR), and temperature for irrigation district Canal de Aragón y Cataluña (CAC), were the two most important factors affecting the estimation of ETo, corn ET (ETc_corn), alfalfa ET (ETc_alf), net corn irrigation water requirements (IRncorn) and net alfalfa irrigation water requirements (IRnalf). Nevertheless, this effect was never greater than ±0.5% over annual scale time. The wind speed variable (Scenario 3) was the third variable more influential in the fluctuations (±) of evapotranspiration, followed by solar radiation. Considering the accuracy for all sensors over annual scale time, the variation was about ±1% of ETo, ETc_corn, ETc_alf, IRncorn, and IRnalf. The fluctuations of evapotranspiration were higher at shorter time scale. ETo daily fluctuation remained lower than 5 % during the growing season of corn and alfalfa. This estimation fluctuation in ETo, ETc_corn, ETc_alf , IRncorn, and IRnalf at daily time scale was within an acceptable range, and it can be considered that the sensor accuracy of the meteorological variables is not significant in the estimation of ETo.
Highlights
Methods and net irrigation requirements of grain corn and alfalfa in three irrigation districts of the middle Ebro River basin
The objective of this paper was to assess the effect of the uncertainty due to random noise in the sensors used for measurement of meteorological variables on the estimation of ETo and the effect of this uncertainty in the estimation of the crop irrigation water requirements of the two most important crops in the Ebro Basin: alfalfa and grain corn
The major differences were found for wind speed: Ejea showed a long-term annual average of 2.7 ms−1, while that for Tamarite was 1.2 ms−1, and that for Granen was between these two values
Summary
Methods and net irrigation requirements of grain corn and alfalfa in three irrigation districts of the middle Ebro River basin. (CAC), were the two most important factors affecting the estimation of ETo, corn ET (ETc corn), alfalfa ET (ETc alf), net corn irrigation water requirements (IRncorn) and net alfalfa irrigation water requirements (IRnalf). This effect was never greater than ±0.5 % over annual scale time. Ing energy balance, andHscyindtirlloomloegtryy, aamnondg others (Allen et al, 2011) These methods are very expensive, time consuming, complex, and reEquairrethwoSrkydsontee mby highly qualified people to obtain data of gooSdcqiueanlitcy.ePsublished uncertainty of these methods is variable – from 5 to 15 % for
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