Land surface modeling informed by earth observation data: toward understanding blue–green–white water fluxes in High Mountain Asia

Environmental Research Letters

High elevation headwater catchments are complex hydrological systems that seasonally buffer water and release it in the form of snow and ice melt, modulating downstream runoff regimes and water availability. In High Mountain Asia (HMA), where a wide range of climates from semi-arid to monsoonal exist, the importance of the cryospheric contributions to the water budget varies with the amount and seasonal distribution of precipitation. Losses due to evapotranspiration and sublimation are to date largely unquantified components of the water budget in such catchments, although they can be comparable in magnitude to glacier melt contributions to streamflow. Here, we simulate the hydrology of three high elevation headwater catchments in distinct climates in HMA over 10 years using an ecohydrological model geared towards high-mountain areas including snow and glaciers, forced with reanalysis data. Our …

Several geoengineering projects are designed to modify solar radiation to limit global warming. These changes in solar radiation can have impacts on ecohydrological systems which are poorly quantified. In this study, CMIP6 outputs were used to calculate sensitivities of global and local near-surface meteorological variables to solar radiation changes. These sensitivities were applied to the currently observed climate to perturb meteorological variables in response to changes in solar radiation. These new conditions were used as inputs to a mechanistic ecohydrological model (T&C) to analyze the partitioning and changes in energy and water fluxes and the response of vegetation productivity in different biomes and climates. Specifically, we run two simulation scenarios to understand the solar radiation impacts on ecohydrological systems. The first scenario focuses only on changes in solar radiation, while the …

EGUsphere

The potential implementation of future geoengineering projects alters solar radiation to counteract global warming trends. These changes could have effects on ecohydrological systems with impacts which are still poorly quantified. Here, we compute how changes in solar radiation affect global and local near surface meteorological variables by using CMIP6 scenario results and we compute climate sensitivities to solar radiation. These sensitivities are used to construct two sets of numerical experiments: the first focuses on solar radiation changes only, and the second systematically modifies precipitation, air temperature, specific humidity, and wind speed using the CMIP6 derived sensitivities to radiation changes, i.e., including its climate feedback. We use those scenarios as input to a mechanistic ecohydrological model to quantify the responses of the energy and water budget as well as vegetation productivity spanning different biomes and climates. In the absence of climate feedback, changes in solar radiation tend to reflect mostly in sensible heat changes, with minor effects on the hydrological cycle and vegetation productivity correlates linearly with changes in solar radiation. When climate feedback is included, changes in latent heat and hydrological variables are much more pronounced, mostly because of the temperature and vapor pressure deficit changes associated with solar radiation changes. Vegetation productivity tends to have an asymmetric response with a considerable decrease in gross primary production to a radiation reduction not accompanied by a similar increase with a radiation increase. These results provide important …

Remote Sensing

Flash droughts tend to cause severe damage to agriculture due to their characteristics of sudden onset and rapid intensification. Early detection of the response of vegetation to flash droughts is of utmost importance in mitigating the effects of flash droughts, as it can provide a scientific basis for establishing an early warning system. The commonly used method of determining the response time of vegetation to flash drought, based on the response time index or the correlation between the precipitation anomaly and vegetation growth anomaly, leads to the late detection of irreversible drought effects on vegetation, which may not be sufficient for use in analyzing the response of vegetation to flash drought for early earning. The evapotranspiration-based (ET-based) drought indices are an effective indicator for identifying and monitoring flash drought. This study proposes a novel approach that applies cross-spectral analysis to an ET-based drought index, i.e., Evaporative Stress Anomaly Index (ESAI), as the forcing and a vegetation-based drought index, i.e., Normalized Vegetation Anomaly Index (NVAI), as the response, both from medium-resolution remote sensing data, to estimate the time lag of the response of vegetation vitality status to flash drought. An experiment on the novel method was carried out in North China during March–September for the period of 2001–2020 using remote sensing products at 1 km spatial resolution. The results show that the average time lag of the response of vegetation to water availability during flash droughts estimated by the cross-spectral analysis over North China in 2001–2020 was 5.9 days, which is shorter than …

