The Indus plains, shared by India and Pakistan, are one of the most productive agricultural zones globally, producing sufficient food for over 300 million people. Agriculture relies heavily on irrigation, creating the world's largest contiguous irrigation system. While monsoon season provides ample surface water, the dry rabi season relies on groundwater extraction, leading to depleting water tables and ecosystem damage. Winter wheat accounts for most dry-season irrigation demands, yet it is a staple crop and crucial for food security. Maintaining regional wheat self-sufficiency is a significant policy objective, linked to the Sustainable Development Goal (SDG2) for zero hunger. The future of wheat production is uncertain due to expected population growth, increasing heat stress impacting yields, and altered surface water availability from climate change and competing water demands. Without adaptation, groundwater dependence will increase, exacerbating trade-offs between short-term wheat production and long-term water security. Previous studies examined adaptation measures but lacked the temporal and spatial detail needed to achieve explicit societal objectives. This study uses a spatiotemporally explicit adaptation pathways approach to address this gap, integrating land and water use strategies to maintain wheat production and sustainable water management (SDG6).

Prior research investigated integrated water-food adaptation in the Indus basin by analyzing numerous adaptation measures. While these studies assessed the potential of specific strategies, they didn't fully demonstrate the scale, timing, and sequencing of actions necessary to achieve water and food security objectives over time. The long-term design and timing of adaptation are challenging due to uncertain climatic and socioeconomic changes. An 'adaptation pathways approach' has been used to develop quantitative adaptation steps incrementally counteracting climate change impacts on global wheat production. This approach embraces uncertainty and allows flexible adaptation development. However, previous quantitative applications primarily focused on climate change adaptation with clearly defined objectives, often lacking a spatial dimension and the capacity to integrate multiple societal processes and objectives. This study addresses these limitations.

This research presents a spatiotemporally explicit adaptation pathways approach capable of simultaneously pursuing multiple water and food security objectives. The approach was applied to construct four sets of pathways with varying objectives and priorities for wheat production and irrigation water savings. The pathways address climatic and population changes for optimistic (SSP1-RCP4.5: moderate climate change, population stabilization) and pessimistic (SSP3-RCP8.5: extreme climate change, continued population growth) scenarios. Three adaptation measures were considered: 1. Laser land leveling (LLLV): Improves wheat yields and reduces irrigation water demands. 2. Production intensification to best practices for crop and farm management (BSPR). 3. Expansion of irrigated wheat production area through partial (PART) or full (FULL) reappropriation of irrigation water savings. These measures created five adaptation options. The effects of these options and climate change on wheat yields and irrigation water demands were spatially simulated using the LPJmL crop-hydrology model. The model also determined how climatic and population changes affect future wheat availability and irrigation water demands without adaptation (Reference pathways). The ensemble of pathways shows the long-term feasibility and trade-offs of integrated adaptation aiming to achieve both SDG2 and SDG6. The methodology advances threshold-based pathways approaches by integrating multiple competing objectives with an explicit spatial dimension. The study area focused on the lower Indus basin, simulated at 5 x 5 arcmin resolution from 1950-2080 with daily timesteps using an adapted LPJmL model. The model was calibrated to historical data, and simulations were conducted for two scenarios (SSP1-RCP4.5 and SSP3-RCP8.5), each with four downscaled GCMs. Five adaptation option datasets were created, representing different combinations of the three adaptation measures. A Spatial Pathways Algorithm was developed to create pathways determining the location and type of adaptation steps needed to achieve predefined objectives. This algorithm iteratively selects the best adaptation option per cell based on defined objectives and constraints (wheat production, irrigated area, water budget). The algorithm considers six spatial simulations (baseline and five adaptation options) to create annual adaptation maps that are appended to form yearly adaptation pathways. The algorithm starts in 2015 and iteratively determines the best cell-specific adaptation to meet the annual production threshold. If the threshold is not met, the algorithm selects adaptation options to reduce the production gap. If overproduction occurs, irrigated area is reduced. The process continues until 2080. Five adaptation configurations (Reference, ClimateProof, WaterSaver, FoodPrint, FoodSec) were defined with different objectives and constraints, applied to both scenarios, resulting in 40 pathways.

