Final Report Summary - DRYIR (Bloom the Dry. The Creation of Traditional Mediterranean Irrigated Fields)
The main target of DryIR has been to study the historical transformation of Mediterranean drylands into fertile and productive irrigated fields, offering information on their genesis and long-term sustainability. The project has merged techniques from the soil sciences (e.g. physico-chemical analyses, soil micromorphology) with FTIR, phytolith quantification, XRF core-scanning and modelling, and has used irrigated systems of Spain and Morocco as case studies.
The project has offered the first absolute date for the diffusion of irrigated agriculture towards the western Mediterranean, a process that took place in the Middle Ages ($>$ AD 632) and that has been labelled as a “Mediterranean Agriculture Revolution” in the scholarly literature. We radiocarbon-dated the original construction of the irrigated fields of Ricote (Murcia, Spain), a huerta first established during the Andalusi period (AD 711-1492) that has been kept operative ever since. The Andalusi period was characterized by the entrance of Arab and Berber tribes and clans to the Iberian Peninsula and by the diffusion of agrarian knowledge related with irrigated agriculture. The radiocarbon dates for Ricote cluster reliably around AD 989-1210 and suggest that the construction of irrigated areas might have not been a preferential option during the first centuries of al-Andalus. These results have implications for the debate on the adoption of irrigation and intensive agrarian systems promoted by Boserup, as well as for our understanding of the diffusion of ancient agricultural systems along the Mediterranean.
Many historical Mediterranean irrigated systems need to be upgraded to better tackle current environmental, social and economical challenges. One of the main pathways for the modernization of historical irrigated fields is the substitution of flood irrigation for drip irrigation, an upgrading process whose impact in the soil had been mostly overlooked. Using the case study of Ricote, we analyzed the edaphological effects derived from this process. We observed that eight years of drip irrigation are enough to foster several relevant changes in the soil: organic matter, available P and N contents are significantly reduced in formerly flood-irrigated soils not directly irrigated by drip emitters. Since large extensions of soil remain abandoned under drip irrigation, drip irrigation uptake might indirectly foster soil degradation at a large scale and favour organic carbon outputs rather than inputs, with those areas excluded from the emitters exposing organic carbon accumulated during years of flood-irrigation to oxidation and eventual loss as atmospheric CO2. These results question the assumption that drip irrigation has no negative environmental consequences whatsoever, and stress the need to properly assess the trade-offs derived from the modernization of long-term irrigated fields.
Being historical irrigated systems a conspicuous example of resilience against social and climatic shocks, it is highly relevant to understand the mechanisms by which they have managed to endure change. One of the main discussions among researchers working on intensive agrarian systems is whether ‘small’ or ‘large’ irrigation systems better manage perturbances. The question of size had been tackled in the literature by means of case studies, yielding contrasting outcomes. In our project we adopted a different approach and modelled the feedbacks between the key size-determining variables, population, water availability and taxation, aiming at understanding the fragilities that arise in irrigation systems due to a change in size. The results indicate that being too small might be more threatening for irrigation systems than being too large when facing demographic stochasticity (e.g. changes in the birth/death rates, immigration-emigration, etc): small groups of irrigators are closer to a collapse trap mechanism which, once triggered due to population drops, causes irrigation systems to collapse and inhibit its own reorganization. This explains why large external injections of assistance (e.g. capital, inputs, subsidy for infrastructure maintenance, or modernization by means of new irrigation technologies) might be necessary to move irrigation systems out of collapse.
Two of the most relevant social and climatic shocks that ancient irrigation systems went through were the feudal conquest, conducted in the context of the Crusades, and the transition from the Medieval Climate Anomaly (MCA, AD 900-1300) to the Little Ice Age (LIA, AD 1300-1850). Properly understanding the effects of past climate and social change in irrigation systems might allow us to increase our capacity for anticipatory learning in the face of rapid climatic, economical and ecological transformations today. With that aim the project collected alluvial sediments from an Andalusi irrigated area in Menorca, where the feudal conquest fully overlapped with the MCA-LIA transition, and assessed the stratigraphy by means of XRF core-scanning. We observed that the combination of these two events led to a 14 to 27-fold increase in sediment accumulation rates from c. AD 1300 onwards. After comparing our results with the literature available on the MCA-LIA transition in the Mediterranean, we concluded that this amplified environmental change resulted from the reinforcing effect of social and climatic events, and cannot be explained linearly as a sum of these factors. The results thus emphasise the implications of paired climatic and social change in irrigation systems and provide a cautionary tale of the unpredictable effects derived from social-ecological dynamics.
Finally, it is worth stressing that irrigation systems are a key resource to ensure food security, and that understanding the links between population and irrigation is paramount to properly address the food demands of an ever-growing population. Our project has also shown that irrigated areas and population are non-linearly related, e.g. irrigated areas increase disproportionally for every increase in population. This scaling relationship has been found to hold for the Americas, Europe, Asia and Africa in all the decades under consideration (1956-2017), and suggest the existence of underlying laws between irrigation and population that transcend local particularities and trajectories. Scaling laws have been previously identified for cities and organisms, and our results suggest that they might apply to agrarian systems as well. From a policy-making standpoint, the results question the use of measures of irrigated area per capita as indicators to compare countries and guide irrigation policies, and stress the need to search for other scaling laws linked to agrarian systems to prevent undesired consequences derived from extending or shrinking irrigated areas.
