Table of Content

    25 August 2018, Volume 40 Issue 8 Previous Issue    Next Issue
    Orginal Article
    The status of China’s overseas farmland investment
    Zhen SUN, Shaofeng JIA, Aifeng LV
    2018, 40 (8):  1495-1504.  doi: 10.18402/resci.2018.08.01
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    The accurate and comprehensive information of overseas farmland investment plays an important role in related studies. This research provides a scientific foundation for the national decision-making departments to guide Chinese enterprises in the overseas farmland investment, and has a great significance for both global and domestic food security. However, due to the lack of valid data about China’s overseas farmland investment, the history and present status of the investment, including the contract area, target country and deal, had rarely been investigated. In current study, based on the GRAIN dataset, Landmatrix dataset, as well as data from China's overseas economic and trade cooperation zone, China’s overseas farmland investment dataset was built. The results illustrated that the contract area of China's overseas farmland investment obtained in this study is more accurate and comprehensive than the existing research results. The target countries in the year 2015 were mainly the ones with low level income and rich farmland resource. Both the contract area and number of deals demonstrated increasing trends, and the distribution of the target countries was more widespread from 2008 to 2015. The scale of China’s overseas farmland investment is still rather limited. The contract area accounts for only 2. 0% of domestic farmland, while the proportion of overseas grain production importing to China is lower than that. This article proposes that China should strengthen the propaganda of the justice about China’s overseas farmland investment activities, and its important contribution to global food security, and further increase the policy support and scientific guidance for Chinese enterprises to invest in overseas farmland

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    The effects of off-farm employment on forestland transfer: the MV Tobit estimation with endogeneity perspectives
    Han ZHANG, Hongqiang YANG, Haibin CHEN, Jing LIU, Shilei XU, Hao LIU, Can LIU
    2018, 40 (8):  1505-1514.  doi: 10.18402/resci.2018.08.02
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    After the new round of collective forest tenure reform, the forestland transactions seem still inactive in China, which is not as expected as policymakers. Under this background, it is crucial to understand what are the factors that determine farmers’ behavior of forestland transfer. To investigate whether off-farm employment hinders forestland transfer, we established a household decision model, where the forestland transfer decision and off-farm employment decision are endogenous. Then the empirical analysis is performed based on a household survey dataset, which involves 1497 households from 9 provinces in China. This dataset is collected by the State Forestry Administration and is ranged from 2003 to 2013. Given the endogeneity of farmers’ decision-making process, the off-farm employment should be regarded as an endogenous variable. Meanwhile, the fact that the majority of households didn’t transfer their forestland implies that the explained variable is censored. Hence, the multivariate Tobit approach is applied to deal with the endogeneity and censoring issues. The results show that off-farm employment has a significantly negative effect on forestland rent-in, while the effect on rent-out is insignificant. This insignificance might be owing to the long-period feature of forestland transfer contracts and the role of forestland on household livelihood. For rural farmers, forestlands are considered to be a “safety net” once they lose their employments in off-farm sector. Moreover, transaction cost is an important factor that influence the decision of forestland transfer. That is, the variable of transaction cost imposes a negative effect on both rent-in and rent-out at the 1% statistical level. Besides, off-farm wage rate, timber prices, forestland area, forestland fragmentation, and the amount of household members also have significant effects on behaviors of forestland transfer. Their effects are opposite with regard to rent-in and rent-out behaviors. These findings will facilitate policymakers to understand what factors determine forestland transfer, and will provide beneficial suggestions in the following-up reform.

