Satellite Observations of Water Origins Reveal New Dimensions of Hydroclimate Vulnerability of Global Croplands

Food security depends on water availability; understanding the sources of atmospheric moisture for different crop producing regions is thus critical. Here, using Earth observations and physical and statistical models over the period 2003-2019, we explore the extent to which atmospheric moisture for the world’s major crops originates from oceans versus land. By integrating precipitation isotope observations and two satellite-derived atmospheric water isotope products, we find that the percentage of crop water originating from land varies from ~25% to 75% over the year, with strong variation over crop growing seasons and crop phenological stages. Although patterns vary by region, ocean-originating moisture tends to provide most precipitation during the vegetative and reproductive stages of the main crop growing season. Linking source and water supply information shows that crop water stress becomes more likely later during the reproductive period, due to continuous and increasing soil moisture depletion, and this phenomenon is much stronger for croplands dependent on land-originating moisture. This stress is highly associated with crop productivity as measured by greenness (NIRv): we find that croplands with ≥40% of moisture derived from land are more susceptible to water stress than those with <40%. Importantly, when disaggregated by crop type, we find that over 40% of the world’s maize and over 50% of the world’s wheat receive more than 40% of their moisture from land during the critical reproductive stage. For these areas, simple hydrological metrics -- integrated rainwater supply and root-zone soil moisture -- explain up to 60% of inter-annual variability in crop greenness. These results thus provide valuable insights for understanding dimensions of the vulnerability of global crop production and potential adaptation responses, including protection of local land moisture sources, selection of suitable crops, and design of smart irrigation strategies at sub-seasonal scales.