Mapping cropland extent of Southeast and Northeast Asia using multi-year time-series Landsat 30-m data using a random forest classifier on the Google Earth Engine Cloud

Cropland extent maps are useful components for assessing food security. Ideally, such products are a useful addition to countrywide agricultural statistics since they are not politically biased and can be used to calculate cropland area for any spatial unit from an individual farm to various administrative unites (e.g., state, county, district) within and across nations, which in turn can be used to estimate agricultural productivity as well as degree of disturbance on food security from natural disasters and political conflict. However, existing cropland extent maps over large areas (e.g., Country, region, continent, world) are derived from coarse resolution imagery (250 m to 1 km pixels) and have many limitations such as missing fragmented and\or small farms with mixed signatures from different crop types and\or farming practices that can be, confused with other land cover. As a result, the coarse resolution maps have limited useflness in areas where fields are small (<1 ha), such as in Southeast Asia. Furthermore, coarse resolution cropland maps have known uncertainties in both geo-precision of cropland location as well as accuracies of the product. To overcome these limitations, this research was conducted using multi-date, multi-year 30-m Landsat time-series data for 3 years chosen from 2013 to 2016 for all Southeast and Northeast Asian Countries (SNACs), which included 7 refined agro-ecological zones (RAEZ) and 12 countries (Indonesia, Thailand, Myanmar, Vietnam, Malaysia, Philippines, Cambodia, Japan, North Korea, Laos, South Korea, and Brunei). The 30-m (1 pixel = 0.09 ha) data from Landsat 8 Operational Land Imager (OLI) and Landsat 7 Enhanced Thematic Mapper (ETM+) were used in the study. Ten Landsat bands were used in the analysis (blue, green, red, NIR, SWIR1, SWIR2, Thermal, NDVI, NDWI, LSWI) along with additional layers of standard deviation of these 10 bands across 1 year, and global digital elevation model (GDEM)-derived slope and elevation bands. To reduce the impact of clouds, the Landsat imagery was time-composited over four time-periods (Period 1: January- April, Period 2: May-August, and Period 3: September-December) over 3-years. Period 4 was the standard deviation of all 10 bands taken over all images acquired during the 2015 calendar year. These four period composites, totaling 42 band data-cube, were generated for each of the 7 RAEZs. The reference training data (N = 7849) generated for the 7 RAEZ using sub-meter to 5-m very high spatial resolution imagery (VHRI) helped generate the knowledge-base to separate croplands from non-croplands. This knowledge-base was used to code and run a pixel-based random forest (RF) supervised machine learning algorithm on the Google Earth Engine (GEE) cloud computing environment to separate croplands from non-croplands. The resulting cropland extent products were evaluated using an independent reference validation dataset (N = 1750) in each of the 7 RAEZs as well as for the entire SNAC area. For the entire SNAC area, the overall accuracy was 88.1% with a producer’s accuracy of 81.6% (errors of omissions = 18.4%) and user’s accuracy of 76.7% (errors of commissions = 23.3%). For each of the 7 RAEZs overall accuracies varied from 83.2 to 96.4%. Cropland areas calculated for the 12 countries were compared with country areas reported by the United Nations Food and Agriculture Organization and other national cropland statistics resulting in an R2 value of 0.93. The cropland areas of provinces were compared with the province statistics that showed an R2 = 0.95 for South Korea and R2 = 0.94 for Thailand. The cropland products are made available on an interactive viewer at www.croplands.org and for download at National Aeronautics and Space Administration’s (NASA) Land Processes Distributed Active Archive Center (LP DAAC): https://lpdaac.usgs.gov/node/1281

