HydroSat: geometric quantities of the global water cycle from geodetic satellites

Abstract

Abstract. Against the backdrop of global change, in terms of both climate and demography, there is a pressing need for monitoring of 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 have been 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 database containing geometric quantities of the global water cycle from geodetic satellites. HydroSat provides time series and their uncertainty in water level from satellite altimetry, surface water extent from satellite imagery, terrestrial water storage anomaly represented in equivalent water height from satellite gravimetry, lake and reservoir water volume anomaly from a combination of satellite altimetry and imagery, and river discharge from either satellite altimetry or imagery. The spatial and temporal coverage of these datasets varies and depends on the availability of geodetic satellites. These products, which are complementary to existing products, can contribute to our understanding of the global water cycle within the Earth system in several ways. They can be incorporated for hydrological modeling, they can be complementary to current and future spaceborne observations, and they can define indicators of the past and future state of the global freshwater system. HydroSat is publicly available through http://hydrosat.gis.uni-stuttgart.de (last access: 18 May 2022​​​​​​​). Moreover, a snapshot of all the data (taken in April 2021) is available in GFZ Data Services at https://doi.org/10.5880/fidgeo.2021.017 (Tourian et al., 2021).

Remote Sensing-Based Extension of GRDC Discharge Time Series - A Monthly Product with Uncertainty Estimates

“…Over the past three decades, satellite altimetry has emerged as a valuable technique for monitoring inland water surfaces and studying the hydrological cycle 23 – 25 . The availability of satellite altimetry data sets has facilitated the development of numerous research initiatives and collaborations, leading to the establishment of valuable databases like Hydroweb 26 , HydroSat 9 and Database for Hydrological Time Series of Inland Waters (DAHITI) 27 . In this study, river water height time series data were collected from the HydroSat ( http://hydrosat.gis.uni-stuttgart.de ) and DAHITI ( https://dahiti.dgfi.tum.de ) databases.…”

“…Remote sensing (RS)-based discharge estimates can address the lack of a global discharge record. A promising approach is to develop empirical models, such as rating curves which establish a relationship between the ground-based river discharge and space-based measurements of a hydraulic parameter like river water level 5 – 9 or river width 10 – 11 or even a non-hydraulic quantity such as the ratio of surface reflectance between water and land pixels 12 , 13 . Once the model is developed, discharge can be estimated through remote sensing observations alone.…”

AltiMaP: Altimetry Mapping Procedure for Hydrography Data

“…Although satellite altimetry missions were developed for ocean surface observations, they have increasingly been applied to 110 observe lakes and rivers (Abdalla et al, 2021;Calmant et al, 2008;Calmant and Seyler, 2006;Yang et al, 2022). Several agencies have already processed their original satellite altimetry data and produced data archives for studying WSEs, including the HydroWeb (Crétaux et al, 2011;Santos da Silva et al, 2010), Hydrosat (Tourian et al, 2016(Tourian et al, , 2022, Database for Hydrological Time Series of Inland Waters (DAHITTI; Schwatke et al, 2015), Global Reservoirs and Lakes Monitor (G-REALM; Birkett and Beckley, 2010), Copernicus Global Land Service (CGLS; Calmant et al, 2013;Crétaux et al, 2011), 115 River & Lake (Birkett et al, 2002), Hidrosat (Santos da Silva et al, 2010;da Silva et al, 2012), and Global River Radar Altimetry Time Series (GRRATS; Coss et al, 2020) archives. In this study, we used satellite altimetry data from HydroWeb for its accessibility and global coverage.…”

Water Resources in Africa: The Role of Earth Observation Data and Hydrodynamic Modeling to Derive River Discharge

“…Thanks to these methodologies, a number of studies have employed the satellite multi-mission databases to estimate river discharge (since the pioneering study in an African basin from Coe and Birkett 2004 on Lake Tchad basin, to recent ones such as Papa et al 2010;Paris et al 2016;Tourian et al 2016;Bogning et al 2018;Scherer et al 2020;Pujol et al 2020;Malou et al 2021). Despite the huge contribution provided by multi-mission approaches, the combination of different altimetry measurements represents still a challenge because of the inter-satellite biases (Normandin et al 2018) which impede a straightforward combination of water level measurements (Tourian et al 2022). The inter-satellite bias depends not only on the mission but also on the atmospheric corrections (Fernandes et al 2014) or the retracker algorithm (Kitambo et al 2021), and therefore it cannot be considered global, but it needs to be estimated at regional scale.…”