ENVIRONMENTAL FACTORS CONTROLLING EVAPOTRANSPIRATION OVER AXONOPUS COMPRESSUS GRASS IN AKURE

Abstract

Evapotranspiration is one of the major hydrological processes that links energy, water, and carbon cycles or carbon fluxes in terrestrial ecosystems and water-use efficiency in plant communities and also serves as a key regulator of the ecosystem processes. The aim of this study is to estimate evapotranspiration and to examine the environmental factors controlling evapotranspiration over Axonopus Compressus, using the BREB micrometeorological technique. The analyses was done using a two year Dataset (January 2014 to December 2015), using R programming software to assess the diurnal and seasonal variation of the variables being studied. This study was conducted at the West African Science Services Centre on Climate Change and Adopted Land Use (WASCAL) meteorological observatory at the Federal University of Technology, Akure where ten minutes climatic data recorded for two years between 2014 and 2015 was gotten from. Results from the study shows that ET rates were high during the Dry (JF14 & DJF15), (13.5mm/hr) and Dry to wet (MAM14 & MAM15), (12.5mm/hr) and relatively low during the Wet (JJA14 & JJA15), (11.6mm/hr) and Wet to Dry (SON14 & SOND15), (12.3mm/hr) seasons. During the Dry season (JF14 & DJF15), the available energy was partitioned into 72% LE and 28% H, while in the Dry to Wet periods (MAM14 and MAM15), the available energy was partitioned into 70% LE and 30% H. During the Wet season, available energy was partitioned into 68% LE and 32% H, it was partitioned into 72% LE and 28% H during the Wet to Dry season. During the study, RN was more correlated to LE during the Dry, R2 = 0.99 and Dry to Wet period, R2 = 1, while VPD was more correlated to LE during the Wet season, R2 = 0.66. Therefore, the energy partitioning was driven by RN in the Dry and Dry to Wet season and it was driven by VPD in the Wet season. The correlation between ET and GS was high during the Wet season (R2 = 0.27) while the correlation was low during the Dry to Wet Season (R2 = vi | P a g e 0.088). This results reveals that GS had a greater influence over ET during the Wet period, than in other seasons during the study period. The result shows that RS is more correlated to ET in the Dry seasons, R2 = 0.96 than in the Wet season, R2 = 0.87. The correlation between ET and VPD shows that ET and VPD were more correlated in the Dry and Dry to Wet Season as a function of high soil moisture (Soil moisture range 0.10-0.25, R2 = 0.57 and Soil moisture range 0.05-0.1, R2 = 0.46). However, in the Wet and Wet to Dry season, VPD was more correlated to ET with low soil moisture (Soil moisture range 0.10- 0.25, R2 = 0.66 and Soil moisture range 0.05-0.1, R2 = 0.67). Recommendation was given to carry out further studies to have a better understanding about the environmental factors controlling Evapotranspiration.