Modelling the impacts of climate change on blue and green water interchange, crop yields, and virtual water trade under drought and post-drought conditions in Nelson River Basin
Creators: Khalili, Pouya
Publisher: name: University of Alberta Library
Year: 2023

<p>The unfolding climate change crisis poses a growing challenge to water and food security, and yet the reliability of the global breadbaskets and their relation with water resources in the future is poorly understood. The global breadbaskets are defined as key production regions for food grains and recognized for their vital contribution to global food security. In the mid-to-high latitude regions, especially in the higher latitudes of the temperate zone, the global breadbaskets are projected to receive an overall increased precipitation and improved crop yields under the effects of global warming scenarios, which is often perceived as beneficial to crop production and export potentials in the future (Myers et al., 2017; IPCC, 2021).  However, the extreme warm-dry events, anticipated as a consequence of global warming, can significantly affect the agro-hydrological processes, crop yields, and therefore export potential of the crops from these regions. This research examines the potential impacts of future droughts and post-droughts on hydrology, crop yields, and their linkages through assessing net virtual water export (NVWE), the water embodied in the production process of the crops that are exported to international countries. The study takes Nelson River Basin (NRB), a large agricultural watershed in western Canada and a global breadbasket located in higher latitudes of the temperate zone, as an example and it provides insights for future planning and informed decisions for water and food security.<br>
To understand the hydrological processes affecting crop yield and soil nutrients (i.e., nitrogen in this study) and their relation with changes in climate, this study employs a semi-distributed process-based agro-hydrologic model to an agricultural catchment in the NRB, i.e., Red Deer River Basin (RDRB), in the province of Alberta, Canada. Specifically, the research explores the effects of climate change and availability of soil water, as well as nitrogen fertilizer application scenarios on crop yields. The study examines the impacts on rainfed spring wheat, which is a dominant crop grown in most of NRB and in the RDRB. The results indicate that nitrogen stress may dominate other stress factors in producing rainfed wheat yields in the future as compared to the historical conditions that water-stress has been a dominant factor in the region. This is likely due to the overall increase in the soil moisture in the future that when compounded with a warmer temperature, triggers crop growth and potential yields, demanding more nitrogen in the soil. However, a regional assessment of the soil water availability, which affects nutrient and water uptakes by crops and their evapotranspiration rates (ET, green water), and the effects on hydrological water balance under extreme climatic events such as droughts in the future, is required.<br><br>
In a closed hydrological system, i.e., a watershed, the blue water (BW, or net annual freshwater generated in a catchment) and green water (GW, or actual evapotranspiration) are interlinked through numerous climate, soil, and plant processes. Their relationship has reportedly been non-stationary, with an anticipated shift from BW to GW in the future. Given that GW accounts for over 70% of water consumption in global food production, further research in this study scrutinizes the interlinkages between BW and GW and their potential shifts, primarily in response to future extreme warm-dry events. The results indicate dissimilarity in the physical processes that link GW and BW across different ecohydrological regions, and therefore, disproportional projected changes in BW and GW, and their linkages across regions. Mountainous and natural lands exhibit a shift from BW to GW, due to legacy soil moisture from earlier seasons and groundwater contributions. Conversely, in crop lands, there is a significant decrease in both BW and GW with no notable shift from BW to GW, posing severe threats to local and regional food production.<br>
Lastly, the research evaluates the effects of drought and subsequent post-drought conditions on crop production and its relation to watershed hydrology (i.e., blue water- also defined as water yield (WYLD) in this study) through assessment of NVWE. Contrary to prevalent long-term average projections of a wetter future for higher latitude regions of the temperate zone, the investigation of the longest and the most severe drought (LMD) in this study, indicate a substantial reduction in precipitation, Y (rainfed wheat and canola in this study), as well as WYLD in the future. The reductions in these agro-hydrological variables are likely to be more severe than historical drought conditions under SSP126. The slight improvement under the SSP585 scenario due to the CO2 effects on plant photosynthesis processes is not uniform across region and crop types. In central areas, which are prominent for crop production, the canola Y demonstrated less improvement as compared to the wheat Y, which is also compounded with a greater VWC of canola than wheat. The larger VWC of canola suggests larger crop water consumption in production of a tonne of crop, resulting in a considerable reduction of WYLD as compared to wheat crop and relative to the other regions across NRB. Overall, the regional scale WYLD, Y, and VWC show improvement during SSP585 droughts as compared to those of SSP126; however, they remain considerably lower than the average historical conditions regardless of crop type and the geographic location.<br><br>
During post-droughts, the study reveals variable recovery times for WYLD, Y, and NVWE in the future, with the WYLD demonstrating the slowest recovery time as compared to Y and NVWE during the years after the LMD. Given the projected frequent droughts in the future, the slow recovery of the WYLD after droughts can be a limiting factor for sustainable production and export potentials as it can deteriorate environment and several economic sectors. Our study lays a strong basis for examination of a strategic crop selection and diversification, which can be considered as an adaptation measure for conservation of WYLD for an integrated water and food security in the future. </p>