Global River Topology (GRIT)

The Global River Topology (GRIT) is a vector-based, global river network that not only represents the tributary components of the global drainage network but also the distributary ones, including multi-thread rivers, canals and delta distributaries. It is also the first global hydrography (excl. Antarctica and Greenland) produced at 30m raster resolution. It is created by merging Landsat-based river mask (GRWL) with elevation-generated streams to ensure a homogeneous drainage density outside of the river mask (rivers narrower than approx. 30m). Crucially, it uses a new 30m digital terrain model (FABDEM, based on TanDEM-X) that shows greater accuracy over the traditionally used SRTM derivatives. After vectorisation and pruning, directionality is assigned by a combination of elevation, flow angle, heuristic and continuity approaches (based on RivGraph). The network topology (lines and nodes, upstream/downstream IDs) is available as layers and attribute information in the GeoPackage files (readable by QGIS/ArcMap/GDAL). A map of GRIT segments labelled with OSM river names is available here: https://michelwortmann.com/research/gritv05-segments-river-names/ Regions Vector files are provided in 7 regions with the following codes: AF - Africa AS - Asia (excl. Siberia) EU - Europe NA - North America SA - South America SI - Siberia SP - South Pacific/Australia The domain polygons (GRITv06_domain_GLOBAL.gpkg.zip) provide 60 subcontinental catchment groups that are available as vector attributes. They allow for more fine-grained subsetting of data (e.g. with ogr2ogr --where and the domain attribute). Vector files are provided both in the original equal-area Equal Earth Greenwich projection (EPSG:8857) as well as in geographic WGS84 coordinates (EPSG:4326). Change log v0.6 - 2024-05-30 Rivers/streams outside of the GRWL mask forced by all OSM water lines (not only those with waterway=river/canal) Some manual directions in the Irrawaddy delta and fixed erronous sink in the Volga delta v0.5 - 2024-02-14 Cyclicity and discontinuities resolved through improved algorithms, bug fixes, more sophisticated cycle solving algorithms and some manually forced directions. Only insignificant cycles (non-sinks, less than 50) were removed. Added segment and reach attributes Computational domain fixes Segments include OSM river names Asia domain split into Siberia and rest of Asia Vector files available in EPSG:8857 and EPSG:4326 v0.4 - 2023-03-11 First globally complete dataset published Network segments Lines between inlet, outlet, confluence and bifurcation nodes. Files have lines and nodes layers. Attribute description of lines layer Name Data type Description cat integer domain internal feature ID global_id integer global river segment ID, same as FID catchment_id integer global catchment ID upstream_node_id integer global segment node ID at upstream end of line downstream_node_id integer global segment node ID at downstream end of line upstream_line_ids text comma-separated list of global river segment IDs connecting at upstream end of line downstream_line_ids text comma-separated list of global river segment IDs connecting at downstream end of line direction_algorithm float code of RivGraph method used to set the direction of line width_adjusted float median river width in m without accounting for width of segments connecting upstream/downstream length_adjusted float segment length in m without accounting for width of segments connecting upstream/downstream in m is_mainstem integer 1 if widest segment of bifurcated flow or no bifurcation upstream, otherwise 0 strahler_order integer Strahler order of segment, can be used to route in topological order length float segment length in m azimuth float direction of line connecting upstream-downstream nodes in degrees from North sinuousity float ratio of Euclidean distance between upstream-downstream nodes and line length, i.e. 1 meaning a perfectly straight line drainage_area_in float drainage area at beginning of segment, partitioned by width at bifurcations, in km2 drainage_area_out float drainage area at end of segment, partitioned by width at bifurcations, in km2 drainage_area_mainstem_in float drainage area at beginning of segment, following the mainstem, in km2 drainage_area_mainstem_out float drainage area at end of segment, following the mainstem, in km2 bifurcation_balance_out float (drainage_area_out - drainage_area_mainstem_out) / max(drainage_area_out, drainage_area_mainstem_out), dimensionless ratio grwl_overlap float fraction of the segment overlapping with the GRWL river mask grwl_value integer dominant GRWL value of segment name text river name from Openstreetmap where available, English preferred name_local text river name from Openstreetmap where available, local name n_bifurcations_upstream integer number of bifurcations upstream of segment domain text catchment group ID, see domain index file Attribute description of nodes layer Name Data type Description cat integer domain internal feature ID global_id integer global river node ID, same as FID catchment_id integer global catchment ID upstream_line_ids text comma-separated list of global river segment IDs flowing into node downstream_line_ids text comma-separated list of global river segment IDs flowing out of node node_type text description of node, one of bifurcation, confluence, inlet, coastal_outlet, sink_outlet, grwl_change grwl_value integer GRWL code at node grwl_transition text GRWL codes of change at grwl_change nodes cycle integer >0 if segment is part of an unresolved cycle, 0 otherwise continuity_violated integer 1 if flow continuity is violated, otherwise 0 drainage_area float drainage area, partitioned by width at bifurcations, in km2 drainage_area_mainstem float drainage area, following the mainstem, in km2 n_bifurcations_upstream integer number of bifurcations upstream of node domain text catchment group, see domain index file Network reaches Segment lines split to not exceed 1km in length, i.e. these lines will be shorter than 1km and longer than 500m unless the segment is shorter. A simplified version with no vertices between nodes is also provided. Files have lines and nodes layers. Attribute description of lines layer Name Data type Description cat integer domain internal feature ID segment_id integer global segment ID of reach global_id integer global river reach ID, same as FID catchment_id integer global catchment ID upstream_node_id integer global reach node ID at upstream end of line downstream_node_id integer global reach node ID at downstream end of line upstream_line_ids text comma-separated list of global river reach IDs connecting at upstream end of line downstream_line_ids text comma-separated list of global river reach IDs connecting at downstream end of line grwl_overlap float fraction of the reach overlapping with the GRWL river mask grwl_value integer dominant GRWL value of node grwl_width_median float median width of the GRWL river mask, meters grwl_width_std float standard deviation of width of the GRWL river mask, meters length float length of reach in meters sinuousity float ratio of eucledian distance betwen upstream-downstream nodes and line length, i.e. 1 meaning a perfectly straight line azimuth float direction of line connecting upstream-downstream nodes in degrees from North domain text catchment group, see domain index file Attribute description of nodes layer Name Data type Description cat integer domain internal feature ID segment_node_id integer global ID of segment node at segment intersections, otherwise blank n_segments integer number of segments attached to node global_id integer global river reach node ID, same as FID upstream_line_ids text comma-separated list of global river reach IDs flowing into node downstream_line_ids text comma-separated list of global river reach IDs flowing out of node domain text catchment group, see domain index file Catchments Catchment outlines for entire river basins (network components, including coastal drainage areas). Catchments for segments (aka. subbasins) and reaches are also available on request. Attribute description Name Data type Description cat integer domain internal feature ID global_id integer global catchment ID, same as global_id of segment/reach ID if is_coastal == 0 for respective catchments or the catchment_id for component_catchments, same as FID area float catchment area in km2 is_coastal integer 1 for coastal drainage areas, 0 otherwise domain text catchment group, see domain index file Raster Upstream drainage area and other raster-based products are also available upon request.

