2.3. Methods
2.3.1. Trend detection
We analyze and discuss the extreme precipitation over the LP during the
period from 1979 to 2018 by using the Mann-Kendall test and the Sen’s
slope estimator (Hamed 1998). The Mann-Kendall test is used to detect
the significance of the change trend at each grid point. In this study,
there are 13,500 grid points over the LP in the CMFD to be tested. At
the 0.05 significance level, it will yield 675 (13,500 × 0.05) grid
points where the significance cannot be determined, which is too high to
be acceptable. Benjamini and Hochberg (1995) proposed the false
discovery rate (FDR) procedure to apply the multiple Mann-Kendall tests
to adjust the significance level and control the proportion of falsely
rejected null hypotheses relative to the total number of rejected
hypotheses.
The Sen’s slope is applied to estimate the linear trend during 1979 to
2018 for each grid point (Sen and Kumar 1968). A positive slope value
indicates an increasing or upward trend in the time series, while a
negative value reveals a decreasing or downward trend. Similarly, zero
indicates no trend.