Status: this preprint was under review for the journal HESS but the revision was not accepted.
On the Relationship between Teleconnections and Taiwan's Streamflow: Evidence of Climate Regime Shift and Implications for Seasonal Forecasting
Chia-Jeng Chenand Tsung-Yu Lee
Abstract. Interannual variations of catchment streamflow represent an integrated response to anomalies in regional moisture transport and atmospheric circulations, ultimately linked to large-scale climate oscillations. This study investigates the relationship between Taiwan's long-term summertime (July to September, JAS) streamflow and manifold teleconnection patterns. Lagged correlation analysis is conducted to calculate how JAS streamflow data derived at 28 upstream and 13 downstream gauges in Taiwan correlate with 14 teleconnection indices in the concurrent or preceding seasons. Out of the many indices, the West-Pacific and Pacific-Japan (PJ) patterns, both of which play a critical role in determining cyclonic activity in the western North Pacific basin, exhibit the highest concurrent correlations (most significant r = 0.48) with the JAS flows in Taiwan. At a one-month lead time, on the other hand, the Quasi-Biennial Oscillation significantly correlate with the JAS flows (most significant r = −0.66), indicating some forecasting utility. By further examining the correlation results using a 20-year moving window, peculiar temporal variations and possible climate regime shifts (CRS) can be revealed. To identify suspicious, abrupt changes in the correlation, a CRS test is employed. The late 1970s and 1990s are identified as two significant change points, and during the intermediate period, a marked in-phase relationship (r ~ 0.9) between Taiwan's streamflow and the PJ index is observed. It is verified that the two shifts are in concordance with the alteration of large-scale circulations in the Pacific basin. Discussion about the changes in pattern correlation and composite maps before and after the change point is carried out, and our results suggest that empirical forecasting techniques should take into account the effect of CRS on predictor screening.
Received: 09 May 2016 – Discussion started: 15 Jun 2016
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Seasonal forecasting of a region's hydro-climatic variables is not a fantasy as long as such variables are modulated by certain large-scale, reoccurring climate oscillations. In this article, the authors provide both statistical and physical evidence of how Taiwan's summertime streamflow is strongly connected with some climate patterns dominating cyclonic activity in the Northwest Pacific. However, such connection can be strengthened or weakened by climate regime shifts, as a forecasting caveat.
Seasonal forecasting of a region's hydro-climatic variables is not a fantasy as long as such...
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