## 5 Conclusions  
Overall, it can be concluded that the mapping of irrigated area using an NDVI threshold approach highly depends on both the spatial distribution of irrigated fields and the spatial resolution of the observing sensor. The study demonstrates the potential of Sentinel-2 to open a new chapter of irrigation mapping by providing high-spatial-resolution NDVI time series with a temporal resolution of up to 2.5 days and can be applied as a transition from the historical irrigation mapping with wide-swath medium-resolution sensors such as VEGFATION, MODIS and AVHRR to an irrigation monitoring at a high temporal and spatial resolution. Further, the use of the landscape metrics shows the potential to estimate an expected accuracy of irrigation mapping derived by wide-swath medium-resolution satellites such as Sentinel-3. Landscape metrics can identify regions characterized by a high expected loss in irrigation mapping with coarser resolution. The information about the influence of spatial scale on irrigation mapping will increase the accuracy of the estimation of the actual amount of water that is withdrawn from the regional water resources and diverted regionally into the atmosphere by irrigation.  
The next step should be the development of an automatically updated irrigation monitoring system which supplies the users up-to-date information about the state of irrigation in terms of location, area and type. Irrigation monitoring as input information in spatially distributed crop growth models will improve the model results regarding water flows. The comparison of the model results with time series of multispectral remote sensing observations, which document the development of the irrigated crops from seeding to harvest, will allow the traceability of irrigation management such as the used irrigation water by the crops, irrigation water loss through interception or soil evaporation and overall water use efficiency. A remote-sensing-based monitoring system of the described kind is the prerequisite for the improvement of irrigation management towards a less wasteful use of the precious water resources by the farmers and can be a strong instrument in negotiations regarding upstream-downstream water conflicts in large watersheds.  
Conceptualization, J.M. and [PERSON]; methodology, [PERSON] and [PERSON]; software, [PERSON]; formal analysis, [PERSON] and [PERSON]; data curation, [PERSON]; writing--original draft preparation, [PERSON]; writing--review and editing, [PERSON] and [PERSON]; visualization, [PERSON]; supervision, [PERSON] All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Bavarian Environment Agency (Landesamt fur Umwelt, LafU) under the grant number 81-44214.9-89131/2017, 81-4421.9-89123/2017 and 81-4421.992819/2017, by the open access publication fund of the German Aerospace Center (DLR) and to a smaller part by AgRAIN, a project funded by the Federal Ministry of Education and Research (Bundesministerium fur Bildung und Forschung, BMBF) under the grant number 01 LZ1904A.  
The irrigation maps at different spatial scale produced in this study are available from the corresponding author upon reasonable request.  
The authors would like to thank the Vista GmbH--Remote Sensing Applications in Geosciences for providing the processed Sentinel-2 data. We also gratefully acknowledge the anonymous reviewers and editors for constructive comments for improvement of the manuscript. The responsibility for the content of this publication lies with the authors.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.