How will future climates in the Pakistani Punjab rice-wheat system affect the optimal agronomic settings, and can adaptation offset losses?

Pakistan is one of the most vulnerable countries in the world to future climatic changes, already with significant water and food sustainability issues. Rice and wheat production in the Pakistani Punjab is central to national food security and hence of particular concern. We sought to understand what optimal rice-wheat (RW) farmer agronomic practices (those which maximise RW system gross margins (GM) and irrigated water productivity (WPi)) look like under each of 6 projected future climate change scenarios for mid-century (2050). We also examined the impact on 2050 RW production if current farmer practices remained unchanged, to gauge the potential benefits of the optimal adaptations. Cropping systems simulation with a validated model (APSIM) enabled analysis of a broad range of current management practice modifications (6 agronomic management settings parameters, including crop sowing dates, varieties, fertiliser rates, and deficit irrigation strategies) in a large Monte-Carlo Matrix (96,768 elements) for the highest-yielding district in the Punjab, Gujranwala. We evaluated annual crop production, GM, WPi, nitrate leaching, and total system evapotranspiration (ET) for all combinations on an annual basis over a 31-year simulation period for each future climate scenario (as well as the historical record) seeking optimal parameter combinations within each. If current farmer practices were to remain unchanged into the future, we found reductions in farmer GM’s by 35–50% by 2050, with WPi decreasing even further (40–60%). Adaptation of current RW management practices is therefore essential. By adopting optimal practices now (derived using the historical climate record) we found that farmers also place themselves well for future climates and our study suggests they can maintain or maybe even increase current GM’s by 5–30% (depending on climate scenario) through smart adaptation. The best agronomic practices in 2050 look almost indistinguishable from the best agronomic practices now, regardless of future climate scenario chosen. However, compared with a hypothetical farmer operating under optimal practices now, our study suggests that a farmer in 2050 will earn considerably less, with gross margins under optimal practices falling by 25–40%, depending on which future climate scenario is considered. Declines are largely due to falling rice yields under future conditions (20–50% across examined climate scenarios), with wheat yields likely to be maintained or even slightly increased. Our study also indicated an increase in ET (10–15%) across all RW practices (regardless of future climate scenario and despite projections for generally reduced rainfall, runoff and drainage), compared with historical conditions. Our study suggests a rice varietal improvement need for heat tolerance, but that current wheat varieties are suitable to 2050.