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Reconstructing historical land use and land cover change using explicit temporal, quantitative, and spatial information is not only the prerequisite for simulating long-term climate change and ecological effects but is also a scientific basis for comprehensively understanding the process and mechanism of anthropogenic land use alterations. Considering changes in historical borders and administrative divisions, a provincial cropland area dataset for China over the past millennium was created on the basis of existing estimations since the Song Dynasty. Land suitability for cultivation was then assessed by incorporating altitude, slope, soil texture, and the maximum potential productivity of climate. Subsequently, a gridding allocation model for cropland was constructed, and the provincial cropland area for 24 years over the past millennium was allocated into grids with a resolution of 10 km. The cropland area in China increased from 3.71×107 ha in AD 1000 to 12.92×107 ha in AD 1999, with a peak of 13.50×107 ha in AD 1980. The total cropland area in China showed fluctuating increasing trends that can be divided into three phases: fluctuation without notable net change for AD 1000–1290, slow increase for AD 1290–1661, and rapid increase for AD 1661–1999. Spatially, cropland intensified in the middle-lower reaches of the Yellow and Yangtze Rivers and expanded to mountainous and frontier areas over the last millennium. Specifically, over the entire period, the fractional cropland areas (FCAs) in the middle-lower reaches of the Yellow and Yangtze Rivers increased by 1.4 and 0.8 times, respectively. Since the mid-Qing Dynasty, large-scale land reclamation expanded to areas of low reclamation in southwest and northeast China. The FCAs for southwest and northeast China increased from 2.13% and 0.55% in AD 1661 to 18.00% and 26.61% in AD 1999, respectively. For AD 1661–1999, the proportion of cropland increased by 55% in the hills and low mountains and 27% in the middle and high mountains. The comparison with remote sensing cropland data shows that the grid cells with absolute differences of 0–10% accounted for 70.35% of all grid cells, while grids with differences exceeding 60% accounted for only 0.83%. This finding indicates that the reconstruction method is feasible, and the reconstruction results objectively reveal the historical spatiotemporal changes in cropland. [ABSTRACT FROM AUTHOR]

Global historical land use scenarios, including HYDE3.2 and PJ, are widely used in global change research. However, their uncertainties have not been well evaluated. Based on the historical-documents-based Chinese historical cropland dataset (CHCD), we evaluated the uncertainties of the representative global historical land use scenarios in past-millennium cropland reconstruction in China in terms of the area and spatial pattern. The results show that apparent differences exist in cropland area at the national scale between HYDE3.2 or PJ and CHCD for the Song-Liao-Jin Era (AD 1000–1279) and the Qing dynasty to present (AD 1644–1999), with a maximum relative difference ratio (RDR) of about −35% and 112%, respectively. We detected similar differences at the provincial scale, except for Guizhou, Heilongjiang, Jilin, and Xinjiang provinces. Specifically, HYDE3.2 underestimates cropland areas of nine provinces, with an absolute difference of up to 5.2 × 104 km2, while overestimates cropland areas of ten provinces, with an absolute difference of up to 5.1 × 104 km2. As for the spatial pattern, the percentage of grids with an absolute value of RDR greater than 70% between HYDE3.2 and CHCD reach up to 54%–82%, mainly distributed in major agricultural areas, frontier areas, and geographical transition zones. In conclusion, neither HYDE3.2 nor PJ reflects China's cropland area and its past-millennium change accurately, resulting from the differences in data sources, area estimation, and spatial allocation methods. [ABSTRACT FROM AUTHOR]

