Croplands In China Research Articles

Mapping annual 10-m maize cropland changes in China during 2017–2021

China contributed nearly one-fifth of the world maize production over the past few years. Mapping the distributions of maize cropland in China is crucial to ensure global food security. Nonetheless, 10 m maize cropland maps in China are still unavailable, restricting the promotion of sustainable agriculture. In this paper, we collect numerous samples to produce annual 10-m maize cropland maps in China from 2017 to 2021 with a machine learning based classification framework. To overcome the temporal variations of plants, the proposed framework takes Sentinel-2 sequence images as input and utilizes deep neural networks and random forest as classifiers to map maize in a zone-specific way. The generated maps have an overall accuracy (OA) spanning from 0.87 to 0.95 and the maize-cultivated areas estimated by the maps are highly consistent with the records in statistical yearbooks (R2 varying from 0.83 to 0.95). To the best of our knowledge, this is the first annual 10-m maize maps across China, which largely facilitates the sustainable agriculture development in China dominated by smallholder farmlands.

Biodiversity loss through cropland displacement for urban expansion in China

As a result of rapid economic development, urban expansion reduced the cropland in China. To secure the food supply, cropland displacement to maintain the quantity and quality of cropland has been implemented. Here, we quantified the biodiversity losses due to cropland displacement resulting from urban expansion from a telecoupling perspective in China from 1980 to 2020. A comprehensive multimodel assessment demonstrated that the indirect biodiversity losses due to cropland displacement resulting from urban expansion were approximately 2 to 3 times higher than its direct biodiversity losses, at a total loss of approximately 0.6 % to 1.0 %, as indicated by three biodiversity indicators. Displaced cropland with a higher biodiversity cost but lower cropland productivity is the main reason for the excessive indirect losses and suggests that socioecological processes may be detrimental to the synergistic benefits of the UN Sustainable Development Goal (SDG) for food security and terrestrial biodiversity. This study also identified source–sink hotspots for indirect biodiversity losses, which can contribute to improving biodiversity conservation, optimizing the spatial distribution of cropland and thus enhancing socioecological system sustainability.

Impact of straw return combined with different fertilizations on soil organic carbon stock in upland wheat and maize croplands in China: A meta-analysis

Straw return is a vital soil amendment practice in Chinese upland soils, aiming to improve the soil organic carbon (SOC) stock. However, its impact on SOC stock depends on various fertilizer practices, leading to inconclusive results. To address this, we conducted a meta-analysis of 121 peer-reviewed publications to evaluate the effect of straw return combined with different fertilization practices including balanced NPK (BFS), unbalanced NP, NK, PK, or N fertilization (UFS), and no fertilization (NFS) in the wheat-maize cropping system. The results showed that straw return with BFS led to the highest increase in SOC stock (13.3%), followed by UFS (11.4%) and NFS (6.12%), compared to straw removal under the same fertilization conditions. BFS also significantly increased the soil C (15.9%), N (9.62%), and P (6.21%) contents, as well as the C:N (2.48%) and C:P (11.4%) ratios. In contrast, UFS resulted in higher C:N ratios (6.47%) and soil acidification, affecting the SOC stock during straw return. A structural equation model revealed that the presence of BFS positively influenced the association between SOC stock and soil stoichiometry (P ​< ​0.05) compared to UFS, which was influenced by climate and initial soil properties. Additionally, the impact of BFS on SOC stock was more significant in the double cropping system (14.5%) than in the single wheat (8.32%) and single maize (10.8%) cropping systems. A lower initial SOC (<6 ​g ​kg−1) also showed a greater response to BFS compared to a higher initial SOC (>12 ​g ​kg−1). Based on C sequestration efficiency, implementing straw return with BFS could lead to a higher rate of increase in SOC sequestration.