A Review of Earth Observation-Based Drought Studies in Southeast Asia

Drought is a recurring natural climatic hazard event over terrestrial land; it poses devastating threats to human health, the economy, and the environment. Given the increasing climate crisis, it is likely that extreme drought phenomena will become more frequent, and their impacts will probably be more devastating. Drought observations from space, therefore, play a key role in dissimilating timely and accurate information to support early warning drought management and mitigation planning, particularly in sparse in-situ data regions. In this paper, we reviewed drought-related studies based on Earth observation (EO) products in Southeast Asia between 2000 and 2021. The results of this review indicated that drought publications in the region are on the increase, with a majority (70%) of the studies being undertaken in Vietnam, Thailand, Malaysia and Indonesia. These countries also accounted for nearly 97% of the economic losses due to drought extremes. Vegetation indices from multispectral optical remote sensing sensors remained a primary source of data for drought monitoring in the region. Many studies (~21%) did not provide accuracy assessment on drought mapping products, while precipitation was the main data source for validation. We observed a positive association between spatial extent and spatial resolution, suggesting that nearly 81% of the articles focused on the local and national scales. Although there was an increase in drought research interest in the region, challenges remain regarding large-area and long time-series drought measurements, the combined drought approach, machine learning-based drought prediction, and the integration of multi-sensor remote sensing products (e.g., Landsat and Sentinel-2). Satellite EO data could be a substantial part of the future efforts that are necessary for mitigating drought-related challenges, ensuring food security, establishing a more sustainable economy, and the preservation of the natural environment in the region

Operationalization of Remote Sensing Solutions for Sustainable Forest Management

The great potential of remote sensing technologies for operational use in sustainable forest management is addressed in this book, which is the reprint of papers published in the Remote Sensing Special Issue “Operationalization of Remote Sensing Solutions for Sustainable Forest Management”. The studies come from three continents and cover multiple remote sensing systems (including terrestrial mobile laser scanning, unmanned aerial vehicles, airborne laser scanning, and satellite data acquisition) and a diversity of data processing algorithms, with a focus on machine learning approaches. The focus of the studies ranges from identification and characterization of individual trees to deriving national- or even continental-level forest attributes and maps. There are studies carefully describing exercises on the case study level, and there are also studies introducing new methodologies for transdisciplinary remote sensing applications. Even though most of the authors look forward to continuing their research, nearly all studies introduced are ready for operational use or have already been implemented in practical forestry

Examining spatiotemporal changes in the phenology of Australian mangroves using satellite imagery

Nicolás Younes investigated the phenology of Australian mangroves using satellite imagery, field data, and generalized additive models. He found that satellite-derived phenology changes with location, frequency of observation, and spatial resolution. Nicolás challenges the common methods for detecting phenology and proposes a data-driven approach

Earth Observations for Addressing Global Challenges

"Earth Observations for Addressing Global Challenges" presents the results of cutting-edge research related to innovative techniques and approaches based on satellite remote sensing data, the acquisition of earth observations, and their applications in the contemporary practice of sustainable development. Addressing the urgent tasks of adaptation to climate change is one of the biggest global challenges for humanity. As His Excellency António Guterres, Secretary-General of the United Nations, said, "Climate change is the defining issue of our time—and we are at a defining moment. We face a direct existential threat." For many years, scientists from around the world have been conducting research on earth observations collecting vital data about the state of the earth environment. Evidence of the rapidly changing climate is alarming: according to the World Meteorological Organization, the past two decades included 18 of the warmest years since 1850, when records began. Thus, Group on Earth Observations (GEO) has launched initiatives across multiple societal benefit areas (agriculture, biodiversity, climate, disasters, ecosystems, energy, health, water, and weather), such as the Global Forest Observations Initiative, the GEO Carbon and GHG Initiative, the GEO Biodiversity Observation Network, and the GEO Blue Planet, among others. The results of research that addressed strategic priorities of these important initiatives are presented in the monograph

The interactive effects of climate, land cover change and damming on the flow regime and fine sediment dynamics of a tropical river

