Comparisons of cropland area from multiple datasets over the past 300 years in the traditional cultivated region of China

Land use/cover change is an important parameter in the climate and ecological simulations. Although they had been widely used in the community, SAGE dataset and HYDE dataset, the two representative global historical land use datasets, were little assessed about their accuracies in regional scale. Here, we carried out some assessments for the traditional cultivated region of China （TCRC） over last 300 years, by comparing SAGE2010 and HYDE （v3.1） with Chinese Historical Cropland Dataset （CHCD）. The comparisons were performed at three spatial scales： entire study area, provincial area and 60 km by 60 km grid cell. The results show that （1） the cropland area from SAGE2010 was much more than that from CHCD moreover, the growth at a rate of 0.51% from 1700 to 1950 and -0.34% after 1950 were also inconsistent with that from CHCD. （2） HYDE dataset （v3.1） was closer to CHCD dataset than SAGE dataset on entire study area. However, the large biases could be detected at provincial scale and 60 km by 60 km grid cell scale. The percent of grid cells having biases greater than 70% （〈-70% or 〉70%） and 90% （〈-90% or 〉90%） accounted for 56%-63% and 40%-45% of the total grid cells respectively while those having biases range from -10% to 10% and from -30% to 30% account for only 5%-6% and 17% of the total grid cells respectively. （3） Using local historical archives to reconstruct historical dataset with high accuracy would be a valu- able way to improve the accuracy of climate and ecological simulation.

Comparison of changes in land use and land cover in China and the USA over the past 300 years

Comparative studies of changes in land use and land cover between different countries over a long time-scale are helpful in understanding the processes and driving forces of these changes in different situations. We compared and analyzed the temporal and spatial characteristics of cropland, forest and grassland between China＇s mainland and the conterminous USA over the past 300 years. We found that, over the past 300 years, the area of cropland showed an overall increasing trend both in China and in the USA. In China, the area of cropland increased by about 79.46×104 km2 from 1661 to the 1980s, and the per capita cropland decreased from 0.37×104 m2 in 1685 to 0.10×104 m2 in 2000. For the USA, the area of cropland increased by 190.87×104 km2 between 1700 and 1950. The per capita cropland area of each time slice for the past 300 years was greater than 0.60×104 m2 and the maximum value was 2.01×104 m2 in 1890. As a result of the expansion in land reclamation, the forest and grassland areas of the USA have decreased by about 136.98×104 km2 and 136.98×104 km2, respectively, over the past 300 years; the corresponding values for China are about 89.73×104 km2 and 40.00×104 km2, respectively. In terms of the spatial patterns, the expansion in cropland in China mainly occurred in the border areas （including the northeast, southwest and Inner Mongolia） and in the hilly areas. Cropland expansion in the USA mainly occurred in the mid-west regions. In China, population growth is the most important driving factor in changes in land use and land cover, whereas in the USA, government policy plays the most significant role.

基于历史文献的1696–1914年帝俄欧洲部分耕地面积重建

To evaluate the climatic and ecological impacts of anthropogenic activities in global change research,it is essential to reconstruct historical land use and land cover change on regional and global scales.In this study,we reconstructed cropland areas for 54 provinces within the European part of Tsarist Russia(ETR)over the periods of 1696–1914 using historical data,including cropland area,population,grain consumption,and grain yield per unit area.The main results are as follows.(1)Total cropland areas and fractional cropland areas of ETR for 8 time sections during 1696–1914 were reconstructed,the former increased from 31.98×104 km2 to 147.40×104 km2,and the latter increased from 7.89%to 29.20%.The per capita cropland area decreased from 0.0246 km2 to 0.0113 km2 during 1696–1914.(2)Cropland expanded from the central and southwestern ETR to the black soil region,surrounding area of the Volga River,Ukraine region,the new Russia region,the vicinity of Ural,and north Caucasus region.(3)The expansion of territory,increase and migration of population,policies related to agricultural development and foreign trade,and the impacts of climate change were the reasons for the changes in cropland within ETR from 1696 to 1914.(4)In 1914,the cropland area and fractional cropland area of each province varied from 0.16×104 km2 and 0.76%to 5.65×104 km2 and 76.68%,respectively.(5)The comparisons show that the cropland areas of ETR in this study for 1696–1914 are higher than those in the HYDE 3.2 dataset.The main reason for this finding might be the underestimation of per capita cropland areas in the HYDE 3.2 dataset,which values remained at approximately 0.01 km2 from 1700 to 1920.

Spatio-temporal analysis of cropland change in the Guanzhong area, China, from 1650 to 2016

As one of the most critical impact factors of global change,historical land-use change is an indispensable input in climate and environment simulations.To better understand the cropland change in the Guanzhong area,gazetteers,statistics,and survey data were collected as data sources.Methods of registered tax-paying cropland data collection,selection of time points,and data interpolation and calibration were used to reconstruct changes in the cropland area.The cropland area data at the county level were allocated to 1 km×1 km grid cells.The total cropland area in the Guanzhong area was influenced by changes in population,wars,natural disasters,and land-use types,and it fluctuated from 1650 to 2016.From 1780 to 1830,the cropland expanded in the northern and western parts of Guanzhong area,and the cropland in the north of Qinling Mountains increased slightly.The spatial pattern of cropland reached its maximum range in 1980,and the cropland area declined in the whole study area,especially in the cities of Xi’an and Xianyang in 2016.The comparison between HYDE 3.2 and the data obtained in this study showed that the grid cells of HYDE 3.2 exhibit lower values of cropland area fractions in the Guanzhong Basin and higher values in high-altitude areas around the Guanzhong Basin as compared to those in this study.