Possibility of Summer Drought Due to the Recently Reinforced Growth of Vegetation in Spring in Korea

Under the global trend of increased vegetation growth due to global warming, spring vegetation in South Korea and East Asia has shown a pronounced greening trend since the 2000s. Interestingly, during the same period, soil moisture in South Korea during the summer season has exhibited a distinct drying trend. This study confirms through observations and model experiments that these two trends may not be simply coincidental. Instead, they could be the result of the advancement of vegetation growth onset due to the warming trend, leading to increased spring vegetation and evapotranspiration, subsequently resulting in reduced summer soil moisture. The negative correlation between spring vegetation and summer soil moisture has linearly strengthened from the late 20^th century to the present.

In the 2000s, while the variability of summer soil moisture has decreased, the impact of spring vegetation variability on summer soil moisture has been confirmed to increase. CLM5 (Community Land Model 5) Model experiments conducted to verify the mechanism of the changing relationship between spring vegetation and summer soil moisture have shown that an increase in spring vegetation leads to increased evaporation the following month, followed by a decrease in soil moisture the subsequent month, consistent with observations. Furthermore, it has been confirmed that with the projected increase in insolation forcing in the future, the East Asian summer monsoon will intensify, and overall summer precipitation in South Korea is expected to increase. However, it has also been confirmed that the greening trend of vegetation may consistently contribute to the occurrence of summer droughts. Therefore, it is essential to consider the interaction with vegetation when predicting and addressing future drought changes.