The land-water-food nexus

Water and soil are essential but limited resources that support food security and livelihoods across the planet. Population growth, richer diets, and growing bioenergy demand continue to increase competition for these natural resources. In many places soil and water are already being utilized at unsustainable rates (i.e., rates that exceed the pace with which natural systems can regenerate these resources), and there is widespread agreement that humanity must find alternative strategies to meet future human demand and achieve environmental goals together. There is therefore a pressing need to better understand current practices in the use of soil and water resources and to identify solutions that promote a more sustainable management of soil and water resources. By using a nexus approach, it is possible to better understand the synergies and trade-offs of a particular strategy and to highlight pathways that can align with sustainability and food security goals. My thesis work addresses several important needs along these lines by using a Land, Water and Food nexus approach at multiple spatial scales to analyse competition for freshwater and soil by various human uses including the food and industrial sectors. In order to assess global water requirements in agricultural areas and the impact on water and food security of global environmental change (e.g., land use change, climate change, urban expansion), I first developed a spatially distributed vertical soil-water balance model. This model allowed me to evaluate the total amount of water required by crops (i.e., crop water requirement (CWR)) and to disaggregate this demand between green water (GW) (i.e., water provided through rainfall) and blue water (BW) (i.e., water provided through irrigation from surface or groundwater). I then applied this model to evaluate to what extent, in water-limited countries (where there is either a physical lack of freshwater resources or economic water scarcity), improvements in crop yields may be achieved by providing more irrigation water. Interesting results have been obtained for India, where a crop replacement scenario has been assessed to individuate more sustainable uses of freshwater resource and fertile land. Along with sustaining food production, freshwater and fertile soil maintain Earth ecosystems and support other human activities, such as cash crops and timber production. Thus, I focused my attention on rubber plantations that have been experiencing unprecedented and rapid expansion during the last 15 years. Nowadays rubber fields occupy more than 10million hectares and require 149 km3 of water (125 km3 of GW and 24 km3 of BW), significantly affecting food security in some countries such as Indonesia, Thailand and Vietnam. Recognizing the limitation of the agricultural system, the need to reduce greenhouse gas (GHG) emissions, the growing demand for energy and food, and the susceptibility of agricultural yields to climate fluctuations, many governments and corporations have become increasingly active in the purchase of land in response to this uncertainty. Specifically, I analysed the drivers of LSLA such as need of land, lack of water the associated impacts on deforestation and land degradation.

Terra e acqua sono risorse essenziali ma limitate per garantire la sicurezza alimentare e il benessere della popolazione. La crescita della popolazione, i cambiamenti nelle abitudini alimentari, la domanda crescente di biocombustibili accrescono la competizione nell’uso di tali risorse tanto che in diverse aree il prelievo di acqua e l’uso della terra avviene con uno sfruttamento eccessivo e non sostenibile, tale cioè che l’utilizzo supera la capacità di rigenerazione. Pertanto si avverte una crescete attenzione nella ricerca di strategie alternative per soddisfare le richieste umane in un’ottica di sostenibilità per il raggiungimento della sicurezza idrica e alimentare e il mantenimento di un ambiente sano. Nel mio lavoro di tesi ho analizzato la competizione nell’uso di acqua e suolo per soddisfare le esigenze umane legate all’agricoltura (come la produzione di cibo, biocombustibili, fibre…) attraverso l’implementazione di un modello di bilancio idrico nel suolo spazialmente distribuito. Tale modello ha permesso di calcolare la richiesta di acqua per irrigazione a scala globale nella situazione attuale e in diversi scenari di incremento delle rese e redistribuzione delle colture. In un’analisi a tutto tondo sulla competizione nell’uso delle risorse sono poi state affrontate problematiche recenti che riguardano l’utilizzo di acqua e suolo come la rapida espansione di piantagioni, la deforestazione e il fenomeno delle acquisizioni di terra su larga scala.