The Drought Risk Analysis, Forecasting, and Assessment under Climate Change

This Special Issue is a platform to fill the gaps in drought risk analysis with field experience and expertise. It covers (1) robust index development for effective drought monitoring; (2) risk analysis framework development and early warning systems; (3) impact investigations on hydrological and agricultural sectors; (4) environmental change impact analyses. The articles in the Special Issue cover a wide geographic range, across China, Taiwan, Korea, and the Indo-China peninsula, which covers many contrasting climate conditions. Hence, the results have global implications: the data, analysis/modeling, methodologies, and conclusions lay a solid foundation for enhancing our scientific knowledge of drought mechanisms and relationships to various environmental conditions

Spatial-temporal dynamics of grain yield and the potential driving factors at the county level in China

© 2020 Elsevier Ltd Understanding the spatial-temporal dynamics of grain production and the influencing factors at the county level in China may promote the knowledge of land-use management and local policymaking, which are conducive to food security and the sustainable development of society. This study aims to evaluate China's grain yield (GY) from 2000 to 2014 and investigate the potential driving factors (PDFs) that affect the spatial-temporal dynamics of GY, including land, labor force, capital, and macro-background. Specifically, the locational Gini coefficient and exploratory spatial data analysis (ESDA) were used to characterize the spatial patterns of GY and its correlations with PDFs. Spatial regression models (SRMs) were employed to investigate the spatial dependence of GY on each PDF in 2000, 2005, 2010 and 2014. Results reveal that China's grain production has been on the rise with high-yield regions distributed mainly within the northeastern agricultural regions. Moreover, the proportion of counties in the northeastern agricultural regions with high grain yield has increased, while the number of low-yielding counties has increased in other agricultural regions. This finding highlights the increasing trend of spatial polarization in grain production. The significant bivariate Moran's I (p < 0.05) further revealed a global spatial spillover effect in the spatial correlation of GY and four PDFs. The spatial correlations could be categorized into four types: high GY and high PDFs, high GY and low PDFs, low GY and high PDFs, and low GY and low PDFs. SRMs were capable of quantifying the spatial dependence of GY on various PDFs, thereby revealing that land factors had a substantial effect on the grain production dynamics nationwide. The exploration of the spatial relationships between GY and PDFs provide a reference for formulating scientific and reasonable agricultural policies

Chinese cropping systems are a net source of greenhouse gases despite soil carbon sequestration

This work was funded by National Basic Research Program of China (2014CB953800), Young Talents Projects of the Institute of Urban Environment, Chinese Academy of Sciences (IUEMS201402), National Natural Science Foundation of China (41471190, 41301237, 71704171), China Postdoctoral Science Foundation (2014T70144) and Discovery Early Career Researcher Award of the Australian Research Council (DE170100423). The work contributes to the UK-China Virtual Joint Centres on Nitrogen “N-Circle” and “CINAg” funded by the Newton Fund via UK BBSRC/NERC (grants BB/N013484/1 and BB/N013468/1, respectively).Peer reviewedPostprintPostprin

Crop management options to reduce nitrogen pollution in Liangzihu lake basin, Central China

