Nsiah J J, Gyamfi C, Anornu G K, Odai S N
Department of Civil Engineering, Faculty of Civil and Geo Engineering, Kwame Nkrumah University of Science and Technology (KNUST), Kumasi, Ghana.
Department of Civil Engineering, Faculty of Engineering, Takoradi Technical University (TTU), Takoradi, Ghana.
Heliyon. 2021 Apr 21;7(4):e06828. doi: 10.1016/j.heliyon.2021.e06828. eCollection 2021 Apr.
It is important in water resource planning to accurately estimate the spatial distribution of evapotranspiration (ET) as an input parameter for hydrological studies. Although, conventional pan evaporation, lysimetric and eddy covariance techniques have been used, they only estimate point values. Hence, this study aimed at estimating the spatial distribution of ET within the Pra River Basin (a forest ecological zone) of Ghana, using cloud-free Landsat 8 (OLI/TIRS) satellite images employing the SEBAL methodology. The study further estimates the spatial distribution ET in relation to major climatic variables, Land Use Land Cover (LULC) types and energy balance components. The overall spatial distribution of ET had a mean value of 5.63 mm/day. Spatial distribution of ET (mm/day) for water body (5.51-7.81) and uncultivated forest (5.10-7.71) were high, while moderately average values were observed for logged forest (4.80-7.51). Settlement and bare landscapes observed low rates ((2.05-5.10) mm/day). Spatially, ET was higher in the upper western, central and the eastern parts of the basin, but lower in the northern part and pockets of areas at the southern part of the basin where settlement/bare landscape and logged forest dominate. Areas with high temperature and high solar radiation experiences high ET, while low wind speed, low to average temperature and solar radiation areas experience low ET. Also, areas with both high net radiation and ground heat flux but low to average sensible heat flux experiences high ET and vice versa. Linear regression analysis showed good fit with slope of 0.76 and R of 0.93 indicating that 93 % of the variations in observed field measurement of ET fitted perfectly well with ET distributions generated by the SEBAL model.
在水资源规划中，准确估算蒸散量（ET）的空间分布作为水文研究的输入参数非常重要。尽管传统的蒸发皿蒸发、蒸渗仪和涡度相关技术已被使用，但它们仅能估算点值。因此，本研究旨在利用无云的Landsat 8（OLI/TIRS）卫星图像，采用SEBAL方法估算加纳普拉河流域（一个森林生态区）内的ET空间分布。该研究进一步估算了与主要气候变量、土地利用土地覆盖（LULC）类型和能量平衡组分相关的ET空间分布。ET的总体空间分布平均值为5.63毫米/天。水体（5.51 - 7.81）和未开垦森林（5.10 - 7.71）的ET空间分布较高，而采伐森林（4.80 - 7.51）的ET值为中等平均水平。聚落和裸露景观的ET值较低（（2.05 - 5.10）毫米/天）。在空间上，流域的西部上游、中部和东部ET较高，但在北部以及流域南部聚落/裸露景观和采伐森林占主导的区域ET较低。高温和高太阳辐射区域的ET较高，而低风速、低到平均温度和太阳辐射区域的ET较低。此外，净辐射和地面热通量都高但感热通量低到平均的区域ET较高，反之亦然。线性回归分析显示拟合良好，斜率为0.76，R值为0.93，表明观测到的ET实地测量值中93%的变化与SEBAL模型生成的ET分布完美拟合。
