Satellite-based global-ocean mass balance estimates of interannual variability and emerging trends in continental freshwater discharge

Abstract

Freshwater discharge from the continents is a key component of Earth's water cycle that sustains human life and ecosystem health. Surprisingly, owing to a number of socioeconomic and political obstacles, a comprehensive global river discharge observing system does not yet exist. Here we use 13 years (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006) of satellite precipitation, evaporation, and sea level data in an ocean mass balance to estimate freshwater discharge into the global ocean. Results indicate that global freshwater discharge averaged 36,055 km 3 ∕y for the study period while exhibiting significant interannual variability driven primarily by El Niño Southern Oscillation cycles. The method described here can ultimately be used to estimate long-term global discharge trends as the records of sea level rise and ocean temperature lengthen. For the relatively short 13-year period studied here, global discharge increased by 540 km 3 ∕y 2 , which was largely attributed to an increase of globalocean evaporation (768 km 3 ∕y 2 ). Sustained growth of these flux rates into long-term trends would provide evidence for increasing intensity of the hydrologic cycle.climate | global water cycle | hydrology | remote sensing | observations

Air–sea exchanges of CO<sub>2</sub> in the world's coastal seas

“…These processes enhanced rock weathering during the last century (Probst et al, 1994). Intuitively, this fact suggests an increased export of carbon by rivers, but whether the global river runoff has increased is uncertain (Dai et al, 2011;Syed et al, 2010). The construction of dams around the world has caused a substantial fraction of exported sediment to be impounded in recent decades (Chen, 2002;Syvitski et al, 2005).…”

Toward global mapping of river discharge using satellite images and at-many-stations hydraulic geometry

“…Even wellmonitored countries have sparsely distributed networks, thus limiting current understanding of water losses along river courses, habitat changes, and flood risk (3,4). Satellites, in contrast, provide spatially dense coverage globally, attracting calls for a global river discharge mapping capacity from space (5)(6)(7)(8)(9)(10). However, previous efforts to estimate river discharge from remotely sensed observations have all required inclusion of some form of ancillary ground-based information, such as gauge measurements, bathymetric surveys, and/or calibrated hydrology models that are simply unavailable for most of the planet (11)(12)(13)(14)(15)(16)(17)(18).…”

Projecting water yield and ecosystem productivity across the United States by linking an ecohydrological model to WRF dynamically downscaled climate data

“…Mounting evidence has suggested that climate and its change has played an important role in controlling the water cycle by changes in evaporation, transpiration, and runoff (McCabe, 2002;Hamlet et al, 2007;Syed et al, 2010;Wang and Hejazi, 2011;Chien et al, 2013;Hegerl et al, 2014;Huntington and Billmire, 2014;McCabe and Wolock, 2014;Sun et al, 2014). Also, climate can exert a dominant control on vegetation structural and phenological characteristics through variations in air temperature, precipitation, solar radiation, wind, and CO 2 concentration (Nemani et al, 2003;Harding et al, 2011;Wang et al, 2014;Zhang, F. et al, 2014;.…”