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Abstract Following a nuclear war, destruction would extend well beyond the blast zones due to the onset of a nuclear winter that can devastate the biosphere, including agriculture. Understanding the damage magnitude and preparing for the folly of its occurrence are critical given current geopolitical tensions. We developed and applied a framework to simulate global crop production under a nuclear winter using the Cycles agroecosystem model, incorporating ultraviolet (UV)-B radiation effects on plant growth and adaptive selection of crop maturity types (shorter cycle the lower the temperature). Using maize (Zea maizeL.) as a sentinel crop, we found that annual maize production could decline from 7% after a small-scale regional nuclear war with 5 Tg soot injection, to 80% after a global nuclear war with 150 Tg soot injection, with recovery taking from 7 to 12 years. UV-B damage would peak 6–8 years post-war and can further decrease annual maize production by 7%. Over the recovery period, adaptive selection of maize maturity types to track changing temperatures could increase production by 10% compared to a no-adaptation strategy. Seed availability may become a critical adaptation bottleneck; this and prior studies might underestimate food production declines. We propose that adaptation must include the development of Agricultural Resilience Kits consisting of region- and climate-specific seed and technology packages designed to buffer against uncertainty while supply chains recover. These kits would be congenial with the transient conditions during the recovery period, and would also be applicable to other catastrophes affecting food production. 

Water use efficiency (WUE) is a critical ecosystem function and a key indicator of vegetation responses to drought, yet its temporal trajectories and underlying drivers during drought propagation remain insufficiently understood. Here, we examined the trajectories, interdependencies and drivers of multidimensional WUE metrics and their components (gross primary production (GPP), evapotranspiration, transpiration (T), and canopy conductance (Gc)) using a conceptual drought propagation framework. We found that even though the carbon assimilation efficiency per stomata increases during drought, the canopy‐level WUE (represented by transpiration WUE (TWUE)) declines, indicating that stomatal regulation operates primarily at the leaf level and cannot offset the drought‐induced reduction in WUE at the canopy scale. A stronger dependence on T and TWUE indicates that the water–carbon trade‐off relationship of vegetation more inclines toward water transport than carbon assimilation. Gc fails to prevent the sharp decline in GPP during drought and has limited capacity to suppress T, as reflected by the reduction magnitude and the threshold (the turning point at which a component shifts from a normal to drought‐responsive state). The primary drivers of the water–carbon relationship under drought propagation include vapor pressure deficit and hydraulic traits. Among plant functional types, grasslands show the strongest water–carbon fluxes in response to drought, whereas evergreen broadleaf forests exhibit the weakest response. These findings refine our comprehensive understanding of multidimensional ecosystem functional dynamics under drought propagation and enlighten how the physiological response of vegetation to drought affects the carbon and water cycles.