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According to the China Meteorology Administration's guidelines for rainfall event classification, the occurrence frequencies of non-rainy weather and the six categories of rainfall events were calculated (Table 2) for the baseline, QQDC-A1B and SDC-A1B daily precipitation data sets. Table 2 shows that the changes in frequencies of various rainfall events are very small. The occurrence frequency of rainless events would increase by 0.50–1.07% in QQDC-A1B and by 0.15–0.38% in SDC-A1B. The number of rainless days in SDC-A1B should be equal to that of the baseline, but in this work, the dry day statistics also include the light rain days with precipitation of less than 1 mm/d. The likelihood of light rain events exhibits a slight decrease of 1.13–1.50% in QQDC-A1B and 0.46–1.04% in SDC-A1B. Furthermore, considering the magnitude of relative change, the frequencies of extreme events were projected to change significantly. Future severe events such as rainstorm (50–100 mm/d) and heavy rainstorm (100–250 mm/d) might occur more often than the baseline (Table 2). The QQDC method always predicts higher frequencies of these severe storms than the SDC method. For instance, in Shijiao watershed, the heavy rainstorm events in SDC-A1B would occur twice as frequently as those in the baseline, but in QQDC-A1B, the rainstorm events are four times more often than those in the baseline period. In addition, no extreme heavy rainstorm (≥250 mm/d) appears in the baseline and SDC-A1B in Boluo watershed, whereas these extreme events would occur under QQDC-A1B at a frequency of 0.03%. These results imply that, in the future, non-rainy weather is likely to occur slightly more frequently, less light rain events would occur, and the probability of severe rainstorm events would increase considerably. The QQDC-A1B scenario would encounter more severe extreme weather situations with increased rainless days and more frequent storm events.

Table 2

Occurrence frequencies of non-rainy event and six rainfall events for the baseline and future A1B daily precipitation data sets

Frequencies (%)
RegionsData typesNo rain (0–1 mm)Light rain (1–10 mm)Moderate rain (10–25 mm)Heavy rain (25–50 mm)Rainstorm (50–100 mm)Heavy rainstorm (100–250 mm)Extreme heavy rainstorm (≥250 mm)
Wuxuan (West River) Baseline (1961–1990) 49.77 38.53 9.83 1.82 0.05 0.00 0.00 
SDC-A1B (2011–2040) 50.10 ↑ 37.50 ↓ 10.08 ↑ 2.23 ↑ 0.08 ↑ 0.00 0.00 
QQDC-A1B (2011–2040) 50.27 ↑↑ 37.09 ↓↓ 10.15 ↑↑ 2.36 ↑↑ 0.14 ↑↑ 0.00 0.00 
Shijiao (North River) Baseline (1961–1990) 57.15 28.05 10.55 3.49 0.75 0.02 0.00 
SDC-A1B (2011–2040) 57.53 ↑ 27.01 ↓ 10.70 ↑ 3.71 ↑ 1.02 ↑ 0.04 ↑ 0.00 
QQDC-A1B (2011–2040) 58.01 ↑↑ 26.55 ↓↓ 10.23 ↓ 3.93 ↑↑ 1.19 ↑↑ 0.10 ↑↑ 0.00 
Boluo (East River) Baseline (1961–1990) 59.58 25.02 10.02 4.20 1.05 0.13 0.00 
SDC-A1B (2011–2040) 59.73 ↑ 24.56 ↓ 9.98 ↓ 4.18 ↓ 1.38 ↑ 0.17 ↑ 0.00 
QQDC-A1B (2011–2040) 60.65 ↑↑ 23.99 ↓↓ 9.56 ↓↓ 4.06 ↓↓ 1.50 ↑↑ 0.22 ↑↑ 0.03 ↑ 
Frequencies (%)
RegionsData typesNo rain (0–1 mm)Light rain (1–10 mm)Moderate rain (10–25 mm)Heavy rain (25–50 mm)Rainstorm (50–100 mm)Heavy rainstorm (100–250 mm)Extreme heavy rainstorm (≥250 mm)
Wuxuan (West River) Baseline (1961–1990) 49.77 38.53 9.83 1.82 0.05 0.00 0.00 
SDC-A1B (2011–2040) 50.10 ↑ 37.50 ↓ 10.08 ↑ 2.23 ↑ 0.08 ↑ 0.00 0.00 
QQDC-A1B (2011–2040) 50.27 ↑↑ 37.09 ↓↓ 10.15 ↑↑ 2.36 ↑↑ 0.14 ↑↑ 0.00 0.00 
Shijiao (North River) Baseline (1961–1990) 57.15 28.05 10.55 3.49 0.75 0.02 0.00 
SDC-A1B (2011–2040) 57.53 ↑ 27.01 ↓ 10.70 ↑ 3.71 ↑ 1.02 ↑ 0.04 ↑ 0.00 
QQDC-A1B (2011–2040) 58.01 ↑↑ 26.55 ↓↓ 10.23 ↓ 3.93 ↑↑ 1.19 ↑↑ 0.10 ↑↑ 0.00 
Boluo (East River) Baseline (1961–1990) 59.58 25.02 10.02 4.20 1.05 0.13 0.00 
SDC-A1B (2011–2040) 59.73 ↑ 24.56 ↓ 9.98 ↓ 4.18 ↓ 1.38 ↑ 0.17 ↑ 0.00 
QQDC-A1B (2011–2040) 60.65 ↑↑ 23.99 ↓↓ 9.56 ↓↓ 4.06 ↓↓ 1.50 ↑↑ 0.22 ↑↑ 0.03 ↑ 

Symbols ‘ ↑ ’ and ‘ ↓ ’ denote whether the occurrence frequency of a type of rainfall event in the A1B scenarios shows an increasing or decreasing trend relative to the baseline; the double-arrow symbols denote a considerably higher increase or decrease magnitude of the given events in the QQDC-A1B and SDC-A1B scenarios.

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