The Reference pathways showed climate change reducing wheat production by 14% (SSP1-RCP4.5) and almost 20% (SSP3-RCP8.5) by 2080 compared to 2015. Combined with population growth, per capita wheat production would decrease significantly. Even with moderate climate change and population stabilization (SSP1-RCP4.5), wheat production would be inadequate to ensure food security by 2040 without adaptation. Climate change reduced irrigation water demands in both scenarios. The ClimateProof pathways mitigated climate change impacts, requiring gradual production intensification in SSP1-RCP4.5 until 2050 and widespread laser land leveling in SSP3-RCP8.5. Rapid population growth in SSP3-RCP8.5 meant climate change adaptation alone was insufficient for food security. The FoodSec pathways aimed to maintain 200 kg per capita wheat production. This required extensive adaptation in SSP3-RCP8.5, utilizing all adaptation options by 2060, but still maintaining per capita production above 150 kg by 2080. The WaterSaver pathways prioritized minimizing irrigation water demands while maintaining 150 kg per capita production. This was achievable in SSP1-RCP4.5 with over 50% irrigation water reduction. However, in SSP3-RCP8.5, the 150 kg threshold wasn't met after 2050 due to constraints on adaptation options. The FoodPrint pathways minimized water footprints but allowed area expansion if needed. In SSP1-RCP4.5, this combined increased production with water reduction. However, in SSP3-RCP8.5, per capita production fell below 150 kg by 2070. Only the FoodSec pathways ensured self-sufficiency in SSP3-RCP8.5. Smart combinations of production intensification, laser land leveling, and targeted area expansion increased wheat production while reducing water demands in the short term. Long-term success depended strongly on population growth and climate change severity. In scenarios with severe climate change and continued population growth, mutually beneficial adaptation alone was insufficient to sustain per capita wheat production. Pathways prioritizing food security required adaptation steps enhancing yields in Pakistan, which negatively impacted the basin-level water footprint. Water demand reduction pathways focused on improving water productivity in the Indian Punjab, offering limited production gains and failing to meet production thresholds long-term. Pathways addressing climate and population change performed better than those focusing solely on climate change. The spatial dimension of the pathways highlighted that the suitability of adaptation measures varied across the basin, enabling the identification of localized complementary actions to reduce the water footprint and increase total production.

This study demonstrates that strategic adaptation can reconcile water and food security in the Indus basin, especially under moderate climate change and population stabilization. However, under severe climate change and continued population growth, achieving both goals simultaneously is challenging, requiring difficult trade-offs. The spatial explicitness of the pathways approach is critical, showcasing how the suitability of different adaptation measures varies across the basin. The study's model-based nature is a limitation, simplifying the complex interplay of factors influencing water and food security. While the considered adaptation measures are promising, other strategies may offer complementary effects. The pathways primarily focus on optimizing the existing wheat production system, which may be unsustainable under severe future conditions. Future research should explore transformation-oriented pathways addressing systemic change beyond technical optimization. The study provides insights into the interaction between multiple adaptation objectives and drivers, enhancing the integration of climate change with societal development and SDGs. Population change, more than climate change, is identified as the dominant challenge to interlinked water and food security. The approach offers robust short-term options and a flexible framework for evaluating long-term objectives. This approach can be applied to other regions facing similar challenges.

This study demonstrates that carefully designed adaptation strategies can significantly enhance both water and food security in the Indus River basin, but the effectiveness depends heavily on future climate change and population growth. While short-term gains are possible through integrated measures, long-term success requires consideration of both climate and population trends. The spatially explicit adaptation pathways approach offers a valuable framework for planning and decision-making. Future research should investigate other adaptation strategies, address systemic changes, and incorporate socioeconomic and economic factors for a more comprehensive understanding.

The study utilizes a model-based approach, simplifying the complex reality of the Indus basin. Economic factors, farmer knowledge, and other societal aspects were not explicitly included. The three adaptation measures considered may not encompass all possibilities. The study's conclusions rely on the accuracy and assumptions of the LPJmL model and the scenarios used.