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    An empirical study on the influence of agricultural population transfer on urban construction land increase in Jiangxi Province
    Xiuqing ZOU, Meihui XIE, Zegan XIAO, Xiaosong TU, Yan WANG, Guoliang XU
    2018, 40 (8):  1515-1525.  doi: 10.18402/resci.2018.08.03
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    With the rapid development of urbanization in China, the area of urban construction land has been increasing, when a large number of agricultural population keep transferring to cities. The purpose of this paper is to explore the influence of agricultural population transfer on the growth of urban construction land,which is of great significance for promoting the construction of new urbanization and achieving the real transfer of agricultural population.Based on the statistical data of 11 cities in Jiangxi province from 2006 to 2015,the fixed effect and the random effect model were used to study the influence of the agricultural population transfer on the increase of urban total construction land and different types of urban construction land. The results show that the transfer of agricultural population in Jiangxi had a significant positive impact on the growth of urban construction land, and passed the test under one percent level. What's more, the transfer of agricultural population also exerted significant effects on the growths of urban industrial-commercial land, urban residential land and traffic-green-square land, and quite obvious in the scope of ten percent,one percent and five percent respectively, and the influence coefficients correspondingly were 0.167, 0.155, and 0.135. However, with the transfer of agricultural population, there has been no significant growth in urban public facilities-service land.There are regional differences among different cities, when the increase of different types of construction lands are impacted by the agricultural population transfer.Thus, it is concluded that the transfer of agricultural population will enhance the total amount of urban construction land. Thus, according to the process of agricultural population transfer, the government should moderately increase the urban public facilities land, rationally layout different types of urban construction land, for effectively promoting the construction of new urbanization and finally realizing the urbanization of agricultural population.

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    Influence of labor transfer on China's forest transition
    Lingchao LI, Jinlong LIU, Baodong CHENG, Wentao YANG
    2018, 40 (8):  1526-1538.  doi: 10.18402/resci.2018.08.04
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    Forest transition theory elucidates the pathways and mechanisms of the national forest restoration in the past hundreds of years. China has integrated into the global economy since the opening up, embraced a rapid economic growth and forest ecological improvement, and contributed greatly to the global ecological security. Meanwhile, little academic attention has been paid to elaborate the successful experiences of harmonious development between socio-economic and forest ecology against the background of economic globalization. This study extended the theoretical framework of forest transition. Based on the provincial panel data during the period of 1981-2010, considering the spatial correlation between variables, this study explored the impact of and labor migration on forest transition by applying GMM and spatial panel models. The results suggest that the massive afforestation public investment by Chinese government is the main driver of reforestation since the opening up. However, the average forest density decreases at the same time, as new saplings have the low forest volume. The development of China's foreign trade, especially the growth of export-oriented economy in coastal area has triggered labor migrations from inland China to coastal regions. This reduces the consumption of forest resources in inland forest regions, which emerged to be the most significant factor that improves forest quality in China.

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    A study on farmers' land investment behavior in resettlement area based on PVT
    Li REN, Chenlin GAN, Meng WU, Yinrong CHEN
    2018, 40 (8):  1539-1549.  doi: 10.18402/resci.2018.08.05
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    The immigrant resettlement is an important part of the development of water conservancy and hydropower project construction, and a key fundamental work in the development of hydropower resources. For a long time, “agricultural resettlement” is the most basic and common resettlement mode in the practice of immigrant resettlement in China’s rural areas, it has largely solved the practical difficulties of immigrant resettlement during specific historical periods and has made a great contribution to China’s water conservancy and hydropower development. Nowadays, China’s agricultural resettlement mode of non-voluntary migrants is facing a “double low dilemma” of both effect and efficiency. The traditional model of agriculture resettlement needs to reform and innovate urgently. The realistic predicament of the agricultural resettlement mode not only closely related to the local tension of man-earth relationship, but also reflected as the change of the farmers’land investment behavioral intentions and behavior responses. Based on the Perceived Value Theory, with the analysis method of multi-group SEM, we make an empirical study on the land investment behavior of two types of farmers in resettlement area. The results showed that: (1) Farmers’ land investment behavior in resettlement area is a comprehensive result of economic, psychological and situational factors, the effect of the behavior logic in accordance with the path of the paradigm in “Cognitive level→Cognitive balance→Perceived value→Behavior intention→Behavior response”; (2) The results shows that there are significant differences between the two types of farmers’ land investment behavior, specifically, it is the effect values of the influence factors, the indigenous farmers' investment behavior is based on the “objective rationality” of “trade-offs”, while the immigrant farmers shows more “subjective rationality” of “risk aversion”.

