Irrigation in the Mediterranean region has been used for millennia and has greatly expanded with industrialization. Irrigation is critical for climate change adaptation, but it is also an important source of greenhouse gas emissions. This study analyzes the carbon (C) footprint of irrigation in Spain, covering the complete historical process of mechanization. A 21-fold total, 6-fold area-based, and 4-fold product-based increase in the carbon footprint was observed during the 20th century, despite an increase in water use efficiency. CH4 emissions from waterbodies, which had not previously been considered in the C footprint of irrigation systems, dominated the emission budget during most of the analyzed period. Technologies to save water and tap new water resources greatly increased energy and infrastructure demand, while improvements in power generation efficiency had a limited influence on irrigation emissions. Electricity production from irrigation dams may contribute to climate change mitigation, but the amount produced in relation to that consumed in irrigation has greatly declined. High uncertainty in CH4 emission estimates from waterbodies stresses a need for more spatially resolved data and an improved empirical knowledge of the links between water quality, water level fluctuations, and emissions at the regional scale.

Synthetic nitrogen (N) fertilization has helped boost agricultural yields, but it is also responsible for direct and indirect greenhouse gas (GHG) emissions. Fertilizer-related emissions are also promoted by irrigation and manure application, which has increased with livestock industrialization. Spanish agriculture provides a paradigmatic example of high industrialization under two different climates (temperate and Mediterranean) and two contrasting water management regimes (rainfed and irrigated). In this study, we estimated the historical evolution of the C footprint of N fertilization (including all the life cycle GHG emissions related to N fertilization) in Spanish agriculture from 1860 to 2018 at the province level (50 provinces) for 122 crops, using climate-specific N2O emission factors (EFs) adjusted to the type of water management and the N source (synthetic fertilizer, animal manure, crop residues and soil N mineralization) and considering changes in the industrial efficiency of N fertilizer production. Overall, N-related GHG emissions increased ∼12-fold, up to 10–14 Tg CO2e yr−1 in the 2010s, with much higher growth in Mediterranean than in temperate areas. Direct N2O EFs of N fertilizers doubled due to the expansion of irrigation, synthetic fertilizers and liquid manure, associated with livestock industrialization. Synthetic N production dominated the emissions balance (55%–60% of GHGe in the 21st century). Large energy efficiency gains of industrial fertilizer production were largely offset by the changes in the fertilizer mix. Downstream N2O emissions associated with NH3 volatilization and NO3 − leaching increased tenfold. The yield-scaled carbon footprint of N use in Spanish agriculture increased fourfold, from 4 and 5 Mg CO2e Mg N−1 to 16–18 Mg CO2e Mg N−1. Therefore, the results reported herein indicate that increased productivity could not offset the growth in manufacture and soil emissions related to N use, suggesting that mitigation efforts should not only aim to increase N use efficiency but also consider water management, fertilizer type and fertilizer manufacture as key drivers of emissions.

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<p>The agricultural sector is challenged to meet the global food needs of mankind and reduce its environmental impacts. It is well known that the industrialisation of agriculture has led to negative effects such as water pollution, increased erosion, loss of biodiversity, increased zoonotic diseases, high water consumption to the detriment of ecosystem needs and other users, and greenhouse gas emissions, among others.</p><p>However, the proposition and implementation of adequate solutions for these environmental issues are still limited by the epistemological challenge posed by the complexity of socio-ecological processes associated with food production at different spatial and temporal scales. To that respect, different approaches have emerged such as social metabolism, the water-energy-food nexus, coupled social-natural or socio-environmental systems analysis, socio-ecohydrology, hydro-social and socio-hydrological approaches, life cycle assessment, ecological footprint (water footprint and virtual water), energy and matter flow analysis, extended environmental input-output analysis, among others. However, in our opinion, such approaches usually do not address the complex relations between agricultural production and the water cycle, nor the effects of the socio-economic and political context on the biogeochemical cycles, although they are fundamental in the processes occurring in agroecosystems, and their environmental impacts. The present methodological proposal makes a novel integration of approaches from the social sciences (social metabolism) with those from the earth sciences (socioecohydrology) to incorporate such cycles in the analysis of historical metabolic patterns and possible future trajectories of agroecosystems.</p><p>We start with the Agrarian Metabolism approach developed and tested for the metabolic analysis of agriculture in Spain in contemporary history. This methodological core is enriched, including estimations of blue, green, grey and virtual water, estimated through hydrological spatiotemporal-explicit modelling. From this integration, progress is made in the tailoring of new metabolic indicators that account for the thermodynamic cost of landscape alteration over time, as well as the energy efficiency of agroecosystems.</p><p>Southern Spanish (Andalusian) is an important agrarian region, accounting for ~17% of the cultivated area of Spain, presenting different types of agriculture, such as olive orchards (main Spanish producer), greenhouse vegetables, paddy rice, and berries, and also exemplifying diverse water-related environmental problems´ associated to the agricultural production. Thus, the industrialization process of Andalusian agriculture, in the period 1951-2018, is taken as a case study. For the analysis of possible future trajectories, climate change scenarios modelled for the Spanish territory as well as different agroecological management scenarios will be analysed. Hence, this proposal is useful for understanding the effects of agriculture in contemporary history, particularly in its industrialisation phase and, also, the expected results will serve as a scientific basis for decision-making on future actions in the territory and as a tool for analysing different types of scenarios and their comparison with patterns already observed in the recent past.</p>