Sylvain Biancamaria

The SWOT Mission and Its Capabilities for Land Hydrology

Surface water storage and fluxes in rivers, lakes, reservoirs and wetlands are currently poorly observed at the global scale, even though they represent major components of the water cycle and deeply impact human societies. In situ networks are heterogeneously distributed in space, and many river basins and most lakes—especially in the developing world and in sparsely populated regions—remain unmonitored. Satellite remote sensing has provided useful complementary observations, but no past or current satellite mission has yet been specifically designed to observe, at the global scale, surface water storage change and fluxes. This is the purpose of the planned Surface Water and Ocean Topography (SWOT) satellite mission. SWOT is a collaboration between the (US) National Aeronautics and Space Administration, Centre National d’Études Spatiales (the French Spatial Agency), the Canadian Space Agency and the United Kingdom Space Agency, with launch planned in late 2020. SWOT is both a continental hydrology and oceanography mission. However, only the hydrology capabilities of SWOT are discussed here. After a description of the SWOT mission requirements and measurement capabilities, we review the SWOT-related studies concerning land hydrology published to date. Beginning in 2007, studies demonstrated the benefits of SWOT data for river hydrology, both through discharge estimation directly from SWOT measurements and through assimilation of SWOT data into hydrodynamic and hydrology models. A smaller number of studies have also addressed methods for computation of lake and reservoir storage change or have quantified improvements expected from SWOT compared with current knowledge of lake water storage variability. We also briefly review other land hydrology capabilities of SWOT, including those related to transboundary river basins, human water withdrawals and wetland environments. Finally, we discuss additional studies needed before and after the launch of the mission, along with perspectives on a potential successor to SWOT.

Preliminary Characterization of SWOT Hydrology Error Budget and Global Capabilities

River discharge and lake water storage are critical elements of land surface hydrology, but are poorly observed globally. The Surface Water and Ocean Topography (SWOT) satellite mission will provide high-resolution measurements of water surface elevations with global coverage. Feasibility studies have been undertaken to help define the orbit inclination and repeat period. Preliminary error budgets have been computed for estimating instantaneous and monthly river discharge from SWOT measurements (errors are assumed uncorrelated). Errors on monthly discharge due to SWOT temporal sampling were estimated using gauges and their observation times for two SWOT orbits with different inclinations (78° and 74°). These errors have then been extrapolated to rivers globally. The 78° and 74° orbital inclinations allow a good sampling frequency, avoid tidal aliasing and cover almost all the continental surface. For a 22-day repeat orbit, a single point at 72°N is sampled 11 and 16 times during one repeat period for the 78° and 74° inclination orbit, respectively. Errors in instantaneous discharge are below 25% for rivers wider than 50 m (48% of all rivers). Errors in monthly discharge are below 20% for rivers with drainage areas larger than 7000 km2 (34% of all rivers). A rough estimate of global lake storage change has been computed. Currently, available satellite nadir altimetry data can only monitor 15% of the global lake volume variation, whereas from 50% to more than 65% of this variation will be observed by SWOT, thus providing a significant increase in our knowledge of lake hydrology.

Evolution of high‐latitude snow mass derived from the GRACE gravimetry mission (2002–2004)

Abstract: Since March 2002, the GRACE mission provi des monthly global maps of geoid time-variations. These new data carry informatio n on the continental water storage, including snow mass variations, with a ground resolution of ~600-700 km . We have computed monthly snow mass solutions from the inversion of the 22 GRACE geoids (04/2002 - 05/2004). The inverse approach developed here allows to sepa rate the soil waters from snow signal. These snow mass solutions are further compared to predictions from three global land surface models and snow depths derived from satellite microwave data. We find that the GRACE solutions correlate well with the high-latitude zones of strong accumulation of snow. Regional means computed for four large boreal basins (Yenisey, Ob, Mac Kenzie and Yukon) show a good agreement at seasonal scale between the snow mass solutions and model predictions (global rms ~30-40 mm of equivalent-water height and ~10-20 mm regionally). Index terms: GRACE Gravimetry Mission, Hydrolology, Snow cover. hal-00280239, version 1 - 5 Nov 2009

Proof of Concept of an Altimeter-Based River Forecasting System for Transboundary Flow Inside Bangladesh