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    The connotation and realization way of sustainable food consumption in China
    Ling′en WANG, Peng HOU, Xiaojie LIU, Shengkui CHENG
    2018, 40 (8):  1550-1559.  doi: 10.18402/resci.2018.08.06
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    Food consumption is one of the most basic activities for human being’s survival and development. To develop a green lifestyle and promote the strategy of ecological civilization, we must first form a sustainable food consumption pattern and then implement it thereafter. At present, China’s enters a new food consumption period, which presents a significant change in the structure of food consumption and a diversification of people’s consumption pattern, etc. On the other side, great changes and challenges come hand-in-hand with each other during this period. For example, there are several bad trends such as health risks resulting from irrational consumption, serious food waste and frequent food-safety incidents, which to a large extent restricts the sustainable development of China's food consumption. Thus, it is recognized that food consumption, as one of the important part in the whole food safety, is of great importance for China’s social-economic development. The current study discusses the definition, principles and characteristics of sustainable food consumption, and then analyzes the similarities and differences between sustainable food consumption and other relevant concepts respectively. We further put forward the realization ways toward sustainable food consumption in China based on the system designing, program formulation, demonstration & extension, public guiding along with monitoring & evaluation orderly to build sustainable food consumption patterns. Additionally, in considering China's current national conditions, we would better select some aspects or cities as pilot areas before implementing the sustainable food consumption-related policies on a large scale. Therefore, we should highlight the big and medium-size cities, poor rural areas and other key regions, and focus on floating populations, students and other emphatic crowds, as well as households and catering industry, to find breakthroughs and explore food consumption patterns.

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    Targeting of multiple goals in new-stage Sloping Land Conversion Program based on farmers' decision-making autonomy
    Linjing REN, Jie LI
    2018, 40 (8):  1560-1571.  doi: 10.18402/resci.2018.08.07
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    In the new stage of policy adjustment, the New-stage Sloping Land Conversion Program (NSLCP) can aim at multiple policy objectives of ecological benefits, cost-effectiveness and poverty alleviation and whether it could target its multiple goals becomes the key issue in this period. Based on the study of rural households and plots data, this paper evaluated the targeting effects of the NSLCP on the ecological benefit, cost effectiveness, and poverty alleviation. It further explored the role of farmers' decision-making autonomy in the process of converted cropland targeting. The results showed that the NSLCP can aim at the land plots with higher ecological efficiency and lower cost, but it does not target the lands held by the poor households, especially in the case that the rural households do not have the right to target. And the family economic poverty has a significant negative impact on the participation in the NSLCP. The decision-making autonomy of rural households has a positive effect on the multiple targets of the NSLCP. The plots which are targeted by farmers are more cost-effective and the targeting process is more equitable for the poor. Therefore, in order to improve the targeting efficiency of the project, to achieve the cost-effectiveness, the pro-poor effects and the sustainability of the outcomes, the policy should give farmers more decision-making autonomy. It is essential to improve the targeting scheme and its index system in the NSLCP and also the compensation scheme by establishing dynamic and differentiated ecological compensation mechanism.

