RAINFALL TRENDS AND VARIABILITY

CHAPTER ONE

INTRODUCTION

     1.1 BACKGROUND TO THE STUDY

Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated, meaning that they have become heavy enough to fall due to gravity (Mordurch, 1995; Sala and Lauenroth, 1982). Rain is an important part of the water cycle because it is responsible for depositing the majority of the fresh water on Earth. It supports a variety of ecosystems and provides water for hydroelectric power plants and crop irrigation. Many natural occurrences are influenced by rainfall. Rainfall influences the distribution of vegetation and the types of land masses (Ronen and Avinoam, 1999;Tielborger and Kadmon,2000; Shukla et al, 1990). Animal breeding seasons coincide with rainfall seasons (Radford and Du plessis 2003). Crop planting, yields, and harvests are all being tracked.

Rainfall influences these practices, which are carried out in accordance with their respective enabling seasons to ensure increased productivity (Laux et al, 2010; Mudita et al, 2008;Omokhafe and Emuedo 2006). Similarly, rainfall has a significant impact on the gaseous content of soil composition (Lee et al, 2002).

The term “rainfall trend” refers to a significant shift in the spatial and temporal patterns of rainfall. Rainfall trend, in other words, is the general tendency, movement, or direction and pattern of rainfall. Rainfall trend analyses on various spatial and temporal scales, for example, have been of great concern in the global scene over the last century due to the scientific community’s focus on global climate change: they indicate a warming trend. Despite the fact that large areas are characterized by negative trends, there is a small positive global trend (IPCC, 1996). According to Murphy and Timbal (2007), the majority of the rainfall decline (61%) occurred in autumn (March-May) in southeastern Australia. A similar rainfall decline occurred in the southwest of Western Australia around 1970, with many similarities to the decline in southeastern Australia. However, Nicholson (2000) observed that one of the most significant contrasts in rainfall is the multi-decadal persistence of anomalies over northern Africa at the regional level. Nicholson and Grist (2001) identified several changes in the general atmospheric circulation that have coincided with the transition to drier conditions in the West African Sahel. Rotstayn and Lohmann (2002) demonstrated that the drying of the Sahel is a prominent feature.

North Africa and suggest that anthropogenic sulfate’s indirect effects may have contributed to the Sahelian drying trend (Akinremi et al 2001).

Rainfall variability, on the other hand, is the degree to which rainfall amounts vary over time or across an area. Rainfall variability can be used to characterize a region’s climate. Rainfall in Nigeria varies greatly both in time and in space. As a result of climate change, this variability has taken on a more pronounced dimension. Rainfall variability increases from the northwest to the southwest, while between-year (yearly) rainfall variability increases from the north central to the southeast, according to Chidozie et al. This study confirms that rainfall variability over time follows a spatial trend within a given region.

certain arbitrary limit (Laux et al, 2010, Mudita et al 2008).

Moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts is the primary cause of rain production. Precipitation can fall from convective clouds (those with strong upward vertical motion) such as cumulonimbus (thunder clouds) if there is enough moisture and upward motion. Heavy precipitation is possible in mountainous areas where upslope flow is maximized within windward sides of the terrain at elevation, forcing moist air to condense and fall out as rainfall along the sides of the mountains. Desert climate can exist on the leeward side of mountains due to the dry air caused by downslope flow, which causes heating and drying.

the volume of air. Rainy seasons are brought to savannah climes by the movement of the monsoon trough or inter-tropical convergence zone (Laux et al, 2010, Mudita et al 2008). Downwind of cities, the urban heat island effect causes increased rainfall, both in quantity and intensity. Climate change is also causing changes in precipitation patterns around the world, including wetter conditions in Eastern North America and drier conditions in the tropics.

Olaniran (1990, 1992) and Olaniran and summer (1993) investigated rainfall characteristics in Nigeria for dominant trends (1989, 1990). They demonstrated that there has been a progressive early retreat of rainfall across the entire country, and in keeping with this pattern, they reported a significant decrease in rainfall frequency in September and October, respectively. coincide with the end of the rainy season in the country’s north and center. Northern Nigeria’s rainfall pattern is highly variable in both spatial and temporal dimensions, with inter-annual variability ranging from 15 to 20%. (Oladipo, 1993). Because of the large inter-annual variability in rainfall, climate hazards, particularly floods and severe and droughts, with devastating effects on food production and associated calamities and sufferings, occur frequently (Oladipo, 1993; Okorie, 2003; Adejuwon, 2004). Rainfall is one of Nigeria’s most important climatic resources. Rainfall was the primary source of water for crops and animals. It is regarded as the primary determinant of the types of crops that can be grown in the area, as well as the growing season of cultivation of such crops and the farming systems that can be practiced.

