Multiple cropping in global-scale Land-Use Models and the role of Irrigation
Authors: Beier Felicitas , Heinke Jens , Bodirsky Benjamin Leon , Müller Christoph , Ostberg Sebastian , Karstens Kristine , Abrahao Gabriel , Popp Alexander , Lotze-Campen Hermann 
Published: March 2024

Multiple cropping practices, i.e. planting and harvesting crops several times a year at the same plot of land, may increase global food production without further expanding cropland (Wu et al. 2014). Especially the combination of irrigation in the dry season to facilitate multiple harvests a year potentially facilitates more food production on the same amount of land. Global dynamic gridded vegetation models that inform global land-use models usually only model one growing season a year. Neglecting the yield that can be achieved in the second or third season leads to an underestimation of yields and irrigation water requirements and biased projections of the spatial allocation of rainfed and irrigated cropland.With an update of our hydro-economic model (Beier et al. 2023), we are able to estimate multiple cropping potentials and model multiple cropping and irrigation expansion. It is the tandem of these two intensification measures that facilitates production gains without expanding cropland. We estimate multiple cropping potentials considering their interaction with irrigation and water availability limitations to determine how much cropland area can be managed in a multiple cropping system given local crop growth conditions (suitability for multiple cropping), the associated water requirements and locally limited water availability for irrigation. We obtain multiple cropping and irrigation potentials at a 0.5&#176; spatial resolution using biophysical inputs from the global vegetation model LPJmL (Schaphoff et al. 2018, von Bloh et al. 2018). LPJmL provides crop-specific (irrigated and rainfed) crop yields and crop water requirements for the main growing season for 12 crop functional types and gross primary production (GPP) of grass for the entire year at a 0.5&#176; spatial resolution. To derive a metric on the yield increase through multiple cropping, we need an aggregated approach that abstracts from the very high set of potential combinations of crops in multiple cropping. We therefore use the main-season-to-whole-year ratio of grass GPP to obtain the grid-cell-specific potential multiple cropping effect. This ratio is used to scale main season crop yields and crop water requirements. In terms of irrigation water availability, the spatial allocation of irrigation water takes upstream-downstream relationships into account and considers the monetary yield gain through irrigation to determine the location of potentially irrigated areas (Beier et al. 2023).With this, we address the research question: What is the biophysical and economic multiple cropping production potential under consideration of local (spatially explicit) irrigation water availability constraints on current cropland?References Beier, F. et al. (2023a). Technical and Economic Irrigation Potentials within Land and Water Boundaries. Water Resources ResearchBeier, F., et al. (2023b) &#8216;Mrwater: MadRat Based MAgPIE Water Input Data Library&#8217;. 10.5281/zenodo.5801680.Schaphoff, S. et al. (2018). &#8216;LPJmL4 &#8211; a Dynamic Global Vegetation Model with Managed Land &#8211; Part 1: Model Description&#8217;. Geoscientific Model Development 11 (4)Wu, W., et al. (2018) Global cropping intensity gaps: increasing food production without cropland expansion. Land Use Policy 76 (2018)von Bloh, W. et al. (2018). Implementing the Nitrogen Cycle into the Dynamic Global Vegetation, Hydrology, and Crop Growth Model LPJmL (Version 5.0). Geoscientific Model Development 11 (7)