Sea Level Budget Closure Project - Climate Change Initiative programme (SLBC-CCI)

Project summary
Sea level is one of the most widely used indicators of climate change. Within the European Space Agency (ESA) Climate Change Initiative (CCI) programme, consistent and continuous observation data for sea level and other climate-related variables are produced. To improve our understanding of the causes of observed sea level changes, the CCI Sea Level Budget Closure (SLBC_cci) project aims at re-assessing the global sea level budget by estimating each of its components and the pertaining uncertainty. Essentially, observed changes of global mean sea level equal the sum of changes in ocean mass and thermal expansion. Observed ocean mass change equals the sum of global-scale changes in mass of glaciers, ice sheets (Greenland and Antarctica), land water in the form of liquid water and snow and atmospheric water. Each component’s contribution is individually estimated by means of observations or model estimates over 1993-2015 (altimetry period) and 2005-2015 (“golden period” with ARGOS and GRACE1). These estimates are then used to derive long-term trends and inter-annual and, when possible, seasonal variations. The different contributions will be compared to other observational data sources (e.g., CCI data products, GRACE). Along with the assessment of the sea level budget closure, the expected outcome of this project is an improved understanding of the different factors influencing sea level change, and particularly of the sources of error related to the assessment of each of these factors.

1ARGOS and GRACE are satellite-based systems that monitor different Earth-related variables.

Our contribution
Variations in land water storage on multiple time scales (monthly, annual, inter-annual) have an impact on water exchange between land, atmosphere and ocean, ultimately affecting global ocean mass and thus sea level variations. In the frame of the SLBC_cci project, we estimate the land water contribution to ocean mass change with the global hydrological model WaterGAP 2.2. We conceptualize variations of total water mass on the continents as water storage variations in the compartments canopy, soil, snow, glaciers, groundwater and surface water bodies (distinguishing rivers, wetlands, lakes and man-made reservoirs). WaterGAP 2.2 includes all of these compartments except glaciers and computes monthly time series of total water storage (TWS) variations with a spatial resolution of 0.5° grid cells (approximately 55 km by 55 km at the equator) for all continental areas of the globe except Greenland and Antarctica.

Our work focuses on:

  1. Improvement of the simulation of reservoir construction and its impact on continental water storage
  2. Improvement of the estimation of groundwater depletion
  3. Integration of glaciers into WaterGAP 2.2
  4. Computation of an ensemble of TWS variations (based on three different global climate datasets and various plausible water use variants) and quantification of model-based uncertainty range
  5. Derivation of continental mass variations including uncertainty range by combining model-based estimates and GRACE estimates

Denise Cáceres
Prof. Dr. Petra Döll (lead investigator)
Dr. Hannes Müller Schmied

April 2017 – March 2019

European Space Agency in the framework of the Climate Change Initiative programme



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