TRENDS IN RAINFALL AND VARIABILITY
CHAPTER ONE
INTRODUCTION
1.1 THE STUDY’S BACKGROUND
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 influenced by rainfall and 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. Because of the scientific community’s focus on global climate change, rainfall trend analyses on various spatial and temporal scales have been of great concern in the past century: they indicate a small positive global trend, even though large areas are characterized by negative trends (IPCC, 1996).
According to Murphy and Timbal (2007), the majority of the rainfall decline (61 percent) 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 in North Africa is a prominent feature, and they suggest that the indirect effects of anthropogenic sulfate 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 the variability of rainfall over time follows a spatial trend within a specific arbitrary boundary (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. Due to the dry air caused by downslope flow, which causes heating and drying of the air mass, desert climates can exist on the leeward side of mountains.
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 consistent with this pattern, they reported a significant decline in rainfall frequency in September and October, which coincide with the end of the rainy season in the northern and central parts of the country, respectively.
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 time period for cultivating such crops and the farming systems that can be used.
1.2 THE PROBLEM STATEMENT
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 rainfall variability will continue to accelerate, posing significant risks to human health, forests, agriculture, freshwater supplies, coastlines, and other natural resources critical to a country’s economy, environment, and quality of life.
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).
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TRENDS IN RAINFALL AND VARIABILITY