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    Poverty alleviation effect of ecological migrants in southern Shaanxi Province
    Wenlue WANG, Rui GUAN, Masara KAGATSUME, Jin YU
    2018, 40 (8):  1572-1582.  doi: 10.18402/resci.2018.08.08
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    Ecological migration in southern Shaanxi province is an important public policy which aims to complete the relocation of 2. 4 million people and achieves the goals of poverty alleviation and environment protection. It has been more than five years since its implementation. Through the quantitative evaluation on its efficiency in poverty alleviation, enlightenment and reference can be identified for strategies over precision poverty alleviation, immigrant-targeted poverty alleviation and rural revitalization. By utilizing four years’ panel data of over 1000 households in southern Shaanxi and taking the dimension of peasant households in poverty and poverty deprivation score as poverty proxy variable, the evaluation on poverty reduction effect of public policies for ecological migration in southern Shaanxi was carried out through such methods as DID, which is based on propensity score matching and fixed panel effect. The results demonstrated that the ecological migration policy in southern Shaanxi plays an important and significant role in an impact on multidimensional poverty alleviation of migrant peasants. However, the result of relocation will increase the possibility of peasants falling into temporary income poverty as its effect on reducing poverty deprivation score is a little bit weak. The peasants with risk preference are more likely to take part in ecological migration and get more external opportunities such as information and relationships. They can easily find more substitute livelihoods and get rid of poverty through the ecological migration. In the future poverty reduction strategy, the government needs to focus on cultivating industry development to prevent migrant peasants fall into the income poverty trap. Meanwhile, the peasants should be guided in changing risk preference to improve their self-development ability and provided more external opportunities. Eventually, the peasants in ecological vulnerable areas could alleviate poverty and improve the sustainable development ability through ecological migration.

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    Analysis on technical efficiency and influencing factors of large-scale grain-production farmers in Heilongjiang Province
    Lijuan ZHU, Zhiwei WANG
    2018, 40 (8):  1583-1594.  doi: 10.18402/resci.2018.08.09
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    Large-scale farmers are the important contributors of grain production in China. Under the background of rigid resource constraints and rising production costs, improving the technical efficiency of large-scale grain-production farmers is the fundamental way to guarantee the food security and increase the peasant's income of our country. Based on the survey data of 674 large-scale grain-production farmers in Heilongjiang Province, and using the SBM super efficiency DEA model, this study empirically examined the technical efficiency, the distribution of efficiency, the decomposition of efficiency and the slack variables of input. Furthermore, this paper analyzed the main factors influencing the technical efficiency by using the Tobit regression mode. The conclusions are listed as: Firstly, the average comprehensive technical efficiency, pure technical efficiency and scale efficiency are 0.545, 0.635 and 0.871 respectively. The average comprehensive technical efficiency is not high, and the main reason is the low pure technical efficiency. Secondly, the land management scale has a U-shaped curve relationship with the comprehensive technical efficiency, the same relationship as pure technical efficiency. Thirdly, the vast majority of large-scale grain-production farmers have redundancy in the input factors, and the improvement degree of input factors from high to low is land rent, flowing cost, fixed cost and labor cost. Finally, the factors such as the age, total cultivated land, the number of farm population, the number of soil blocks, the largest plot area, the proportion of farmland, the state of irrigation facilities, the way to irrigate, the term of land circulation contract and the availability of formal loans have significant impacts on the technical efficiency of large grain farmers.

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    Research on factors influencing the provincial technical inefficiency of forest parks under multi-output targets in China
    Ansheng HUANG, Siren LAN, Huibing ZOU
    2018, 40 (8):  1595-1607.  doi: 10.18402/resci.2018.08.10
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    Forest parks are designed to provide economic, social and ecological effects. Based on provincial statistical data related to forest parks in mainland China and collection of each year from 2004 to 2015, the present study employed stochastic frontier analysis to demonstrate the provincial technical efficiency and inefficiency of the multiple output targets established for these forest parks, including economic, social, and ecological products. By referring to the supply-demand theory, a Tobit model was used to measure and analyze the effects of supply factors and demand factors on the provincial technical inefficiency of these forest parks. This study showed that the mean of provincial technical efficiency of China’s forest parks was only 0. 3684 from 2004 to 2015, leaving plenty of room for promotion. The average of total inefficiency was as high as 0.6316, and the mean of technical inefficiency was also as high as 0. 5144. The efficiency values of forest parks for the main forest regions in China listed in descending order were: Southwest Forest Region, Southern Forest Region, North Forest Region, Northeast Forest Region and Northwest Forest Region. For influencing factors of demand, a nonlinear and U-shaped relationship was observed between GDP per capita and provincial technical inefficiency of these forest parks. Meanwhile, the population density and urbanization rate did exhibit a positive influence on the provincial technical inefficiency of these forest parks. For influencing factors of supply, high-level tourism resource density, high-grade highway density, forest coverage, and investment intensity illustrated a negative influence on the provincial technical inefficiency of these forest parks to varying degrees.

