The biophysical effects of phenological shifts impact land surface temperature for corn expansion in Northeastern China

In the last two decades, rapid corn expansion has significantly impacted local and regional climates in Northeastern China. However, its climatic effects and underlying biophysical mechanisms have rarely been investigated, particularly in accurately describing the changes in surface physiological structure throughout different phenological stages. This study utilized remote sensing observations and the pair-wise comparison approach to examine land surface temperature (LST) change associated with corn expansion at various phenological stages and whole growth seasons, respectively. We then employed the temperature response model to decompose and quantify the LST changes into radiative processes (albedo) and non-radiative processes (i.e., evapotranspiration and turbulent heat exchange). This study indicated that, except for soybean, the mean LST changes (ΔMean_LST) induced by corn expansion initially decreased and subsequently increased with the phenology shifts. Specifically, the potential warming effect was pronounced during three-leaves (EMV3) to seven-leaves stage (V7) and V7 to jointing date (JD), with the largest warming in Mean_LST occurring when corns were converted into trees (1.24±0.43 K) (mean ± 95 % confidence level) (0.93±0.29 K), followed by grass (0.47±0.37 K) (0.43±0.31 K), rice (0.46±0.23 K) (0.31±0.22 K), wetlands (0.16±0.21 K) (0.15±0.34), respectively. EMV3 to JD dominated the ΔMean_LST for the whole growth season, potentially warming the Mean_LST when trees, grass, rice, and wetlands converted to corn, while cooling the Mean_LST when soybeans converted to corn. Furthermore, The effect of phenological stages on LST varies with latitude. For example, during V7 to JD and Milky date (MID) to Maturity date (MD), the non-radiative warming effect of wetland conversion surpassed that of rice conversion as latitude increased (44°N-47°N). This indicates that the wetland conversion causes intensified warming at high latitudes in these stages. Additionally, non-radiative processes, characterized by varying signs and magnitudes, dominated the LST response to corn expansion. Overall, this study comprehensively investigated the ΔLST of corn expansion at various phenological stages and latitudes through the biophysical mechanism, which could be beneficial in developing adaptive and mitigative agricultural management strategies for climate warming in Northeast China.