Kyle Frankel Davis

Global Spatio-Temporal Patterns in Human Migration: A Complex Network Perspective

Migration is a powerful adaptive strategy for humans to navigate hardship and pursue a better quality of life. As a universal vehicle facilitating exchanges of ideas, culture, money and goods, international migration is a major contributor to globalization. Consisting of countries linked by multiple connections of human movements, global migration constitutes a network. Despite the important role of human migration in connecting various communities in different parts of the world, the topology and behavior of the international migration network and its changes through time remain poorly understood. Here we show that the global human migration network became more interconnected during the latter half of the twentieth century and that migrant destination choice partly reflects colonial and postcolonial histories, language, religion, and distances. From 1960 to 2000 we found a steady increase in network transitivity (i.e. connectivity between nodes connected to the same node), a decrease in average path length and an upward shift in degree distribution, all of which strengthened the ‘small-world’ behavior of the migration network. Furthermore, we found that distinct groups of countries preferentially interact to form migration communities based largely on historical, cultural and economic factors.

Historical trade-offs of livestock’s environmental impacts

Human demand for animal products has risen markedly over the past 50 years with important environmental impacts. Dairy and cattle production have disproportionately contributed to greenhouse gas (GHG) emissions and land use, while crop demands of more intensive systems have increased fertilizer use and competition for available crop calories. At the same time, chicken and pig production has grown more rapidly than for ruminants, indicating a change in the environmental burden per animal calorie (EBC) with time. How EBCs have changed and to what extent resource use efficiency (RUE), the composition of animal production and the trade of feed have played a role in these changes have not been examined to date. We employ a calorie-based perspective, distinguishing animal calorie production between calories produced from feedcrop sources—directly competing with humans for available calories—and those from non-feed sources—plant biomass unavailable for direct human consumption. Combining this information with data on agricultural resource use, we calculate EBCs in terms of land, GHG emissions and nitrogen. We find that EBCs have changed substantially for land (−62%), GHGs (−46%) and nitrogen (+188%). Changes in RUE (e.g., selective breeding, increased grain-feeding) have been the primary contributor to these EBC trends, but shifts in the composition of livestock production were responsible for 12%–41% of the total EBC changes. In addition, the virtual trade of land for feed has more than tripled in the past 25 years with 77% of countries currently relying on virtual land imports to support domestic livestock production. Our findings indicate that important tradeoffs have occurred as a result of livestock intensification, with more efficient land use and emission rates exchanged for greater nitrogen use and increased competition between feed and food. This study provides an integrated evaluation of livestocks impact on food security and the environment.

Environmental consequences of oil production from oil sands

Crude oil from oil sands will constitute a substantial share of future global oil demand. Oil sands deposits account for a third of globally proven oil reserves, underlie large natural forested areas, and have extraction methods requiring large volumes of freshwater. Yet little work has been done to quantify some of the main environmental impacts of oil sands operations. Here we examine forest loss and water use for the worlds major oil sands deposits. We calculate actual and potential rates of water use and forest loss both in Canadian deposits, where oil sands extraction is already taking place, and in other major deposits worldwide. We estimated that their exploitation, given projected production trends, could result in 1.31 km3 yr−1 of freshwater demand and 8700 km2 of forest loss. The expected escalation in oil sands extraction thus portends extensive environmental impacts.

New frontiers of land and water commodification: socio‐environmental controversies of large‐scale land acquisitions

A growing number of regions in the developing world are targeted by transnational investors who are acquiring large amounts of land and natural resources. Driven by the increasing global demand for agricultural products, such investments are often considered an opportunity for economic development in the target country. However, there are concerns about the social and environmental impacts on local communities. In this brief review, we discuss some key socio-environmental controversies surrounding large-scale land acquisitions (LSLAs). LSLAs often target common property systems and lead to privatization and commodification of land through long-term land concessions. There is a debate between supporters of foreign land investments as a means to attract modern agricultural technology that would decrease the yield gap in underperforming agricultural land, and those who question such a development model because it is seldom coupled with policy instruments that would ensure that the benefits improve food security in local populations. Large-scale land investments displace a variety of systems of production ranging from small-scale farming to (arguably) ‘unused’ land such as forests and savannas on which local communities often depend. Moreover, LSLAs entail an appropriation of water resources that may negatively impact local farmers or downstream human and natural systems. In most cases investors keep the land fallow but, when they put it under productive use, they typically change land cover and land use to start intensified commercial farming, often for non-food crops.

Social-environmental controversies of large-scale land acquisitions in developing countries

A growing number of regions in the developing world are targeted by transnational investors who are acquiring large amounts of land and natural resources. Driven by the increasing global demand for agricultural products, such investments are often considered an opportunity for economic development in the target country. However, there are concerns about the social and environmental impacts on local communities. In this brief review, we discuss some key socio-environmental controversies surrounding large-scale land acquisitions (LSLAs). LSLAs often target common property systems and lead to privatization and commodification of land through long-term land concessions. There is a debate between supporters of foreign land investments as a means to attract modern agricultural technology that would decrease the yield gap in underperforming agricultural land, and those who question such a development model because it is seldom coupled with policy instruments that would ensure that the benefits improve food security in local populations. Large-scale land investments displace a variety of systems of production ranging from small-scale farming to (arguably) ‘unused’ land such as forests and savannas on which local communities often depend. Moreover, LSLAs entail an appropriation of water resources that may negatively impact local farmers or downstream human and natural systems. In most cases investors keep the land fallow but, when they put it under productive use, they typically change land cover and land use to start intensified commercial farming, often for non-food crops.