全球河流拓扑（Global River Topology, GRIT）是一套基于矢量的全球河网数据集，不仅涵盖全球排水网络的支流组分，还包含分流系统——包括多河道河流、运河及三角洲分流河道。它也是首套以30米栅格分辨率制作的全球水文数据集（不含南极洲与格陵兰岛）。

该数据集通过融合基于Landsat的河流掩膜产品（GRWL）与高程生成的水系，确保在河流掩膜外（即宽度约小于30米的河道）拥有均匀的排水密度。尤为关键的是，它采用了新型30米数字地形模型（FABDEM，基于TanDEM-X构建），相较于传统使用的SRTM衍生产品具备更高精度。

经过矢量化与修剪后，结合高程、流向角、启发式算法及连续性方法（基于RivGraph）为河网赋予流向属性。河网拓扑结构（包括线要素与节点要素、上下游ID）以图层与属性信息的形式存储于GeoPackage文件中（可通过QGIS/ArcMap/GDAL读取）。

带有OpenStreetMap（OSM）河流名称标注的GRIT河段地图可访问：https://michelwortmann.com/research/gritv05-segments-river-names/

数据集按7个区域提供矢量文件，编码如下：
AF：非洲
AS：亚洲（不含西伯利亚）
EU：欧洲
NA：北美洲
SA：南美洲
SI：西伯利亚
SP：南太平洋/澳大利亚