Global land use/cover change (LUCC) datasets are essential for quantitatively assessing the impacts of LUCC on global change, but many uncertainties in existing global datasets seriously hamper climate modeling. Evaluating the reliability of existing global LUCC datasets is a precondition for improved data quality. In this study, based on the regional historical document-based reconstructions, satellite-based data, and historical reclamation evidence for the Xinjiang area of China, the accuracy and rationality of cropland data for this area in the HYDE 3.2 and SAGE datasets were evaluated by utilizing comparative analysis regarding three aspects, namely the change tendency of the cropland area, the area of cropland, and the differences in spatial pattern. This study concluded that the amount of cropland in the Xinjiang area in the global and regional datasets shows both disparate trends and large differences in absolute values. Spatially, historical reclamation evidence indicated that agricultural cultivation in the Xinjiang area underwent expansion from south to north and from east to west over the past 300 years; however, the global datasets revealed that the cropland spatial patterns in the Xinjiang area in the historical period are similar to those in the current period. These differences are attributable to the uncertainties of the basic assumptions, per capita cropland area estimates, and reconstruction methods in the global datasets. The findings of the study highlight the necessity of regional studies on historical LUCC in the Xinjiang area. [ABSTRACT FROM AUTHOR]

Abstract Global historical land use scenarios are widely used to model human-induced climate change from the regional to global scales. It is necessary to conduct regional scale assessments of these global scenarios, identifying their uncertainties and pointing out directions for improvement. Based on the regional reconstruction Li-dataset, remotely sensed dataset, and grazing intensity dataset, the uncertainties of land use area and geographical distribution in HYDE3.1, HYDE3.2, and SAGE (a global land dataset from the Center for Sustainability and the Global Environment) scenarios for the Qinghai–Tibet Area (QTA) are evaluated. The comparisons show that the cropland areas on the QTA in HYDE3.2 for 1900–2000 are close to those of the Li-dataset, whereas HYDE3.1 underestimated and SAGE overestimated the cropland areas significantly. Spatially, HYDE3.1, HYDE3.2, and SAGE have large uncertainties, which cannot reflect the distribution of cropland on the QTA and its changes for 1900–2000 well, and too much cropland is allocated to southeastern Tibet. HYDE3.1 and HYDE3.2 overestimated the pasture area and its distribution on the QTA significantly. The distribution of pasture in SAGE showed overall an agreement with the spatial pattern for grazing intensity, but changes in grazing intensity for 2000–2010 was not reflected in SAGE. The FAO pasture definition and estimates and the method of using population as a proxy for pasture area are not appropriate for the QTA. Methodology which uses the pasture inventory data to calibrate satellite-based grassland maps to obtain the current pasture maps may also not be appropriate because of the lacking differentiation between natural and anthropogenic grasslands in remotely sensed data. More regional level land use estimates with concise definitions, define the land use more clearly, and stratification reconstruction based on differences in agro-climatic conditions and resource endowments may be used to improve global maps. Graphical abstract Unlabelled Image Highlights • Grazing intensity was used to assess global historical land use scenarios. • HYDE substantially overestimated pasture area and distribution on the QTA. • SAGE pasture distribution matched the spatial pattern of grazing intensity generally. • FAO pasture definition and reconstruction method are not suitable for the QTA. [ABSTRACT FROM AUTHOR]

Global historical land use datasets are widely used in global environmental change studies; however, uncertainties in the included pasture data have not been evaluated. In this study, using trend, relative difference ratio (RDR), and spatial comparisons, we evaluated the accuracy of China pasture data in the HYDE (versions 3.1 and 3.2), SAGE, and PJ datasets using historical document-based reconstructions, including the land use datasets for China covering 1935-1997 (hereafter Ge-dataset) and Northeast China covering the 1700s-2000 (hereafter Ye-dataset), and the satellite-based China’s Land-Use/cover Datasets (CLUDs) for 1980-2015. Four important results were obtained. (1) China pasture area in the HYDE, SAGE, and PJ datasets and grassland area in the Ge-dataset, Ye-dataset, and CLUDs show both disparate trends and large differences in absolute values. (2) Spatially, 50.9%, 52.8%, and 63.0% pasture/grassland grids in 2000 had RDRs greater than 60% between HYDE3.1, HYDE3.2, and SAGE datasets, and CLUDs, respectively. The percentage of grids with RDRs less than 20% were 24.9%, 26.7%, and 16.0%, respectively. (3) Based on HYDE3.2, the spatial distribution of pasture in Northeast China over the last 300 year has expanded, which is in contrast to the results from the Ye-dataset, which shows the spatial distribution of grassland shrinking because of human reclamation activities. (4) The large contrasts between the global datasets and Chinese native datasets are due to differences in pasture/grassland definitions, land use practices, and spatial reconstruction methods. [ABSTRACT FROM AUTHOR]

