Impacts of Changing Climate and Land Cover on Water and Carbon Dynamics in Northern Eurasia

Abstract:

The ecosystems in Northern Eurasia (NE) play an important role in the global climate system due to their vast land coverage, higher-than-global average rate of warming, and the potential feedbacks to the global climate. Water and carbon fluxes interact with each other and vary with climate change and land cover change (LUC). To understand the coupled effects of climate change and LUC on water and carbon dynamics in NE, we modified the algorithms for evapotranspiration (ET), incorporated the effects of forest stand age and fires on these dynamics, and assimilated forest inventory data and eddy covariance observations into the Terrestrial Ecosystem Model (TEM) to better estimate water and carbon fluxes. With consideration of ET from uplands and wetlands, evaporation from water bodies, and snow sublimation, TEM substantially improves its estimation of ET and runoff. Estimated regional ET varies between 263.5–369.3 mm yr^-1 during 1979-2008 depending on the choice of forcing data. With the most accurate available forcing data, modification to TEM results in a decrease of root mean square error from 527.74 km³ yr^-1 to 126.23 km³ yr^-1 for the total discharge estimates of the six largest watersheds in NE. Site-level experiments show that with/without consideration of forest stand age and fires leads to 12.8-53.5% differences in ET estimates, and shifts NE ecosystems between carbon sink and source activities depending on fire severities. Consequently, consideration of these impacts at regional scales may result in large differences in estimates of water and carbon fluxes across NE. Our study highlights the role of snow in the hydrometeorology of NE, and suggests that the quality of forcing data remains a major challenge for accurate quantification of regional water balance, and urges consideration of forest stand age and fires in estimation of water and carbon fluxes in NE.