Spatial patterns in pollution discharges from livestock and poultry farm and the linkage between manure nutrients load and the carrying capacity of croplands in China

The rapid development of livestock and poultry farming in China has resulted in an increasing threat of water pollution. In particular, mitigating livestock-related pollutant discharges is a key issue for environmental sustainability, especially for inland surface water bodies. In order to ensure the effective control of pollution and the efficient utilization management of livestock manure, spatially explicit surveys of pollutant generation and discharge from the livestock sector must be performed. In the present study, we estimated the grid cell-level distributions in the generation and discharge of four typical pollutants (chemical oxygen demand, ammonium nitrogen, total nitrogen and total phosphorus) from the livestock sector across the country with a spatial resolution of 30 arc-seconds. The distributions were estimated using the most recent pollution source census data and multi-sourced ancillary materials by a dasymetric mapping approach. We further investigated the feasibility of the resource utilization of livestock manure by comparing manure-source nutrients with the carrying capacity of adjacent croplands. Our results show that low-intensive farming generated and discharged the majority of livestock farming pollution, with other cattle and pigs breeding identified as the two major sources of pollution from the livestock sector. Southwest, Central and East China suffered the highly densified pollutants generation and discharges. Furthermore, cropland exceeding its carrying capacity was concentrated in these regions. Our findings provide additional insights into livestock and poultry farming in the context of relocation, strengthening regulation, transforming breeding operations, and rationalizing the resource use of manure, all of which are important measures for the sustainable development of both agriculture and the environment.

Untangling the increasing elevation of cropland in China from 1980 to 2020

The redistribution of cropland to areas of higher elevation in China has long affected agricultural development and could seriously threaten national food security. However, there is currently little research reported on this phenomenon, which may limit the improvement of cropland protection policies. To fill this gap, we analyzed the spatiotemporal characteristics and driving mechanisms of increased cropland elevation in China during the period 1980–2020. The average cropland elevation in China increased by 17.38 m from 1980 to 2020. The gravity center of the cropland area and average cropland elevation in China moved to the northwest by 81.00 km and 51.47 km, respectively. The amount of newly added cropland in eastern China was less than that in occupied regions; however, the average elevation of newly added cropland was greater than that of occupied cropland, though the opposite phenomenon was observed in western China. Slope, temperature, land-use intensity, population, economic density, and distance to main roads were the main factors affecting the redistribution of cropland to areas of higher elevation. The effects of these major driving factors exhibited significant spatial and temporal variations in China. This study has important implications for improving existing cropland protection policies and developing more effective cropland management systems in China.

Impacts of straw return coupled with tillage practices on soil organic carbon stock in upland wheat and maize croplands in China: A meta-analysis

Despite numerous individual studies evaluating the impact of straw return on soil organic carbon (SOC) stock in upland wheat and maize croplands in China using no-tillage (NTS), rotary tillage (RTS), and deep tillage (DTS) practices, the results have shown inconsistency. In addition, several factors influence the effects of various tillage practices with straw return on SOC stock that are not well understand. In this study, we conducted a meta-analysis of 764 comparisons to determine the combined impact of SOC stock in the topsoil (0–20 cm) and subsoil (20–40 cm) layers, while considering factors such as climate conditions, management practices, and initial soil properties. The results indicate that straw return with different tillage practices significantly improved SOC stock in both soil layers compared to straws removal. The increase in topsoil SOC stock was nearly identical for NTS (7.38 %) and DTS (7.17 %), compared to the RTS. However, the increase in subsoil SOC stock was significantly higher for DTS (28.8 %). According to subgroup analysis, NTS has been more effective in increasing topsoil SOC stock in regions with medium temperature (10–15 °C) and low precipitation (<400 mm), when used in a single cropping system. However, in regions with higher temperature (>15 °C) and precipitation (>800 mm), DTS is more effective in increasing SOC stock in both topsoil and subsoil layers in a double cropping system. Long-term (11–20 years) DTS resulted in a significant increase in SOC stock in the topsoil (19.2 %) and subsoil (18.5 %), while the increased effects of NTS on SOC stock were only in topsoil layer (17.1 %). The effects of straw return on SOC stock were also found to be associated with soil texture, with NTS having a greater impact on sandy to loam soils, and DTS having a greater impact on clay soils. Furthermore, a significant (P < 0.01) positive linear relationship was observed between annual carbon (C) input and SOC sequestration in the topsoil under NTS, as well as in both soil layers under DTS. These findings have important implications for enhancing SOC in Chinese upland wheat and maize cropland soils through optimizing straw return, given that more than 518 million tons of crop straw are produced annually.