Recent work by Biancamaria (Geophysical Research Letters, 2011) has demonstrated the potential of satellite altimetry to forecast incoming transboundary flow for downstream nations by detecting river levels at locations in upstream nations. Using the Ganges-Brahmaputra (GB) basin as an example, we assessed the operational feasibility of using JASON-2 satellite altimetry for forecasting such transboundary flow at locations further inside the downstream nation of Bangladesh by propagating forecasts derived from upstream (Indian) locations through a hydrodynamic river model. The 5-day forecast of river levels at upstream boundary points inside Bangladesh were used to initialize daily simulation of the hydrodynamic river model and yield the 5-day forecast river level further downstream inside Bangladesh. The forecast river levels were then compared with the 5-day-later “nowcast” simulation by the river model based on in-situ river level at the upstream boundary points in Bangladesh. Results show that JASON-2 retains good fidelity at 5-day lead forecast with an average RMSE (relative to nowcast) ranging from 0.5 m to 1.5 m and a mean bias (underestimation) of 0.25 m to 1.25 m in river water level estimation. Based on the proof-of-concept feasibility, a 4 month-long capacity building of the Bangladesh flood forecasting agency was undertaken. This facilitated a 20-day JASON-2 based forecasting of flooding during Aug 1, 2012 to Aug 20, 2012 up to a 5 day lead time in a real-time operational environment. Comparison against observed water levels at select river stations revealed an average error of forecast ranging from -0.4 m to 0.4 m and an RMSE ranging from 0.2 m to 0.7 m. In general, this study shows that satellite altimeter such as JASON-2 can indeed be an efficient and practical tool for building a robust forecasting system for transboundary flow.

Western Siberia wetlands as indicator and regulator of climate change on the global scale

Western Siberia is a unique bog region. Siberian peatlands have been a major sink of atmospheric carbon since the last deglaciation and, on the other hand, in some epochs – like the present – they are the most powerful source of methane emission. About 104 Mha of Russian peatlands are located in Western Siberia, which consists almost completely of pristine peatland ecosystems. This paper considers the role of the Western Siberian peatlands in a global carbon balance and their possible influence on the formation of Earth’s climate.

Global surveys of reservoirs and lakes from satellites and regional application to the Syrdarya river basin

Large reservoirs along rivers regulate downstream flows to generate hydropower but may also store water for irrigation and urban sectors. Reservoir management therefore becomes critical, particularly for transboundary basins, where coordination between riparian countries is needed. Reservoir management is even more important in semiarid regions where downstream water users may be totally reliant on upstream reservoir releases. If the water resources are shared between upstream and downstream countries, potentially opposite interests arise as is the case in the Syrdarya river in Central Asia. In this case study, remote sensing data (radar altimetry and optical imagery) are used to highlight the potential of satellite data to monitor water resources: water height, areal extent and storage variations. New results from 20 years of monitoring using satellites over the Syrdarya basin are presented. The accuracy of satellite data is 0.6 km3 using a combination of MODIS data and satellite altimetry, and only 0.2 km3 with Landsat images representing 2–4% of average annual reservoir volume variations in the reservoirs in the Syrdarya basin. With future missions such as Sentinel-3A (S3A), Sentinel-3B (S3B) and surface water and ocean topography (SWOT), significant improvement is expected. The SWOT missions main payload (a radar interferometer in Ka band) will furthermore provide 2D maps of water height, reservoirs, lakes, rivers and floodplains, with a temporal resolution of 21 days. At the global scale, the SWOT mission will cover reservoirs with areal extents greater than 250 × 250 m with 20 cm accuracy.

Crossing the “Valley of Death”: Lessons Learned from Implementing an Operational Satellite-Based Flood Forecasting System

More than a decade ago, a National Research Council (NRC) report popularized the term “valley of death” to describe the region where research on weather satellites had struggled to reach maturity for societal applications. A similar analogy can be drawn for other satellite missions, since their vantage point in space can be highly useful for some of the worlds otherwise fundamentally intractable operational problems. One such intractable problem is flood forecasting for downstream nations where the f looding is transboundary. Bangladesh fits in this category by virtue of its small size and location at the sink of the mighty Ganges and Brahmaputra. There has been the claim made that satellites can be a solution for Bangladesh in achieving forecasts with lead times beyond three days. This claim has been backed up by scientific research done by numerous researchers, who have shown proof of concept of using satellite data for extending flood forecasting range. This article aims to take the reader on a journe...

