DETECTING CLIMATE-INDUCED PATTERNS USING WAVELET ANALYSIS

One of the difficulties encountered in the detection of ecosystem resp onses to climate change is distinguishing climate-induced patterns fro m those created by other sources. For example, changes in the trend of stream discharge records over time may reflect a composite response o f changes in the climate (i.e. precipitation and temperature), land-us e (e.g. timber harvesting and grazing), and local basin characteristic s. Methods which quantify and relate information of temporal and spati al patterns across scales are critical to assess climatically induced changes in the forest and stream ecosystems. A methodology utilizing w avelet analysis is introduced for the purpose of identifying and isola ting inferred climatic components of the hydrologic record Trends obse rved in, stream discharge records from eastern Oregon, USA are identif ied and used to illustrate the utility of a new time series technique, wavelet analysis, as a complementary approach for discerning pattern. This methodology affords an informed procedure for choosing filter di mensions for the purpose of signal decomposition. The wavelet cross-co variance is applied to precipitation and discharge records to identify the climatic component in the discharge record. Reconstruction of the se dominant frequencies is effected to isolate the climatic components . The discharge pattern shows two dominant scales of pattern coinciden t with the precipitation record. A 3-year half-period pattern is found to be correlated with the Southern Oscillation Index at the same freq uency.