Abstract
Climate warming has changed vegetation phenology, and the phenology-associated impacts on terrestrial water fluxes remain largely unquantified. The impacts are linked to plant adjustments and responses to climate change and can be different in different hydroclimatic regions. Based on remote sensing data and observed river runoff of hydrological station from six river basins across a hydroclimatic gradient from northeast to southwest in China, the relative contributions of the vegetation (including spring and autumn phenology, growing season length (GSL), and gross primary productivity) and climatic factors affecting the river runoffs over 1982–2015 were investigated by applying gray relational analysis (GRA). We found that the average GSLs in humid regions (190–241 days) were longer than that in semi-humid regions (186–192 days), and the average GSLs were consistently extended by 4.8–13.9 days in 1982–2015 period in six river basins. The extensions were mainly linked to the delayed autumn phenology in the humid regions and to advanced spring phenology in the semi-humid regions. Across all river basins, the GRA results showed that precipitation (r = 0.74) and soil moisture (r = 0.73) determine the river runoffs, and the vegetation factors (VFs) especially the vegetation phenology also affected the river runoffs (spring phenology: r = 0.66; GSL: r = 0.61; autumn phenology: r = 0.59), even larger than the contribution from temperature (r = 0.57), but its relative importance is climatic region-dependent. Interestingly, the spring phenology is the main VF in the humid region for runoffs reduction, while both spring and autumn growth phenology are the main VFs in the semi-humid region, because large autumn phenology delay and less water supply capacity in spring amplify the effect of advanced spring phenology. This article reveals diverse linkages between climatic and VFs, and runoff in different hydroclimatic regions, and provides insights that vegetation phenology influences the ecohydrology process largely depending on the local hydroclimatic conditions, which improve our understanding of terrestrial hydrological responses to climate change.
Highlights
Climate warming has substantially extended the length of vegetation growing period in temperate and boreal zones (Piao et al, 2019; Menzel et al, 2020) and sequentially resulted in a widespread increase of leaf area index (LAI) over the past decades (Zhu et al, 2016; Piao et al, 2020)
We found large spatial heterogeneity but consistent temporal patterns, i.e., earlier start of growing season (SOS) and later end of growing season (EOS) resulted in longer growing season length (GSL), which is in line with previous studies, and a warming spring could help vegetations meet their forcing demands earlier and more accumulation of gross primary productivity (GPP) would prolong the life of leaves and delay the EOS (Piao et al, 2019; Geng et al, 2020)
Six river basins in the humid and semi-humid regions in China were selected to analyze the temporal changes in runoff and vegetation dynamics during 1982–2015
Summary
Climate warming has substantially extended the length of vegetation growing period in temperate and boreal zones (Piao et al, 2019; Menzel et al, 2020) and sequentially resulted in a widespread increase of leaf area index (LAI) over the past decades (Zhu et al, 2016; Piao et al, 2020). The recent studies have found that under the interactive effect of these two aspects, i.e., increase in LAI and decrease in stomatal conductance, the river runoff at basin scales has experienced generally decreasing trends (Xu et al, 2018; Gao et al, 2019; Li et al, 2019), the increased trends were reported in some regions (Xi et al, 2018). This inconsistent result may be related to the different roles of vegetation on water cycles at different climate zones. To the best of our knowledge, there is still a lack of studies on the quantification of vegetation effects on river runoff across basins with hydroclimatic gradients
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