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Abstract
Abstract. The relationship between terrestrial water storage (TWS) and atmospheric processes has important implications for predictability of climatic extremes and projection of future climate change. In places where moisture availability limits evapotranspiration (ET), variability in TWS has the potential to influence surface energy fluxes and atmospheric conditions. Where atmospheric conditions, in turn, influence moisture availability, a full feedback loop exists. Here we developed a novel approach for measuring the strength of both components of this feedback loop, i.e., the forcing of the atmosphere by variability in TWS and the response of TWS to atmospheric variability, using satellite observations of TWS, precipitation, solar radiation, and vapor pressure deficit during 2002–2014. Our approach defines metrics to quantify the relationship between TWS anomalies and climate globally on a seasonal to interannual timescale. Metrics derived from the satellite data were used to evaluate the strength of the feedback loop in 38 members of the Community Earth System Model (CESM) Large Ensemble (LENS) and in six models that contributed simulations to phase 5 of the Coupled Model Intercomparison Project (CMIP5). We found that both forcing and response limbs of the feedback loop in LENS were stronger than in the satellite observations in tropical and temperate regions. Feedbacks in the selected CMIP5 models were not as strong as those found in LENS, but were still generally stronger than those estimated from the satellite measurements. Consistent with previous studies conducted across different spatial and temporal scales, our analysis suggests that models may overestimate the strength of the feedbacks between the land surface and the atmosphere. We describe several possible mechanisms that may contribute to this bias, and discuss pathways through which models may overestimate ET or overestimate the sensitivity of ET to TWS.
Highlights
Land–atmosphere feedbacks can result from the coupling of the terrestrial moisture state with temperature, precipitation, or radiation (Betts et al, 2014; Findell and Eltahir, 1997; Guillod et al, 2015; Koster et al, 2004)
A comparison of the months of maximum and minimum terrestrial water storage as determined by climatologies of Gravity Recovery and Climate Experiment (GRACE) and the Large Ensemble (LENS) ensemble mean indicated that the model largely reproduces the timing of TWS anomaly (TWSA) seasonality evident in the satellite observations (Fig. 2)
Geographic patterns of seasonality were consistent between the model and observations, though a phase shift in the drawdown interval is apparent in eastern Canada and central Eurasia where LENS had a 1-month early bias for both the maximum and minimum TWSA, in southeast North America where the onset of the modeled drawdown interval was slightly later than the observations, and in parts of east Asia and Australia where the modeled drawdown interval ended earlier than in the observations
Summary
Land–atmosphere feedbacks can result from the coupling of the terrestrial moisture state with temperature, precipitation, or radiation (Betts et al, 2014; Findell and Eltahir, 1997; Guillod et al, 2015; Koster et al, 2004). Land–atmosphere coupling occurs when terrestrial moisture anomalies influence the partitioning of surface energy between latent and sensible heat fluxes that, in turn, influence the development of the planetary boundary layer (PBL) (Seneviratne et al, 2010). Precipitation coupling can lead to both positive and negative feedbacks, as the influence of EF on the development of the PBL can serve to either enhance or suppress cloud formation and precipitation (Findell and Eltahir, 2003; Guillod et al, 2015). Temperature, precipitation, and radiation feedbacks each stem from coupling between terrestrial moisture and evapotranspiration (ET), which occurs most strongly in conditions of intermediate moisture availability (Seneviratne et al, 2010)
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