High-resolution Digital Elevation Model (DEM) data provides essential information for pluvial flood simulation. Although the increased accessibility and quality of publicly available DEM datasets can facilitate geospatial analysis at various scales, existing DEM datasets with global coverage mostly lack sufficient spatial resolution for pluvial flood simulations, which require detailed topographic information to be included in the simulation. Simulating flood scenarios with low-resolution DEMs (> 30m) can result in substantial deviations from real cases. This issue becomes even more severe for flood-prone areas in data-scarce developing countries.Image super-resolution is a technique for reconstructing low-resolution information into high-resolution data. Various deep-learning models have been employed for this task, primarily focusing on generating high-resolution natural-colour images. However, the effects of these …

Global Change Biology

The ascent of water from the soil to the leaves of vascular plants, described by the study of plant hydraulics, regulates ecosystem responses to environmental forcing and recovery from stress periods. Several approaches to model plant hydraulics have been proposed. In this study, we introduce four different versions of plant hydraulics representations in the terrestrial biosphere model T&C to understand the significance of plant hydraulics to ecosystem functioning. We tested representations of plant hydraulics, investigating plant water capacitance, and long‐term xylem damages following drought. The four models we tested were a combination of representations including or neglecting capacitance and including or neglecting xylem damage legacies. Using the models at six case studies spanning semiarid to tropical ecosystems, we quantify how plant xylem flow, plant water storage and long‐term xylem damage …

During dry and hot years in the Swiss Alps, melt water from glaciers can moderate streamflow deficits caused by reduced precipitation and enhanced evapotranspiration rates. However, little is known about how glacier melt water contribution to streamflow varies sub-seasonally and in space, especially further downstream from glacierized catchments, where additional streamflow contributions are modulated primarily by rainfall and the biosphere (vegetation, soils).We study distributed catchment hydrology in Switzerland using a land surface model that constrains energy and mass fluxes using advanced physical representations of both cryospheric and biospheric processes at a 250 m spatial resolution. We simulate catchment runoff in Switzerland during the past 6 years, including two recent severe drought years (2018 and 2022), characterized by particularly warm summers and reduced precipitation. The model is …

Global Change Biology

Wildfires are increasing in frequency, intensity, and extent globally due to climate change and they can alter forest composition, structure, and function. The destruction and subsequent regrowth of young vegetation can modify the ecosystem evapotranspiration and downstream water availability. However, the response of forest recovery on hydrology is not well known with even the sign of evapotranspiration and water yield changes following forest fires being uncertain across the globe. Here, we quantify the effects of forest regrowth after catastrophic wildfires on evapotranspiration and runoff in the world's tallest angiosperm forest (Eucalyptus regnans) in Australia. We combine eddy covariance measurements including pre‐ and post‐fire periods, mechanistic ecohydrological modeling and then extend the analysis spatially to multiple fires in eucalypt‐dominated forests in south‐eastern Australia by utilizing remote …

Urbanisation substantially alters the permeability of the land surface and modifies the vegetation cover extent and type. These landcover changes profoundly affect the hydrological and energy budget. While the role of urbanization on the local flood response has been extensively studied, its effect on the long-term hydrological budget is much less known as computing the latent heat flux (evapotranspiration) in urban areas is still challenging. However, knowledge on the urban hydrological budget is important as many cities are planning water sensitive urban designs and water harvesting could be key to support an increasing amount of urban vegetation.This study quantifies how urbanization changed the long-term hydrological budget of the island city state Singapore for the period between 1982 to 2021. To do so, we use two state-of-the-art mechanistic models which include all the major hydrological components …

Hydrology and Earth System Sciences Discussions

Evapotranspiration (ET) is critical for understanding the earth climate system and the complex heat/water exchange mechanisms between the land surface and the atmosphere in the high-altitude Tibetan Plateau (TP) region. However, the performance of ET products over TP has not been adequately assessed, and there is still significant uncertainty regarding the amount of water vapour released by the TP into the atmosphere, as well as its variation. In this study, we evaluated 22 ET products over TP by validating with the in-situ observations and basin-scale water balance estimations. This study also inter-compared their spatiotemporal variations and components to clarify the ET magnitude and variability in TP. The results showed that the remote sensing high-resolution global ET data from ETMonitor and PMLV2 demonstrated high accuracy comparable to the regional MOD16STM ET product, with overall better accuracy than other global ET data with fine spatial resolution (~1 km), when comparing with in-situ observation. Their accuracy was also presented when compared with the water balance-based ET at basin scale, which further indicated the overall accuracy of GLEAM and TerraClimate for the coarse-resolution ET products. Different products showed different spatiotemporal variation patterns, with large discrepancy occurring in the middle to western TP. The multiple-year averaged ET over TP by these products was found to have an average value (standard deviation) of 350.34 (42.46) mm/yr. The different components (plant transpiration, soil evaporation, canopy rainfall interception evaporation, open water evaporation, and snow/ice …