In Central China, high mineral nitrogen (N) application rates lead to low N recovery and high N losses. Large amounts of the nitrate-N leached from agricultural soil end up in aquatic ecosystems, which negatively affects both ecosystem and human health. Such effects are particularly pronounced in the Liangzihu Lake basin, Central China, where application of mineral N to the predominating maize-wheat rotation systems on coarse-textured soils can exceed 300 kg ha-1. We hypothesize that improved crop management can reduce the current nitrate-N pollution while enhancing system performance. The present study initially identified the main drivers of excessive N use by household surveys. Subsequent field experiments between 2012 and 2013 evaluated the effects of modified fertilizer-N management and the use of N-catching cover crops on soil-N dynamics, N-use efficiency, yield of maize and wheat, and nitrate-N leaching. Finally, the field trial data were used to parameterize the Environmental Policy Integrated Climate (EPIC) model to estimate N leaching losses under current and alternative crop and N management. Current N application rates average 229 kg N ha-1 season-1, which is higher than the cereal crop requirements of 150-180 kg N ha-1. The main reasons for the excessive use of mineral N are related to low farmland productivity (r = -0.184, p = 0.003), small farm size (r = -0.168, p = 0.006), a high share of off-farm income (coefficient = 25.94, p = 0.003), and a low education level of the household head (coefficient = -11.20, p = 0.034). The field experiment could show that cultivating a cover crop combined with a reduced application rate (290 kg N ha-1 in 3 splits) and multiple splitting of mineral N fertilizer can achieve similar yields (6.4-6.9 Mg ha-1) to those obtained with current management (470 kg N ha-1 in 2 splits). In addition, this alternative crop and fertilizer management increased the agronomic N-use efficiency by 7 kg grain kg-1 N applied in both wheat and maize, and enhanced the N-fertilizer recovery by 15% in wheat and 20% in maize. In addition, nitrate-N leaching was reduced by 15 kg N ha-1 in both the first-year maize and wheat crops. Once calibrated with the data from the field experiment, the EPIC model was able to predict crop biomass and the soil water content under moderate (long-term mean) climate conditions with a determination coefficient higher than 0.5 and a model bias of less than 3%. However, the model underestimated the soil water content in the drought seasons with a bias of >36%. Moreover, it tended to slightly overestimate nitrate-N leaching with 13-181 kg N ha-1 for the entire experimental period and in both 1 m and 1.8 m soil depths. It is concluded that (1) the current N application rate in the study area is excessive because of insufficient awareness and the easy and low-cost availability of mineral-N fertilizers, (2) the currently high N losses from crop fields can be substantially reduced by reducing application rates and by replacing bare fallow periods with legume cover crops without negative trade-offs in crop yields, and (3) the calibrated EPIC model can be used to predict the aboveground crop biomass and the soil water content, but it tends to overestimate nitrate-N leaching. Consequently, there is a need to inform farmers about the negative effects of excessive N use, popularize alternative agronomic management options, and adapt the existing EPIC model to improve the prediction of nitrate pollution in Central China

Towards sustainable chemical fertilizer management in China : from theory to farm household

