Abstract

Against the backdrop of global change, both in terms of climate and demography, there is a pressing need for monitoring the global water cycle. The publicly available global database is very limited in its spatial and temporal coverage worldwide. Moreover, the acquisition of in situ data and their delivery to the database are in decline since the late 1970s, be it for economical or political reasons. Given the insufficient monitoring from in situ gauge networks, and with no outlook for improvement, spaceborne approaches have been under investigation for some years now. Satellite-based Earth observation with its global coverage and homogeneous accuracy has been demonstrated to be a potential alternative to in situ measurements. This paper presents HydroSat as a repository of global water cycle products from spaceborne geodetic sensors. HydroSat provides time series and their uncertainty of: water level from satellite altimetry, surface water extent from satellite imagery, terrestrial water storage anomaly from satellite gravimetry, lake and reservoir water storage anomaly from a combination of satellite altimetry and imagery, and river discharge from either satellite altimetry or imagery. These products can contribute to understanding the global water cycle within the Earth system in several ways. They can act as inputs to hydrological models, they can play a complementary role to current and future spaceborne observations, and they can define indicators of the past and future state of the global freshwater system. The repository is publicly available through http://hydrosat.gis.uni-stuttgart.de.

Highlights

  • To understand the global hydrological cycle and the Earth system in general, measurements are needed to estimate storages and fluxes on a spatial scale from local to continental, and on a temporal scale sufficient to resolve even diurnal variations (Lettenmaier, 2006)

  • 485 The development of repositories and services to provide global water cycle products from spaceborne sensors is getting more attention than ever before, which is motivated by the urgent need for more hydrological evidence, the absence of perspective for improving in situ data, the existence of an abundance of satellite missions, the prospect of cutting-edge missions such as the SWOT mission, and the promise of operational satellites in space

  • Such products support studies focused on understanding the water cycle and the Earth system in general

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Summary

Introduction

To understand the global hydrological cycle and the Earth system in general, measurements are needed to estimate storages and fluxes on a spatial scale from local to continental, and on a temporal scale sufficient to resolve even diurnal variations (Lettenmaier, 2006). This necessity arises from the above mentioned limited knowledge of the spatial and temporal dynamics of the freshwater variations and fluxes (Sneeuw et al, 2014) Given such a pressing need, spaceborne geodetic sensors, with their global coverage and homogeneous accuracy, are viable choices over in situ measurements. HydroSat hosts global water cycle products from spaceborne sensors: 1) surface 60 water extent of lakes and rivers, 2) water level of inland water bodies, 3) water storage anomaly of hydrological basins, lakes and reservoirs, and 4) river discharge for large and small rivers. These products are the results of research studies and projects on the application of spaceborne geodetic sensors for hydrology conducted at the Institute of Geodesy (GIS), University of Stuttgart. Some representative examples are given to support the product description

Inland water level from satellite altimetry
Standard-Rate water level time series from satellite altimetry
High-Rate water level time series from satellite altimetry
SR lake water level time series 3 Yes 2 3 HR lake water level time series
High-Rate altimetric water level over rivers
Surface water extent from satellite imagery
Water storage anomaly from GRACE and GRACE Follow On
Lake and reservoir water storage anomaly
River discharge from space
High-Rate river discharge
Summary, conclusion and outlook
Findings
555 7 Data availability

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