Allometric scaling relations are widely used to link biological processes in nature. They are typically expressed as power laws, postulating that the metabolic rate of an organism scales as its mass to the power of an allometric exponent, which ranges between 2/3 and 3/4. Several studies have shown that such scaling laws hold also for natural ecosystems, including individual trees and forests, riverine metabolism, and river network organization. Here, we focus on allometric relations at watershed scale to investigate “catchment metabolism”, defined as the set of ecohydrological and biogeochemical processes through which the catchment maintains its structure and reacts to the environment. By revising existing plant size-density relationships and integrating them across large-scale domains, we show that the ecohydrological fluxes (representative of metabolic rates of a large and diverse vegetation assemblage …

Quarterly Journal of the Royal Meteorological Society

Accurately predicting weather and climate in cities is critical for safeguarding human health and strengthening urban resilience. Multimodel evaluations can lead to model improvements; however, there have been no major intercomparisons of urban‐focussed land surface models in over a decade. Here, in Phase 1 of the Urban‐PLUMBER project, we evaluate the ability of 30 land surface models to simulate surface energy fluxes critical to atmospheric meteorological and air quality simulations. We establish minimum and upper performance expectations for participating models using simple information‐limited models as benchmarks. Compared with the last major model intercomparison at the same site, we find broad improvement in the current cohort's predictions of short‐wave radiation, sensible and latent heat fluxes, but little or no improvement in long‐wave radiation and momentum fluxes. Models with a …

Mountain regions, and the European Alps in particular, are warming faster than other land areas or the global average. The Alps are among the most sensitive terrestrial systems and have rapid and substantial responses to climate change. Consequently, the carbon cycle in high Alpine regions is expected to be significantly impacted by changes in vegetation cover and dynamics. Only a few studies offer insights into how vegetation types and carbon dynamics evolve at high elevation, considering changes in climate and soil conditions. We investigated changes in climate and soil nutrient development due to changes in vegetation type and cover amount using an ecohydrological model (T&C) and focused on the impacts of the changes on the carbon cycle in the Swiss Alps, where extensive glacier retreat is expected. Specifically, we used the Advanced Weather GENerator (AWE-GEN) model to simulate future …

Earth Science Informatics

This work presents an improved gravimetric algorithm to derive reference soil moisture, with removal of some of the hypothesis on which its original expression was based, and addition of a new corrective term that takes into account the interdependence between temperature and non-unitary water density. The temperature correction term improves reference measurements by up to 0.55% of their values in the temperature range 10–35℃. The temperature-corrected reference measurements were applied to the calibration of a hand-held soil moisture meter (Lutron PMS-714) for three soil texture types: medium, fine, and very fine. Linear regression models were used to calibrate the meter for each soil type, and the resulting calibration equations were validated with field data sampled from Sondu-Miriu watershed in Western Kenya. The validation produced errors (RMSE = 0.022, 0.010, 0.010 m3/m3) that are …

The Peruvian Andes contains the largest mass of glaciers in the tropics and these glaciers have shown considerable decay over the past 4 decades and into the present day. The historic and future runoff is tied to the cryospheric changes in the region and this could have important consequences for water resources, given the importance of snow and ice melt for dry season runoff. To disentangle the role of the cryosphere in the water cycle in the tropical Andes we run the fully distributed, hourly glacier-hydrological model TOPKAPI-ETH, both in the past (from 1987) and into the future over the upper Rio Santa catchment in the Cordillera Blanca. Meteorological forcing is provided by bias-corrected WRF simulations, which are also used for statistical downscaling of CMIP5 model projections to provide the future climatology. Calibration of model parameters is conducted using a step-wise approach using a wealth of …

