Asymmetric effects of daytime and nighttime warming on vegetation greenness in the Mongolian Plateau

Asymmetric warming of land surface temperatures during the daytime and nighttime has significantly influenced global vegetation growth. This study examines the spatio-temporal patterns of daytime and nighttime temperatures, as well as vegetation growth, in the Mongolian Plateau using ERA-5 data and GIMMS Normalized Difference Vegetation Index (NDVI) data from 1982 to 2022. Through partial correlation and multiple regression analyses, the study further investigates the asymmetric responses of vegetation growth to variations in daytime and nighttime temperatures across the region. The key findings of the study are as follows: (1) Between 1982 and 2022, both daytime and nighttime temperatures in the Mongolian Plateau showed an increasing trend. The rate of increase in daytime temperature (0.44 °C/decade) was 1.22 times that of nighttime temperature (0.36 °C/decade). NDVI values generally exhibited an upward trend, with a growth rate of approximately 0.004/decade. (2) Vegetation growth responses to daytime and nighttime temperatures were asymmetric across the Mongolian Plateau. In 77.95 % of the region, increases in nighttime temperatures were positively correlated with vegetation growth, while 86.46 % of the same regions showed a negative correlation between daytime temperature increases and vegetation growth. (3) Over time, the correlation and sensitivity of NDVI to both daytime and nighttime temperatures have weakened. The inverse responses of NDVI to daytime and nighttime temperature variations may be attributed to the arid climatic conditions of the Mongolian Plateau. Additionally, the weakening of these responses over time may reflect an increasing adaptability of vegetation to the region's climate aridity.