Hydrologic modeling over the NEESPI domain: Challenges and
progress
Tara J. Troy1 and Eric F. Wood1
1 Dept.
of Civil and Environmental Engineering, Princeton University, Princeton, NJ, USA
Corresponding Author: Eric F. Wood (efwood@princeton.edu)
Northern Eurasia encompasses a vast region of the earth’s extratropical land area with a variety
of climatic regions and biomes, from deserts in the south to frozen tundra in the north. In
addition to its varied climate and ecosystems, it is a region of interest because of its changing
hydrology. Discharge has increased by 7% since 1930 [Peterson et al., 2002], active layer
thickness has increased in permafrost zones [Romanovsky et al., 2007], and some of the
strongest warming over the 20th century occurred in northern Eurasia [IPCC, 2007].
Observations over the region are sparse due to its size and harsh climate, making it difficult to
fully understand the hydroclimatology and its changes. Hydrologic modeling can bridge the gap
in observations and can be used to simulate hydrologic states and fluxes across a domain
continuously in time and space as well as provide hydrologic information for related vegetation
and biogeochemical studies.
In order to simulate the land surface hydrology of the high latitudes, a number of processes
must be parameterized that may be insignificant in other regions, such as permafrost dynamics,
snow sublimation/blowing snow parameterizations, and lakes and wetlands. These processes
have been included in the physically-based Variable Infiltration Capacity (VIC) land surface
model [Cherkauer and Lettenmaier, 1999; Cherkauer et al., 2003; Liang et al., 1994; Liang et
al., 1996], and the model has performed well in high latitude environments [Su et al., 2005; Su
et al., 2006]. The inclusion of these processes has an effect on the water budgets, as is shown
below with the inclusion of a lake model.
Peatlands cover a significant portion of western Siberia, and lakes and wetlands are critical land
cover types to be included in hydrologic modeling across northern Eurasia. Lakes act as
storage for runoff, particularly during the spring snowmelt season, capturing runoff and retaining
it, rather than allowing it to continue unchecked into the stream channel. This allows the lake to
perform two important hydrologic functions: the slowed release of water into the stream channel,
reducing the discharge peak, and providing a free water surface to evaporate into the
atmosphere. The VIC land surface model includes a physically-based lake model that includes
lake freeze/thaw, inundation, evaporation, and runoff release through a weir equation.
Figure 1 demonstrates the effect that the inclusion of lakes has on model performance for the
Iset River at Isetskoje, a small basin (56,000 km2) in the Ob River watershed. The left panel
shows the modeled seasonal cycle of runoff (averaged from 1940 to 2000) with and without the
lake parameterization (black and blue, respectively). Inclusion of the lake model reduces the
April peak runoff by 27% and also reduces the annual runoff totals. The panel on the right
shows the effect of lakes on the evaporation budget. Annual evapotranspiration increases from
344 mm/yr without lakes to 407 mm/yr with lakes, an increase of 18%. The difference in
modeled evapotranspiration has an effect on modeled streamflow, but it also has an effect on
the interactions between the land surface and atmosphere. In regions with significant lake
coverage, such as the portions of northern Eurasia, coupled models that use simplified land
surface schemes without lake models may be underestimating the evapotranspiration from the
land surface, which may then have an effect on other processes.
As the high latitudes of Eurasia receive more attention due to climate change, it is important that
the hydrological parameterizations in land surface models are sufficiently accurate that they can
be used to attribute land use and land cover change (LULCC) and climate change. The areas
where improvements in parameterizations are required include lakes, with which VIC has made
progress but other land surface models (LSMs) have not; parameterization of peatlands, which
are poorly represented in most models (but they cover a significant portion of western Siberia
and other areas across the pan-Arctic); improved modeling of permafrost temperatures that
requires modeling of deep soil layers; and the inclusion of a water table for the deep soil layers.
Advances in modeling these processes are being made, but progress must continue with robust
testing of the parameterizations. NEESPI needs to encourage the intercomparison of LSM
parameterizations and to test the ability of LSMs to evaluate anthropogenic influences and test
attribution hypotheses. Finally, there is the modeling concern that a scale mismatch exists
between the observation scale and the LSM modeling scale. Thus, there is a need to explore
the potential of remote sensing to bridge this gap so as to improve our understanding of the
water and energy cycles across the NEESPI domain.
References
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Figure legends
Figure 1. The top panel demonstrates the reduction in runoff with the inclusion of the lake
model, and the bottom panel shows the effect of including lake processes on the seasonal
evapotranspiration budget.
Figure 1. The top panel demonstrates the reduction in runoff with the inclusion of the lake
model, and the bottom panel shows the effect of including lake processes on the seasonal
evapotranspiration budget.