Terrestrial ecosystems have been serving as a strong carbon sink that offsets one quarter of anthropogenic CO 2 emissions. Carbon use efficiency (CUE), the percentage of photosynthesized carbon that is available for biomass production and other secondary carbon products, is one factor determining the carbon sink size. The global variation in CUE remains unclear, however, as recent reports disagree over the responses of CUE to temperature, dryness, forest types and stand age, and there are limited direct observations to constrain the related uncertainty. Here, we propose to infer CUE from spatially distributed observations of land-atmosphere CO 2 exchange from global eddy covariance sites based on first principles of ecosystem respiration-photosynthesis coupling. Across 2737 site-years, CUE derived from eddy covariance observations is 0.43±0.11, consistent with previous inventory-based estimates (0.46±0.12, n= 244) but with a better representation of spatial-temporal variation in CUE. We find that CUE consistently decreases with temperature, precipitation, light availability and stand age, with a significant difference in the baseline CUE among biomes. Importantly, CUE of deciduous forests is typically 15% higher than that of evergreen forests, suggesting that over long-term deciduous forests are more efficient in using photosynthate. Our study advances the understanding of the global variation in CUE and provides new insights to guide best practices of forest conservation, management, and restoration for carbon sequestration.

Tropical forests account for approximately one-fourth of the global terrestrial carbon sink, playing an important role in the Earth’s carbon cycle. Importantly, mainland Southeast Asia has the densest vegetation surface but its ecohydrology is historically understudied due to the paucity of field observations and modelling studies. Leveraging on existing flux tower data, remote sensing products, and the mechanistic ecohydrological model T&C, we provide an enhanced understanding of carbon and water exchanges in mainland Southeast Asia. The T&C model is tested to reproduce various ecosystem types of Southeast Asia, including tropical evergreen forests, subtropical deciduous forests, savannas, rubber plantations, and rice fields. The flux tower data including gross primary productivity (GPP) and evapotranspiration (ET) along with remote sensing data of leaf area index and other vegetation indexes, allow us to …

Geo-spatial Information Science

As a key climate variable, soil moisture plays a crucial role in drought detection, flood warning, and crop yield prediction. In recent years, the demand for high-spatial-resolution soil moisture has increased, particularly in environmental management. In this study, Copernicus Sentinel-1 synthetic aperture radar data, Sentinel-2 multi-spectral data, and other auxiliary data (land cover types, soil texture, etc.) were used to retrieve surface soil moisture (10 m) in the cloud environment (Google Earth Engine + Google Colab + Google Drive) over the Tibetan Plateau, and an entirely data-driven machine learning-based model called Deep Forest was adopted. We discussed the application of the Deep Forest model and compared it with other machine learning models. Overall, on the basis of 10-fold cross-validation, the modified Deep Forest model performed the best, with estimate accuracy of 0.834 and 0.038 m3·m−3 in terms …

Geo-Spatial Information Science

Remote sensing provides us with an approach for the rapid identification and monitoring of spatiotemporal changes in the urban ecological environment at different scales. This study aimed to construct a remote sensing assessment index for urban ecological livability with continuous fine spatiotemporal resolution data from Landsat and MODIS to overcome the dilemma of single image-based, single-factor analysis, due to the limitations of atmospheric conditions or the revisit period of satellite platforms. The proposed Ecological Livability Index (ELI) covers five primary ecological indicators – greenness, temperature, dryness, water-wetness, and atmospheric turbidity – which are geometrically aggregated by non-equal weights based on an entropy method. Considering multisource time-series data of each indicator, the ELI can quickly and comprehensively reflect the characteristics of the Ecological Livability Quality …

Geo-spatial Information Science

Accurate estimation of Timber Product Output (TPO) is important for carbon budget accounting, since wood products can act as delayed release carbon pools. However, the existing timber harvest data in the US relies on Forest Service’s TPO survey, and the survey does not happen every year. In this study, we proposed a methodological framework to produce annual TPO volume estimates for seven southeastern states (North Carolina, South Carolina, Alabama, Florida, Georgia, Mississippi, and Tennessee) of the US by integrating TPO survey data, Landsat Time Series Stacks (LTSS), and National Land Cover Database (NLCD). First, a forest disturbance product was derived based on Vegetation Change Tracker (VCT) algorithm using LTSS from 1985 to 2016. Then, by linking the predictor variables derived from the disturbance data and the TPO survey data, two regression algorithms were tested and compared …

