Determining Irrigated Areas and QuantifyingBlue Water Use in Europe Using Remote Sensing Meteosat Second Generation (MSG) products and Global Land Data AssimilationSystem (GLDAS) Data

摘要

In this paper, we propose an innovative method for identifying irrigated areas and quantifying the blue evapotranspiration (ETb), or irrigation water evapotranspired from the field. The method compares actual ET (ETactuai), or crop water use, values from the Global Land Data Assimilation System (GLDAS) and remote sensing based (ET_(actua)) estimates obtained from Meteosat Second Generation (MSG) satellites. Since GLDAS simulations do not account for extra water supply due to irrigation, it is expected that they underestimate ET_(actual )during the cropping season in irrigated areas. However, remote sensing techniques based on the energy balance are able to observe the total ET_(actua). In order to isolate irrigation effects from other fluctuations that may lead to discrepancies between the different ET_(actual) products, the bias between model simulations and remote sensing observations was estimated using reference targets of rainfed (non-irrigated) croplands on a daily basis in different areas across the study region (Europe). Analysis of the yearly values of ETb (irrigated area and volume obtained for croplands in Europe for 2008) showed that the method identified irrigation when yearly values were higher than 50 mm. The accuracy of the methodwas assessed by analyzing the spatial representativity of the calculated biases and evaluating the daily ET_b values obtained. The irrigated areas were compared with the results provided by Siebert et al.(2007) and Thenkabail et al.(2009b), obtaining a spatial match of 47 and 72 percent, respectively, with overestimation of irrigated area on a country scale. Additional evaluation with the ETb results of Mekonnenand Hoekstra (2011) showed 75 percent of overlap for ±50 mm range. Finally, validation with in situ data on irrigation volumes proved the cogency of our method with less than 20 percent difference between derived and measured values.