Tropical river ecosystems are being increasingly modified by the accelerated construction of hydropower dams. Dams are known to have detrimental effects on downstream flows and sediment transport, with long-lasting implications for fluvial processes, habitats and ecosystems. The tropics are also experiencing high rates of deforestation and forest degradation. These types of land use change can alter components of the hydrological cycle through the modification of terrain characteristics, evapotranspiration and fine sediment runoff. Moreover, predictions of increased temperatures and changes in precipitation in tropical regions may further modify the hydrological cycle and, in turn, river flows. The state of Sarawak, Malaysia, is witnessing the construction of 12 mega-dams as part of the Sarawak Corridor of Renewable Energy. The compounding effects of these dams, land use change and climate change pose a significant threat to the hydrology and overall functioning of rivers in Sarawak, but this threat has received little scientific attention. Baleh river was chosen as the study site because it is a typical Malaysian river surrounded by intact forest and its catchment is a headwater region with clear hydropower potential that will soon be realized. Thus, it is an area which can provide highly valuable new information on how large dams interact with landcover and climate change to alter river dynamics. This study therefore aimed to assess how damming, land cover and climate change interact and influence runoff of water and sediment in the River Baleh, a naturally forested tropical catchment in Sarawak. It incorporates two main components: (i) long-term land cover change assessment, and (ii) hydrological modelling of the impacts of the dam, climate and land cover change on flows and sediment loads in the Baleh. The land cover change assessment involved processing multi-temporal satellite images in Google Earth Engine (GEE) and carrying out supervised classification in ArcGIS. Besides providing empirical data on the magnitude and nature of land cover change across the Baleh catchment, the classified image outputs from this component formed input data for the second component - the catchment hydrological modelling. For the hydrological modelling, the Soil and Water Assessment Tool (SWAT) was used to simulate discharge and fine sediment loads for the whole of the catchment. The model was calibrated and validated using observed flow data. The performance of SWAT on daily and monthly time-steps was good (NSE > 0.62). Baseline conditions in the catchment were established with SWAT before running the future climate, land cover and dam scenarios; baseline models runs used the most recent five-year period. The future scenarios modelled the influence of land cover change with both low and high deforestation rates as well as climate models that involved increased temperature and decreased rainfall. Two operational scenarios were devised for the dam: a non-hydropower regime simply balancing dam outflow and inflows, to maintain lake levels and avoid dam spilling, while a hydropower regime was created which involved the dam operating at specific percentages of its capacity over the course of the year. Analysis of satellite images indicated that there has been very minimal land cover change in the Baleh catchment over the last two decades (<2% reduction in forest cover) but a significant expansion of logging roads; these roads may promote future deforestation. SWAT models suggested that even high deforestation rates (loss of 5% per year) will not cause major hydrological changes in the Baleh River, but the models indicated dramatic increases in sediment yield from sub-catchments and, in turn, increases in the total amount of sediment exported by the catchment (up to 736% increase by 2050, compared to baseline). Modelling of climate scenarios suggested a counter-acting effect, with predicted lower rainfall and high temperature decreasing flow and sediment loads. SWAT simulations suggest that the dam will have a greater impact on flow and sediment loads in the Baleh catchment than the future land cover and climate change scenarios that were modelled. The presence of the dam has the greatest impact on flow and sediment at the dam site, reducing sediment loads by approximately 95% and reducing discharge variability. Simulations suggest that impacts on flow are still evident almost 100 km downstream, despite tributary inputs. Impacts on sediment loads at the catchment outlet are more difficult to understand, because of how the river might adjust to cumulative alterations in flow, competence and supply over decadal timescales. Preliminary analysis for the first five years of dam operation suggests that sediment yield at the basin outlet may differ from baseline much less than it does at the dam site but further work on this is needed, particularly because of the sensitivity to exact dam operational regimes (which at present are unclear). The high sediment yield from the upper sub-catchments has implications for the operation of the Baleh dam due to siltation, but the large size of the reservoir means that even by 2050 its storage capacity will have been reduced by only around 5%. Overall, this study demonstrates how models such as SWAT can be used to provide insights into the complex interacting effects of anthropogenic stressors in tropical catchments. It is recommended that a period of 10-30 years is used for SWAT studies of the downstream effects of dams, to capture the sequences of transient states which will evolve in response to altered flow regimes and sediment supply. The traits of tropical rivers such as the Baleh (high discharge and sediment loads relative to catchment area) and the numerous tributaries create the potential for more rapid downstream ‘recovery’ than in other hydroclimatic settings, but this is confounded by ongoing climate and land cover changes which modify boundary conditions. Modelling assessments of the type presented here should be complemented by empirical studies of fluvial adjustment, to fully understand the habitat and ecological changes that follow impoundment

The interactive effects of climate, land cover change and damming on the flow regime and fine sediment dynamics of a tropical river

