# Shifts in stream hydrochemistry in responses to typhoon and non-typhoon precipitation

Climate change is projected to increase the intensity and frequency of extreme climatic events such as tropical cyclones. However, few studies have examined the responses of hydrochemical processes to climate extremes. To fill this knowledge gap, we compared the relationship between stream discharge and ion input–output budget during typhoon and non-typhoon periods in four subtropical mountain watersheds with different levels of agricultural land cover in northern Taiwan. The results indicated that the high predictability of ion input–output budgets using stream discharge during the non-typhoon period largely disappeared during the typhoon periods. For ions such as Nainline-formula+, NHinline-formula $M2inlinescrollmathml{}_{normal 4}^{+}$ 8pt15ptsvg-formulamathimg0bd088c5a706fdd4e7871717c05b4b3f bg-15-2379-2018-ie00001.svg8pt15ptbg-15-2379-2018-ie00001.png , and POinline-formula $M3inlinescrollmathml{}_{normal 4}^{normal 3-}$ 13pt17ptsvg-formulamathimgcc7f70959be1563870c0a598e9dbdedc bg-15-2379-2018-ie00002.svg13pt17ptbg-15-2379-2018-ie00002.png , the typhoon period and non-typhoon period exhibited opposite discharge–budget relationships. In other cases, the discharge–budget relationship was driven by the typhoon period, which consisted of only 7 % of the total time period. The striking differences in the discharge–ion budget relationship between the two periods likely resulted from differences in the relative contributions of surface runoff, subsurface runoff and groundwater, which had different chemical compositions, to stream discharge between the two periods. Watersheds with a 17–22 % tea plantation cover showed large increases in NOinline-formula $M4inlinescrollmathml{}_{normal 3}^{-}$ 9pt16ptsvg-formulamathimg0723f17b5be9fc41c36a5585631feb47 bg-15-2379-2018-ie00003.svg9pt16ptbg-15-2379-2018-ie00003.png export with increases in stream discharge. In contrast, watersheds with 93–99 % forest cover showed very mild or no increases in NOinline-formula $M5inlinescrollmathml{}_{normal 3}^{-}$ 9pt16ptsvg-formulamathimg8c72af1edd6d67ed562efcaf5163d22b bg-15-2379-2018-ie00004.svg9pt16ptbg-15-2379-2018-ie00004.png export with increases in discharge and very low levels of NOinline-formula $M6inlinescrollmathml{}_{normal 3}^{-}$ 9pt16ptsvg-formulamathimga6a4c5911a740e8377438efb607d4b86 bg-15-2379-2018-ie00005.svg9pt16ptbg-15-2379-2018-ie00005.png export even during typhoon storms. The results suggest that even mild disruption of the natural vegetation could largely alter hydrochemical processes. Our study clearly illustrates significant shifts in hydrochemical responses between regular and typhoon precipitation. We propose that hydrological models should separate hydrochemical processes into regular and extreme conditions to better capture the whole spectrum of hydrochemical responses to a variety of climate conditions.

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Chang, Chung-Te / Huang, Jr-Chuan / Wang, Lixin / et al: Shifts in stream hydrochemistry in responses to typhoon and non-typhoon precipitation. 2018. Copernicus Publications.

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