Time scale and influencing factor variations of Water and Heat fluxes in
Sandy Land
Abstract
The transfer process and variation characteristics of water and heat
fluxes play an important role in both ecosystems function and climatic
patterns of arid and semi-arid areas. However, both water (latent heat
flux, Fe) and heat (sensible heat flux, Fh) fluxes and the impact
factors have different time scales. Therefore, the wavelet
transformation was used to reconstruct water and heat flux data measured
by an eddy covariance system installed in Horqin sandy land, China. Then
the distribution and response regularity of water and heat flux to the
control factors were analyzed under different time scales. The results
indicated that the responses of Fe and Fh to controlling factors were
similar on 30min and daily scales, in which the energy terms (net
radiation, Fn and available energy, Fa) showed extremely significant
positive contribution. The part of water condition (vapor pressure
deficit, VPD and relative humidity, RH) were the main influencing
factors at monthly scale. At the seasonal scale, Fe was positively
correlated with Fa and Fn, but negatively correlated with soil heat flux
(Fg), RH and wind speed (WS). On the contrary, Fh was positively
correlated with RH, but negatively correlated with Fn. At the annual
scale, Fe and Fh showed a significant positive correlation with all
factors. Generally, at the daily and annual scales, there is a high
correlation between Fe, Fh and the control factors, and exhibits
pronounced periodicity. These results suggest that the time scales of
flux and impact factors should be both considered when doing water and
heat fluxes analysis of sandy land or others ecosystem.