Organic amendments effects on soil aggregation and carbon sequestration in saline‐alkaline croplands in China

AbstractSaline‐alkaline soils are wide‐spread and approximately 6.5% of the world's land area is reported as being saline and sodic. Increasing soil organic carbon (SOC) concentration and aggregate stability in saline‐alkaline soils has been challenging due to the deleterious effects of soil salinity and sodicity. To address this issue, a 2‐year filed experiment was conducted to evaluate the effects of biochar (BC), farmyard manure (FM), corn straw (CS), and sheep manure (SM) in combination of chemical fertilizer (CK) on soil aggregation and C sequestration in mildly and moderately alkaline soils in Hetao Irrigation District, China. For mildly alkaline soil, the proportion of macroaggregates (&gt;0.25 mm) was significantly higher under FM, CS, and SM (34.6%–51.2%) compared with CK (13.2%). The mean weight diameter (MWD) and geometric mean diameter (GMD) of water‐stable aggregates significantly increased under FM, CS, and SM by an average of 172.7% and 58.7% over CK. In addition, FM, CS, and SM enhanced the distribution of organic carbon (OC) in macroaggregates (&gt;0.25 mm) and accelerated the accumulation of particulate organic matter within macroaggregates. Treatment BC enhanced OC distribution in microaggregates (0.053–0.25 mm) and exhibited a 7.40 g kg−1 SOC content, followed by SM and FM which exhibited SOC contents of 7.10 and 6.76 g kg−1. For moderately alkaline soil, data obtained in this study showed a slight influence from organic amendments on soil aggregates and C sequestration, suggesting that the moderately alkaline soil was not as sensitive to organic amendments as the mildly alkaline soil. Overall, the results of this study demonstrated that FM and SM combined with chemical fertilizer were the top organic amendments to improve soil aggregation and C sequestration in the mildly alkaline soil but not the moderately alkaline soil over the short term.

Response of Soil Organic Carbon Accumulation in Paddy Fields in Fujian Province to Future Temperature Increases

Understanding the effect of the soil carbon "source-sink" in cropland in China under future warming scenarios is the basis for making reasonable carbon neutralization policies. This study focused on the paddy soil in Fujian Province, a typical subtropical region in China including 84 counties (cities and districts). We employed the 1:50000 soil database and biogeochemical process model (DNDC) to simulate the dynamic changes in paddy soil organic carbon under different warming scenarios for the period of 2017-2053. The results indicated that in the context of normal temperature (control run) and 2, 4, and 6℃ of warming, the total amounts of carbon sequestration of paddy soil in Fujian Province were 11.56,9.44, 7.08, and 4.91 Tg, respectively; accordingly, the average annual carbon sequestration rates (expressed by C) were 173, 141, 106, and 74 kg·(hm2·a)-1, indicating that the rate of carbon sequestration was decreasing with the increase in future temperature. However, overall, the paddy field soil in the province was still a "carbon sink" under the warming of 6 (C. We also found that the gleyed paddy soil was mostly affected by the increase in temperature, and the decrease in carbon sequestration rate ranged from 20% to 69% using different treatments. In contrast, the salinized paddy soil was slightly affected, with a 14%-43% decrease in carbon sequestration rates. As for the different administrative regions, Sanming City was the most affected by temperature increase, with the rate of carbon sequestration decreasing by 27%-83% using different treatments. However, it was reduced by only 10%-41% and 14%-42% in Quanzhou and Putian (coastal areas), respectively. Overall, due to different soil properties, fertilization management, and climatic environment, there was a strong variability in the carbon sequestration rates of paddy soil for different soil subtypes and administrative regions in Fujian in response to future climatic warming.