Snow Cover and Spring Flood Flow in the Northern Part of Western Siberia (the Poluy, Nadym, Pur, and Taz Rivers)

AbstractThe paper aims to quantitatively estimate the role of snowmelt in the spring flood flow and the redistribution of river runoff for the northern (Arctic) part of the western Siberian Plain (the rivers Poluy, Nadym, Pur, and Taz). In this region, the presence of wetlands and thermokarst lakes significantly influences the seasonal redistribution of river discharge. First the study region is described, and the snow regime from in situ observations at the Tarko-Sale meteorological station is analyzed. As Special Sensor Microwave Imager (SSM/I) estimates of snow depth for this region are lower than in situ observations, a correction of the SSM/I snow depth estimates is done using snow parameters measured on the snow transect near the meteorological station Tarko-Sale for 1991–96. This reestimated snow depth is then used to assess the volume of water stored every winter on the watersheds for 1989–2006. This snow product is compared with the spring flood streamflow estimated from in situ observations, and...

Uncertainties in Mean River Discharge Estimates Associated With Satellite Altimeter Temporal Sampling Intervals: A Case Study for the Annual Peak Flow in the Context of the Future SWOT Hydrology Mission

In the context of the Surface Water and Ocean Topography (SWOT) mission, investigations are needed to refine the error budget for discharge estimations. This letter proposes to evaluate the uncertainties in the estimation of mean river discharge around the seasonal peak flow due to the satellite temporal sampling intervals. The daily time series of in situ river discharge measurements for 11 large rivers are used to analyze the uncertainties associated with the sampling of four altimeter repeat cycles: the 35-, 22-, and 10-day repeat cycles in the nadir-looking configuration of current altimeters and the 22-day repeat cycle in the SWOT wide-swath configuration, where a given location is observed every cycle twice at the equator and six times in higher latitudes. Results show that, for boreal rivers, a sampling of 35 or 22 days from current nadir altimeters is too coarse to give an accurate estimate of the average discharge around the seasonal peak flow, whereas for all watersheds, the uncertainties associated with a 10-day repeat cycle or the 22-day repeat cycle in the SWOT wide-swath configuration are within the range of acceptable uncertainties (15%-20%). In addition, the absolute maximum mean discharge uncertainties associated with the SWOT time sampling have a strong relationship with the variance of the river discharge. This suggests that, rather than the commonly used basin area, the magnitude of the short-time-scale variance of the discharge could be used as a predictor of the uncertainties associated with temporal sampling intervals when estimating average discharge around the seasonal peak flow.

A Promising Radar Altimetry Satellite System for Operational Flood Forecasting in Flood-Prone Bangladesh

Building on a recent suite of work that has demonstrated theoretical feasibility and operational readiness of a satellite altimeter based flood forecasting system, we recently put a progressively designed altimeter based transboundary flood forecasting system to the ultimate test of real-time operational delivery in Bangladesh. The JASON-2 satellite altimeter, which was in orbit at the time of writing this manuscript, was used as the flagship altimeter mission. This paper summarizes the entire process of designing the system, customizing the workflow, and putting the system in place for complete ownership by the Bangladesh stakeholder agency for a 100 day operational skill test spanning the period of June 1 2013 through Sept. 9, 2013. Correlation for most of the flood warning stations ranged between 0.95 to 0.80 during the 1 day to 8 days lead time range. The RMSE of forecast typically ranged between 0.75m to 1.5m at locations where the danger level relative to the river bed was more than an order higher (i.e., >20m). The RMSE of forecast at the 8 days lead time did not exceed 2m for upstream and mid-stream rivers inside Bangladesh. The RMSE of forecast at the 8 days lead time exceeded 2m at a few estuarine river locations affected by tidal effects, where danger level relative to river bed was smaller (i.e., <;20m). Such a satellite altimeter system, such as one based on the JASON-2 altimeter, is now poised to serve the entire inhabitants of the Ganges-Brahmaputra-Meghna river basins as well as 30 or more flood-prone downstream nations currently deprived of real-time flow data from upstream nations.