Junguo Liu

Reduced carbon emission estimates from fossil fuel combustion and cement production in China

Nearly three-quarters of the growth in global carbon emissions from the burning of fossil fuels and cement production between 2010 and 2012 occurred in China. Yet estimates of Chinese emissions remain subject to large uncertainty; inventories of China’s total fossil fuel carbon emissions in 2008 differ by 0.3 gigatonnes of carbon, or 15 per cent. The primary sources of this uncertainty are conflicting estimates of energy consumption and emission factors, the latter being uncertain because of very few actual measurements representative of the mix of Chinese fuels. Here we re-evaluate China’s carbon emissions using updated and harmonized energy consumption and clinker production data and two new and comprehensive sets of measured emission factors for Chinese coal. We find that total energy consumption in China was 10 per cent higher in 2000–2012 than the value reported by China’s national statistics, that emission factors for Chinese coal are on average 40 per cent lower than the default values recommended by the Intergovernmental Panel on Climate Change, and that emissions from China’s cement production are 45 per cent less than recent estimates. Altogether, our revised estimate of China’s CO2 emissions from fossil fuel combustion and cement production is 2.49 gigatonnes of carbon (2 standard deviations = ±7.3 per cent) in 2013, which is 14 per cent lower than the emissions reported by other prominent inventories. Over the full period 2000 to 2013, our revised estimates are 2.9 gigatonnes of carbon less than previous estimates of China’s cumulative carbon emissions. Our findings suggest that overestimation of China’s emissions in 2000–2013 may be larger than China’s estimated total forest sink in 1990–2007 (2.66 gigatonnes of carbon) or China’s land carbon sink in 2000–2009 (2.6 gigatonnes of carbon).

A high-resolution assessment on global nitrogen flows in cropland

Crop production is the single largest cause of human alteration of the global nitrogen cycle. We present a comprehensive assessment of global nitrogen flows in cropland for the year 2000 with a spatial resolution of 5 arc-minutes. We calculated a total nitrogen input (IN) of 136.60 trillion grams (Tg) of N per year, of which almost half is contributed by mineral nitrogen fertilizers, and a total nitrogen output (OUT) of 148.14 Tg of N per year, of which 55% is uptake by harvested crops and crop residues. We present high-resolution maps quantifying the spatial distribution of nitrogen IN and OUT flows, soil nitrogen balance, and surface nitrogen balance. The high-resolution data are aggregated at the national level on a per capita basis to assess nitrogen stress levels. The results show that almost 80% of African countries are confronted with nitrogen scarcity or nitrogen stress problems, which, along with poverty, cause food insecurity and malnutrition. The assessment also shows a global average nitrogen recovery rate of 59%, indicating that nearly two-fifths of nitrogen inputs are lost in ecosystems. More effective management of nitrogen is essential to reduce the deleterious environmental consequences.

A GIS-based tool for modelling large-scale crop-water relations

Recent research on crop-water relations has increasingly been directed towards the application of locally acquired knowledge to answering the questions raised on larger scales. However, the application of the local results to larger scales is often questionable. This paper presents a GIS-based tool, or a GEPIC model, to estimate crop water productivity (CWP) on the land surface with spatial resolution of 30arc-min. The GEPIC model can estimate CWP on a large-scale by considering the local variations in climate, soil and management conditions. The results show a non-linear relationship between virtual water content (or the inverse of CWP) and crop yield. The simulated CWP values are generally more sensitive to three parameters, i.e. potential harvest index for a crop under ideal growing conditions (HI), biomass-energy ratio indicating the energy conversion to biomass (WA), and potential heat unit accumulation from emergence to maturity (PHU), than other parameters. The GEPIC model is a useful tool to study crop-water relations on large scales with high spatial resolution; hence, it can be used to support large-scale decision making in water management and crop production.

Physical and virtual water transfers for regional water stress alleviation in China

Significance Freshwater resources are unevenly distributed in China. This situation drives a significant amount of water flow both physically and virtually across China. Here, we report on our quantification of China’s physical and virtual water flows and associated water stress at the provincial level. In 2007, interprovincial physical water flows amounted to only a small part of China’s total water supply, but virtual water flows amounted to over one-third of supply. We found that both physical and virtual water flows exacerbated water stress for the main water-exporting provinces. The results highlight the need for more emphasis to be placed on water demand management rather than the current focus on supply-oriented management. Water can be redistributed through, in physical terms, water transfer projects and virtually, embodied water for the production of traded products. Here, we explore whether such water redistributions can help mitigate water stress in China. This study, for the first time to our knowledge, both compiles a full inventory for physical water transfers at a provincial level and maps virtual water flows between Chinese provinces in 2007 and 2030. Our results show that, at the national level, physical water flows because of the major water transfer projects amounted to 4.5% of national water supply, whereas virtual water flows accounted for 35% (varies between 11% and 65% at the provincial level) in 2007. Furthermore, our analysis shows that both physical and virtual water flows do not play a major role in mitigating water stress in the water-receiving regions but exacerbate water stress for the water-exporting regions of China. Future water stress in the main water-exporting provinces is likely to increase further based on our analysis of the historical trajectory of the major governing socioeconomic and technical factors and the full implementation of policy initiatives relating to water use and economic development. Improving water use efficiency is key to mitigating water stress, but the efficiency gains will be largely offset by the water demand increase caused by continued economic development. We conclude that much greater attention needs to be paid to water demand management rather than the current focus on supply-oriented management.

