Trends in Extreme Precipitation Indices in Northwest Ethiopia: Comparative Analysis Using the Mann–Kendall and Innovative Trend Analysis Methods

Abstract

This study analyzed long-term extreme precipitation indices using 4 × 4 km gridded data obtained from the National Meteorological Agency of Ethiopia between 1981 and 2018. The study examined trends in extreme precipitation over three districts (Lay Gayint, Tach Gayint, and Simada) in the northwestern highlands of Ethiopia. Innovative Trend Analysis (ITA) and Mann–Kendall (MK) trend tests were used to study extreme precipitation trends. Based on the ITA result, the calculated values of nine indices (90% of the analyzed indices) showed significant increasing trends (p < 0.01) in Lay Gayint. In Tach Gayint, 70% (seven indices) showed significantly increasing trends at p < 0.01. On the other hand, 60% of the extreme indices showed significant downward trends (p < 0.01) in Simada. The MK test revealed that 30% of the extreme indices had significantly increasing trends (p < 0.01) in Lay Gayint. In Tach Gayint, 30% of the extreme indices showed significant increasing trends at p < 0.05, while 10% of the extreme indices exhibited significant increasing trends at p < 0.01. In Simada, 20% of the extreme indices showed significant increasing trends at p < 0.05. Overall, the results showed that the ITA method can identify a variety of significant trends that the MK test misses.

Historical Trend Analysis and Future Projections of Rainfall in Amhara, Ethiopia

“…Although ITA and the MK tests may result in similar trends, the ITA test outperforms the MK trend test because it does not have preconditions; the MK test has preconditions such as distribution type, size of dataset, and existence or non-existence of serial autocorrelation (Seenu & Jayakumar, 2021). Other studies conducted in Ethiopia reported that the ITA test can identify various significant trends not detected by the MK test (Likinaw et al, 2023) and was preferred to the MK test (Gedefaw, 2023). This study resulted in similar trend values for f = 73 and f = 80.08 with Eq.…”