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    Monitoring of maize planting area based on time-series Sentinel-1A SAR data
    Li LI, Qingling KONG, Pengxin WANG, Lei WANG, Lan XUN
    2018, 40 (8):  1608-1621.  doi: 10.18402/resci.2018.08.11
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    Maize is one of the three typical crops in China. Monitoring the distribution of maize is of vital importance in understanding the scope of corn cultivation and ensuring food security. Multi-temporal ESA Sentinel-1A C-band Synthetic Aperture Radar (SAR) VV and VH polarization data at a 20 m spatial resolution were used to identify maize identity for Zhuozhou City in Hebei province, China. Based on the analysis of the scattering characteristics for different crops, as well as the backscattering coefficients variability of different crop structures at different growth and development stages of the study area, dual-polarized backscatter coefficients from appropriate phases were selected. To assess the performance of different backscattering coefficients forms in classification, both σ0 and γ0 data were used. Compared with the sampling data from the field campaign, the results showed that a high recognition accuracy of maize can be obtained using support vector machine (SVM) method if time series data are used. Classification result obtained from time series radar images has a higher accuracy and kappa coefficient than those from a single image. For example, results gotten from long time series σ0 data have the ideal performance with overall accuracy of 92.96% and a Kappa coefficient of 0.91. Data from sowing to silking of spring maize and sowing to jointing of summer maize (April 19, May 30, June 11, and July 17) can effectively obtain maize information under different cropping patterns. The increase data of August and September would have little impact on the accuracy of maize identification. The differences between σ0 and γ0 data are relatively moderate. However, the classification accuracy obtained with long time series γ0 data can be improved by 3% than that with σ0 data for the forest area.

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    Statistical evaluation of proxies for the R factor of the Universal Soil Loss Equation
    Xiaoqing MA, Mingguo ZHENG
    2018, 40 (8):  1622-1633.  doi: 10.18402/resci.2018.08.12
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    The accurate estimation of rainfall erosivity (R) is significant for soil erosion prediction. However, the algorithm for the R factor of the universal soil loss equation (USLE), the most widely used algorithm to calculate R, needs pluviograph data with high temporal resolution. Thus, studies have developed a large number of proxies for the R factor (PR) using daily, monthly, yearly rainfall data instead of pluviograph data. It is noted that the statistical evolutions of the PRs is desirable, which is currently lacking. This study aimed to evaluate 15 widely used PRs, including two yearly, six monthly, and seven daily ones, and further rank them in terms of their correlation with R using a stepwise Meng’s test procedure and data collected at 14 rainfall stations in the eastern China. The results indicated that the 15 PRs under examination were all significantly correlated with R (r > 0.59, p < 0.03), implying all of them can be reasonably used as an R predictor. The stepwise Meng’s test illustrated that the daily PRs were better correlated with R than the monthly and yearly PRs with four daily PRs, which included three developed in China and one developed in Australia, ranking the first (r > 0.99) between the 15 PRs. Additional examination did show that the Australia PR exhibited a relative error that increased with the latitude and thus should be calibrated by means of the regression equation we developed. One of the three Chinese PRs did not show a systematic error and can be directly used to estimate R without calibration. The two other PRs showed approximately 30% overestimation and also be calibrated by the developed regression equations. We also recommended the PRs to be used if only the monthly or yearly rainfall data is available.