Geo-Spatial Information Science

Mixed reality technology has been increasingly used for navigation. While most MR-based navigation systems are currently based on hand-held devices, for example, smartphones, head-mounted MR devices have become more and more popular in navigation. Much research has been conducted to investigate the navigation experience in MR. However, it is still unclear how ordinary users react to the first-person view and FOV (field of view)-limited navigation experience, especially in terms of spatial learning. In our study, we investigate how visualization in MR navigation affects spatial learning. More specifically, we test two related hypotheses: incorrect virtual information can lead users into incorrect spatial learning, and the visualization style of direction can influence users’ spatial learning and experience. We designed a user interface in Microsoft HoloLens 2 and conducted a user study with 40 participants. The …

Geo-spatial Information Science

Validation studies of global Digital Elevation Models (DEMs) in the existing literature are limited by the diversity and spread of landscapes, terrain types considered and sparseness of groundtruth. Moreover, there are knowledge gaps on the accuracy variations in rugged and complex landscapes, and previous studies have often not relied on robust internal and external validation measures. Thus, there is still only partial understanding and limited perspective of the reliability and adequacy of global DEMs for several applications. In this study, we utilize a dense spread of LiDAR groundtruth to assess the vertical accuracies of four medium-resolution, readily available, free-access and global coverage 1 arc-second (30 m) DEMs: NASADEM, ASTER GDEM, Copernicus GLO-30, and ALOS World 3D (AW3D). The assessment is carried out at landscapes spread across Cape Town, Southern Africa (urban/industrial …

Geo-spatial Information Science

The accurate three-dimensional wind field obtained from a Doppler lidar not only helps to comprehend the refined structure of complex airflow but also provides important and valuable solutions for many fields. However, the underlying homogeneity assumption of the typical wind retrieval methods, such as Doppler Beam Swinging (DBS) and Velocity Azimuth Display (VAD) based on a single-lidar, will introduce the measurement uncertainty in complex terrain. In this paper, a new design of a wind measurement campaign involving seven lidars was carried out, which contained the three-lidar-based Virtual Tower (VT) using a time-space synchronization technique and four single-lidars with different elevation angles. This study investigates the performance of VT and VAD measurements under various conditions and evaluates the sensitivity of wind measurement uncertainty of VAD to the horizontal spatial- and probe …

Geo-Spatial Information Science

Stone Pine (Pinus pinea L.) is currently the pine species with the highest commercial value with edible seeds. In this respect, this study introduces a new methodology for extracting Stone Pine trees from Digital Surface Models (DSMs) generated through an Unmanned Aerial Vehicle (UAV) mission. We developed a novel enhanced probability map of local maxima that facilitates the computation of the orientation symmetry by means of new probabilistic local minima information. Four test sites are used to evaluate our automated framework within one of the most important Stone Pine forest areas in Antalya, Turkey. A Hand-held Mobile Laser Scanner (HMLS) was utilized to collect the reference point cloud dataset. Our findings confirm that the proposed methodology, which uses a single DSM as an input, secures overall pixel-based and object-based F1-scores of 88.3% and 97.7%, respectively. The overall median …

Geo-spatial Information Science

Landform mapping is the initial step of many geomorphological analyses (e.g. assessment of natural hazards and natural resources) and requires vast resources to be applied to wide areas at high-resolution. Among geomorphological objects, we focus on glacial moraine mapping, since it is a task relevant to many fields (e.g. paleoclimate and glacial geomorphology). Here we proposed to exploit the potential of Deep Learning-based approaches to map moraine landforms by exploiting multi-source remote sensing imagery. To this end, we propose the first Deep Learning model to map glacial moraines, namely MorNet. As multi-source remote sensing information, we combine together three different sources: Topographic (Pleiades-derived DSM), Multispectral (Sentinel-2), and SAR (Sentinel-1) data. To cope with such heterogeneous information, the proposed model has a dedicated branch for each input source …

Geo-spatial Information Science

OpenStreetMap (OSM) is a dataset in constant change and this dynamic needs to be better understood. Based on 12-year time series of seven OSM data contribution activities extracted from 20 large cities worldwide, we investigate the temporal dynamic of OSM data production, more specifically, the auto- and cross-correlation, temporal trend, and annual seasonality of these activities. Furthermore, we evaluate and compare nine different temporal regression methods for forecasting such activities in horizons of 1–4 weeks. Several insights could be obtained from our analyses, including that the contribution activities tend to grown linearly in a moderate intra-annual cycle. Also, the performance of the temporal forecasting methods shows that they yield in general more accurate estimations of future contribution activities than a baseline metric, i.e. the arithmetic average of recent previous observations. In particular, the …

