Abstract
Climate change will affect the terrestrial water cycle during the next decades by impacting the seasonal cycle, interannual variations, and long-term linear trends of water stored at or beyond the surface. Since 2002, terrestrial water storage (TWS) has been globally observed by the Gravity Recovery and Climate Experiment (GRACE) and its follow-on mission (GRACE-FO). Next Generation Gravity Missions (NGGMs) are planned to extend this record in the near future. Based on a multi-model ensemble of climate model output provided by the Coupled Model Intercomparison Project Phase 6 (CMIP6) covering the years 2002–2100, we assess possible changes in TWS variability with respect to present-day conditions to help defining scientific requirements for NGGMs. We find that present-day GRACE accuracies are sufficient to detect amplitude and phase changes in the seasonal cycle in a third of the land surface, whereas a five times more accurate double-pair mission could resolve such changes almost everywhere outside the most arid landscapes of our planet. We also select one individual model experiment out of the CMIP6 ensemble that closely matches both GRACE observations and the multi-model median of all CMIP6 realizations, which might serve as basis for satellite mission performance studies extending over many decades to demonstrate the suitability of NGGM satellite missions to monitor long-term climate variations in the terrestrial water cycle.
Highlights
Increasing global concentrations of greenhouse gases raise the ability of our planet to absorb solar energy and lead to globally rising temperatures
We consider both the fit of the model run to Gravity Recovery and Climate Experiment (GRACE) observations in the GRACE time span and to the MMMed in the projected time span
We investigate to which extent changes as projected with Coupled Model Intercomparison Project Phase 6 (CMIP6) models will be detectable with gravity missions such as GRACE/GRACE-FO or a Next Generation Gravity Missions (NGGMs)
Summary
Increasing global concentrations of greenhouse gases raise the ability of our planet to absorb solar energy and lead to globally rising temperatures. In addition to projections from coupled climate models more and more evidence is emerging from satellite and in situ observations that changes in the terrestrial water cycle as triggered by modified precipitation pattern and intensities are already happening today [1]. Changes in the magnitude and occurrence frequency of extreme events [4] and interannual variations are expected [5]. Those changes pose a challenge for water management authorities engaged in balancing requirements on water consumption, renewable energy production, and flood control, which can only be met with a broad information basis provided by a well developed observing system
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