Does GRACE see the terrestrial water cycle “intensifying”?

Abstract

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 Gravity Recovery and Climate Experiment (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 Niño that partially masks long-term changes, using a new method, accelerations of up to 12 mm/yr 2 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 and 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 toward a better representation of long-term water cycle evolution.

El Niño, La Niña, and the global sea level budget

“…Regional distributions of ENSO-related terrestrial water storage, which are ultimately coupled to the barystatic contributions to GMSL fluctuations through mass conservation, are explored in past papers (Llovel et al, 2011;Boening et al, 2012;Phillips et al, 2012;Fasullo et al, 2013;de Linage et al, 2013;Eicker et al, 2016); they are not revisited here. However, ENSO-related GMSL behavior owing to steric effects is not as well understood.…”

A global reconstruction of climate‐driven subdecadal water storage variability

“…Launched in 2002, the Gravity Recovery and Climate Experiment (GRACE) mission has provided the first global observations of TWS changes [Wahr et al, 2004;Tapley et al, 2004]. As TWS is a key variable of the Earth's climate, impacting both surface water and energy budgets, these new observations have had important implications for the assessment of projected changes in the water cycle under current and future climate conditions [Famiglietti, 2014;Eicker et al, 2016;Reager et al, 2016]. The GRACE mission has also provided novel opportunities to diagnose and to identify systematic deficiencies in global hydrological and land surface models (LSMs) [Swenson and Milly, 2006;Güntner, 2008].…”

Large-Scale Total Water Storage and Water Flux Changes over the Arid and Semiarid Parts of the Middle East from GRACE and Reanalysis Products

“…However, this operation has a smoothing effect, and therefore, a proper filter should be applied to P-E-R to avoid possible phase shifts. This is done by convolving an optimum (temporal) central smoothing filter (2/44, 11/44, 18/44, 11/44, 2/44) with DDK2-filtered reanalysis TWF (P-E-R) time series as suggested by Eicker et al (2015).…”

“…The decline is believed to be mainly due to the climate change, as well as increasing demands on freshwater (surface water and groundwater) needed to support food production and economic activities of the increasing population in the region (UNEP 2003;Gleick 2004). In fact, decreasing the large-scale total water flux (TWF), known as precipitation 'P' minus evapotranspiration 'E' minus surface runoff 'R' (P-E-R), reflects a cumulative impact of direct and indirect anthropogenic modifications of the water cycle (e.g., Famiglietti and Rodell 2013;Eicker et al 2015), and can be considered as an indicator of the 'meteorological drought' (e.g., Kusche et al 2016). Kaniewski et al (2012) discuss the climate change and water variability within the northwest part of the Middle East and show that variability in precipitation plays a critical role on crop yields, productivity, and economic systems within the region.…”