Abstract
Abstract. Interannual variations in catchment streamflow represent an integrated response to anomalies in regional moisture transport and atmospheric circulations and are ultimately linked to large-scale climate oscillations. This study conducts correlation analysis to calculate how summertime (July–September, JAS) streamflow data derived at 28 upstream and 13 downstream gauges in Taiwan correlate with 14 teleconnection indices in the current or preceding seasons. We find that the western Pacific (WP) 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. 50) with the JAS flows in Taiwan. Alternatively, the Quasi-Biennial Oscillation (QBO) averaged over the period from the previous October to June of the current year is significantly correlated 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 (CRSs) can be revealed. A CRS test is employed to identify suspicious and abrupt changes in the correlation. The late 1970s and 1990s are identified as two significant change points. During the intermediate period, Taiwan's streamflow and the PJ index exhibit a marked in-phase relationship (r > 0. 8). It is verified that the two shifts are in concordance with the alteration of large-scale circulations in the Pacific basin by investigating the changes in pattern correlation and composite maps before and after the change point. Our results suggest that empirical forecasting techniques should take into account the effect of CRSs on predictor screening.
Highlights
Hydro-climatic forecasting is a crucial issue, for those regions suffering increased rainfall intensity and/or reoccurring, persistent droughts in a changing climate
Since the western Pacific (WP) and Pacific– Japan (PJ) indices are associated with cyclonic activity in the western North Pacific (WNP), the strong concurrent correlations with the JAS runoff indicate the direct influence of typhoons on Taiwan in summer
The number of catchments with significant temporal correlations has exceeded the critical value of field significance (p = 0.05) from the empirical null distribution (Fig. S3) developed by using a Monte Carlo technique similar to those suggested by Livezey and Chen (1983) and Wilks (2011); 2000 Monte Carlo trials are used, and each trial depicts a significant local test for correlations between the “randomly ordered” Quasi-Biennial Oscillation (QBO) index and streamflow data at the 41 catchments, resulting in a count of the number of catchments with significant temporal correlations constituting the null distribution
Summary
Hydro-climatic forecasting is a crucial issue, for those regions suffering increased rainfall intensity and/or reoccurring, persistent droughts in a changing climate. Prominent teleconnection patterns have proven useful for regional climate prediction with lead times from weeks to months In Taiwan, the development of such a prediction model is challenging because of mixed weather systems in different seasons, including spring rains, Mei-Yu, and East Asian monsoons from spring to summer, typhoons from summer to autumn, and the Mongolian high-pressure system and associated northeastern monsoons in winter (Yihui and Chan, 2005; Chen and Chen, 2011). The influence of those weather systems on precipitation can further be modulated by the Central Mountain Range (topographic variations) and varied climate zones (latitudinal differences, Huang et al, 2012). The search for the relationship between Taiwan’s climate in the wet season and large-scale circulations can guide the development of a hydro-climatic forecasting framework beneficial to water resource management in this area
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