Abstract
Abstract. 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 Na+, NH4+, and PO43-, 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 NO3- export with increases in stream discharge. In contrast, watersheds with 93–99 % forest cover showed very mild or no increases in NO3- export with increases in discharge and very low levels of NO3- 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.
Highlights
One of the major concerns of global climate change is increases in extreme climatic events such as flooding, droughts, and tropical cyclones (Phillips, 2017)
A large number of studies have reported that replacing natural forests with agricultural lands causes large increases in surface runoff, sediment yield and nutrient export (Kosmas et al, 1997; Hill et al, 1998; Gessesse et al, 2015)
This study was conducted at the 303 km2 subtropical Feitsui Reservoir Watershed (FRW) in northern Taiwan (Fig. 1a)
Summary
One of the major concerns of global climate change is increases in extreme climatic events such as flooding, droughts, and tropical cyclones (Phillips, 2017). Predicting ecological effects of climate extremes is challenging because their effects on ecosystems could be dramatically different from “typical” or “normal” climatic variability (Smith, 2011). A large number of studies have reported that replacing natural forests with agricultural lands causes large increases in surface runoff, sediment yield and nutrient export (Kosmas et al, 1997; Hill et al, 1998; Gessesse et al, 2015). In a study of nutrient cycling in upstream watersheds of northern Taiwan, the replacement of 22 % of the natural forests by tea plantations reduced the nitrogen retention ratio by 50 % (Lin et al, 2015).
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