Global vegetation greenness interannual variability and its evolvement in recent decades

The interannual variability (IAV) of global vegetation greenness needs careful assessment as it relates to the stability of the climate, conservation of biodiversity, sustainable ecosystem services, and global food security. Here, we investigated the spatial feature and temporal evolvement of global vegetation greenness interannual variability from 1982 to 2015 using the Global Inventory Modeling and Mapping Studies (GIMMS) Normalized Difference Vegetation Index third generation (NDVI3g) data. Generally, regions with herbaceous and short woody plants had larger IAV of vegetation greenness than those with tall woody biome types (7.9% versus 2.9%). On average, all the biomes displayed increasing IAV of vegetation greenness from 1982 to 2015, with notable increases over northern high latitudes (0.135%/year), Eastern Europe (0.037%//year), and Central Australia (0.231%/year). Croplands in China and India experienced decreasing IAV of vegetation greenness (–0.037%/year for China and –0.004%/year for India). The changing IAV of vegetation greenness had implications for climatic, environmental, and anthropogenic changes that influence vegetation dynamics. Some note-worthy factors include climate warming, the CO2 fertilization effect, agricultural practice improvement, cropland abandonment, and China’s Grain-for-Green Program.

Spatiotemporal Changes of Ecosystem Service Values in Response to Land Cover Dynamics in China from 1992 to 2020

Global land cover changed significantly in the last several decades due to strong climate warming and intensive human activities, and those changes greatly affected ecosystem services all over the world. Using CCI-LC land cover data from 1992 to 2020, the spatiotemporal characteristics of land cover change in China were investigated, and the annual ecosystem service values (ESVs) were estimated with the equivalent factor method. The results showed that: (1) The overall accuracy and Kappa coefficient of CCI-LC products in China were 71.1% and 0.65, respectively. (2) From 1992 to 2020, the area of cropland in China increased generally first before 2004 then decreased after 2008; the area of forest land decreased before 2003 then increased after 2015; the area of grassland and bare land consistently decreased; and the area of built-up land continuously increased, with a total increase of 113,000 km2. The primary characteristics of land cover transitions in China were the mutual conversion of cropland, forestland, and grassland as well as the continuous increase of built-up land. (3) Forest land was the most significant contributor of ESV in China, making 62.9% of the total ESV by multi-year average, followed by grassland (18.5%) and water (10.3%); the ESV was roughly high in the southeast China and low in the northwest. (4) The total ESV in China decreased generally before 2015 and got stable in the last five years. The hot spots with rising ESV were mainly concentrated in the western, northern and southwestern parts of China, while the cold spots with declining ESV were mainly concentrated in the economically developed eastern and southern China. (5) Cropland, forest land, grassland, and water were the positive contributors to ESV change in China, while built-up land and bare land were the negative contributors. The findings provide a theoretical foundation for China’s harmonized socioeconomic and environmental development.

The pattern of abandoned cropland and its productivity potential in China: A four-years continuous study

The increased requirement of food production with the rising population challenges limited cultivation land in China. The abandoned cropland has high potential in grain production to ensure China's food security. However, the spatial distributions of abandoned cropland in China are understudied and therefore it is difficult to estimate its potential grain production. Our study proposed a new definition of abandoned cropland considering unique multiple cropping systems in China, and estimate the abandoned cropland distribution and grain productivity potential by using Landsat-8 and GF-1 images under deep learning technology. The area of abandoned cropland in three main grain-producing regions was approximately 1.53 million hectares during 2014–2017. The estimated images agreed with the field survey and the national agricultural statistical data with the accuracy larger than 87 %. The spatial distribution of abandoned cropland in China was scattered and a high abandonment rate observed in the Middle-lower Yangtze River Plain. Moreover, the uncultivated cropland accounted for approximately 50 % of the total area of abandoned cropland. The maximum production potential of abandoned cropland could reach 8.5 million tons, including 2.7, 2.5 and 3.3 million tons of maize, wheat and rice, respectively. The exploitation of abandoned cropland is also beneficial for additional soybean production in China. National-scale estimation of abandoned cropland in China is crucial for land use policy making and cropland protection, as well the implementation of national food security strategy.

