Trend analysis of hydro-meteorological variables in the coastal area of Lagos using Mann-Kendall trend and Standard Anomaly Index methods

Abstract

This paper presents the application of Mann-Kendall trend test and Standard Anomaly index onhydro-meteorological variables in the coastal area of Lagos state in order to determine the nature of trend and level of significance. The hydro-meteorological data such as air temperature, relative humidity, wind speed, rainfall and sea level rise were obtained from Nigeria meteorological agency (NIMET) Oshodi, Lagos. Variables such as rainfall, relative humidity, wind speed and sea level rise exhibited positive Kendall’s (S) values indicate upward trend and imply an increase of the parameters over time. However, temperature showed negative Kendall’s (S) which indicates downward trend and implies decrease over time. Sea level rise, rainfall, relative humidity and wind speed has mean statistics Zs of 3.9855, 1.9668, 3.0895 and 2.2553 respectively which are more than 1.96 (test statistics for a significant level of 5% that is (Z_0.025 =1.96), this implies that the upward trend is significance and there is tendency to continue. Temperature has statistic Zs of 0.0309 which is less than 1.96 and implies no significance, thus the reduction may not be noticed. The auto correlation factor values ranges from 0.59 to 0.99 for all the parameters, indicating a good fit. Standard Anomaly index (SIA) results showed that trends for the temperature depicts downward trend with the slope of the trend equations are negative, this implies that temperature has tendency to decrease. Rainfall, relative humidity and sea level rise exhibited upward trend which implies tendency to increase. However, the mean wind speed exhibited upward trend while both maximum and minimum wind speed exhibited downward trend, but not noticeable. It can be inferred that both Mann-Kendall trend test and standard anomaly index showed that there is tendency for trend increase in rainfall, humidity, windspeed and sea level rise, while temperature has tendency to decrease. This could be due to impact of climate variability which can influence flooding pattern in the coastline of Lagos State.

Keywords: Climate variables, Mann-Kendall test, Standard Anomaly index, hydro-Meteorological variables, Lagos coast