1.2       THE STATEMENT PROBLEM

Variations in rainfall trends are still hotly debated research topics. The major factors influencing rainfall trend and variability have been identified as global warming and climate change. Climate change, in particular, poses a significant threat to rainfall patterns, which will have an indirect or direct impact on ecosystems. According to the Washington Department of Ecology, rising levels of carbon dioxide and other heat-trapping gases in the atmosphere have warmed the Earth and are causing a wide range of effects, including rising sea levels, melting snow and ice, more extreme heat events, fires, and drought, and more extreme storms, rainfall, and floods.

Furthermore, scientists predict that the variability in rainfall trends will continue to accelerate, posing significant risks to human health, our forests, and our ecosystems. Agriculture, freshwater supplies, coastlines, and other natural resources that are critical to a country’s economy, environment, and quality of life are examples of natural resources. Because climate affects so many systems, a change in climate can affect many related aspects of where and how people, plants, and animals live, such as food production, water availability and use, and health risks. Furthermore, a shift in the usual timing of rains or temperatures can influence when plants bloom and set fruit, insects hatch, or streams are at their fullest. This can have an impact on historically synchronized crop pollination, food for migrating birds, fish spawning, water supplies for drinking and irrigation, forest health, and more (Todd et al 2001; Dominic et al 2004; Adams & Faure 1997).

1.3       SIGNIFICANCE OF STUDY

As a result of anthropogenic factors such as urbanization, climate change and global warming have increased at an alarming rate. As a result, the study is important because it will help researchers understand the future consequences of rainfall variation caused by climate change. This is because climate change has been linked to the climate, which in turn affects where and how people make a living, how flora and fauna species thrive, and how food is produced, which is influenced by water availability. According to research, both plants and animals require a certain amount of water to survive, and an excess or insufficient supply of water can lead to their demise. Carbon dioxide is being emitted into the atmosphere at an increasing rate, and Also, the ozone layer has been depleted, causing the earth’s surface to heat up.

1.4       AIM AND OBJECTIVES OF THE STUDY

The purpose of this research is to look into the changes in rainfall over Ibadan from 1982 to 2011. Among the specific goals are:

From 1982 to 2011, the monthly variation in rainfall was calculated.
To calculate the annual variation in rainfall from 1982 to 2011.
From 1982 to 2011, the biannual variation in rainfall was determined.
To forecast Ibadan’s rainfall for the next 30 years.

1.5       HYPOTHESIS

i. There is a significant difference in monthly rainfall trends between 1982 and 2011.

ii. Annual rainfall trends show a significant variation from 1982 to 2011.

iii. There is a significant difference in biannual rainfall trends between 1982 and 2011.

iv. Annual rainfall is expected to increase over the next 30 years.

1.6       STUDY AREA

1.6.1    Location

Ibadan is located approximately 145 kilometers north of Lagos on longitude 30 541 East of the Greenwich meridian and latitude 70 231 North of the Equator (Figure 1). A network of roads, railways, and air routes connects Ibadan to many towns throughout Nigeria. The city’s physical setting is made up of ridges of hills that run roughly northwest to southeast. The largest of these ridges runs through the city center and includes peaks such as Mapo, Mokola, and Aremo. These hills, which range in elevation from 160 to 275 meters above sea level, provide visitors with a panoramic view of the city.

Figure 1: Location of Study: Ibadan, Oyo State.

1.6.2    Climate  

Ibadan has a tropical wet and dry climate, with a long wet season and relatively consistent temperatures all year. The rainy season in Ibadan lasts from March to October, with a brief respite in August. This lull almost splits the wet season into two distinct wet seasons. The remaining months constitute the dry season in the city. Ibadan, like much of West Africa, is affected by the Harmattan between November and February. The tropical rainfall regime in Ibadan is bi-modal, convectional, and follows the apparent movement of the sun, with both the length of the rainy season and the yearly total rainfall decreasing as one moves away from the equator. August is the coldest month, and it coincides with the August vacation. While the dusty and cold harmattan winds conveyed from the Sahara by the north-east trade winds are notable in December and January.

 

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