CUHK
News Centre

A research team led by The Chinese University of Hong Kong (CUHK), in collaboration with Chongqing University, The University of Hong Kong, and Lanzhou University, has for the first time identified irrigation, in addition to industrial aerosol cooling, as a crucial factor explaining why China’s warming over the past half-century has been markedly slower than in most other regions of the world. The study, which provides the first quantitative assessment of irrigation’s contribution to climate moderation in China, has recently been published in the leading international journal Geophysical Research Letters.

Irrigation mitigates surface warming during farming season

While scientists have long attributed the nation’s relatively subdued warming to industrial aerosol pollution, which scatters sunlight and cools the land surface, the CUHK-led team found that aerosols alone could not explain regional differences – in particular, why the heavily irrigated North China Plain, home to more than one-third of China’s irrigated cropland, has recorded unusually mild warming, despite rapid urban and industrial growth.

By combining over 50 years of meteorological records (1961-2016) with detailed regional climate model simulations, the team discovered that irrigation expansion produced net daytime cooling of about 0.19°C per decade between 1961 and 2005 in spring (April-June), nearly offsetting greenhouse gas-driven warming.

Professor Amos Tai Pui-kuen, the study’s principal investigator from CUHK’s Department of Earth and Environmental Sciences, explained: “Our findings show that irrigation made a significant contribution to the slower warming in China, and helped alleviate daytime heat stress in agricultural regions. The evaporation of irrigation water acted like a powerful air conditioner that quietly countered part of the greenhouse effect, especially during the farming season.”

Since the mid-2000s, however, this cooling benefit has weakened as irrigation expansion has plateaued and water-saving techniques have become more widespread. The research model projects that, under a medium-emission scenario, continued irrigation could offset nearly half of springtime warming in northern China by 2050, though its protective effect will decline if irrigation water use continues to shrink.

From water saving to climate-smart irrigation

With growing water scarcity, China has been pressing ahead with water-saving irrigation to address critical challenges such as groundwater depletion, land subsidence and river drying. Professor Tai emphasised that conserving water must remain a top priority – yet it brings a new climatic dilemma: less evaporative cooling may lead to heightened exposure to extreme heat.

Dr Yuan Tiangang, the first author of the study and a former Postdoctoral Fellow at CUHK, said: “We cannot abandon water conservation – that would be environmentally disastrous. But we also cannot ignore that irrigation offers a climate-cooling co-benefit that relieves both water and heat stress. Smarter, integrated water-climate management will be crucial to sustaining China’s food and climate security.”

Professor Li Jianfeng, another coauthor of the study, from CUHK’s Department of Geography and Resource Management, added: “Water saving doesn’t have to mean climate vulnerability. By integrating precision irrigation and ecological restoration, we can deliver co-benefits among water conservation, agriculture and climate resilience.”

The study recommends adopting a multi-pronged climate-smart approach:

1. Precision irrigation with climate feedback – using real-time soil and weather data to calculate the appropriate amount of water for both efficient crop growth and local temperature moderation.
2. Enhancing soil health and vegetation cover – through measures such as mulching, organic amendments and cover crops, to naturally retain moisture and reinforce microclimate stability.
3. Coordinated water-climate governance – aligning irrigation scheduling, crop selection and energy use to reduce both water stress and thermal risk.
4. Nature-based cooling solutions – restoring wetlands and implementing managed aquifer recharge to recreate part of irrigation’s evaporative buffering effect.

This study was funded by the Research Grants Council (Collaborative Research Fund and General Research Fund), the Innovation and Technology Fund of Hong Kong and the National Natural Science Foundation of China.