域多边形文件（GRITv06_domain_GLOBAL.gpkg.zip）包含60个次大陆集水区分组，以矢量属性形式存储，可实现更精细的数据子集提取（例如通过ogr2ogr的--where参数结合域属性进行筛选）。

矢量文件同时提供原始等面积Equal Earth格林威治投影（EPSG:8857）以及地理坐标系WGS84（EPSG:4326）两种格式。

## 更新日志
### v0.6 - 2024-05-30
1. 将GRWL掩膜外的河道/溪流纳入所有OSM水线（而非仅waterway=river/canal类型）；
2. 修复伊洛瓦底江三角洲的部分手动流向，并修正伏尔加河三角洲的错误汇流点。

### v0.5 - 2024-02-14
1. 通过改进算法、漏洞修复与更成熟的循环求解算法解决了河网环与不连续问题，仅移除非汇点且数量少于50个的无关循环；
2. 新增河段与路径属性，包含OpenStreetMap河流名称的河段数据；
3. 修正计算域，将亚洲域拆分为西伯利亚与亚洲其余区域；
4. 提供EPSG:8857与EPSG:4326两种投影格式的矢量文件。

### v0.4 - 2023-03-11
发布首套全球完整数据集。

## 网络河段
指入口、出口、汇流与分流节点之间的线要素。文件包含线要素与节点要素图层。

### 线要素图层属性说明
| 字段名 | 数据类型 | 描述 |
| ---- | ---- | ---- |
| cat | 整数型 | 域内部要素ID |
| global_id | 整数型 | 全球河段ID，与FID一致 |
| catchment_id | 整数型 | 全球集水区ID |
| upstream_node_id | 整数型 | 线段上游端的全球河段节点ID |
| downstream_node_id | 整数型 | 线段下游端的全球河段节点ID |
| upstream_line_ids | 文本型 | 以逗号分隔的上游连接河段的全球ID列表 |
| downstream_line_ids | 文本型 | 以逗号分隔的下游连接河段的全球ID列表 |
| direction_algorithm | 浮点型 | 用于确定线段流向的RivGraph方法代码 |
| width_adjusted | 浮点型 | 未计入上下游连接河段宽度的河道中位宽度（单位：米） |
| length_adjusted | 浮点型 | 未计入上下游连接河段宽度的河段长度（单位：米） |
| is_mainstem | 整数型 | 若为分流河道中最宽的河段，或上游无分流，则取值为1，否则为0 |
| strahler_order | 整数型 | 河段的斯特拉勒（Strahler）级数，可用于按拓扑顺序进行路径追踪 |
| length | 浮点型 | 河段长度（单位：米） |
| azimuth | 浮点型 | 连接上下游节点的线段方位角，以正北为0度，单位：度 |
| sinuosity | 浮点型 | 上下游节点间欧氏距离与线段长度的比值，取值为1代表完全直线 |
| drainage_area_in | 浮点型 | 河段起点处的集水面积（按分流处河道宽度分配），单位：平方千米 |
| drainage_area_out | 浮点型 | 河段终点处的集水面积（按分流处河道宽度分配），单位：平方千米 |
| drainage_area_mainstem_in | 浮点型 | 沿主干流方向的河段起点处集水面积，单位：平方千米 |
| drainage_area_mainstem_out | 浮点型 | 沿主干流方向的河段终点处集水面积，单位：平方千米 |
| bifurcation_balance_out | 浮点型 | (drainage_area_out - drainage_area_mainstem_out) / max(drainage_area_out, drainage_area_mainstem_out)，无量纲比值 |
| grwl_overlap | 浮点型 | 河段与GRWL河流掩膜的重叠比例 |
| grwl_value | 整数型 | 河段的主导GRWL值 |
| name | 文本型 | 若有可用数据，为来自OpenStreetMap的河流名称，优先使用英文名称 |
| name_local | 文本型 | 若有可用数据，为来自OpenStreetMap的河流本地语言名称 |
| n_bifurcations_upstream | 整数型 | 河段上游的分流数量 |
| domain | 文本型 | 集水区分组ID，详见域索引文件 |

