Crop Production under Increased Water Stress and Soil Salinity Conditions

Feeding a growing population vulnerable to food shortages is a pressing challenge in the context of changing diets impacting consumption patterns, of climate change variabilities, and the strain on soil due to salinization and erosion, as well as the stress on water resources caused by crop water scarcity, impacting production patterns. Employing sustainable agricultural practices, implementing efficient water management strategies, and strengthening resilience to climatic variability are pivotal in safeguarding global food security. Within the broader context of water-food nexus, addressing the escalating levels of soil salinity and water stress presents a significant intertwined challenge for agricultural production systems. Among the climate change side effects, higher temperatures leading to increased evapotranspiration (ET) rates, is worsening the presence of salt in the soil, left behind after water evapotranspires from soil surface. This requires a comprehensive assessment of water demand and crop sensitivity to saline conditions in root zone. Indeed, soil salinity induces osmotic stress within the plant's root zone, impeding water absorption and, thus, evapotranspiration. ET plays a crucial role in regulating the water balance of crops, influencing productivity through mechanisms such as water and heat stress, susceptibility to drought, and alter the plant seeding and harvesting dates. In this thesis, a new modelling layer has been integrated into the water CROP Agri-hydrological model to account for soil salinity in the root zones of agricultural fields. This advancement allows the model to (i) simulate more realistic crop evapotranspiration rates and (ii) estimate irrigation water demand associated with different soil salinity levels. The model has been updated to assess the most up-to-date crop water demand using the most recent agricultural dataset (referred to year 2015). Thus, the model was adopted to explore the spatial-temporal variability of crop water demand by running simulations in years 2000 and 2015. In this thesis, the model has been adopted with global coverage and at a spatial resolution of 5 arc minute (9 km by 9 km at the equator), with daily resolution. The key study crops are wheat, rice, maize, and soybean (staple crops) and broad bean, cabbage, potatoes, and tomatoes (salt-sensitive crops). The results highlight the variability in water demand for different crops and spatial heterogeneity of the actual ET. According to the crop selected the ET changes globally also because of the growing period associated that varies for tropical (e.g. Africa and India) and temperate regions (e.g. Europe and USA). Moreover results show new insights on actual irrigation demand of salt-sensitive crops that display a decrease in green water for rainfed scenarios and increase in blue water demand in irrigated scenarios. Eventually the thesis shows the variation between the two reference years of 2000 and 2015, manifesting worsening condition associated with the introduction of salinity conditions, especially in some climatic hotspots such as China, India and Mexico region along with the most susceptible crops to salinity. We thus demonstrate than selecting agricultural crops that are better suited to withstand climate pressures and salinity conditions, thus delaying water stress, is crucial for ensuring food security and mitigating the risk of worsening the already critical levels of blue water demand.