Tropical river ecosystems are being increasingly modified by the accelerated construction of hydropower dams. Dams are known to have detrimental effects on downstream flows and sediment transport, with long-lasting implications for fluvial processes, habitats and ecosystems. The tropics are also experiencing high rates of deforestation and forest degradation. These types of land use change can alter components of the hydrological cycle through the modification of terrain characteristics, evapotranspiration and fine sediment runoff. Moreover, predictions of increased temperatures and changes in precipitation in tropical regions may further modify the hydrological cycle and, in turn, river flows. The state of Sarawak, Malaysia, is witnessing the construction of 12 mega-dams as part of the Sarawak Corridor of Renewable Energy. The compounding effects of these dams, land use change and climate change pose a significant threat to the hydrology and overall functioning of rivers in Sarawak, but this threat has received little scientific attention. Baleh river was chosen as the study site because it is a typical Malaysian river surrounded by intact forest and its catchment is a headwater region with clear hydropower potential that will soon be realized. Thus, it is an area which can provide highly valuable new information on how large dams interact with landcover and climate change to alter river dynamics. This study therefore aimed to assess how damming, land cover and climate change interact and influence runoff of water and sediment in the River Baleh, a naturally forested tropical catchment in Sarawak. It incorporates two main components: (i) long-term land cover change assessment, and (ii) hydrological modelling of the impacts of the dam, climate and land cover change on flows and sediment loads in the Baleh. The land cover change assessment involved processing multi-temporal satellite images in Google Earth Engine (GEE) and carrying out supervised classification in ArcGIS. Besides providing empirical data on the magnitude and nature of land cover change across the Baleh catchment, the classified image outputs from this component formed input data for the second component - the catchment hydrological modelling. For the hydrological modelling, the Soil and Water Assessment Tool (SWAT) was used to simulate discharge and fine sediment loads for the whole of the catchment. The model was calibrated and validated using observed flow data. The performance of SWAT on daily and monthly time-steps was good (NSE > 0.62). Baseline conditions in the catchment were established with SWAT before running the future climate, land cover and dam scenarios; baseline models runs used the most recent five-year period. The future scenarios modelled the influence of land cover change with both low and high deforestation rates as well as climate models that involved increased temperature and decreased rainfall. Two operational scenarios were devised for the dam: a non-hydropower regime simply balancing dam outflow and inflows, to maintain lake levels and avoid dam spilling, while a hydropower regime was created which involved the dam operating at specific percentages of its capacity over the course of the year. Analysis of satellite images indicated that there has been very minimal land cover change in the Baleh catchment over the last two decades (<2% reduction in forest cover) but a significant expansion of logging roads; these roads may promote future deforestation. SWAT models suggested that even high deforestation rates (loss of 5% per year) will not cause major hydrological changes in the Baleh River, but the models indicated dramatic increases in sediment yield from sub-catchments and, in turn, increases in the total amount of sediment exported by the catchment (up to 736% increase by 2050, compared to baseline). Modelling of climate scenarios suggested a counter-acting effect, with predicted lower rainfall and high temperature decreasing flow and sediment loads. SWAT simulations suggest that the dam will have a greater impact on flow and sediment loads in the Baleh catchment than the future land cover and climate change scenarios that were modelled. The presence of the dam has the greatest impact on flow and sediment at the dam site, reducing sediment loads by approximately 95% and reducing discharge variability. Simulations suggest that impacts on flow are still evident almost 100 km downstream, despite tributary inputs. Impacts on sediment loads at the catchment outlet are more difficult to understand, because of how the river might adjust to cumulative alterations in flow, competence and supply over decadal timescales. Preliminary analysis for the first five years of dam operation suggests that sediment yield at the basin outlet may differ from baseline much less than it does at the dam site but further work on this is needed, particularly because of the sensitivity to exact dam operational regimes (which at present are unclear). The high sediment yield from the upper sub-catchments has implications for the operation of the Baleh dam due to siltation, but the large size of the reservoir means that even by 2050 its storage capacity will have been reduced by only around 5%. Overall, this study demonstrates how models such as SWAT can be used to provide insights into the complex interacting effects of anthropogenic stressors in tropical catchments. It is recommended that a period of 10-30 years is used for SWAT studies of the downstream effects of dams, to capture the sequences of transient states which will evolve in response to altered flow regimes and sediment supply. The traits of tropical rivers such as the Baleh (high discharge and sediment loads relative to catchment area) and the numerous tributaries create the potential for more rapid downstream ‘recovery’ than in other hydroclimatic settings, but this is confounded by ongoing climate and land cover changes which modify boundary conditions. Modelling assessments of the type presented here should be complemented by empirical studies of fluvial adjustment, to fully understand the habitat and ecological changes that follow impoundment

