Can forest water yields be increased with increased precipitation in a Qinghai spruce forest in arid northwestern China?

- Understanding of the Qinghai spruce canopies transpiration interannual variation.
- Determining all of components about the forest water balance at the stand level.
- Insight into the links between precipitation variability and forest water yields.

Climate-induced changes in regional precipitation are projected to affect forest water yields, although the effects are expected to vary. Few studies, in fact, have examined the response of conifer forests to increases or decreases in precipitation, in arid regions. To answer the question posed above, we investigated the variability of forest canopy transpiration versus precipitation during the 2011-2013 growing seasons, and constructed a complete hydrological budget of an arid montane spruce forest by directly measuring its main component at the stand level, at long-term experimental catchments on Qilianshan Mountain, located in the upper Heihe River Basin, in the arid region of northwest China. It was found that total precipitation during the 2012 and 2013 growing seasons was 12.3% and 36.5% higher, respectively, than during the 2011 growing season, and total stand transpiration during the 2012 and 2013 growing season was 12.5% and 21.7% higher, respectively, than during the 2011 growing season. In the study period, transpiration, soil and moss evaportranspiration, canopy evaporation, and the drainage and change in soil water storage accounted for 71.1%, 19.9%, 5.3%, and 3.8% of the precipitation, respectively. Although the precipitation increased during this study period, the increase was not sufficient to increase the forest water yield. In the future, though, if the precipitation continues to increase in this forest, it may be sufficient to effect such an increase in forest water yield.