Estimation of Reference Evapotranspiration Using Penman-Monteith Equation and Time Series Model in some Selected States in Northern Nigeria

Abstract

Based on the problem of climate change which greatly affect agriculture and water management in Northern Nigeria, this study estimated reference evapotranspiration using Penman-Monteith equation and time series models in some selected states in Northern Nigeria. The study covered 16 states in Northern Nigeria which were selected using purposive sampling techniques. The materials used for the study consist of secondary data of daily mean records of air temperature, wind speed, solar radiation, and relative humidity from 1^st January 1984 to December 2022. From the data, the daily reference Evapotranspiration were computed using Penman-Monteith equation. Based on this, daily and mean annual reference evapotranspiration was obtained. From the result obtained on the daily and annual mean reference evapotranspiration, the time series models were plotted. The time series models plotted consist of daily reference evapotranspiration against time and mean annual reference evapotranspiration against time.  The time series plots provided random, nonlinear trend plot which is aperiodic. The plot of the mean and variance of reference evapotranspiration of states against latitudinal trend showed that R² >0.60, which indicated that the mean and variance of reference evapotranspiration has a strong relationship with latitudinal trend of the states and thus can be used for predictive purpose. This latitudinal trend behavior of the mean and variance of reference evapotranspiration is further supported using spatial distribution map of Northern Nigeria which showed that the lowest mean reference evapotranspiration is location within FCT-Abuja and Jos while the highest mean reference evapotranspiration is located within Sokoto, Kebbi and Gusau.