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    A meta-analysis of wetland CVM studies in China
    Qingbo LI, Changlin AO, Wei YUAN, Qin GAO
    2018, 40 (8):  1634-1644.  doi: 10.18402/resci.2018.08.13
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    Meta-analysis is an effective method of benefit transfer, which has been widely used in the evaluation of wetland resources. However, due to the existence of publication selection bias in the sample data, the accuracy of the evaluation result is affected. In order to solve this problem, we constructed a meta-regression model which can eliminate the influence of publication selection bias. The value transfer database was established through collecting the empirical research results of the application of CVM to evaluate the value of wetlands in China and an appropriate meta-regression model was chosen by examining the existence of the publication selection bias in the database or not. Then, the model of value transfer was established, and the effectiveness of out-of-sample value transfer was examined. FAT-PET test results show that there is no publication selection bias in the database, which demonstrates that the sample of the literature selected in this paper is more representative and the sample data are not affected by publication selection bias. Meta-regression results indicate that the types of wetland services, wetland location, wetland type, wetland area, number of beneficiaries and the difference in the format of the questionnaire will lead to the difference in the valuation of wetland value. However, the way of questionnaire survey, per capita GDP, research time and periodical quality had no significant impact on the valuation of wetland value. The error range of out-of-sample benefit transfer in meta-regression model was 0.08%~39.02%, and the average error was 9.58%. Thus, the meta-regression model can be used for out-of-sample benefit transfer.

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    Dynamic evolution analysis of reclamation in Jinzhou Bay based on multi source remote sensing images
    Lina KE, Jun CAO, Hongqing WU, Quanming WANG, Hui WANG
    2018, 40 (8):  1645-1657.  doi: 10.18402/resci.2018.08.14
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    Reclamation not only increases the land resources, but also has a profound impact on the ecological environment. It is essential to monitor the land reclamation. Based on Landsat TM image data in 1991, 1995 and 2000, SPOT satellite image in 2005, HJ-1 CCD in 2010 and SPOT remote sensing image data in 2014, a method of shoreline extraction based on CA was constructed. The reclamation distribution, intensity index, centroid coordinates and their utilization in the sea area near Jinzhou bay were analyzed in depth. The research results show that: (1) The coastline near Jinzhou bay has increased by 20.07 km for last 23 years, in particular between 1991—1995 and 2005—2010; (2) The displacement of coastline in Beigang town, Niuyingzi and west Haikou in the central part of Jinzhou bay is relatively large, and the reclamation intensity is relatively high; (3) The newly increased reclamation area in Jinzhou bay is 50.67 km2, and its utilization type is mainly urban construction. The area of port construction and reclamation has steadily increased, the area of salt industry is reduced, and the proportion of unused land is increasing year by year; (4) The center of gravity of the reclamation in Jinzhou Bay is generally shifted to the northeast, with the sea near the west of Haikou as the center. A large number of new port construction site was created. Therefore, we should strengthen the ecological transformation and protection of the shoreline that has been filled, standardize the human development activities, reduce the ecosystem pressure in the coastal zone of this region, and further carry out the ecological environment assessment of the gulf at the same time to provide theoretical guidance and scientific basis for the sustainable development of the region.

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    Evapotranspiration simulation and its spatio-temporal variation characteristics in Fenqin Region
    Xiang HAN, Yunhe YIN, Shaohong WU, Haoyu DENG
    2018, 40 (8):  1658-1671.  doi: 10.18402/resci.2018.08.15
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    Evapotranspiration (ET) is a critical component in the surface energy budget as well as the water cycle. ET is also a key bond that connects the soil-vegetation-atmosphere system. With the climate change, studying the spatio-temporal distribution of ET has great implications in the reasonable allocation of regional water resources. This paper simulated the monthly ET based on water balance method using Gravity Recovery and Climate Experiment (GRACE) data in Fenqin Region from 2003 to 2015, and then analyzed its spatio-temporal dynamics in different time scales. It was found that the ET simulated by water balance method considering the water storage changes were more stable in the time series (the coefficient of variation, the standard variation, and the extreme values respectively reduced 0.12, 5.50mm, 3.20%), and more accurately in reflecting the temporal variations of annual and seasonal ET in Fenqin Region, comparing to the results simulated by water balance method neglecting the water storage changes. Average annual ET was 530.19mm in Fenqin Region from 2003 to 2015. There was a spatial distribution of increasing from north to south. Moreover, ET fluctuated quite smoothly during the study period with a lowest value in 2010 (478.22mm) and a highest value in 2011 (614.57mm), and the coefficient of variation was 0.08. At seasonal scale, ET was highest in summer (263.36mm) which accounted for 49.67% of annual ET and lowest in winter (19.50mm). Besides, the degree of dispersion was relatively higher in winter and lower in summer. The temporal variation of ET in Fenqin Region from 2003 to 2015 was mainly affected by precipitation and temperature, and the fluctuation of annual ET was mainly related to precipitation.

