Drought Trend Analysis in Kano Using Standardized Precipitation Index (SPI)

Abstract

The trend analysis was carried out using non-parametric Mann-Kendall trend test for Kano using a long term 100 years rainfall data. In other to assess the short term, seasonal, annual and long term droughts, the study employed the Standardized Precipitation Index (SPI) to 3, 6, 9, 12 and 24 month time scales using the rainfall time series data. The SPI values computed for all the time scales revealed a non significant increasing trend for the entire study period (1911-2010), while period 1911-1995 revealed a significant decreasing trend especially in August, September and October. For comparison between different time periods, the 100 years series was sub-divided into 30 years overlapping time period. Period 1951-1980 and 1961-1990 revealed the highest number of statistically significant downward trend. The Z values from Mann-Kendall test ranges from 4.05 to -2.86, which shows how erratic the rainfall could be in Kano. All the analyzed months for periods 1911-1940, 1971-2000, 1981-2010 and 1941-1970 (except May in 1941-1970) showed a general increasing trend for all the time scales. However, periods 1971-2000 and 1981-2010 showed a significant increasing trend which implies that rainfall over the station is at the increase. The value of the slope ranges between -0.053 and 0.118 for all the time scales. High slope values were more prevalent in the higher time scales.