To deal with global warming and biodiversity loss, historical land use in South Asia received wide attention because of its huge population and rich biodiversity. We reviewed representative global and regional historical land use reconstructions for South Asia from their data sources, methods of area estimation and spatial mapping, and outcomes. Then we made some prospects on developing historical land use for South Asia. The land use area of South Asia in global reconstructions was mainly estimated using population. For the spatial pattern, most of them assumed that the historical distribution of land use in South Asia mimics satellite-based land use patterns or that the land use area was pixelized based on land suitability for cultivation and grazing. Large discrepancies exist among these global reconstructions in the land use area and spatial patterns with increasing magnitude with time in the past. The regional reconstructions of historical land use for South Asia used more regional historical records, but most covered only about one hundred years. The closer to the past, the lower the spatial-temporal resolution of these regional reconstructions. Great discrepancies also exist between these regional reconstructions because of the differences in cropland definition. Expansion of archaeological data sources, meta-analysis, and crowdsourcing will bring insights into area estimation of historical land use. Remote sensing and machine learning will facilitate spatial pattern mapping. Reconstruction region-by-region, and then integration, is also a solution for current challenges in reconstructing historical land use for South Asia. [ABSTRACT FROM AUTHOR]

The spatially explicit reconstruction of historical forest plays an important role in understanding human modifications of land surfaces and its environmental effects. Based on an analysis of the forest change history of China, we devised a reconstruction method for the historical forest cover in China. The core idea of the method is that the lands with high suitability for cultivation will be cultivated and deforested first, spreading to marginal lands with lower suitability for cultivation. By determining the possible maximum distribution extent of the forest, as well as devising the land suitability for cultivation assessment model and provincial forest area allocation model, we created 10 km forest cover maps of China for the years 1700 to 2000 with 10 year intervals. By comparison with satellite-based data in 2000, we found that the grids within 25% differences account for as much as 66.07% of all grids. The comparison with the historical documents-based data in northeast China indicated that the number of counties within 30% relative differences is 99, accounting for 74.44% of all counties. Therefore, the forest area allocation model we devised can accurately reproduce the spatial patterns of historical forest cover in China. Our reconstruction indicates that from 1700 to the 1960s, the deforestation mainly occurred in southwest China, the hilly regions of south China, the southeast of Gansu province, and northeast China; from the 1960s to 2000, the reforestation occurred in most traditional forested regions of China, particularly in the Tibet Plateau, hilly regions of south China and the Greater Khingan Mountains. The spatially explicit forest cover data sets we reconstructed can be used in global or regional climatic models to study the impact of land cover change on climate change. [ABSTRACT FROM AUTHOR]

Spatially explicit reconstruction of historical land cover change is a prerequisite for a more comprehensive understanding of environmental changes. Anthropogenic activities have dramatically altered the land cover of the conterminous United States (CONUS), encroaching heavily on the primary vegetation. However, few datasets exist that depict the historical trajectory of forest and grassland cover changes in CONUS over the last millennium, and previous efforts have only focused on reconstructions for the last four centuries. By integrating remote sensing-derived land use/cover change (LUCC) data and potential vegetation data, we determined the potential extent of natural forest (PENF) and grassland (PENG) in CONUS. Based on a qualitative analysis of the trends and driving forces of forest and grassland changes, we devised a method of subtracting reconstructed historical cropland (1000–2000 AD) and built-up land (1850–2000 AD) from PENG and PENF to reconstruct a 5 min × 5 min grid dataset of forest and grassland cover at 13 time-points over the past millennium. The results showed that forest and grassland cover in CONUS underwent a slow decline (1000–1600 AD), an accelerated decline (1600–1800 AD), a dramatic decline (1800–1950 AD), and finally, a recovery (1950–2000 AD) over the study period. The modelled forest fraction decreased from 49% in 1000 AD to 33% in 2000 AD, representing a 32% area reduction, whereas the modelled grassland fraction decreased from 37% to 22%, representing a 42% area reduction. The reduction occurred primarily in the last 200 years, with forest and grassland reductions accounting for 86% and 97% of the total reduction over the millennium, respectively. Spatially, more than 80% of the land was originally covered by forests and grasslands, and the loss occurred mainly in the eastern CONUS and Great Plains over the past millennium. After the 1930s, farmland abandonment began in central and eastern CONUS, simultaneously with environmental protection laws. Federal government regeneration programs for forest and grassland resources and the Shelterbelt Project all contributed to a slowdown in forest and grassland decline and recovery in cover. [ABSTRACT FROM AUTHOR]