FORECAST OF WATER DEMAND IN WEINAN CITY IN CHINA USING WDF-ANN MODEL

Domestic water use is generally the most important component of urban water consumption.In this paper, the relatively new technique of artificial neural network (ANN) is proposed to model and forecast the water demand in urban areas.Results indicate that the WDF-ANN (water demand forecast using artificial neural network) model offers an effective way to formulate domestic water demand in Weinan City in China.The model evaluation shows that the correlation coefficients are more than 90% both for the training data and the testing data. � 2003 Elsevier Science Ltd.All rights reserved.

Historical Trends in China's Virtual Water Trade

Abstract Increasing water scarcity in China demands a more detailed analysis of water use in different sectors. In this paper, Chinas food import and export levels are analyzed in light of water availability. Their contributions to national water management in the form of virtual water are also evaluated. The findings show that the virtual water trade has developed unconsciously. This trend has been greatly influenced by micro- and macro-economic conditions, as well as fluctuations in weather conditions. Given the intensification of water scarcity, future food policy should promote an active application of virtual water strategies (such as virtual water trade and agricultural structure adjustment) to improve food security and sustainable water uses. With the progressive liberalization of food markets in China, virtual water trade is likely to play a more important role in future water resources management.

Cropland for sub‐Saharan Africa: A synergistic approach using five land cover data sets

This paper presents a methodology for the creation of a cropland map for Africa through the combination of five existing land cover products: GLC-2000, MODIS Land Cover, GlobCover, MODIS Crop Likelihood and AfriCover. A synergy map is created in which the products are ranked by experts, which reflects the likelihood or probability that a given pixel is cropland. The cropland map is then calibrated with national and sub-national crop statistics using a novel approach. Preliminary validation of the map was undertaken and the results are presented. The resulting cropland map has an accuracy of 83%, which is higher than the accuracy of any of the individual maps. The cropland map is freely available at agriculture.geo-wiki.org.

A Global and Spatially Explicit Assessment of Climate Change Impacts on Crop Production and Consumptive Water Use

Food security and water scarcity have become two major concerns for future humans sustainable development, particularly in the context of climate change. Here we present a comprehensive assessment of climate change impacts on the production and water use of major cereal crops on a global scale with a spatial resolution of 30 arc-minutes for the 2030s (short term) and the 2090s (long term), respectively. Our findings show that impact uncertainties are higher on larger spatial scales (e.g., global and continental) but lower on smaller spatial scales (e.g., national and grid cell). Such patterns allow decision makers and investors to take adaptive measures without being puzzled by a highly uncertain future at the global level. Short-term gains in crop production from climate change are projected for many regions, particularly in African countries, but the gains will mostly vanish and turn to losses in the long run. Irrigation dependence in crop production is projected to increase in general. However, several water poor regions will rely less heavily on irrigation, conducive to alleviating regional water scarcity. The heterogeneity of spatial patterns and the non-linearity of temporal changes of the impacts call for site-specific adaptive measures with perspectives of reducing short- and long-term risks of future food and water security.

Food Losses and Waste in China and Their Implication for Water and Land

Conventional approaches to food security are questionable due to their emphasis on food production and corresponding neglect of the huge amount of food losses and waste. We provide a comprehensive review on available information concerning Chinas food losses and waste. The results show that the food loss rate (FLR) of grains in the entire supply chain is 19.0% ± 5.8% in China, with the consumer segment having the single largest portion of food waste of 7.3% ± 4.8%. The total water footprint (WF) related to food losses and waste in China in 2010 was estimated to be 135 ± 60 billion m(3), equivalent to the WF of Canada. Such losses also imply that 26 ± 11 million hectares of land were used in vain, equivalent to the total arable land of Mexico. There is an urgent need for dialogue between actors in the supply chain, from farmer to the consumer, on strategies to reduce the high rates of food losses and waste and thereby make a more worthwhile use of scarce natural resources.

Manage water in a green way

Reliance on “hard,” human-engineered structures—“gray” infrastructure—has been the conventional way to manage water needs for economic development. But building dams, piping water, and constructing protective barriers is capital intensive and may address only a few water problems (1). Gray infrastructure often damages or eliminates biophysical processes necessary to sustain people, ecosystems and habitats, and livelihoods. Consequently, there is renewed focus on “green” infrastructure, which can be more flexible and cost effective for providing benefits besides water provision. Supplementing or integrating gray infrastructure with biophysical systems is critical to meeting current and future water needs. Gray and green infrastructures combined are synergistic and can have superior results to one or the other.