Climate change is altering patterns of weather and water around the world, causing water shortages and droughts in some areas. Studying the forest ecosystems, its water retention service in particular, can help to solve the insufficiency of water. The accuracies of data achieved from hydrological models and remote sensing data are far lower than those of observational data on site. However, due to the difficulty in the data acquisition, empirical models are rarely adopted in national-scale studies.  

SHI Wenjiao and TAO Fulu, professors at Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, estimated forest water retention based on the collected data from 1,045 observation sites across China by using the empirical model. This model is a relatively comprehensive way by combining canopy interception amount (CIA), litter maximum water-holding amount (LWHA), and soil water storage amount (SSA). The random forest (RF) model was used to predict the spatial pattern of forest water retention based on on-site data and influencing factors. Then they explored the large spatial variations in different layers of the forest water retention including canopy, litter, and soil at the national and basin scales.  

Under the guidance of SHI Wenjiao and TAO Fulu, a graduate student WU Xi conducted the analysis. The results indicated that the method of combining RF model and site-observational data exhibited large variations for CIA, LWHA, SSA and WRA in different basins and forest types across China. The forest water retention sites should be collected on a global scale to verify more universal application of this method. 

The WRA in the basins of southern China were higher than that of northern China, and the total WRA in China was 2325.87×10⁸ m³. The WRAs of cold and temperate forest types were higher in the Songhua River Basin (SHRB), Liao River Basin (LRB), Northwest Rivers Basin (NWRB), Hai River Basin (HRB) and Yellow River Basin (YRB) than in other basins, and the WRAs of subtropical and tropical forests types were higher in the Yangtze River Basin (YTRB), Southeast Rivers Basin (SERB), Southwest Rivers Basin (SWRB), and Pearl River Basin (PRB) than in the other basins. This work was published in the journal Ecological Indicators. 

Reference: Wu Xi, Shi Wenjiao*, Tao Fulu*. Estimations of forest water retention across China from an observation site-scale to a national-scale. Ecological Indicators, 2021. 132: 108274. DOI: 10.1016/j.ecolind.2021.108274.