### 节点要素图层属性说明
| 字段名 | 数据类型 | 描述 |
| ---- | ---- | ---- |
| cat | 整数型 | 域内部要素ID |
| global_id | 整数型 | 全球河流节点ID，与FID一致 |
| catchment_id | 整数型 | 全球集水区ID |
| upstream_line_ids | 文本型 | 以逗号分隔的流入该节点的河段全球ID列表 |
| downstream_line_ids | 文本型 | 以逗号分隔的流出该节点的河段全球ID列表 |
| node_type | 文本型 | 节点类型，可选值为分流、汇流、入口、海岸出口、汇点出口、GRWL变化节点 |
| grwl_value | 整数型 | 节点处的GRWL代码 |
| grwl_transition | 文本型 | GRWL变化节点处的GRWL代码变化情况 |
| cycle | 整数型 | 若节点属于未求解循环则取值>0，否则为0 |
| continuity_violated | 整数型 | 若存在流量连续性违反情况则取值为1，否则为0 |
| drainage_area | 浮点型 | 节点处的集水面积（按分流处河道宽度分配），单位：平方千米 |
| drainage_area_mainstem | 浮点型 | 沿主干流方向的节点处集水面积，单位：平方千米 |
| n_bifurcations_upstream | 整数型 | 节点上游的分流数量 |
| domain | 文本型 | 集水区分组，详见域索引文件 |

## 网络路径
指被拆分至长度不超过1千米的河段线段，即此类线段长度介于500米至1千米之间，若原始河段更短则不受此限制。同时提供无节点间顶点的简化版本。文件包含线要素与节点要素图层。

### 线要素图层属性说明
| 字段名 | 数据类型 | 描述 |
| ---- | ---- | ---- |
| cat | 整数型 | 域内部要素ID |
| segment_id | 整数型 | 对应路径所属的全球河段ID |
| global_id | 整数型 | 全球路径ID，与FID一致 |
| catchment_id | 整数型 | 全球集水区ID |
| upstream_node_id | 整数型 | 路径上游端的全球路径节点ID |
| downstream_node_id | 整数型 | 路径下游端的全球路径节点ID |
| upstream_line_ids | 文本型 | 以逗号分隔的上游连接路径的全球ID列表 |
| downstream_line_ids | 文本型 | 以逗号分隔的下游连接路径的全球ID列表 |
| grwl_overlap | 浮点型 | 路径与GRWL河流掩膜的重叠比例 |
| grwl_value | 整数型 | 节点处的主导GRWL值 |
| grwl_width_median | 浮点型 | GRWL河流掩膜的河道中位宽度（单位：米） |
| grwl_width_std | 浮点型 | GRWL河流掩膜的河道宽度标准差（单位：米） |
| length | 浮点型 | 路径长度（单位：米） |
| sinuosity | 浮点型 | 上下游节点间欧氏距离与线段长度的比值，取值为1代表完全直线 |
| azimuth | 浮点型 | 连接上下游节点的线段方位角，以正北为0度，单位：度 |
| domain | 文本型 | 集水区分组，详见域索引文件 |

### 节点要素图层属性说明
| 字段名 | 数据类型 | 描述 |
| ---- | ---- | ---- |
| cat | 整数型 | 域内部要素ID |
| segment_node_id | 整数型 | 河段节点相交处的全球ID，无相交情况则为空 |
| n_segments | 整数型 | 附着于该节点的河段数量 |
| global_id | 整数型 | 全球路径节点ID，与FID一致 |
| upstream_line_ids | 文本型 | 以逗号分隔的流入该节点的路径全球ID列表 |
| downstream_line_ids | 文本型 | 以逗号分隔的流出该节点的路径全球ID列表 |
| domain | 文本型 | 集水区分组，详见域索引文件 |

## 集水区
包含完整河流流域（网络组分，含沿海排水区）的集水轮廓。针对河段（又称子流域）与路径的集水区可按需获取。

集水区属性说明
| 字段名 | 数据类型 | 描述 |
| ---- | ---- | ---- |
| cat | 整数型 | 域内部要素ID |
| global_id | 整数型 | 全球集水区ID，若对应集水区的is_coastal=0则与河段/路径的global_id一致，若为组分集水区则与catchment_id一致，与FID一致 |
| area | 浮点型 | 集水区面积（单位：平方千米） |
| is_coastal | 整数型 | 沿海排水区取值为1，内陆排水区取值为0 |
| domain | 文本型 | 集水区分组，详见域索引文件 |

## 栅格产品
上游集水面积及其他基于栅格的产品可按需获取。