Does GRACE see the terrestrial water cycle ‘intensifying’?

Annette Eicker (1) , Ehsan Forootan (1) , Anne Springer (1) , Laurent Longuevergne (2) , Jürgen Kusche (1)

1 IGG - Institute of Geodesy and Geoinformation [Bonn]
2 GR - Géosciences Rennes

Several researchers have postulated that, under a changing climate due to anthropogenic forcing, an intensification of the water cycle is already under way. This is usually related to increases in hydrological fluxes as precipitation (P), evapotranspiration (E), and river discharge (R). It is under debate, however, whether such observed or reconstructed flux changes are real and on what scales. Large-scale increase or decrease of the flux deficit (P-E-R), i.e. flux changes that do not compensate, would lead to acceleration or deceleration of water storage anomalies potentially visible in GRACE data. In agreement with earlier studies, we do find such accelerations in global maps of gridded GRACE water storage anomalies over 2003-2012. However, these have been generally associated with interannual and decadal climate variability. Yet, we show that even after carefully isolating and removing the contribution of El Nino that partially masks long-term changes, using a new method, accelerations of up to 12mm/yr2 remain in regions such as Australia, Turkey, and Northern India. We repeat our analysis with flux fields from two global atmospheric reanalyses that include land surface models (ERA-Interim, MERRA-Land). While agreeing well with GRACE on shorter time scales, they fall short in displaying long-term trends corresponding to GRACE accelerations. We hypothesize that this may be due to time-varying biases in the reanalysis fluxes as noticed in other studies. We conclude that even though its data record is short, GRACE provides new information that should be used to constrain future reanalyses towards a better representation of long-term water cycle evolution.

Domains: Hydrology

Annette Eicker, Ehsan Forootan, Anne Springer, Laurent Longuevergne, Jürgen Kusche. Does GRACE see the terrestrial water cycle ‘intensifying’?. Journal of Geophysical Research: Atmospheres, 2016, 121 (2), pp.733-745. ⟨10.1002/2015JD023808⟩. ⟨insu-01250011⟩