The Global Streamflow Indices and Metadata Archive (GSIM) – Part 1: The production of a daily streamflow archive and metadata

Abstract

This is the first part of a two-paper series presenting the Global Streamflow Indices and Metadata archive (GSIM), a worldwide collection of metadata and indices derived from more than 35 000 daily streamflow time series. This paper focuses on the compilation of the daily streamflow time series based on 12 free-toaccess streamflow databases (seven national databases and five international collections). It also describes the development of three metadata products (freely available at https://doi.pangaea.de/10.1594/PANGAEA.887477):(1) a GSIM catalogue collating basic metadata associated with each time series, (2) catchment boundaries for the contributing area of each gauge, and (3) catchment metadata extracted from 12 gridded global data products representing essential properties such as land cover type, soil type, and climate and topographic characteristics. The quality of the delineated catchment boundary is also made available and should be consulted in GSIM application. The second paper in the series then explores production and analysis of streamflow indices. Having collated an unprecedented number of stations and associated metadata, GSIM can be used to advance large-scale hydrological research and improve understanding of the global water cycle. flow archive. Firstly, there are threats to the quantity of data, such as political sensitivities (Nelson, 2009), cost recovery and strict access policies (Hannah et al., 2011), unavailability in an electronic format, consistency of data formats, limited documentation, missing metadata, and a lack of resources for database maintenance and updating. Secondly, there are difficulties associated with the quality of the data in many regions, such as poor spatial coverage, poor quality control, variable quality control between regions, inconsistent metadata, imprecise geographic coordinates of the site, changes in the density of stream gauges, and variable record lengths. Lastly, even in locations where there are abundant and highquality streamflow observations, there can be questions over its utility in specific research such as climate sensitivity analysis due to the manifestation of human impacts -for example, urbanization, land-use changes, channelization, and upstream dams (Hannah et al., 2011).Published by Copernicus Publications.

The Global Streamflow Indices and Metadata Archive (GSIM) – Part 2: Quality control, time-series indices and homogeneity assessment

“…Until now, most relevant in situ observations have been held by national and regional authorities, and despite their best efforts, international data centres only have access to a small subset of the full observed record (Do et al, 2018a). This situation stands in contrast to the fact that monitoring data are increasingly being made publicly available through regional and national authorities (Do et al, 2018a).…”

“…Until now, most relevant in situ observations have been held by national and regional authorities, and despite their best efforts, international data centres only have access to a small subset of the full observed record (Do et al, 2018a). This situation stands in contrast to the fact that monitoring data are increasingly being made publicly available through regional and national authorities (Do et al, 2018a). In this paper series, we present an international collection of river and streamflow observations that covers more than 30 000 stations around the globe, highlighting the fact that these are among the best monitored variables of the terrestrial water cycle (Fekete et al, 2012(Fekete et al, , 2015Gudmundsson and Seneviratne, 2015;Hannah et al, 2011).…”

“…In this paper series, we present an international collection of river and streamflow observations that covers more than 30 000 stations around the globe, highlighting the fact that these are among the best monitored variables of the terrestrial water cycle (Fekete et al, 2012(Fekete et al, , 2015Gudmundsson and Seneviratne, 2015;Hannah et al, 2011). Part 1 of the paper series (Do et al, 2018a) documents the data-collection process together with a meta-database that allows users to recreate the collection from the original data sources. In addition, Part 1 of this paper series also presents auxiliary data including catchment boundaries delineated from global digital elevation models as well as selected properties (e.g.…”

“…While the data collection outlined in Part 1 (Do et al, 2018a) increases the spatial and temporal availability of streamflow records at the global scale, it is important to also consider the quality of the data. This is especially relevant for this merged data product combining information from several databases, which might have been set up with different objectives.…”

“…This is Part 2 of a two-paper series presenting the Global Streamflow Indices and Metadata Archive (GSIM), which is a collection of daily streamflow observations at more than 30 000 stations around the world. While Part 1 (Do et al, 2018a) describes the data collection process as well as the generation of auxiliary catchment data (e.g. catchment boundary, land cover, mean climate), Part 2 introduces a set of quality controlled time-series indices representing (i) the water balance, (ii) the seasonal cycle, (iii) low flows and (iv) floods.…”