Analyzing rainfall trend and drought occurences in Sudan Savanna of Nigeria

Abstract

Monthly precipitation data that span from 1986 – 2019 (34) years were downloaded from the website of Nigeria Meteorological Agency, (NIMET), Abuja, Nigeria and were used to assess rainfall trend and drought occurrences in the Sudan Savanna of Nigeria. The non-parametric Mann – Kendall test was employed to test for trends while Standardized Precipitation Index (SPI) was used to generate SPI values and graphs. Our findings show that rainfall is on the declining trend in Gombe (z-value = -0.5930) and Kaduna (z-value = -2.520) but on increasing trend in Sokoto (z-value = 1.9272). Kaduna alone with P-value of 0.0117 which is less than 0.05 level of significance showed monotonic declining trend. In Sokoto, even though there is an increase, it is not monotonic since the P- value of 0.0540 is greater than the significant value of 0.05. The SPI values show only two extreme droughts in Kaduna in 2004 and 2013 with SPI of -2.04 and -2.08 respectively. Some of the years experienced between moderate to severe drought in all the stations while near normal condition is predominant in all the stations. Apart from the only incidence of extreme flooding in Sokoto in 2019 with SPI of 2.755, there were a few incidences of severe wetness or moderate wetness for the other years in all the stations.