Abstract
In this paper, the monthly variation of Surface Water Vapour Density (SWVD) with meteorological parameters of monthly average daily mean temperature, relative humidity, surface pressure, cloud cover and sunshine hours during the period of sixteen years (2000 – 2015) for Owerri (Latitude 5.48°N, Longitude 7.00°E, and 91m above sea level) were investigated. The daily variation of surface water vapour density for the two distinct seasons considering two typical months in each during the period of year 2015 was examined. The results showed fluctuation in the amount of surface water vapour density in each day of the month for the period under investigation. The monthly average daily values indicated that the surface water vapour densities are greater during the raining season than in the dry season. It was observed that the maximum average value of surface water vapour density of 21.002gm-3 occurred in the month of June during the raining season and minimum value of 14.653gm-3 in the month of January during the dry season. The highest value of surface water vapour density was observed on 9th May, 2015 and the lowest on 14th January, 2015. The comparison assessment of the developed SWVD based models was carried out using statistical indices of coefficient of determination (R2), Mean Bias Error (MBE), Root Mean Square Error (RMSE), Mean Percentage Error (MPE), Nash – Sutcliffe Equation (NSE) and Index of Agreement (IA). The developed multivariate correlation regression model that relates temperature and relative humidity with R2=99.9% MBE=0.1259 RMSE=0.1462 MPE=-0.6739 NSE=99.8402% and IA=99.9611% was found more suitable for surface water vapour density estimation with good fitting and therefore can be used for estimating surface water vapour density in the location under investigation and region with similar climatic information. The results of the descriptive statistical analysis revealed that the surface water vapour density, mean temperature, relative humidity, cloud cover and sunshine hours data spread out more to the left of their mean value (negatively skewed), while the surface pressure data spread out more to the right of their mean value (positively skewed). The surface water vapour density data have positive kurtosis which indicates a relatively peaked distribution and possibility of a leptokurtic distribution while the mean temperature, relative humidity, surface pressure, cloud cover and sunshine hours data have negative kurtosis which indicates a relatively flat distribution and possibility of platykurtic distribution.
Highlights
The connection between the surface and the atmosphere in the hydrological cycle is normally referred to as Water vapour
The daily and monthly average minimum temperature, maximum temperature, relative humidity, surface pressure, cloud cover and sunshine hours meteorological data used in this study were obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) at 2m height for Owerri, Imo state located in the South Eastern, Nigeria during the period of sixteen years (2000 – 2015)
It was observed that the values of Surface Water Vapour Density (SWVD) decreases in the month of July and August immediately after its maximum value in the month of June and later increases in the month of September; this observation is in line with the result reported by Adeyemi and Ogolo [2] for Ikeja and Ibadan located in the Southern zone of Nigeria
Summary
The connection between the surface and the atmosphere in the hydrological cycle is normally referred to as Water vapour. As the Earth’s surface temperature increases, the atmosphere tends to hold more water vapour This atmospheric water vapour, acts as a greenhouse gas thereby absorbing energy that would otherwise cause attenuation of electromagnetic radiation travelling through the atmosphere, the consequences of these could be atmospheric or global warming. The proportion by volume of water vapour in the air at the ground level on the average changes from less than 0.001%in the arctic to more than 6% in the tropics [4]. This proportion decreases speedily with height [4]
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