Operational monitoring of daily evapotranspiration by the combination o of MODIS NDVI and ground meteorological data: Application and evaluation in Central Italy
2014
MASELLI Fabio | PAPALE Dario | CHIESI M. | MATTEUCCI Giorgio | ANGELI Luca | RASCHI Antonio | SEUFERT Guenther
Time-varying crop coefficients (Kc) can be obtained from remotely sensed data and combined with daily potential evapotranspiration estimates for the operational prediction of actual evapotranspiration (ETA). This approach, however, presents relevant limitations when applied in mixed, water stressed ecosystems. The current paper addresses these issues by introducing two innovations. First, fractional vegetation cover (FVC) is derived from NDVI and utilized to split evaporating and transpiring surfaces, whose behaviour is simulated under fully watered conditions by the use of generalized Kc. Next, the short term effects of water shortage are taken into account by means of downregulating factors which act differently for vegetated and not vegetated surfaces. The effects of possible irrigation on annual crops can also be taken into account by the elaboration of meteorological and NDVI data. The new method is tested against 25 latent heat of evaporation (LE) measurements taken by the eddy covariance technique in six sites of Central Italy representative of various forest and herbaceous ecosystems. In this experiment the method is driven by 1-km meteorological data obtained from a pan-European archive and by 250 m MODIS NDVI imagery. Satisfactory accuracies are obtained in all experimental situations, which encourages the application of the method for the operational monitoring of ETA on regional scale.
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