Hydrological effects of change in vegetation components across global catchments

As an important component of the terrestrial system, vegetation plays a pivotal role in hydrological processes and water yield. Many studies have examined hydrological effects of changes in total vegetation coverage and density, whereas the impact of change in vegetation components (i.e., proportion of different vegetation types) is rarely considered and little known. Actually, even though the changes in total vegetation coverage and density are similar, the differences in vegetation components alteration among catchments can be pronounced, and thus result in distinct hydrological consequence. Here, using a state-of-the-art dataset of vegetation composition including tree canopy (TC) cover, short vegetation (SV) cover and bare ground (BG) cover, we quantitatively assess the hydrological consequences of vegetation components change in 76 large catchments globally under the water balance framework. We find SV is apparently the most sensitive vegetation component for runoff change, which is reinforced in regions with a drier climate. Attributing water yield change shows that runoff variations caused by TC change are usually offset by those caused by SV change. In typical afforested catchments across the world, the loss of SV can alleviate 39.3-108.7% runoff decrease due to the expansion of TC and the contraction of BG. Our results imply that hydrological sensitivity is much diverse among vegetation types, and trade-offs exist among the hydrological effects of different vegetation components. These previously unrevealed findings suggest that more vegetation properties (including vegetation composition) should be accounted when evaluating the impact of vegetation change on regional water resources.