The project has offered the first absolute date for the diffusion of irrigated agriculture towards the western Mediterranean, a process that took place in the Middle Ages ($>$ AD 632) and that has been labelled as a “Mediterranean Agriculture Revolution” in the scholarly literature. We radiocarbon-dated the original construction of the irrigated fields of Ricote (Murcia, Spain), a huerta first established during the Andalusi period (AD 711-1492) that has been kept operative ever since. The Andalusi period was characterized by the entrance of Arab and Berber tribes and clans to the Iberian Peninsula and by the diffusion of agrarian knowledge related with irrigated agriculture. The radiocarbon dates for Ricote cluster reliably around AD 989-1210 and suggest that the construction of irrigated areas might have not been a preferential option during the first centuries of al-Andalus. These results have implications for the debate on the adoption of irrigation and intensive agrarian systems promoted by Boserup, as well as for our understanding of the diffusion of ancient agricultural systems along the Mediterranean.
Many historical Mediterranean irrigated systems need to be upgraded to better tackle current environmental, social and economical challenges. One of the main pathways for the modernization of historical irrigated fields is the substitution of flood irrigation for drip irrigation, an upgrading process whose impact in the soil had been mostly overlooked. Using the case study of Ricote, we analyzed the edaphological effects derived from this process. We observed that eight years of drip irrigation are enough to foster several relevant changes in the soil: organic matter, available P and N contents are significantly reduced in formerly flood-irrigated soils not directly irrigated by drip emitters. Since large extensions of soil remain abandoned under drip irrigation, drip irrigation uptake might indirectly foster soil degradation at a large scale and favour organic carbon outputs rather than inputs, with those areas excluded from the emitters exposing organic carbon accumulated during years of flood-irrigation to oxidation and eventual loss as atmospheric CO2. These results question the assumption that drip irrigation has no negative environmental consequences whatsoever, and stress the need to properly assess the trade-offs derived from the modernization of long-term irrigated fields.
Being historical irrigated systems a conspicuous example of resilience against social and climatic shocks, it is highly relevant to understand the mechanisms by which they have managed to endure change. One of the main discussions among researchers working on intensive agrarian systems is whether ‘small’ or ‘large’ irrigation systems better manage perturbances. The question of size had been tackled in the literature by means of case studies, yielding contrasting outcomes. In our project we adopted a different approach and modelled the feedbacks between the key size-determining variables, population, water availability and taxation, aiming at understanding the fragilities that arise in irrigation systems due to a change in size. The results indicate that being too small might be more threatening for irrigation systems than being too large when facing demographic stochasticity (e.g. changes in the birth/death rates, immigration-emigration, etc): small groups of irrigators are closer to a collapse trap mechanism which, once triggered due to population drops, causes irrigation systems to collapse and inhibit its own reorganization. This explains why large external injections of assistance (e.g. capital, inputs, subsidy for infrastructure maintenance, or modernization by means of new irrigation technologies) might be necessary to move irrigation systems out of collapse.
Two of the most relevant social and climatic shocks that ancient irrigation systems went through were the feudal conquest, conducted in the context of the Crusades, and the transition from the Medieval Climate Anomaly (MCA, AD 900-1300) to the Little Ice Age (LIA, AD 1300-1850). Properly understanding the effects of past climate and social change in irrigation systems might allow us to increase our capacity for anticipatory learning in the face of rapid climatic, economical and ecological transformations today. With that aim the project collected alluvial sediments from an Andalusi irrigated area in Menorca, where the feudal conquest fully overlapped with the MCA-LIA transition, and assessed the stratigraphy by means of XRF core-scanning. We observed that the combination of these two events led to a 14 to 27-fold increase in sediment accumulation rates from c. AD 1300 onwards. After comparing our results with the literature available on the MCA-LIA transition in the Mediterranean, we concluded that this amplified environmental change resulted from the reinforcing effect of social and climatic events, and cannot be explained linearly as a sum of these factors. The results thus emphasise the implications of paired climatic and social change in irrigation systems and provide a cautionary tale of the unpredictable effects derived from social-ecological dynamics.
Finally, it is worth stressing that irrigation systems are a key resource to ensure food security, and that understanding the links between population and irrigation is paramount to properly address the food demands of an ever-growing population. Our project has also shown that irrigated areas and population are non-linearly related, e.g. irrigated areas increase disproportionally for every increase in population. This scaling relationship has been found to hold for the Americas, Europe, Asia and Africa in all the decades under consideration (1956-2017), and suggest the existence of underlying laws between irrigation and population that transcend local particularities and trajectories. Scaling laws have been previously identified for cities and organisms, and our results suggest that they might apply to agrarian systems as well. From a policy-making standpoint, the results question the use of measures of irrigated area per capita as indicators to compare countries and guide irrigation policies, and stress the need to search for other scaling laws linked to agrarian systems to prevent undesired consequences derived from extending or shrinking irrigated areas.