Impact of Vegetation Physiology and Phenology on Watershed Hydrology in a Semiarid Watershed in the Pacific Northwest in a Changing Climate
2021
Zhu, Bowen | Huang, Maoyi | Cheng, Yanyan | Xie, Xianhong | Liu, Ying | Bisht, Gautam | Chen, Xingyuan
Changes in carbon dioxide (CO₂) concentration and nitrogen (N) availability can affect land surface processes by regulating physiological (e.g., stomatal opening and closure) and phenological (e.g., leaf area index) responses, which in turn influence terrestrial water cycle dynamics. In this study, we apply the Community Land Model version 5 to investigate how projected environment changes in the 21st century can affect the hydrologic budget in the Upper Columbia‐Priest Rapids watershed, a typical semiarid watershed located in the Pacific Northwest of the United States. Nine numerical experiments were performed to quantifying contributions of climate change, CO₂ concentration, and N availability to the watershed hydrologic budget under two Representative Concentration Pathways (RCPs) (i.e., RCP4.5 and RCP8.5). Our results show that compared to its historical value, evapotranspiration (ET) over the watershed increases by 15% and 12% by the end of the century under RCP4.5 and RCP8.5 in responses to changes in meteorological forcing, and further increases by 16% and 11% when elevated CO₂ concentrations are accounted for. The effect of N availability on the water balance is insignificant. Such an increase in ET is contributed by the overall increase in leaf area index of vegetation in response to increases in precipitation and CO₂ concentration. However, corn‐dominated regions can respond to these changes differently, caused by its increased stomatal resistance under an elevated CO₂ concentration with limited N. Our results demonstrate physiological and phenological responses can modulate watershed hydrologic budgets under projected future changes.
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