Quantifying the Strength of Soil Moisture–Precipitation Coupling and Its Sensitivity to Changes in Surface Water Budget

Abstract

This paper presents a new index to quantify the strength of soil moisture-precipitation coupling in AGCMs and explores how the soil moisture-precipitation coupling in Community Atmosphere Model version 3 (CAM3)-Community Land Model version 3 (CAM3-CLM3) responds to parameterizationinduced surface water budget changes. Specifically, this study (a) compares the regions of strong coupling identified by the newly proposed index and the index currently used in the Global Land-Atmosphere Coupling Experiment (GLACE); (b) examines how the surface water budget changes influence the strength of soil moisture-precipitation coupling as measured by the two indexes, respectively; and (c) examines how these changes influence the memory of the coupled land-atmosphere system as measured by the correlation between soil moisture and subsequent precipitation. The new index and the GLACE index are consistent in identifying central North America and West Africa as major regions of strong coupling during JuneAugust (JJA). However, in some areas of western Europe and of subtropical South America where the GLACE index is low, the new index suggests a modest significant coupling during JJA. In response to the surface water budget changes that presumably favor a stronger soil moisture-precipitation coupling, the new index increases, but the GLACE index decreases in a majority of the regions of modest-to-strong coupling, although both show some mixed response. Changes in the land-atmosphere system memory suggest an increase of coupling strength, consistent with results from the new index. The strong dependence of the GLACE index on the relative importance of atmospheric internal variability is identified as a potential cause for the differences between the two indexes. The two indexes emphasize different aspects of soil moisture-precipitation coupling, and one might be more suitable than the other depending on the purpose of individual studies.

Precipitation, Recycling, and Land Memory: An Integrated Analysis

“…Unlike other experiments that have established ''hot spots'' for land-atmosphere interaction (e.g., Koster et al 2004;Wang et al 2007), this study does not base its conclusions solely on the behavior of GCMs. Each dataset used is constrained in large part by atmospheric observations.…”

Global Meteorological Drought: A Synthesis of Current Understanding with a Focus on SST Drivers of Precipitation Deficits

“…Notably, the effect of land surface-atmosphere interactions, in the form of soil moisture-precipitation coupling, is essential in the development of drought in southern South America (Xue et al 2006;Wang et al 2007;Ma et al 2010;Sörensson and Menéndez 2011). Barreiro and Diaz (2011) noted that improved seasonal forecasts over South America require the proper representation of the teleconnection processes and regional land-atmosphere interactions need to be adequately resolved.…”

Effect of Soil Moisture on Diurnal Convection and Precipitation in Large-Eddy Simulations

“…Given the importance of the soil moisture-precipitation feedback in regulating the global and continental hydrological cycle, many studies have tried to estimate its more likely sign and magnitude using either observations (e.g., Miralles et al 2014;Ford et al 2015), coarseresolution models with parameterized convection (e.g., Schär et al 1999;Wang et al 2007), convection-permitting models with explicit convection (e.g., Hohenegger et al 2009;Schlemmer et al 2012), or conceptual models (e.g., Findell and Eltahir 2003a;Tawfik et al 2015;Gentine et al 2013). The main problem regarding observational studies is that the effect of synoptic variability is difficult to filter out.…”