Global warming intensifies the hydrological cycle, resulting in more frequent extreme climate events. Relative humidity (RH) is a core indicator of atmospheric aridity that regulates ecosystem functions, environmental quality, human health, and agricultural production. Therefore, reconstructing its historical evolution holds significant scientific and practical value.

The Chinese Loess Plateau (CLP), located in northwest China, is a critical ecological barrier and dryland farming region where water availability is crucial for regional sustainability. However, existing dendroclimatological studies of the CLP have predominantly focused on its western and northeastern margins, and reconstructions have largely been limited to temperature, precipitation, and the Palmer Drought Severity Index. Notable gaps remain regarding relative humidity.

In a new study published in the Journal of Forestry Research on April 8, researchers from the Institute of Earth Environment of the Chinese Academy of Sciences have developed a tree-ring width chronology using 51 cores from 27 Pinus tabulaeformis Carr. trees in the southeastern CLP. Their analysis identified that RH from April to mid-August (RH_c10-23) was the main factor limiting the radial growth of P. tabulaeformis in the study area. Based on this relationship, they reconstructed an RH_c10-23 record spanning nearly two centuries, from 1844 to 2023, which explains 45.4% of the variance in instrumental records.

This reconstruction shows a long-term drying trend and a "warm-dry/cold-wet" climate pattern. There were relatively dry periods from 1844 to 1846, from 1898 to 1901, from 1926 to 1935, from 1974 to 1980, and from 1997 to 2023. There were relatively wet periods from 1850 to 1890, from 1910 to 1916, and from 1951 to 1966. 

The reconstruction also reveals a consistent drying trend since 1844 and documents three significant historical droughts in northern China (around 1900, the late 1920s, and 1940–1943), as well as an unprecedented, prolonged drought from 1997 to 2023. Despite its exceptional severity, the 1997–2023 drought caused comparatively limited economic losses and societal disruption, reflecting modern society's substantially enhanced climate resilience. 

Further analysis shows that regional RH variability is influenced by several large-scale climate systems, including the Asian Summer Monsoon, Atlantic Multidecadal Variability/Oscillation, El Niño-Southern Oscillation, and the Indian Ocean Dipole.

Together, these findings provide a clearer picture of the hydroclimatic evolution of the Loess Plateau. They demonstrate the practical value of proactive human adaptation strategies in mitigating the impacts of climate change and offer valuable scientific support for water resource management and climate change mitigation.

This work was mainly supported by the National Natural Science Foundation of China and the Natural Science Basic Research Program of Shaanxi.