The Global Food‐Energy‐Water Nexus

Water availability is a major factor constraining humanitys ability to meet the future food and energy needs of a growing and increasingly affluent human population. Water plays an important role ...

A global reference database of crowdsourced cropland data collected using the Geo-Wiki platform

A global reference data set on cropland was collected through a crowdsourcing campaign using the Geo-Wiki crowdsourcing tool. The campaign lasted three weeks, with over 80 participants from around the world reviewing almost 36,000 sample units, focussing on cropland identification. For quality assessment purposes, two additional data sets are provided. The first is a control set of 1,793 sample locations validated by students trained in satellite image interpretation. This data set was used to assess the quality of the crowd as the campaign progressed. The second data set contains 60 expert validations for additional evaluation of the quality of the contributions. All data sets are split into two parts: the first part shows all areas classified as cropland and the second part shows cropland average per location and user. After further processing, the data presented here might be suitable to validate and compare medium and high resolution cropland maps generated using remote sensing. These could also be used to train classification algorithms for developing new maps of land cover and cropland extent.

Ancient water supports today's energy needs

The water footprint for fossil fuels typically accounts for water utilized in mining and fuel processing, whereas the water footprint of biofuels assesses the agricultural water used by crops through their lifetime. Fossil fuels have an additional water footprint that is not easily accounted for: ancient water that was used by plants millions of years ago, before they were transformed into fossil fuel. How much water is mankind using from the past to sustain current energy needs? We evaluate the link between ancient water virtually embodied in fossil fuels to current global energy demands by determining the water demand required to replace fossil fuels with biomass produced with water from the present. Using equal energy units of wood, bioethanol, and biodiesel to replace coal, natural gas, and crude oil, respectively, the resulting water demand is 7.39 × 1013 m3y−1, approximately the same as the total annual evaporation from all land masses and transpiration from all terrestrial vegetation. Thus, there are strong hydrologic constraints to a reliance on biofuel energy produced with water from the present because the conversion from fossil fuels to biofuels would have a disproportionate and unsustainable impact on the modern water. By using fossil fuels to meet todays energy needs, we are virtually using water from a geological past. The water cycle is insufficient to sustain the production of the fuel presently consumed by human societies. Thus, non-fuel based renewable energy sources are needed to decrease mankinds reliance on fossil fuel energy without placing an overwhelming pressure on global freshwater resources.

Alternative cereals can improve water use and nutrient supply in India

Replacing rice with other cereals offers benefits in terms of both reducing freshwater use and enhancing nutrient production. Humanity faces the grand challenge of feeding a growing, more affluent population in the coming decades while reducing the environmental burden of agriculture. Approaches that integrate food security and environmental goals offer promise for achieving a more sustainable global food system, yet little work has been done to link potential solutions with agricultural policies. Taking the case of cereal production in India, we use a process-based crop water model and government data on food production and nutrient content to assess the implications of various crop-shifting scenarios on consumptive water demand and nutrient production. We find that historical growth in wheat production during the rabi (non-monsoon) season has been the main driver of the country’s increased consumptive irrigation water demand and that rice is the least water-efficient cereal for the production of key nutrients, especially for iron, zinc, and fiber. By replacing rice areas in each district with the alternative cereal (maize, finger millet, pearl millet, or sorghum) with the lowest irrigation (blue) water footprint (WFP), we show that it is possible to reduce irrigation water demand by 33% and improve the production of protein (+1%), iron (+27%), and zinc (+13%) with only a modest reduction in calories. Replacing rice areas with the lowest total (rainfall + irrigation) WFP alternative cereal or the cereal with the highest nutritional yield (metric tons of protein per hectare or kilograms of iron per hectare) yielded similar benefits. By adopting a similar multidimensional framework, India and other nations can identify food security solutions that can achieve multiple sustainability goals simultaneously.

Understanding dietary and staple food transitions in China from multiple scales

China is facing both non-communicable diseases (NCDs) and micronutrient deficiency, which have been largely related to transitions within Chinese diets, for example, the overconsumption of vegetable oils and animal-source products and decreasing consumption of coarse staple foods. In this study, we use three metrics—dietary diversity score (DDS), staple diversity score (SDS) and the proportion of coarse staple consumption (PoCS)- to investigate overall dietary transitions as well as trends in staple food consumption for nine provinces in China from 1997 to 2009. We also investigated how household characteristics, community urbanicity, and provincial conditions have affected household diets and the relationship between overall diet and staple diet across socio-economic gradients. Overall dietary diversity (DDS) showed consistent growth across all the provinces and subpopulations and was strongly associated with a household’s socio-economic status. However, staple indicators (SDS and PoCS) showed notable difference both geographically and socio-economically. The relationship between overall dietary indicator (DDS) and staple indicators (SDS, PoCS) across SES gradients revealed that education is a more important influence than income in ensuring dietary balance and nutritional quality. Our findings show that programs aimed at promoting dietary balance and healthy staple diets must account for differences between provinces in terms of agronomic, nutritional, social, and economic conditions. By identifying the socio-economic characteristics and locations of the most nutritionally vulnerable populations, this study also points toward the need for policies that incorporate nutritional considerations into grain production systems and provide a strategy for enhancing China’s national food security.