Abstract:
This study examined the trends in annual rainfall and temperature extremes over
the Vea catchment for the period 1985–2016, using quality-controlled stations and a high resolution
(5 km) Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) data. The CHIRPS
gridded precipitation data’s ability in reproducing the climatology of the catchment was evaluated.
The extreme rainfall and temperature indices were computed using a RClimdex package by
considering seventeen (17) climate change indices from the Expert Team on Climate Change
Detection Monitoring Indices (ETCCDMI). Trend detection and quantification in the rainfall
(frequency and intensity) and temperature extreme indices were analyzed using the non-parametric
Mann–Kendall (MK) test and Sen’s slope estimator. The results show a very high seasonal correlation
coefficient (r = 0.99), Nash–Sutcliff efficiency (0.98) and percentage bias (4.4% and 8.1%) between the
stations and the gridded data. An investigation of dry and wet years using Standardized Anomaly
Index shows 45.5% frequency of drier than normal periods compared to 54.5% wetter than normal
periods in the catchment with 1999 and 2003 been extremely wet years while the year 1990 and 2013
were extremely dry. The intensity and magnitude of extreme rainfall indices show a decreasing trend
for more than 78% of the rainfall locations while positive trends were observed in the frequency
of extreme rainfall indices (R10mm, R20mm, and CDD) with the exception of consecutive wet
days (CWD) that shows a decreasing trend. A general warming trend over the catchment was
observed through the increase in the annual number of warm days (TX90p), warm nights (TN90p)
and warm spells (WSDI). The spatial distribution analysis shows a high frequency and intensity of
extremes rainfall indices in the south of the catchment compared to the middle and northern of part
of the catchment, while temperature extremes were uniformly distributed over the catchment.
