CHAPTER ONEINTRODUCTION1.1 Background of the StudyClimate change is the rise in average surface temperatures on earth, mostly due to the burning of fossil fuels. Also, climate change is a long-term change in the earth’s climate, especially a change due to an increase in the average atmospheric temperature. An overwhelming scientific consensus maintains that climate change is due primarily to the human use of fossil fuels, which releases carbon dioxide and other greenhouse gases into the air. The gases trap heat within the atmosphere, which can have a range of effects on ecosystems, including rising sea levels, severe weather events, and droughts that render landscapes more susceptible to wildfires.The primary cause of climate change is the burning of fossil fuels, such as oil and coal, which emits greenhouse gases into the atmosphere primarily carbon dioxide. Other human activities, such as agriculture and deforestation, also contribute to the proliferation of greenhouse gases that cause climate change. Even small increases in earth’s temperature caused by climate change can have severe effects. Rising sea levels due to the melting of the polar ice caps (again, caused by climate change) contribute to greater storm damage; warming ocean temperatures are associated with stronger and more frequent storms; additional rainfall, particularly during severe weather events, leads to flooding and other damage; an increase in the incidence and severity of wildfires threatens habitats, homes, and lives; and heat waves contribute to human deaths and other consequences. In arid or semi-arid regions, minor variations in precipitation and temperature easily induced significant changes in hydrological processes (Gan, 2000; Ma et al., 2004).Evaporation is the conversion of moisture into vapor form and its removal and transport upwards into the atmosphere. Pan evaporation is a measurement that combines or integrates the effects of several climate elements: temperature, humidity, rain fall, drought dispersion, solar radiation, and wind. Evaporation is greatest on hot, windy, dry, sunny days; and is greatly reduced when clouds block the sun and when air is cool, calm, and humid (Howard, 1996). Pan evaporation measurements enable farmers and ranchers to understand how much water their crops will need (Gan, 2000).Evapotranspiration is an important flux term in the water cycle that integrates atmospheric demands and surface conditions. Furthermore, evapotranspiration is also a factor determining climatic drought in arid and semi-arid regions. Any variations in meteorological variables induced by climate change will affect evapotranspiration or crop water requirements. Eventually, climate change will increase or decrease the dry conditions in the arid regions of the world by increasing or decreasing potential evapotranspiration.Potential evapotranspiration (PET) can be generally defined as the amount of water that could evaporate and transpire from a vegetated landscape without restrictions other than the atmospheric demand (Thornthwaite, 1999; Penman, 1948; Jensen, 2004). The concept of PET provides a convenient index to represent or estimate the maximum water loss to the atmosphere. Estimates of PET are necessary in many of the rainfall-runoff and ecosystem models that are used in global change studies (Band et al., 2006; Hay and McCabe, 2002). Potential evapotranspiration is also used as an index to represent the available environmental energies and ecosystem productivity (Currie, 1991). For example, in the four vertebrate classes studied, Currie (1991) found that 80 to 93 percent of the variability in species richness could be statistically explained by ecosystem PET.
A study on the trend of potential evapotranspiration in some parts of Nigeria (1961 – 1991) showed a decline in annual rainfall, a 1.5 increase in air temperature and an increasing trend in potential evapotranspiration, although not significant (Hess, 2008). With evidence indicating that atmospheric concentrations of green house gases are increasing, there is growing concern that these changes will have significant impacts on water within the hydrologic cycle in many regions of the world (Skiles and Hanson, 1994).
1.2 Statement of ProblemClimate change is the greatest environmental threat humanity has ever faced and the biggest challenge. It is a global problem felt today. It is caused by the burning of fossil fuels, such as oil and coal, which emits greenhouse gases into the atmosphere primarily carbon dioxide. Other human activities, such as agriculture and deforestation, also contribute to the proliferation of greenhouse gases and destruction of areas that stores massive amount of carbon like the world’s rainforest. Its effect is already harming our people and ecosystem. It is therefore pertinent to study the effect of climate change on pan evaporation and potential evapotranspiration trend in Ibesikpo Asutan, Akwa Ibom State.
1.3 Objectives of the StudyThe objectives of the study are as follows:To determine the trend of pan evaporation and potential evapotranspiration in the study area.To determine the effect of climate change on pan evaporation and potential evpotranspiration in the study area.