For the millions living in Northwest China's arid expanse, where water scarcity has shaped life for centuries, a quiet question has emerged: why is it getting wetter?
Now, scientists who have spent their careers studying this region offer a surprising answer. The recent increase in precipitation is not arriving from afar. It is, instead, mostly rising up from the land itself.
Published in Advances in Atmospheric Sciences , the study was conducted by researchers from the Northwest Institute of Eco-Environment and Resources at the Chinese Academy of Sciences, Lanzhou University, and the Lanzhou Institute of Arid Meteorology of China Meteorological Administration. The team shares deep roots in the region they study.
Lead author Professor Haipeng Yu first arrived in Lanzhou as a student in 2005, drawn to study China's dryland climate. He never left. Senior authors Professors Jianping Huang and Qiang Zhang were both born in Northwest China and have devoted their entire careers to understanding its arid and semi-arid regional climate.
Their combined decades of observation have tracked a fundamental shift.
A Turning Point in the 1990s
Traditionally, precipitation in Northwest China was thought to depend heavily on moisture carried in from outside. The new research confirms that while external moisture still dominates the long-term average, the region's trend toward humidification since the late 20th century is being driven largely by local sources: enhanced evaporation from soil, plants, and water bodies—a process intensified by warming temperatures and ecological changes.
The research identifies the late 1990s as a critical turning point. Around that time, summer precipitation shifted from a long-term decline to a sustained increase. Spatially, the changes are uneven—western areas around the Tianshan and Altun Mountains have seen substantial increases, while some eastern parts have experienced drying trends.
Tracing the Source
Using a Dynamic Recycling Model, the team quantified the contributions of different moisture sources. Comparing 1961–1997 with 1998–2020, they found that annual precipitation increased by 10.62 mm (9.18%), while local evapotranspiration rose by 10.42 mm (9.12%). Crucially, nearly 78% of the increase in precipitation came from locally recycled moisture , with only about 22% from enhanced external transport.
This marks a fundamental shift in understanding. More than half of the region's average precipitation still comes from outside, but the increase since the late 1990s is overwhelmingly local in origin.
Land–Atmosphere Coupling
Warmer temperatures, increased meltwater from glaciers and snowpack, and vegetation recovery have all contributed to rising evapotranspiration, creating a feedback loop that fuels additional precipitation.
"For decades, the textbook answer was that Northwest China's rain comes from somewhere else," says Yu. "Our findings show that since the late 1990s, the dominant contribution to precipitation growth has shifted to local moisture recycling. After spending my entire adult life here, it's remarkable to see the data confirm that something fundamental is shifting."
Implications and Uncertainties
The study notes that large-scale oceanic variability, such as the Atlantic Multidecadal Oscillation, may add complexity to future projections. The authors also caution that the current trend may not be sustainable. As glaciers and snow reserves decline under continued warming, the meltwater that supports enhanced evapotranspiration could diminish, potentially slowing or reversing the humidification.
"This work provides quantitative evidence that local hydrological feedbacks have become the dominant mechanism behind recent precipitation increases," says Professor Zhang. "That has important implications for drought monitoring, prediction, and water-resource management."
"The warm–wet shift reflects an integrated response of the regional water cycle to warming, cryospheric changes, and ecosystem recovery.” Professor Huang adds: Having grown up here, I know these aren't abstract questions—they affect real communities, real farms, real lives."
Advances in Atmospheric Sciences
Local Evapotranspiration and Atlantic Decadal Variability Dominate the Humidification of Northwest China
7-Feb-2026