Seit den siebziger Jahren des vergangenen Jahrhunderts hat sich im Gebiet südlich der Stadt Gadarif im Ostsudan, am Ostende der Sahelzone gelegen, nicht nur infolge des Klimawandels, sondern auch aufgrund extremer agrarischer Nutzung eine signifikante Veränderung der Vegetationsbedeckung ergeben. Stark reduzierte Bodenerträge führten in den neunziger Jahren zu Stilllegungen von Ackerland. Mittels multitemporaler Satellitenbilddaten konnte die neuerliche Entwicklung der natürlichen Vegetationsverjüngung auf den Brachen nachgewiesen werden. Weiterer Schutz dieser Gebiete kann künftig die vollständige Regeneration der früheren Maximalvegetation eines Savannenwaldes zwischen den Äckern ermöglichen. Die festgestellten Landnutzungsbefunde werden mit den klimatischen Veränderungen in der östlichen Sahelzone in Verbindung gebracht. / The period since the 1970s has seen significant changes to the vegetation cover in the region south of the city of Gadarif in East Sudan, at the eastern end of the Sahel, due to both the current climate change and extreme agricultural use. Seriously degraded harvests led to the abandoning of agricultural land in the 1990s. By means of multi-temporal satellite imagery, it has been possible to demonstrate the development of vegetation renewal on such land. Further protection of the areas could permit complete future regeneration of the previous maximum natural vegetation of a savannah between the agricultural fields. The ascertained land use changes are linked to the climatic changes in the Eastern Sahel.

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This thesis consists of three chapters, each dealing with a different aspect of the impact of climate change on agriculture: the analysis of past evidence, the possible new solutions and the anticipation of future problems. The topics chosen are different but complementary and reflect the complex and multifaceted impact of this phenomenon on agriculture. This work uses global spatial data and information from the literature, combines weather forecast with a crop model, and uses an economic model coupled with robust econometric estimation approaches. The findings indicate that major crop yields in tropical and subtropical regions will likely suffer adverse effects, while temperate and continental areas, historically less favourable for agriculture, may experience mainly positive impacts. Under a medium development scenario, global crop production is projected to remain largely unaffected, masking a compensatory mechanism between tropical and temperate regions. Adaptation covers a significant positive role, and short- and medium-range weather forecasting can be an important and affordable tool for farmers to adapt their agricultural practices, if they know how to use it. The adoption of such meteorological information can enable rural households in developing countries to increase yields of staple crops, although the potential contribution of it may be hampered by social and economic barriers. However, adaptation in agriculture can have negative externalities, potentially creating a vicious circle, and the livestock sector is particularly vulnerable. Indeed, changing climate conditions may induce farmers to adjust the distribution of grazing livestock per unit of land in order to maximise profits. Temperate and continental countries may increase the number of grazing livestock per unit of land as climatic conditions improve for agricultural purposes, thereby increasing carbon dioxide emissions. On the other hand, tropical areas, mainly populated by developing countries, will see a deterioration of agricultural conditions and less livestock can be raised on rangelands and pasturelands. Once again, countries with pressing agricultural productivity needs bear a disproportionate burden of climate change effects, exacerbating already precarious living conditions. Conversely, northern countries, primarily developed, are likely to experience more beneficial effects.

This dissertation analyzes the impact of climate, and atmospheric carbon dioxide (CO2) on crop yields and grain transportation. The analysis of crop yields endeavors to advance the literature by statistically estimating the effects of atmospheric carbon dioxide (CO2) on observed crop yields. This is done using an econometric model estimated over pooled historical data for 1950-2009 and data from the free air CO2 enrichment experiments. The main findings are: 1) yields of soybeans, cotton, and wheat directly respond to the elevated CO2, while yields of corn and sorghum do not; 2) the effect of crop technological progress on mean yields is non-linear; 3) ignoring atmospheric CO2 in an econometric model of crop yield likely leads to overestimates of the pure effects of climate change and technological progress on crop yields; and 4) average climate conditions and climate variability contribute in a statistically significant way to average crop yields and their variability. To examine climate change impacts on grain transportation flows, this study employs two modeling systems, a U.S. agricultural sector model and an international grain transportation model, with linked inputs/outputs. The main findings are that under climate change: 1) the excess supply of corn and soybeans generally increases in Northern U.S. regions, while it declines in Central and Southern regions; 2) the Corn Belt, the largest producer of corn in the U.S., is anticipated to ship less corn; 3) the importance of lower Mississippi River ports, the largest current destination for U.S. grain exports, diminishes under the climate change cases, whereas the role of Pacific Northwest ports, Great Lakes ports, and Atlantic ports is projected to increase; 4) the demand for grain shipment via rail and truck rises, while demand for barge transport drops.

Increasingly unpredictable, extreme and erratic rainfall with higher temperatures threatens to undermine the adaptive capacity of food systems and ecological resilience of smallholder landscapes. Despite growing concern, land managers still lack quantitative techniques to collect empirical data about the potential impact of climatic variability and change. This thesis aims to assess how ecosystem services and function and how this links with biodiversity and human wellbeing in smallholder agro-ecosystems in a changing climate. To this end, rather than relying on scenarios or probabilistic modelling, space was used as a proxy for time to compare states in disparate climatic conditions. Furthermore, an integrated methodological framework to assess ecosystem services at the field and landscape level was developed and operationalised, the results of which can be modelled with measures of wellbeing. Various multidisciplinary analytical tools were utilised, including ecological and socio-economic surveys, biological assessments, participatory open enquiry, and documenting ethnobotanical knowledge. The study was located within monsoon rice farms in the Terai Plains of Nepal, and dry season vegetable farms in Northern Ghana. Sites were selected that are climatically and culturally diverse to enable comparative analysis, with application to broad areas of adaptive planning. The linkages that bring about biophysical and human changes are complex and operate through social, political, economic and demographic drivers, making attribution extremely challenging. Nevertheless, it was demonstrated that within hotter and drier conditions in Ghana long-tongued pollinators and granivores, important for decomposition processes and pollination services, are more abundant in farms. Results further indicated that in cooler and drier conditions in Nepal, the taxonomic diversity of indigenous and close relative plant species growing in and around farms, important for the provisioning of ecosystem services, decreases. All other things equal, in both Nepal and Ghana findings indicate that overall human wellbeing may be adversely effected in hotter conditions, with a potentially significantly lower yields, fewer months of the year in which food is available, higher exposure to natural hazards and crop loss, unemployment, and psychological anxiety. Yet, surveys indicate smallholders continue to maintain a fair diversity of species in and around farms, which may allow them to secure basic necessities from provisioning ecosystem services. Moreover, farmers may employ adaptive strategies such as pooling labour and food sharing more frequently, and may have greater access to communication, technology, and infrastructure. Novel methodological and empirical contributions of this research offer predictive insights that could inform innovations in climate-smart agricultural practice and planning.