Effect of cropland withdrawal on soil organic carbon in China, 1990–2018

AbstractSoil organic carbon (SOC) is one of the most important soil attributes responsible for the sustainable maintenance of soil quality. In recent years, cropland withdrawal (CWD) (i.e., conversion into natural landscapes) in China has become a remarkable phenomenon of land use changes, driven by the spontaneous cropland abandonment by rural households and government‐led conversion of cropland to forest and grassland. The CWD may affect SOC content and storage in China. Therefore, this study estimated the variation in SOC caused by CWD between 1990 and 2018 based on the grid data of land use and soil organic matter (SOM). The results showed that CWD had a significant effect on SOC. (1) From 1990 to 2018, the total area of CWD was about 358 × 103 km2, an area that represented about 20% of the total area of cropland in China in 1990. In addition, within the total area of CWD, the proportions represented by the conversion of cropland to forest and grassland were the highest, reaching 58% and 39%, respectively. The former was mainly distributed in the southern part of China, especially in the southwestern mountainous area. The latter was largely concentrated in the northern part of China, especially in the Loess Plateau; (2) From 1990 to 2018, the average SOC content of CWD increased by about 10%, representing an increase of 193 Tg in soil organic carbon storage (SOCS). This is equivalent to six times the carbon emissions from agricultural land in China in 2019; (3) Among eight agricultural regions in China, the middle‐lower Yangtze Plain had the largest area of CWD, which accounted for 19.9% of the total CWD of the whole country.

The Impact of Cropland Use Changes on Terrestrial Ecosystem Services Value in Newly Added Cropland Hotspots in China during 2000–2020

The assessment of ecosystem services value is the basis for the realization of integrated management of these services. In recent decades, the hotspots of China’s newly added cropland have shifted to the Xinjiang oasis areas, where the ecological environment is relatively fragile. However, the impact of changes in cropland use on the terrestrial ecosystem services value (TESV) in Xinjiang, China, has not been studied in depth, and it is related to the sustainability of the dynamic balance between China’s cropland and the sustainable management of natural resources in Xinjiang. This study focuses on Xinjiang and employs the benefit transfer method and five phases (2000, 2005, 2010, 2015 and 2020) of high-resolution and finely classified remote sensing monitoring data of land use to evaluate the impact of changes in cropland use on the TESV from 2000 to 2020. The findings suggest the following: (1) The cropland area in Xinjiang grew from 6.5682 million ha in 2000 to 8.9874 million ha in 2020, demonstrating significant expansion, and it has gone through four stages: rapid expansion, steady expansion, rapid expansion and relative stability. (2) A sharp mutual conversion trend is observed between cropland and other types of land use in Xinjiang. Grassland and unused land are the main sources of new cropland, while lost cropland has been mainly converted back into grassland and construction land. (3) During 2000–2020, although the extensive expansion of cropland and conversion of cropland mainly at the expense of ecological land in Xinjiang have significantly enhanced the provision services of the terrestrial ecosystem (539.49 million USD), ecosystem regulation services (−1508.47 million USD), support services (−1084.47 million USD) and cultural services (−565.05 million USD) experienced losses. Consequently, an overall loss in the TESV has ensued. This study provides new insights that help re-examine the sustainability issue of the spatial transfer of cropland in China, and it also offers guidance for the realization of the sustainable management of natural resources in Xinjiang.

Soil organic carbon sequestration in croplands can make remarkable contributions to China's carbon neutrality

The vast cropland in China is an important carbon pool with substantial carbon sequestration potential. Here, this study estimated the soil organic carbon stock in China's croplands based on a comprehensive investigation of 7.5 million soil samples from 2209 counties. We show that China's croplands (0–20 cm) store 4.53–4.98 Pg organic carbon in total. The soil organic carbon stock increased from 29.13–34.54 to 33.51–36.90 Mg C ha−1 during 1980–2010, with an annual average increase rate of 113.33 kg C ha−1 yr−1. The increase in soil organic carbon stock was mainly driven by the increasing inputs of crop residue and livestock manure. Furthermore, we designed four scenarios with different crop residue, livestock manure, and nitrogen fertilizer inputs to assess the soil organic carbon sequestration potential in China's croplands. The results show that the soil organic carbon storage is projected to reach 6.98–7.89 Pg by 2060, representing 6.1%–13.3% of the annual negative carbon emissions required by 2060 China's carbon neutrality target. We also proposed targeted strategies to further increase the soil organic carbon stock of cropland in different regions by considering characteristics such as soil properties and agricultural management practices.