To evaluate and improve datasets of anthropogenic land cover change used in local and global climate models, great efforts were made to reconstruct historical land use, including the LandCover 6k project which dedicated to reconstructing human land use over the past 10,000 years. In this study, we utilized historical records, including taxed-cropland and cropland measurement areas, and data on the number of households in eastern China between the 10th century and 13th century in concert with coefficient calibration, model allocation, and per capita cropland estimation to reconstruct areas of provincial cropland for 22 provinces over five time periods. Our reconstructions indicate that total cropland areas of eastern China for AD 1000, 1066, 1078, 1162, and 1215 are 34.74 × 106 ha, 49.42 × 106 ha, 51.62 × 106 ha, 35.21 × 106 ha, and 51.21 × 106 ha, respectively. And the cropland area fluctuated because of dynasty shift and went through three phases. Cropland expansion and contraction mainly occurred in the middle and lower reaches of the Yangtze and Yellow Rivers as well as the Huaihe River Basin, while in some regions far away from battlefields, including northeastern and southern China, cropland area expanded continuously throughout the study period. [ABSTRACT FROM AUTHOR]

Different from other similar studies, in this paper, most of the data were excerpted from historical archives and documents, and were used to study the spatiotemporal dynamics of cultivated land resources in China during the last 300 years. It is clear that these data may help reveal land use change dynamics and its regional differences, but they may be problematic due to the constraints of the original data in the Qing Dynasty, Conversion of Land Area for the purpose of collecting land taxes, and the deliberate or inadvertent omission of cultivated land area during land surveys, therefore, such data were adjusted to our need. In processing the data, we made great efforts to analyze the historical context of their sources and reduced the possible errors. The results show that the cultivated land area increased most quickly in the early Qing Dynasty, and slowed down after the middle Qing Dynasty, and then was stable in the late Qing Dynasty until 1949, and has been decreasing since then. It is also found that the cultivated land use varied greatly in different regions. The east of the country was cultivated much more heavily than the west, but in some western provinces cultivated land area increased more quickly. It is considered that the driving factors of such cultivated land area change include the increase of the population, the political issues, and the impacts of wars. Natural environmental factors and the introduction of new crops might also have affected the cultivated land use change in the past 300 years. [ABSTRACT FROM AUTHOR]

Abstract: The Yu-Xue-Fen-Cun (YXFC) is one of the government archives of the Qing Dynasty (1644–1911) in China. It records the beginning/ending dates, duration and rainfall infiltration depths into soil and snowfall accumulation for individual precipitation event. By comparing YXFC with instrumental data, a set of criteria used to identify the rainy season was established. This set of criteria was used to reconstruct the initial/final dates and length of rainy season during 1736–1900 and 1955–2000 at three sites (including Taiyuan, Datong and Yulin) based on both YXFC records and instrumental data. The results show that there is evident inter-decadal variation in rainy season length, with periodicity of 16–20a, 30–40a and 50–60a. The length of the rainy season gradually increases before the mid-19th century and decreases afterward, and the length of rainy season in 1736–1840 is statistically significantly longer than that in 1955–2000. These findings suggest that the intensity of the East Asian Summer Monsoon (EASM) became weaker from the mid-19th century, reaching the weakest condition in 1955–2000 during the context of the past 260 years. [Copyright &y& Elsevier]