Application of the ITA approach to analyze spatio-temporal trends in monthly maximum rainfall categories in the Vu Gia-Thu Bon, Vietnam

This study aims to investigate the trend behavior of monthly maximum in daily rainfall categories in the Vu Gia-Thu Bon river basin located in central Vietnam. Daily maximum rainfall series from 12 rainfall stations for the period 1979–2018 were utilized to characterize six categories of the intensity of daily maximum rainfall: light (0–4 mm/day, category A), mild-moderate (4–16 mm/day, category B), moderate-heavy (16–32 mm/day, category C1), heavy (32–64 mm/day, category C2), heavy-torrential (64–128 mm/day, category D1), and torrential (≥ 128 mm/day, category D2). The new approach of the Innovative Trends Analysis was then applied to the six classified categories. The results revealed that category B had a dominant increasing trend (32% of rain events) for all the stations in January (5.85%) and February (3.44%). In March and April, category A was dominant with 45% and 20%, respectively. In July, category C1 was dominant with 25%, while in August and September, category C2 prevailed over all stations with 45% (all stations) and 20%, respectively. The categories D1 and D2 were observed at all stations in December and November, with 26% and 31% of events, respectively. These results indicate an increasing trend in the categories B, C1, C2, and D1.