Worldwide water constrains on closing yield gaps

By 2050 a doubling of crop production may be necessary to meet the growing worldwide food demands. Several studies have indicated the potential to increase crop production by reducing the so-called yield gap, i.e. the difference between potential crop production and actual crop production. The focus is commonly on closing the yield gap by increasing nutrient supply through fertilization and/or by increasing irrigated cropland extent. This could potentially achieve water-limited production (limited by rainfall) in rain-fed croplands and climate-limited production (limited by temperature and radiation) in irrigated croplands. For irrigated croplands this assumes sufficient water availability for irrigation. However, water availability for irrigation may be insufficient under higher nutrient supply. In addition, irrigation expansion in upstream areas might negatively affect water availability in downstream areas.

We aim to quantitatively assess the worldwide water constrains to close yield gaps, accounting for various nutrient inputs. To assess water constrains we integrated a macro-scale hydrological model, the Variable Infiltration Capacity model (VIC-5 including human impacts; Droppers et al. in review), with a crop production model, the World Food Studies (WOFOST; de Wit et al. 2019) model. The VIC and WOFOST models were coupled for two-way interactions. The VIC model simulates the water and energy balance, including runoff, evapotranspiration, discharge and water stress for crop growth. Water stress is used in the WOFOST model to limit and adapt crop growth, e.g. limited biomass production and adjusted relative root production. Simulated crop characteristics (height, leaf area index, CO2 effects) are subsequently returned to VIC. By coupling these models we are able to assess the feedbacks between crop production and water availability globally.

References:

Droppers, B., Franssen, W. H. P., van Vliet, M. T. H., Nijssen, B., and Ludwig, F.: Simulating human impacts on global water resources using VIC-5. Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2019-251, in review, 2019.

de Wit, A., Boogaard, H., Fumagalli, D., Janssen, S., Knapen, R., van Kraalingen, D., ... & van Diepen, K. (2019): 25 years of the WOFOST cropping systems model. Agricultural Systems, 168, 154-167, https://doi.org/10.1016/j.agsy.2018.06.018.