Observationally based analysis of land–atmosphere coupling

Abstract

Abstract. The temporal variance of soil moisture, vegetation and evapotranspiration over land has been recognized to be strongly connected to the temporal variance of precipitation. However, the feedbacks and couplings between these variables are still not well understood and quantified. Furthermore, soil moisture and vegetation processes are associated with a memory and therefore they may have important implications for predictability.In this study we apply a generalized linear method, specifically designed to assess the reciprocal forcing between connected fields, to the latest available observational data sets of global precipitation, evapotranspiration, vegetation and soil moisture content. For the first time a long global observational data set is used to investigate the spatial and temporal land variability and to characterize the relationships and feedbacks between land and precipitation.The variables considered show a significant coupling among each other. The analysis of the response of precipitation to soil moisture evidences a robust coupling between these two variables. In particular, the first two modes of variability in the precipitation forced by soil moisture appear to have a strong link with volcanic eruptions and El Niño-Southern Oscillation (ENSO) cycles, respectively, and these links are modulated by the effects of evapotranspiration and vegetation. It is suggested that vegetation state and soil moisture provide a biophysical memory of ENSO and major volcanic eruptions, revealed through delayed feedbacks on rainfall patterns. The third mode of variability reveals a trend very similar to the trend of the inter-hemispheric contrast in sea surface temperature (SST) and appears to be connected to greening/browning trends of vegetation over the last three decades.

<strong>New insights on land surface-atmosphere feedbacks over tropical South America at interannual timescales</strong>

“…In summary, under the ENSO influence, T2m is not only a key variable to diagnose the dynamics of interannual LAFs but also has a substantial role on the dynamics and thermodynamics of the lower troposphere and soil interfaces over TropSA [2,3,44,73,80]. Besides, interannual anomalies in PRC are associated with perturbations of the surface water balance at regional scale by controlling T2m inside the dissected interactions of VSW and EVP [10,17,30,31,45,48,[81][82][83]. On the contrary, in the group of least ENSO-related graphs that reveals a direct relation between VSW-SH 925 , T2m is not fundamental in the relational structure among variables.…”

“…Traditionally, the study of LAFs have been approached from physical modelling and numerical experiments [7][8][9][10][11][12][13]; analysis of observations and models with statistical tools [3,[14][15][16][17]; traces of moisture trajectories [18,19], among others. An important body of literature has focused on the role Figure 1.…”

New Insights on Land Surface-Atmosphere Feedbacks over Tropical South America at Interannual Timescales

“…Under the ENSO influence, T is not only a key variable in the diagnostics of the dynamics of interannual LAFs but also has a substantial role in the dynamics and thermodynamics of the lower troposphere and soil interfaces over TropSA [2,3,40,44,69,75]. Besides, interannual anomalies in P are associated with perturbations of the surface water balance at the regional scale by controlling T interactions with Θ and E [10,17,30,31,45,49,[76][77][78].…”

“…The study of LAFs has been approached from physical models and numerical experiments [7][8][9][10][11][12][13]; analysis of observations and models with statistical tools [3,[14][15][16][17]; and traces of moisture trajectories [18,19], among others. An important body of literature has focused on the role of vegetation and land uses in the dynamics of LAFs [20][21][22][23][24], and the conditions under which LAFs determine the stability of the lower atmosphere [25][26][27].…”

Land surface albedo and vegetation feedbacks enhanced the millennium drought in south-east Australia

“…The multiple mechanistic pathways and the non-linear nature of the connection between the smoothly varying soil moisture field and highly episodic precipitation makes the feedback strength difficult to quantify with confidence. While some studies have used observations to quantify the soil moisture-precipitation feedback (Findell and Eltahir, 1999;Taylor et al, 2011Taylor et al, , 2012Catalano et al, 2016), more common is the use of model experiments to isolate and allow quantification of this behaviour (Schar et al, 1999;Koster et al, 2006;Seneviratne et al, 2013;Hirsch et al, 2014). Other slowly varying surface variables that have been found to provide feedbacks to precipitation include albedo (Charney et al, 1975;Lofgren, 1995;Zaitchik et al, 2007;Teuling and Seneviratne, 2008;Meng et al, 2014b) and vegetation (Pielke et al, 1998;Zeng and Neelin, 2000;Wang et al, 2006;Meng et al, 2014a).…”