  The land-atmosphere coupling strength has been defined as the percentage of
precipitation variability explained by the variation of soil moisture in the
Global Land-Atmosphere Coupling Experiment (GLACE). While it is useful to
identify global hotspots of land-atmosphere interaction, this coupling strength
is different from coupling sensitivity, which directly quantifies how
precipitation generation responds to the perturbation of soil moisture and is
essential for our understanding of the global water cycle. To disentangle these
two quantities, here we theoretically explore the relationships among coupling
strength, sensitivity, and soil moisture variances. We use climate model
outputs to show that the largest soil moisture variances are located in the
transitional climate zones and the variations of soil moisture largely account
for the geographical patterns of coupling hotspots. The coupling sensitivity is
not necessarily low in non-hotspot regions, which could impose great impacts on
the development of extreme climate events. We therefore call for more research
attention on coupling sensitivity to improve our understanding of the climate
system.