Land Use and Land Cover Mapping in a Changing World

It is increasingly being recognized that land use and land cover changes driven by anthropogenic pressures are impacting terrestrial and aquatic ecosystems and their services, human society, and human livelihoods and well-being. This Special Issue contains 12 original papers covering various issues related to land use and land use changes in various parts of the world (see references), with the purpose of providing a forum to exchange ideas and progress in related areas. Research topics include land use targets, dynamic modelling and mapping using satellite images, pressures from energy production, deforestation, impacts on ecosystem services, aboveground biomass evaluation, and investigations on libraries of legends and classification systems

Land Use and Land Cover Mapping in a Changing World

It is increasingly being recognized that land use and land cover changes driven by anthropogenic pressures are impacting terrestrial and aquatic ecosystems and their services, human society, and human livelihoods and well-being. This Special Issue contains 12 original papers covering various issues related to land use and land use changes in various parts of the world (see references), with the purpose of providing a forum to exchange ideas and progress in related areas. Research topics include land use targets, dynamic modelling and mapping using satellite images, pressures from energy production, deforestation, impacts on ecosystem services, aboveground biomass evaluation, and investigations on libraries of legends and classification systems

GIS applications for poverty targeted aquaculture development in the lower Mekong Basin.

In the lower Mekong Basin, marginal socio-economic conditions prevail amongst rural small scale farming households which heavily depend on highly seasonal, rain-fed farming systems for their livelihood. Persistent rural poverty is aggravated by frequently occurring droughts and floods. A yearly flood-drought cycle, while essential to their household economy based on rice and fisheries, renders rural poor livelihoods vulnerable to recurrent periods of food insecurity. This research demonstrates how a combination of publicly accessible Remote Sensing imagery and disaggregated poverty maps, within a comprehensive rural development framework, can provide an effective method to target pro-poor aquaculture development interventions at the local level. An agro-ecosystems analysis is performed in order to capture the seasonal dynamics of water- and aquatic resource exploitation. A holistic farming systems approach emphasises the potential of ponds in integrated rural smallholder systems to reduce poverty and vulnerability under rain fed conditions. A Geographic Information System (GIS), an efficient spatial inventory tool and decision support system in resolving real world problems, is used to identify where rural poor households can potentially benefit from the integration of aquaculture into existing production systems. A time series of satellite derived vegetation index data reveals distinct agro-ecosystem seasonality over large parts of the study area, which is indicative for farming systems under rain fed conditions. The developed methodology is capable of identifying functionally different agro-ecosystems. Socio-economic indicators for Cambodian parts of the lowland areas point to widespread rural poverty and vulnerability to recurrent food insecurity, which is directly related to agro-ecosystems seasonality and annual climate variability. Dependence of farming households on low productivity rain fed rice agro-ecosystems in Cambodia’s southern provinces is in stark contrast to the highly productive farming systems directly bordering it, in the freshwater fluvial zone of the Vietnamese Mekong Delta. A rapid increase in rice productivity in this densely populated area went hand-in hand with a considerable reduction in rural poverty. In this flood-prone but fertile area, resource competition and falling market prices of rice may have prompted the development of a range of integrated farming systems. The incorporation of ponds on farm in these systems facilitates reuse of nutrients from farm by-products for low-input aquatic resource production. In Northeast Thailand, crop production and low-input aquaculture have been successfully integrated along a tradition of water- and living aquatic resources management in farmer managed systems under resource poor conditions. A spatially linked commune level rural development database for Sisaket province in Northeast Thailand provides a useful framework for planning of aquaculture development through systems that are appropriate and relevant to local socio-economic and agro-ecological conditions. It was concluded that the socio-economic and agro-ecological context of rural poverty in Southeast Cambodia offers scope for similar pathways to improve rural wellbeing and reduce vulnerability to poverty and food insecurity by integrating aquatic resources development in pond based systems as part of an interdisciplinary approach towards rural development