Geo-spatial Information Science

Polarimetric calibration is essential for the pre-processing of Polarimetric Synthetic Aperture Radar (PolSAR) data because it effectively mitigates polarimetric distortions in the measured PolSAR data. Traditional methods of polarimetric calibration employ man-made calibrators that offer high accuracy. However, the frequency of calibration is often limited due to the labor-intensive and time-consuming nature of deploying such calibrators. Some polarimetric calibration methods based on distributed targets in nature enable more frequent calibration. Nevertheless, these methods are constrained by the availability of specific distributed targets with known polarimetric properties for estimating parameters related to co-polarization channel imbalance (co-pol-imba) parameters. If distributed targets are not appropriately selected or suitable targets are absent within the image scene, the accuracy of calibration will be …

Geo-Spatial Information Science

Mixed reality technology has been increasingly used for navigation. While most MR-based navigation systems are currently based on hand-held devices, for example, smartphones, head-mounted MR devices have become more and more popular in navigation. Much research has been conducted to investigate the navigation experience in MR. However, it is still unclear how ordinary users react to the first-person view and FOV (field of view)-limited navigation experience, especially in terms of spatial learning. In our study, we investigate how visualization in MR navigation affects spatial learning. More specifically, we test two related hypotheses: incorrect virtual information can lead users into incorrect spatial learning, and the visualization style of direction can influence users’ spatial learning and experience. We designed a user interface in Microsoft HoloLens 2 and conducted a user study with 40 participants. The …

Geo-Spatial Information Science

Remote sensing provides us with an approach for the rapid identification and monitoring of spatiotemporal changes in the urban ecological environment at different scales. This study aimed to construct a remote sensing assessment index for urban ecological livability with continuous fine spatiotemporal resolution data from Landsat and MODIS to overcome the dilemma of single image-based, single-factor analysis, due to the limitations of atmospheric conditions or the revisit period of satellite platforms. The proposed Ecological Livability Index (ELI) covers five primary ecological indicators – greenness, temperature, dryness, water-wetness, and atmospheric turbidity – which are geometrically aggregated by non-equal weights based on an entropy method. Considering multisource time-series data of each indicator, the ELI can quickly and comprehensively reflect the characteristics of the Ecological Livability Quality …

Geo-spatial Information Science

Validation studies of global Digital Elevation Models (DEMs) in the existing literature are limited by the diversity and spread of landscapes, terrain types considered and sparseness of groundtruth. Moreover, there are knowledge gaps on the accuracy variations in rugged and complex landscapes, and previous studies have often not relied on robust internal and external validation measures. Thus, there is still only partial understanding and limited perspective of the reliability and adequacy of global DEMs for several applications. In this study, we utilize a dense spread of LiDAR groundtruth to assess the vertical accuracies of four medium-resolution, readily available, free-access and global coverage 1 arc-second (30 m) DEMs: NASADEM, ASTER GDEM, Copernicus GLO-30, and ALOS World 3D (AW3D). The assessment is carried out at landscapes spread across Cape Town, Southern Africa (urban/industrial …

Geo-spatial Information Science

With the recent increase in studies on spatial heterogeneity, geographically weighted (GW) models have become an essential set of local techniques, attracting a wide range of users from different domains. In this study, we demonstrate a newly developed standalone GW software, GWmodelS using a community-level house price data set for Wuhan, China. In detail, a number of fundamental GW models are illustrated, including GW descriptive statistics, basic and multiscale GW regression, and GW principle component analysis. Additionally, functionality in spatial data management and batch mapping are presented as essential supplementary activities for GW modeling. The software provides significant advantages in terms of a user-friendly graphical user interface, operational efficiency, and accessibility, which facilitate its usage for users from a wide range of domains.