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    Analysis of temporal and spatial variation of extreme temperature in Guizhou Province
    Dayun ZHU, Kangning XIONG, Hua XIAO
    2018, 40 (8):  1672-1683.  doi: 10.18402/resci.2018.08.16
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    With global warming, the extreme weather events in southwest China have become more frequent and the damage is also deepening, posing a serious threat to national economic development and ecological environment protection. Based on daily temperature data sets of 33 stations in Guizhou Province, spatial and temporal changes of extreme temperature and its influence factors were analyzed during the period of 1960-2016, by using the methods of linear regression, Inverse Distance Weighted (IDW) and Mann-Kendall(M-K) test. The results showed that in the last 57 years the climate of Guizhou is getting warmer and accelerating the trend in the 21st century. The extreme high temperature indices, i. e. summer day, the percentile value of warm day, the duration of warmness and the frequency of the duration of warmness have all increased, with the velocity of 0.6d/10a、2.7d/10a、0.02d/10a、and 0.2times/10a, respectively. And the extreme low temperature indices, i. e. frost day, the percentile value of cold day, the duration of coldness and the frequency of the duration of coldness have decreased, with the velocity of -1.6d/10a、-8.0d/10a、 -0.5d/10a、and -1.0times/10a, respectively. In addition, the extreme temperatures show asymmetry pattern. For example, the change range of extreme low temperature indices is greater than that of extreme high temperature indices, the tropical days and cold days have the largest variation. There is a close relationship between the extreme temperature indices and altitude. Moreover, most abrupt change of climate occurred in the late 19th and early 2000s. El Niño has a significant impact on the extreme warm series index, and La Nina has a greater influence on the extreme cold series index. The impact of La Nina on the extreme cold series index reached its highest level in the following year.

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    Diurnal asymmetry of temperature and its effect on NDVI in Loess Plateau
    Liqun MA, Fen QIN, Jiulin SUN, Hao WANG, Haoming XIA
    2018, 40 (8):  1684-1692.  doi: 10.18402/resci.2018.08.17
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    In this paper, the meteorological observation data of 102 meteorological stations in the Loess Plateau and its surrounding areas in 1982-2015 were selected. The Normalized Difference Vegetation Index (NDVI) and vegetation type data were used. And the Mann-kendall (m-k) Nonparametric test method and the second-order partial correlation analysis were adopted. The time series change trend and spatial pattern in the growing seasonal minimum temperature (Tmin) and maximum temperature (Tmax) over the Loess Plateau between 1982 and 2015 were analyzed, and the effects of asymmetric warming on different vegetation type were discussed. The results show that: ① We found a persistent increase (P<0.01) in the growing seasonal Tmin and Tmax over the Loess Plateau between 1982-2015, whereas the rate of increase of Tmin was 1.6 times that of Tmax. ②The influence of diurnal asymmetry on vegetation dynamics showed an obvious difference, and NDVI and Tmin showed a more significant correlation than NDVI and Tmax in vegetative growth season. The effect of nighttime warming on NDVI in the Loess plateau is more significant than that of daytime warming. ③We also found diverse responses of vegetation type to daytime and night-time warming across the Loess Plateau. We found that the partial correlation between NDVI and Tmax was positive (P<0.05) except grassland and crop. The partial correlation between Tmin and NDVI of crop was negative (P<0.01), and the partial correlation between Tmin and NDVI of other vegetation was positive (P<0.05). Our results provide a demonstration for studying regional responses of vegetation to climate extremes under global climate change.

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