Over the past few decades, Chinas grain production has expanded drastically. On the one hand, this has eliminated food shortages and allowed China to feed its huge and still growing population. On the other hand, the rapid growth in grain productivity has come at a heavy cost. Excessive fertilizer use has led to a variety of negative consequences that threaten national food security and environmental sustainability. Since the 2010s, the Chinese government and academia have made considerable efforts to reduce the consumption of chemical fertilizers and improve nutrient management. These include a wide range of regulations to control or guide chemical fertilizer use, policies to eliminate subsidies for the fertilizer industry, and nationwide promotion of scientific fertilizer application methods. In response to these efforts, Chinas overall fertilizer application rate has been declining since 2016. However, China still applies far more fertilizers than its crops need, and the current crop Nitrogen Use Efficiency (NUE) and Phosphorus Use Efficiency (PUE) in China are both below the global average. Therefore, reducing dependence on chemical fertilizers for crop production and sustainably feeding a large population remains a key challenge for China. This dissertation aims to contribute to sustainable nutrient management in China by providing a comprehensive and in-depth understanding of fertilizer use and management at the national, regional, farm and household levels. In the first study (Chapter 2), a systematic review of the historical development and current status of chemical fertilizer use and management in China at the national level is presented. In addition, fertilizer nutrient surpluses are estimated for 30 provinces in China and the regional and temporal variations are visualized. In the second study (Chapter 3), the relationship between fertilizer nutrient surpluses and the regional economy at the provincial level is examined within the framework of the Environmental Kuznets curve (EKC) hypothesis. A panel cointegration approach is employed, using time-series data from 1988 to 2019. In the third study (Chapter 4), the research focus is further narrowed to the farm household resolution. Using cross-sectional survey data from 774 maize-growing farms in northern China in 2019, the study investigates the role of farm characteristics, farmers knowledge, perceptions, and socioeconomic context in farmers fertilizer use strategies. The studies confirm that by 2021, China has reached zero growth in fertilizer use and fertilizer nutrient surpluses at the national and regional level. However, regions with a high proportion of cash crops, such as the southeast coast and northwest, still suffer from high nutrient surpluses. Furthermore, in circa 2012, China has reached its EKC turning point between fertilizer nutrient surpluses and GDP per capita. With further economic growth, the fertilizer surpluses in most Chinese provinces will decrease, indicating a moderating of the tension between economic development and the environment. Looking at the farm and household level, the study shows that in northern China, small farms are more likely to overuse fertilizers in maize cultivation without further yield improvement. Current extension programs have had a positive impact on farmers fertilizer use strategies and environmental awareness; nevertheless, the coverage and effectiveness of trainings should be improved. In summary, the dissertation identifies the following key factors that impede sustainable chemical fertilizer management in China: small farm size; regional economic dependence on cash crops; the large discrepancy between farmers practices and scientific production guidelines; and the shrinking and aging of Chinas rural labor force. To address these aspects, the dissertation proposes recommendations at the national strategic level, policy level and implementation level, respectively. The findings and recommendations of this dissertation can serve as a robust decision support and scientific basis for policy makers, stakeholders and researchers in the field of sustainable nutrient management in China.In den letzten Jahrzehnten ist die Getreideproduktion in China drastisch gestiegen. Einerseits hat dies die Nahrungsmittelknappheit beseitigt und China in die Lage versetzt, seine riesige und wachsende Bevölkerung zu ernähren. Andererseits wurde der rasche Anstieg der Getreideproduktivität mit einem