Characterization of CO2 and water vapor fluxes in a summer maize field with wavelet analysis

Knowledge of water vapor and carbon dioxide (CO2) fluxes in agricultural lands is crucial to estimate carbon and water cycles as well as to investigate global warming potentials. In this study, the continuous wavelet transform technique along with cross-wavelet and wavelet coherence methods was applied to characterize half-hourly CO2 flux (Fc) and water vapor (LE) flux data obtained with the eddy covariance technique in a summer maize field located in the North China Plain. Our motivation was to highlight the multiple time scale properties and to exam the possible connections between the flux exchanges and the concurrent micro- meteorological variations. Results show that both Fc and LE could be characterized by the wavelet coefficients for the time scale ranged from 60–110 days. Peaks of CO2 exchange were corresponded to the in-phase trough points of water vapor flux exchange rates on the 110 day, 64 day and 32 day time scales. Intra-seasonal oscillations in both water and CO2 flux exchanges were associated with the patterns of photosynthetically active radiation, air temperature, vapor pressure deficient, and precipitation. Our study also showed that wavelet transforms had prospect in making a physical explanation of the temporal structure of the flux exchanges between the crop biosphere and atmosphere in response to ambient variables. This study suggests that cross-wavelet analysis and wavelet coherence could be powerful methods for probing the dynamical relationship between the flux exchange and the dominant modes of climate variability.