Surface energy partitioning and evapotranspiration in a Pinus tabuliformis plantation in Northeast China

Examining the land-atmosphere interaction in vegetation rehabilitation areas is important for better understanding of land surface processes affected by human activities. In this study, energy flux observations were used to investigate surface energy partitioning and evapotranspiration (ET) in a Pinus tabuliformis plantation in Northeast China in 2020 and 2021. The sensible heat flux (H) was the dominant component of R_n, and the ratio of H to the latent heat flux was higher than 1 at all growth stages. The two most important factors influencing the midday evaporative fraction and daily ET were the normalized difference vegetation index (NDVI) and soil water content at 10 cm depth (SWC₁₀). Cumulative precipitation (P) minus ET was 62.83 and 239.90 mm in 2020 (annual P of 435.2 mm) and 2021 (annual P of 632.8 mm), respectively. The midday Priestley-Taylor coefficient (α), surface conductance (g_s), and decoupling coefficient increased gradually from the onset of the mid-growing stage and decreased from the later growing stage. Midday α and g_s increased with NDVI and SWC₁₀ increasing until the NDVI (0.5) and SWC₁₀ (0.17 mm³ mm^-3) thresholds were reached, respectively. Midday α and g_s were significantly influenced by vapor pressure deficit below 3 kPa, and the threshold value of midday g_s was approximately 12 mm s^-1. In conclusion, this Pinus tabuliformis plantation regulated surface energy partitioning properly, and left a part of P for surface runoff and groundwater recharge in the semiarid region of Northeast China.