Soil quality assessment of cropland in China and its relationships with climate and topography

AbstractAssessing soil quality (SQ) of cropland is fundamental for food security and sustainable land management. However, there is limited information regarding SQ assessment on a national scale, which is vital to answer important SQ‐related questions in quantitative terms on that scale. Here, the SQ of cropland in China was assessed by constructing a minimum data set (MDS) from 23 soil physicochemical properties based on principal component analysis. The interaction roles and relative contributions of climate and topography on SQ was evaluated by a structural equation model. The MDS comprised eight indicators: proportion of silt, bulk density, total phosphorus, total potassium, available nitrogen, exchangeable calcium, chlorite, and vermiculite. The soil quality index (SQI) varied from 0.245 to 0.705 and showed a clear pattern of decreasing quality from the north to the south of the country. Of the total cropland area in China, the largest share (27.91%) was of soils of high quality, followed by those of moderate quality (24.63%), low quality (20.37%), very high quality (14.18%), and very low quality (12.91%). The north and the south differed significantly in terms of total potassium, exchangeable calcium, chlorite, and vermiculite, which are the four most important indicators of SQ. Climate and elevation explained about 2.2%–30.1% of the variation in SQ on the national and regional scales. These findings suggest that croplands in southern China will benefit from potassium and calcium fertilizers, which will contribute to enhance food security and promote sustainable land management in China.

Reveal the severe spatial and temporal patterns of abandoned cropland in China over the past 30 years

The abandonment phenomenon is familiar in China. It threatens food security and seriously affects the sustainable development of society, the economy, and the natural environment. However, monitoring and mapping abandoned cropland on a large scale remains a challenge because of its complex land-use change process. According to the World Food and Agriculture Organization, cropland not used for agricultural production for more than 5 years is defined as abandoned cropland. This study uses the Landsat high-precision long-time series product to detect cropland nationwide from 1990 to 2019 by using the sliding window method on Google Earth Engine to profile the spatial distribution, intensity, trend, frequency, and recultivation of abandoned cropland. Between 1992 and 2015, the results illustrate that the total area of abandoned cropland in China was 559,170.26 km2, 18.59 % of the cropland area. Excluding the recultivated cropland area, China's abandoned cropland area amounted to 392,156.24 km2, 13.03 % of the total cropland. Cropland abandonment is mainly distributed in the second terrain gradient in midwestern and southwestern regions such as Inner Mongolia and Gansu. It rarely happens in western and eastern coastal areas. A high abandonment rate area usually has high elevation and slope. The light index is negatively correlated with the abandonment rate in suburban areas. This study is the first to map the spatiotemporal distribution of abandoned cropland in China with high precision at 30 m resolution. It provides an important basis for policies regarding the recultivation of abandoned cropland.

Assessing the Lead Accumulation Risks of Wheat Grain by Developing a Source-Specific Accumulation Risk Assessment Model

Characterizing the lead (Pb) transfer in the "source-soil-wheat" chain is of great importance for the prevention and control of the Pb accumulation risk in wheat grain harvested from the croplands of China. In this study, we used the Jiyuan City, northern China, as a case study to investigate the influence of contamination sources and soil factors on the accumulation of Pb in wheat grain. A site-specific source risk assessment model (SRAM), coupling the positive matrix factorization model, Freundlich-type function, and the Monte Carlo simulation method, was developed to estimate the risk of Pb accumulation in wheat grain harvested from different scenarios. Based on the results of the spatial analysis, the effectiveness and potential risk of the control measures applied in the study area was also evaluated. Atmospheric deposition and phosphate fertilizer application were identified as major sources contributing to 29.0% of the Pb accumulations in wheat grain. Soil pH and cation-exchange capacity (CEC) were the primary causative factors affecting the Pb accumulation in wheat grain. Cropping wheat in the high Pb continuation risk areas (western and northwestern areas) of Jiyuan City caused a 10.5% likelihood of Pb to accumulate above the China food standard limit of 0.2 mg·kg-1 (DW). This risk was significantly decreased to 2.39% when the CEC levels of affected soils was improved to 20 cmol·kg-1 and above.

