Abstract
It is common practice in water resource management to estimate evaporation of water from reservoirs using nearby measurements of pan evaporation. With the emergence of water supply and food security issues as a result of increasing population and climate change pressures, the need for efficient use of available water supplies is paramount. Management of available resources and improved efficiency require accurate knowledge of evaporation, which is a major water loss pathway. This study used Autoregressive Integrated Moving Average (ARIMA) models to forecast pan-evaporation data. The historical data on pan evaporation (1982 – 2012) at Osogbo, southwest Nigeria, was initially subjected to a regression analysis which showed that the data has an increasing trend, while the plot of autocorrelation function indicated that the data is not stationary. Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC), as well as diagnostics of residuals confirmed that ARIMA(3,4,3) is a good fit for both short term data forecast and data generation for pan-evaporation. Estimated long term reservoir evaporation series (2013 – 2062) was applied to the reservoir capacity curve and compared to the water demand curve. The results showed that with the increasing evaporation trend the reservoir will not be able to serve the various benefitting towns after year 2038. This implies that new water sources would be needed to meet the increasing water demand due to increasing population.
Highlights
The rapidly growing population of the world is putting increasing pressure on fresh water supplies
Autoregressive Integrated Moving Average (ARIMA) model is an extension of autoregressive moving average (ARMA) model in the sense that including autoregressive and moving average has an extra part of differencing the time series
After an ARIMA model has been carefully selected for the long term monthly data generation of the pan-evaporation data, the monthly evaporation data series was estimated with the formula http://www.ijSciences.com
Summary
The rapidly growing population of the world is putting increasing pressure on fresh water supplies Adding to this pressure is the potential changes to rainfall timing and amount due to climate change. Water scarcity is a major challenge facing a lot of nations especially the third world countries in the present time (Adeboye, et al 2009) This can be attributed to climate change, increasing demand for freshwater by the competing users in different sectors and more importantly the environmentally induced problems such as desertification and overexploitation of the existing water resources (Pereira, 2005). Precipitation for example is the major input to a watershed Climatic factors, such as temperature, humidity, and wind, govern water loss through evaporation and transpiration.
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