hohen Preis bezahlt. Der übermäßige Einsatz von Düngemitteln führte zu einer Reihe negativer Konsequenzen, die die nationale Ernährungssicherheit und die ökologische Nachhaltigkeit bedrohen. Seit den 2010er Jahren haben die chinesische Regierung und die Wissenschaft erhebliche Anstrengungen unternommen, um den Einsatz von chemischen Düngemitteln zu reduzieren und das Nährstoffmanagement zu verbessern. Dazu gehören eine Vielzahl von Vorschriften zur Kontrolle und Steuerung des Einsatzes von chemischen Düngemitteln, Maßnahmen zur Abschaffung von Subventionen für die Düngemittelindustrie und die landesweite Förderung wissenschaftlicher Methoden zur Verwendung von Düngemitteln. In Folge dieser Bemühungen ist die Gesamtmenge des verwendeten Düngers in China seit 2016 rückläufig. Allerdings wird in China immer noch weit mehr Düngemittel ausgebracht als nötig und die derzeitige Stickstoffnutzungseffizienz (NUE) und Phosphornutzungseffizienz (PUE) in China liegen beide unter dem weltweiten Durchschnitt. Daher bleibt die Verringerung der Abhängigkeit von chemischen Düngemitteln für die Pflanzenproduktion und die nachhaltige Ernährung einer großen Bevölkerung eine zentrale Herausforderung für China. Diese Dissertation soll einen Beitrag zum nachhaltigen Nährstoffmanagement in China leisten, indem sie einen umfassenden und tiefgehenden Einblick über den Düngemitteleinsatz und -management auf nationaler, regionaler, betrieblicher und Haushaltsebene gewährt. Die erste Studie (Kapitel 2) gibt einen systematischen Überblick über die historische Entwicklung und den derzeitigen Stand der Nutzung von chemischen Düngemitteln in China auf nationaler Ebene. Darüber hinaus werden die Düngeüberschüsse für 30 Provinzen in China berechnet und die regionalen und zeitlichen Schwankungen dargestellt. In der zweiten Studie (Kapitel 3) wird die Beziehung zwischen Düngemittelüberschüssen und der regionalen Wirtschaft auf Provinzebene im Rahmen der Umwelt-Kuznets-Kurve (EKC) Hypothese untersucht. Es wird ein Panel-Kointegrationsansatz mit Zeitreihendaten von 1988 bis 2019 verwendet. In der dritten Studie (Kapitel 4) wird der Forschungsschwerpunkt weiter auf die Ebene der landwirtschaftlichen Haushalte eingegrenzt. Unter Verwendung von Querschnittserhebungsdaten von 774 Maisbetrieben in Nordchina aus dem Jahr 2019 untersucht die Studie den Einfluss verschiedener Faktoren auf die Einsatzstrategie von Düngemitteln wie betriebliche Merkmale, Wissen und Auffassungen der Landwirte und sozioökonomischer Kontext. Die Studien bestätigen, dass China seit 2021 auf regionaler und nationaler Ebene ein Nullwachstum beim Düngemitteleinsatz und bei Düngemittelüberschüssen erreicht hat. Jedoch leiden Regionen deren Produktion einen hohen Anteil an Cash Crops aufweist, wie die Südostküste und der Nordwesten, immer noch unter hohen Düngemittelüberschüssen. Darüber hinaus hat China um das Jahr 2012 den EKC-Wendepunkt zwischen Düngemittelüberschüssen und BIP pro Kopf erreicht. Mit weiterem Wirtschaftswachstum werden die Düngemittelüberschüsse in den meisten chinesischen Provinzen abnehmen, was auf einen Nachlass des Spannungsverhältnisses zwischen wirtschaftlicher Entwicklung und Umwelt hindeutet. Beim Betrachten einzelner Betriebe und Haushalte zeigt die Studie, dass in Nordchina kleine Betriebe zum übermäßigen Verbrauch von Düngemittel, welcher sich nicht in Ertragssteigerungen widerspiegelt, neigen. Die derzeitigen Beratungsprogramme haben sich positiv auf die Strategien und das Umweltbewusstsein der Landwirte beim Düngemitteleinsatz ausgewirkt. Die Reichweite und Wirksamkeit von Schulungen sollte jedoch verbessert werden. Zusammenfassend werden in der Dissertation die folgenden Schlüsselfaktoren identifiziert, die ein nachhaltiges Management chemischer Düngemittel in China behindern: geringe Betriebsgröße, regionale wirtschaftliche Abhängigkeit von Cash Crops, starke Diskrepanz zwischen den Praktiken der Landwirte und der wissenschaftlichen Produktionsrichtlinien sowie Chinas schrumpfende und alternde ländliche Arbeitskräfte. Um die oben genannten Probleme anzugehen, werden in dieser Dissertation Vorschläge für eine nationale Strategie, für die Politik und für deren Realisierung vorgetragen. Die Ergebnisse und Vorschläge dieser Dissertation können politischen Entscheidungsträgern, Interessengruppen und Forschern im Bereich des nachhaltigen Nährstoffmanagements in China als fundierte Entscheidungsgrundlage und wissenschaftliche Basis dienen

