Eco‐hydrological controls on summertime convective rainfall triggers

Triggers of summertime convective rainfall depend on numerous interactions and feedbacks, often compounded by spatial variability in soil moisture and its impacts on vegetation function, vegetation composition, terrain, and all the complex turbulent entrainment processes near the capping inversion. To progress even within the most restricted and idealized framework, many of the governing processes must be simplified and parameterized. In this work, a zeroth‐order representation of the dynamical processes that control convective rainfall triggers – namely land surface fluxes of heat and moisture – is proposed and used to develop a semianalytical model to explore how differential sensitivities of various ecosystems to soil moisture states modify convective rainfall triggers. The model is then applied to 4 years (2001–2004) of half‐hourly precipitation, soil moisture, environmental, and eddy‐covariance surface heat flux data collected at a mixed hardwood forest (HW), a maturing planted loblolly pine forest (PP), and an abandoned old field (OF) experiencing the same climatic and edaphic conditions. We found that the sensitivity of PP to soil moisture deficit enhances the trigger of convective rainfall relative to HW and OF, with enhancements of about 25% and 30% for dry moisture states, and 5% and 15% for moist soil moisture states, respectively. We discuss the broader implications of these findings on potential modulations of convective rainfall triggers induced by projected large‐scale changes in timberland composition within the Southeastern United States.

[1]  S. Zilitinkevich,et al.  On the determination of the height of the Ekman boundary layer , 1972 .

[2]  Roland B. Stull,et al.  The Energetics of Entrainment Across a Density Interface , 1976 .

[3]  Peter S. Eagleson.  The Emergence of Global‐Scale Hydrology , 1986 .

[4]  R. Stull.  An Introduction to Boundary Layer Meteorology , 1988 .

[5]  J. Garratt.  The Atmospheric Boundary Layer , 1992 .

[6]  J. I. MacPherson,et al.  Budget analysis of the boundary layer grid flights during FIFE 1987 , 1992 .

[7]  Kerry Emanuel,et al.  On large-scale circulations in convecting atmospheres , 1994 .

[8]  J. Pal,et al.  Relationship between surface conditions and subsequent rainfall in convective storms , 1996 .

[9]  T. Haiden.  An analytical study of cumulus onset , 1997 .

[10]  G. Katul,et al.  A Lagrangian dispersion model for predicting CO2 sources, sinks, and fluxes in a uniform loblolly pine (Pinus taeda L.) stand , 1997 .

[11]  Dara Entekhabi,et al.  Feedbacks in the Land-Surface and Mixed-Layer Energy Budgets , 1998 .

[12]  G. Katul,et al.  WATER BALANCE DELINEATES THE SOIL LAYER IN WHICH MOISTURE AFFECTS CANOPY CONDUCTANCE , 1998 .

[13]  K. Findell,et al.  Analysis of the pathways relating soil moisture and subsequent rainfall in Illinois , 1999 .

[14]  J. Sperry.  Hydraulic constraints on plant gas exchange , 2000 .

[15]  K. E. Moore,et al.  Boundary Layer Clouds and Vegetation–Atmosphere Feedbacks , 2001 .

[16]  W. Oechel,et al.  FLUXNET: A New Tool to Study the Temporal and Spatial Variability of Ecosystem-Scale Carbon Dioxide, Water Vapor, and Energy Flux Densities , 2001 .

[17]  A. Pitman,et al.  Relative climatic effects of landcover change and elevated carbon dioxide combined with aerosols: A comparison of model results and observations , 2001 .

[18]  S. Kanae,et al.  Impact of Deforestation on Regional Precipitation over the Indochina Peninsula , 2001 .

[19]  K. Findell.  Atmospheric Controls on Soil Moisture-Boundary Layer Interactions , 2001 .

[20]  Roger A. Pielke,et al.  Modelled changes in arctic tundra snow, energy and moisture fluxes due to increased shrubs , 2002 .

[21]  A Case Study of the Morning Evolution of the Convective Boundary Layer Depth , 2002 .

[22]  D. Wear,et al.  Southern Forest Resource Assessment Southern Forest Resource Assessment , 2002 .

[23]  G. Katul,et al.  Relationship between plant hydraulic and biochemical properties derived from a steady‐state coupled water and carbon transport model , 2003 .

[24]  R. Oren,et al.  Carbon dioxide and water vapor exchange in a warm temperate grassland , 2003, Oecologia.

[25]  Elfatih A. B. Eltahir,et al.  Atmospheric Controls on Soil Moisture-Boundary Layer Interactions. Part II: Feedbacks within the Continental United States , 2003 .

[26]  S. Pacala,et al.  Impact of historical land cover change on the July climate of the United States , 2003 .

[27]  R. Oren,et al.  Species differences in stomatal control of water loss at the canopy scale in a mature bottomland deciduous forest , 2003 .

[28]  Stefan Emeis,et al.  Atmospheric boundary-layer structure from simultaneous SODAR, RASS, and ceilometer measurements , 2004 .

[29]  Paolo D'Odorico,et al.  Preferential states in soil moisture and climate dynamics , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[30]  Tod A. Laursen,et al.  Finite element tree crown hydrodynamics model (FETCH) using porous media flow within branching elements: A new representation of tree hydrodynamics , 2005 .

[31]  R. Dickinson,et al.  Warm‐season rainfall variability over the U.S. Great Plains and its correlation with evapotranspiration in a climate simulation , 2005 .

[32]  Jehn-Yih Juang,et al.  Variability in net ecosystem exchange from hourly to inter-annual time scales at adjacent pine and hardwood forests: a wavelet analysis. , 2005, Tree physiology.

[33]  R. Oren,et al.  Canopy leaf area constrains [CO2]-induced enhancement of productivity and partitioning among aboveground carbon pools , 2006, Proceedings of the National Academy of Sciences.

[34]  Jehn-Yih Juang,et al.  Hydrologic and atmospheric controls on initiation of convective precipitation events , 2007 .