Restructuring lucerne planting can improve production and environmental co-benefits in Northwest China

As China's cornerstone lucerne production region, Gansu Province plays a pivotal role in sustaining national forage security and livestock systems, yet the climate resilience of this strategic crop remains critically unassessed. Here we present a multi-objective optimization framework integrating process-based modeling and climate change projections under SSP245 and SSP585 scenarios to reconcile lucerne biomass and protein production, irrigation water productivity, and global warming potential from field (GWP-field) trade-offs. We project that lucerne biomass and protein production in Gansu will increase 5.7 %-25.3 % by the 2090 s, but with a 6.0 %-10.1 % decrease in protein concentration, primarily as temperature-affected biomass increases mask the declines in protein concentration. Strategic spatial restructuring of cultivation could achieve synergistic benefits - elevating biomass and protein yield by 1.4 %-2.0 % while simultaneously diminishing irrigation and GWP-field by 1.4 %-3.9 %. The new planting patterns identified 4238–5521 ha of priority expansion in Longzhong and Longdong, where phased cultivar deployment could maximize benefits of production (1.4–2.0 % increase), resource use (3.4–3.9 % decrease), and environmental impact (1.4–1.9 % decrease). However, increasing lucerne production to expand cattle and sheep feeding would result in an additional 17.9–20.0 thousand CO2-eq of emissions due to enteric fermentation and manure management, even taking into account the benefits of restructuring lucerne planting and irrigation saving on GWP. Our findings underscore the imperative of multidimensional optimization in balancing agronomic gains against environmental impacts in cropping systems of arid regions.