Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2017
Publication Date: 5/9/2017
Citation: Ouyang, Y., Parajuli, P., Li, Y., Leininger, T., Feng, G.G. 2017. Identify temporal trend of air temperature and its impact on forest stream flow in Lower Mississippi River Alluvial Valley using wavelet analysis. Journal of Hydrology. doi:10.1016/j.jenvman.2017.05.014. Interpretive Summary: Wavelet analysis technique has been applied to assess climate change and its impact on forest stream flows. Four USGS surface water monitoring stations in LMRAV were selected to obtain discharge and air temperature data for the analysis. These stations are situated near the headwater areas of forest lands and were selected because they have a long-term discharge data ranged from 60 to 90 years with very few land use disturbances, which provide a unique opportunity for analyzing how the climate changes affect the historic forest stream flows. Although the descriptive statistical analysis provided some useful information on stream flow and air temperature, it could not tell if the climate change occurred in LMRAV and how this change affects stream flow. However, with the application of wavelet analysis, an increasing temporal trend of air temperature around its mean value was detected for the past several decades in this region. Results demonstrated that the climate in LMRAV did get warmer as time elapsed. In contrast, a decreasing temporal trend of stream discharge around its mean value was detected for the past several decades in LMRAV. The decrease in stream flow corresponded well to the increase in air temperature during the same time period. Results confirmed that stream flows in the LMRAV were affected by climate change due to a warmer air temperature. A best way to estimate the temporal trends of air temperature and stream flow was to perform the wavelet transformation around their mean values. This approach is novel in wavelet analysis because it has not been reported in the literature. Further study is therefore warrant to apply the same approach to identify temporal trends for other climate and hydrological variables.
Technical Abstract: Characterization of stream flow is essential to water resource management, water supply planning, environmental protection, and ecological restoration; while climate change can exacerbate stream flow and add instability to the flow. In this study, the wavelet analysis technique was employed to assess climate change and its impact upon forest stream flows using the Lower Mississippi River Alluvial Valley (LMRAV) as a study site. Four surface water monitoring stations, which locate near the headwater areas with very few land use disturbances and long-term data records (60 to 90 years) in LMRAV, were selected to obtain stream discharge and air temperature data. Our wavelet analysis showed that air temperature had an increasing temporal trend around its mean value during the past several decades in LMRAV, whereas stream flow had a decreasing temporal trend around its average value at the same time period in LMRAV. Results demonstrated that the climate in LMRAV did get warmer as time elapsed and the streams were drier due to climate change as a result of warmer air temperature. Our study further revealed that a best way to estimate the temporal trends of air temperature and stream flow was to perform the wavelet transformation around their mean values. This approach is somewhat novel in applying wavelet analysis because it has not been reported in the literature.