Effects of Nitrogen Limitation on Hydrological Processes in CLM4-CN
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MITJPSPGC_Rpt212.pdf
Description
Main article
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6.03 MB
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Author(s)
Lee, E.
Felzer, B.S.
Date Issued
March 2012
Publisher
MIT Joint Program on the Science and Policy of Global Change
Citation
Report no. 212
Series/Report no.
Joint Program Report Series;212
Abstract
The role of nitrogen limitation on photosynthesis downregulation and stomatal conductance has a
significant influence on evapotranspiration and runoff. In the current Community Land Model with
coupled Carbon and Nitrogen cycles (CLM4-CN), however, the carbon and water coupling in stomata
is not linked to nitrogen limitation. We modify the incomplete linkages between carbon, nitrogen, and
water, and examine how nitrogen limitation affects hydrological processes in CLM4-CN. In addition,
we evaluate if the modification can improve the simulation of carbon and water fluxes. Applying the
effects of nitrogen limitation on stomatal conductance significantly decreases leaf photosynthesis. It
leads to a reduction in canopy transpiration, thereby increasing total runoff, mainly due to increasing
subsurface runoff. More available soil water for vegetation from the reduced transpiration helps
increase gross primary productivity (GPP) in the relatively moisture-limited regions of
grassland/steppe and savanna. But, in the tropics and boreal forest regions, changes in soil water by
nitrogen limitation are insignificant, and GPP decreases directly by down-regulated leaf
photosynthesis. Decreasing canopy transpiration and increasing runoff from nitrogen limitation
improve simulating latent heat flux and runoff by reducing high biases for latent heat flux in the
tropics and low biases for runoff in the tropics and northern high-latitudes. In addition, the CLM4-CN
with leaf-level nitrogen limitation reduces high model biases in tropical GPP. Thus, nitrogen
limitation on the leaf-level significantly affects hydrological processes in CLM4-CN and improves the
simulation of carbon and water fluxes.
Description
http://globalchange.mit.edu/research/publications/2253
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