Geo-spatial Information Science

Multiple Geographical Feature Label Placement (MGFLP) has been a fundamental problem in geographic information visualization for decades. Moreover, the nature of label positioning has proven to be an Nondeterministic polynomial-time hard (NP-hard) problem. Although advances in computer technology and robust approaches have addressed the problem of label positioning, the lengthy running time of MGFLP has not been a major focus of recent studies. Based on a hybrid of the fixed-position and sliding models, a Message Passing Interface (MPI) parallel genetic algorithm is proposed in the present study for MGFLP to label mixed types of geographical features. To evaluate the quality of label placement, a quality function is defined based on four quality metrics: label-feature conflict; label-label conflict; label association with the corresponding feature; label position priority for all three types of features. The …

Geo-spatial Information Science

Mountains are important suppliers of freshwater to downstream areas, affecting large populations in particular in High Mountain Asia (HMA). Yet, the propagation of water from HMA headwaters to downstream areas is not fully understood, as interactions in the mountain water cycle between the cryo-, hydro- and biosphere remain elusive. We review the definition of blue and green water fluxes as liquid water that contributes to runoff at the outlet of the selected domain (blue) and water lost to the atmosphere through vapor fluxes, that is evaporation from water, ground, and interception plus transpiration (green) and propose to add the term white water to account for the (often neglected) evaporation and sublimation from snow and ice. We provide an assessment of models that can simulate the cryo-hydro-biosphere continuum and the interactions between spheres in high mountain catchments, going beyond …

Geo-spatial Information Science

Digital Elevation Model (DEM) errors tend to be spatially correlated, inevitably affecting DEM-based topographic change detection. Traditional topographic change detection methods often ignore the spatial distribution of the DEM error. This paper aims to develop a workflow that considers the spatial autocorrelation of the error in topographic change detection. Firstly, the DEM of Difference (DoD) is obtained from two-period DEMs, and the Monte Carlo method is employed to evaluate the Spatially Distributed Errors (SDE) in DEMs. Secondly, DoD errors are calculated by propagation based on spatially distributed DEM errors. At the same time, its spatial distribution is quantified using the semi-variance function. Finally, topographic changes (erosion, deposition, and net changes) are calculated based on the spatial distribution analysis and significance detection. The results in two small catchments indicate that DEM …

Geo-spatial Information Science

Megaregion has emerged as a global urban form, typically based on the polycentric strategy to enhance regional development. How to measure megaregional spatial structure and discriminate different roles of cities has become increasingly important to enrich the knowledge of the formation of a megaregion. Meanwhile, various indices have been used to identify vital nodes in the field of complex network. Which indices, however, are suitable for megaregion analysis remain unsolved. To address this requirement, this study first reviewed the typical indices for identifying vital nodes in the complex network theory, and pointed out that in a weighted city network scenario, weighted degree centrality, hub & authority score, and S-core decomposition (which represent network centrality, connectivity, and structures, respectively) are suitable for analyzing megaregional spatial structures. Then, we explored the city …

Geo-spatial Information Science

Mountains are important suppliers of freshwater to downstream areas, affecting large populations in particular in High Mountain Asia (HMA). Yet, the propagation of water from HMA headwaters to downstream areas is not fully understood, as interactions in the mountain water cycle between the cryo-, hydro- and biosphere remain elusive. We review the definition of blue and green water fluxes as liquid water that contributes to runoff at the outlet of the selected domain (blue) and water lost to the atmosphere through vapor fluxes, that is evaporation from water, ground, and interception plus transpiration (green) and propose to add the term white water to account for the (often neglected) evaporation and sublimation from snow and ice. We provide an assessment of models that can simulate the cryo-hydro-biosphere continuum and the interactions between spheres in high mountain catchments, going beyond …

Geo-spatial Information Science

GraCT and ContaCT were the first compressed data structures to represent object trajectories, demonstrating that it was possible to use orders of magnitude less space than classical indexes while staying competitive in query times. In this paper we considerably enhance their space, query capabilities, and time performance with three contributions. (1) We design and evaluate algorithms for more sophisticated nearest neighbor queries, finding the trajectories closest to a given trajectory or to a given point during a time interval. (2) We modify the data structure used to sample the spatial positions of the objects along time. This improves the performance on the classic spatio-temporal and the nearest neighbor queries, by orders of magnitude in some cases. (3) We introduce RelaCT, a tradeoff between the faster and larger ContaCT and the smaller and slower GraCT, offering a new relevant space-time tradeoff for large …