Impact of cropland displacement on the potential crop production in China:a multi-scale analysis

Changes in the amount and location of cropland areas may affect the potential crop production at different spatial scales. However, most studies ignore the impacts of cropland displacement on potential crop production. In many countries, cropland protection policies mainly aim for no loss in cropland area, while there is no restriction on change of cropland location. Taking China as the study area, we analyze the impacts of cropland displacement on potential crop production at four administrative levels during the period 2000 and 2018. At the national level, we find a net decrease in cropland area of 0.81 Mha, while another 19.63 Mha was displaced. The former led to a decrease of 4.20 Mton in potential crop production, while the latter resulted in a decrease of 43.26 Mton as a result of lower quality of the newly cultivated lands. In other words, cropland displacement explains 91% of the total loss in potential crop production at the national scale. However, the contribution of cropland displacement to total change in potential crop production is increasingly smaller at provincial level, municipal level, and county levels. These findings highlight the importance of geographic location on crop production and suggest that cropland policies should consider geographic location in addition to cropland area

Land Quality and Landscape Processes

This monograph contains a selection of scientific papers presented on the conference on Land Quality and Landscape Processes, hold in Keszthely, Hungary. It covers topics related to various aspects of land quality including : concepts of assessment; evaluation of biomass productivity ; bioindicators of land quality ; quality assessment of degraded land ; land use related data processingJRC.H.5-Land Resources Managemen

The impact of agricultural irrigation on land surface characteristics and near surface climate in China

It is well known that land cover and land use change can significantly influence the climate system by modulating surface-atmosphere exchanges. Land management, such as irrigation, also has a profound influence on the climate system. Irrigation can alter the water and energy flux from ground surface to the atmosphere and further influence near surface climate. Considering its dramatic expansion during the last century, the widespread use of irrigation has had an ongoing impact on our climate system. However, until now, this relationship between increased irrigation and its effect on climate system has not been well examined. The main objective of this dissertation is to quantify the irrigation impacts on land surface characteristics and near surface climate over China by using both observational (remote sensing and meteorological observation) and modeling studies with four specific questions: Where are the irrigated areas in China? What might have happened in the past? What will happen as a result of irrigation expansion in the future? And what is the relationship between the land cover land use change (LCLUC) impact and the irrigation impact on near surface climate in China? To answer these questions, I 1) developed three irrigation potential indices and produced a high resolution irrigation map of China; 2)analyzed and compared meteorological and remote sensing observations in irrigated and non-irrigated agriculture areas of China; 3) simulated both irrigation and LCLUC impact on land surface energy balance components (i.e., land surface temperature, latent flux, and sensible flux) and near surface climate (i.e., air temperature, water vapor, relative humidity) of China in the past (1978-2004) and also in two future time periods (2050 and 2100) by using the Community Land Model and compared the impact of irrigation with that of LUCC. Meteorological observations in Jilin Province show that the temperature differences between highly and lightly irrigated areas are statistically significant. The differences are highly correlated with the effective irrigation area (EIA) and sown area of crop (CSA). Results from satellite observations show that highly irrigated areas corresponded to lower albedo and daytime land surface temperature (LST), and higher normalized difference vegetation index (NDVI) and evapotranspiration (ET). The difference between highly and lightly irrigated areas is bigger in drier areas and in drier years. The modeling studies show that the irrigation impact on temperature is much less in the future than in the 20th century and that irrigation impacts more on the maximum air temperature than on the minimum air temperature. Both contemporary and future irrigation simulations show, nationally, irrigation decreases daily maximum temperature (Tmax) but increase daily minimum temperature (Tmin). Daily mean temperature (Tmean) decreases in contemporary irrigation simulations but increases in most of the cases in future irrigation simulations. In the 20th century, nationally, the spray irrigation leads to a decrease in Tmax of 0.079K and an increase in Tmin of 0.022K. Nationally, the spray irrigation leads to a decrease in Tmax between 0.022K and 0.045K and an increase in Tmin between 0.019K and 0.057K under future scenarios. This study demonstrates that the irrigation patterns (flood irrigation and spray irrigation) have statistically significant impacts on local climate. Moreover, this study suggests that, in the national respective, the impacts of changes in land management on climate are not comparable to the impacts of changes in land cover land use. This dissertation on irrigation and its impact is the first study which focuses solely on China using observational and modeling methods. The results from this dissertation contribute to a better understanding of the irrigation impact on near-surface climate which can improve our knowledge of how human activities influence climate, guide future policies aimed at mitigating or adapting to climate change, and help design a precise model to project the impact of irrigation on the climate system and irrigation requirements in the future. It can also be useful in assessing future food and water security issues