Impacts of drought, woody encroachment, and gap-filling technique on estimated land-atmosphere coupling strength and scale

Abstract:

Investigations of land-atmosphere coupling have shown that surface conditions influence local boundary layer development and precipitation likelihood from sub-daily to seasonal time scales. With recent severe droughts and predictions of increased drought risk in the Central US, understanding how local land management practices may exacerbate or mitigate drying conditions has become especially important. Long-term, high-frequency observations from three eddy covariance towers on prairie sites with differing management practices and burn regimes provide a unique opportunity to investigate the influence of grassland management and woody encroachment on local land-atmosphere coupling strength. Observations from 2008 through 2014 are used to calculate time series of a detailed metric of land-atmosphere coupling strength, while self-organizing maps (SOM) are used to identify a comprehensive range of significant meteorological states. SOM classifications of meteorological variables are used in order to identify the sensitivity of coupling strength to environmental states more complex than conventional binary soil moisture classification and to determine if coupling metrics are able to capture this sensitivity. Periods of heavily gap-filled data stood out in a unique SOM class with unusual coupling characteristics, raising concern over how the technique used to gap fill observations can influence coupling estimates and related research. Wavelet analysis and spectra are used to determine the contribution of specific timescales to coupling under different characteristic environmental states. SOM and temporal analysis approaches of this study offer insight on the response of land-atmosphere interactions to variables beyond soil moisture status and improve understanding of how historical changes in land use and the transformation of most grasslands in the Central Great Plains has altered regional drought resilience through modified coupling characteristics.