Mapping irrigated croplands in China using a synergetic training sample generating method, machine learning classifier, and Google Earth Engine

Agricultural irrigation is an important vehicle for increasing crop yield, but large-scale irrigation has posed great challenges to global and regional water availability and climate change via altering land–atmosphere interactions. The knowledge of irrigation distribution is essential to understand regional water cycles and guide agricultural management decision-making, but such information is scarce in China. We developed a remote sensing-dominated framework to map irrigated croplands in China at 500 m resolution using a synergetic training sample generating method, machine learning classifier, and a cloud computing platform (Google Earth Engine, GEE). To overcome the challenges of lacking nationwide training samples, we first produced two provisional irrigation maps by fusing statistics and MODIS-derived annual peak greenness indices. The two provisional irrigation maps were then spatially filtered with an existing irrigation product (GRIPC) to construct the initial training sample pool. Next, to enhance the robustness and cover more irrigated candidates, we screened and introduced the irrigated croplands in three land use/cover maps (CCI-LC, GLC_FCS, and NLCD) to supplement the training data pool. Afterward, we utilized locally adaptive random forest classifiers and data cubes (MODIS-derived spectral indices, climatic and topographic variables) to generate irrigation maps in each province of China on GEE. The resulting map outperformed other current irrigation maps with an overall accuracy of 79.2% . The map also showed a reasonable consistency with statistical data at the province and prefecture levels, with the determination coefficient (R2) of 0.89 and 0.77, respectively. In total, we identified 87.04 million hectares of irrigated croplands in mainland China in 2015. Using the resulting map and water use statistics, we found a high correlation between irrigation area and agricultural water use in Northwest, Northeast, and South China, and a low correlation in North China Plain. This map is expected to serve national water resource management and assist decision-making in improving agricultural adaption to climate change.

Rising temperature threatens China’s cropland

The rising demand for calories and protein together with urbanization, pose significant challenges to China’s food security. The determination of policy actions requires accurate estimates of climatic impacts on both crop yields (intensive margin) and cropland area (extensive margin). However, the analysis of the latter has been limited, especially in developing countries. Here, we assess the impact of temperature on land use in China by matching high-resolution satellite data on land use with daily weather data from 1980 to 2010. We find that extremely hot weather (daily average temperature above 30 °C) has a long-lasting effect on reducing cropland in China. Combining climate projections from 39 downscaled climate models, we predict that climate change is likely to reduce China’s cropland area by 2.09%–25.51% under IPCC’s slowest and fastest-warming scenarios by the end of this century. In addition, we find that non-irrigated land is more susceptible to rising temperatures in the short term; however, irrigated land is subject to a similar impact in the long term. This result suggests that the adaptive effect of irrigation could be limited under persistent rising in temperature.

IrriMap_CN: Annual irrigation maps across China in 2000–2019 based on satellite observations, environmental variables, and machine learning

Agricultural irrigation, as an important practice to protect crops from drought and promote grain yield, has a long history in China. A timely and precise dataset about the extent and dynamics of irrigated areas is necessary for water allocation and agricultural management but is scarce in China. Here we developed annual irrigated cropland maps across China (IrriMap_CN) at 500-m resolution from 2000 to 2019, using MODIS data, machine-learning method, and Google Earth Engine platform. First, we generated annual nationwide training samples by strictly screening the existing irrigation maps downscaled from the statistical data. Second, we implemented locally adaptive random forest classifiers in 511 nominal 1° × 1° grid cells across China with MODIS vegetation indices, climatic factors, and topography variables. Third, we conducted nationwide pixel-wise validation of the IrriMap_CN using independent samples. The validation results based on more than 3000 ground truth points revealed that IrriMap_CN had high accuracies ranging from 77.2% to 85.9%. The time series of IrriMap_CN detected substantial expansion of irrigated areas in Xinjiang and Heilongjiang (more than 50% in total) and pronounced decreases in Sichuan, Jiangsu, and Hebei. The analyses of irrigation frequency, start time, and end time implied that North China Plain was the most intensive irrigated area; but the irrigation area showed a decreasing trend since 2000, consistent with the reduced agricultural water consumption. The annual irrigation datasets allow us to understand the spatiotemporal dynamics of irrigated croplands in China and are expected to contribute to the improvement of earth system models and facilitate sustainable agricultural water management.