Climate, land-use change reduced flows in 70% of China’s river stations

A range of natural and human-induced factors have caused declines in the flows of at least 70% of hydrological stations in China, the most comprehensive analysis of this kind attempted in the country has found.

Changes in land-use and vegetation cover (LUCC) were the most important cause of such declines, followed by climate change-induced variability (CCV), and water abstraction, diversion and regulation (WADR).

There are 1,046 such stations distributed across the major mainstreams and tributaries of the nearly 1,500 rivers in China. They monitor water flow for major infrastructure projects.

Scientists at China’s Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, analysed data from all of these stations over 1956-2016, segregated the factors that influenced these flows, and assessed their relative contributions. The study was published in Science Advances on August 6.

For their analysis, the researchers grouped the factors influencing streamflow into three major drivers: CCV, LUCC, and WADR. CCV included anthropogenic climate change and natural climate variability.

Recent studies, the authors said, highlight climate change’s dominance in altering historical streamflow whereas others underscore the role of natural variability in short-term variations and the strong effects of vegetation greening and human water withdrawals on streamflow reductions. In their assessment the researchers said both factors contributed “almost equally” to changes in streamflow although natural climate variability had “a slightly stronger contribution”.

For their analysis, the scientists computed changes in water-flow at the 1,046 stations with the year 1986 as a fulcrum year of comparison. Around 750 stations reported a declining trend while the remainder reported an increasing trend. For these 756 stations, CCV enhanced the decrease at 53% and dampened it at 358 stations (47%), suggesting a counterbalancing effect.

For the 290 stations with increasing flow, CCV enhanced the increase at 92% of stations and dampened it at 8%, suggesting climate change had a greater propensity to increase flows when the average flow was increasing.

“China’s future water security would be determined by the extent to which ACC increases in the coming decades,” the authors wrote. “We encourage greater cooperation between climate and hydrology sciences to improve the accuracy of mid- and long-term national streamflow projections.”

“The streamflow declines across more than 70% of measured stations may pose a threat to ecosystems, environments, socioeconomics, and agriculture. In dry regions of northern China, such declines, if maintained, could lead to water crises in the foreseeable future,” the authors added.

Lower  streamflow was broadly seen in central and northern China, with 593 stations decreasing up to 40% and 163 stations decreasing by more than 40%. A total of 433 stations displayed significant decreasing trends including 273 stations with reductions up to 40% and 160 stations with decreases exceeding 40%. Increases in streamflow were also reported from the lower reaches of the Yangtze River.

While the analysis was specific to China, it mirrors tropical hydrological situations like in India, which has also reported fluctuations in river-flow patterns. The Central Water Commission has 901 hydro-meteorological stations across all the major river basins.

The Ministry of Water Resources had said in March that the annual average flow data maintained by the CWC, for the last 20 years for major/important rivers, “did not indicate any significant decline in water availability.” However, the per capita annual water availability in the country has progressively dropped due to increasing population, urbanisation, and better lifestyles of residents, it added.