Impact of Moisture Flux and Vertical Wind Shear on Forecasting Extreme Rainfall Events in Nigeria

Olumide A Olaniyan,Kamoru A Lawal,Vincent O Ajayi,Ugbah Paul Akeh

doi:10.1007/978-3-030-42091-8_98-1

Abstract

AbstractThis chapter investigates extreme rainfall events that caused flood during summer months of June–September 2010–2014. The aim is to determine the impact of horizontal moisture flux divergence (HMFD) and vertical wind shear on forecasting extreme rainfall events over Nigeria. Wind divergence and convective available potential energy (CAPE) were also examined to ascertain their threshold values during the events. The data used include rainfall observation from 40 synoptic stations across Nigeria, reanalyzed datasets from ECMWF at 0.125° × 0.125° resolution and the Tropical Rainfall Measuring Mission (TRMM) dataset at resolution of 0.25° × 0.25°. The ECMWF datasets for the selected days were employed to derive the moisture flux divergence, wind shear, and wind convergence. The derived meteorological parameters and the CAPE were spatially analyzed and superimposed on the precipitation obtained from the satellite data. The mean moisture flux and CAPE for some northern Nigerian stations were also plotted for 3 days prior to and 3 days after the storm. The result showed that HMFD and CAPE increased few days before the storm and peak on the day of the storms, and then declined afterwards. HMFD values above 1.0 × 10−6 g kg−1 s−1 is capable of producing substantial amount of rainfall mostly above 50 mm while wind shear has a much weaker impact on higher rainfall amount than moisture availability. CAPE above 1000 Jkg−1 and 1500 Jk−1 are favorable for convection over the southern and northern Nigeria, respectively. The study recommends quantitative analysis of moisture flux as a valuable short-term severe storm predictor and should be considered in the prediction of extreme rainfall.

Highlights

Human-induced climate change has increased the amount of water vapor in the atmosphere and has caused adverse effects on different regions, ecosystems, and economies across the world (Nwankwoala 2015)
Days of unusually high amount of rainfall during the months of June–September were selected from 2010 to 2014. Derived meteorological parameters such as moisture flux, convective available potential energy (CAPE), vertical wind shear, monsoon depth, the strengths of African Easterly Jet (AEJ) and Tropical Easterly Jet (TEJ) were evaluated on these specific days to ascertain the characteristics of atmospheric dynamics during the occurrences of extreme rainfall events
The mean of derived parameters such as moisture flux and CAPE 3 days prior and after the rainfall events are calculated to assess their characteristics during the period. (12.00°N, 8.59°E), Maiduguri (11.83 N, 13.15°E), Sokoto (13.01° N, 5.25°E), and Yelwa (10.83°N, 4.74°E) were chosen, because according to Omotosho (1985), about 90% of rainfall over these stations is attributed to Mesoscale Convective Systems (MCSs)

Summary

Introduction

Human-induced climate change has increased the amount of water vapor in the atmosphere and has caused adverse effects on different regions, ecosystems, and economies across the world (Nwankwoala 2015). Studying this may enhance the assessment of the manner in which extreme rainfall events evolve and provide a short-term early warning method to forecasters It will assist in understanding the evolution of some derived meteorological parameters such as the moisture flux which determines the quantity of rainfall and the wind shear which determines the life span of the storm (Weisman et al 1988). The aim of this chapter is to determine the impact of moisture flux, vertical wind shear, and other derived meteorological parameters such as wind divergence and convective available potential energy (CAPE) on MCSs during extreme rainfall events over Nigeria. Days of unusually high amount of rainfall during the months of June–September were selected from 2010 to 2014

Research Methodology

Result

Findings

Conclusion