A key shortcoming of past studies of future climate and drought is that the land surface representations used in the climate models, in general, have not been able to produce realistic land surface hydrologic conditions. Furthermore, past studies that

1
North American Drought in the 21st Century
Evaluation and Enhancement of Community Land
Model Hydrology Dennis P. Lettenmaier1, Eric.
F. Wood, Gordon B. Bonan3, Kaiyuan Y. Li1, and
Justin Sheffield2 1. Department of Civil and
Environmental Engineering, University of
Washington 2. Department of Civil and
Environmental Engineering, Princeton University
3. National Center for Atmospheric Research
1
The HAPEX-MOBILHY Soybean Site (43.7ºN 0.1ºW)
Introduction
The Colorado basin
(4) 10 CLM layers are aggregated back to 3 VIC
layers and base flow is calculated using VIC
drainage formulation modified soil moisture is
carried to the next time step, and the loop
repeats with step 1.

• VIC reproduced both the latent and sensible heat
  reasonably well, while CLM underestimated latent
  heat and overestimated sensible heat for the
  growing season.
• In the non-growing season (before sowing, Jan.
  Apr., and after harvest, Oct Dec) CLM markedly
  overestimated bare ground evaporation and hence
  underestimated soil moisture content as compared
  to the observation and VIC simulation. This
  underestimation of soil moisture by CLM for the
  period before planting (Jan. Apr.) subsequently
  led to the underestimation of evapotranspiration
  for the growing period of early May through late
  August.
• The canopy interception for CLM is similar to
  the one for VIC.

A key shortcoming of past studies of future
climate and drought is that the land surface
representations used in the climate models, in
general, have not been able to produce realistic
land surface hydrologic conditions. Furthermore,
past studies that have evaluated the potential
for future drought have not considered the
possible role of vegetation change. We propose
to use the Community Climate System Model (CCSM),
in conjunction with a upgraded version of the
Community Land Model (CLM) to evaluate the
susceptibility of the U.S. to drought over the
next century. Existing studies have shown that
CLM has serious deficiencies in terms of
hydrologic predictions , and therefore evaluation
and enhancement of CLM hydrology are necessary
before it is coupled into CCSM to predict the
future drought. During the first phase of the
project, we have made great efforts on evaluating
and upgrading the CLM hydrology. The results
summarized in this poster include (1) Brief
description of the basins and point sites, as
well as datasets used for the model evaluation
(2) the model evaluation aimed at identifying the
weakness of the CLM hydrology (3) the
methodology for incorporating VIC surface runoff
and baseflow parameterization into CLM and (4)
the performance evaluation of the Upgraded CLM
hydrologic prediction.

• VIC well reproduced the observed streamflow both
  in terms of magnitude and seasonality.
• CLM largely overestimated runoff, and the
  snow-melting dominated runoff peak came one month
  earlier than observation.

10-Layer CLM
3-Layer VIC
VIC Upper Layer
3.43 m
VIC Lower Layer
2
Basin/site and dataset description
We evaluate CLM by comparing with VIC in terms of
their ability to reproduce observed water and
energy fluxes in off-line tests for three large
basins with contrasting hydroclimatic conditions
spanning the range from temperate continental to
Arctic, and four point (column flux) sites
spanning the range from tropical to arctic. The
three large basins are Arkansas-Red and Colorado
basins in U.S., and Torne-Kalix in northern
Scandinavia. The forcing data, soil and
vegetation parameters are from LDAS and PILPS
projects, and the naturalized streamflow data
used to evaluate the model are from the Tulsa
District of the U.S. Army Corps of Engineers for
the Arkansas-Red basin and from the U.S. Bureau
of Reclamation for the Colorado basin. The
column flux evaluations are for a tropical forest
site at Reserva Jaru (ABRACOS) in Brazil, a
prairie site near Manhattan (FIFE), Kansas in
central U.S., a soybean site at Caumont
(HAPEX-Monbilhy) in France, and a small grassland
catchment at Valdai in central Russia.
Dynamic Depth
Fixed Depth
Diagram Matching CLM layer scheme to VIC Layer
scheme
The Valdai Grassland Site (57.6ºN 33.1ºE)
VIC parameters required in Upgraded CLM
The FIFE Prairie Site (39.0ºN 96.5ºW)

1. b_infil Infiltration parameter
2. Depth Upper layer depth (first plus second VIC
   layer depth)
3. Ws Fraction of maximum soil moisture content
   when baseflow occurs
4. Dsmax Maximum velocity of baseflow
5. Ds Fraction of Dsmax where non-linear baseflow
   occurs.

• The Upgraded CLM performed similarly to VIC in
  terms of surface and baseflow prediction, while
  the original CLM overestimated the surface runoff
  compared to VIC.
• The Upgraded CLM significantly reduced the
  surface runoff compared to the original CLM,
  thereby correcting the underestimation of the
  subsurface soil moisture and the latent heat, and
  the slight overestimation of the sensible heat by
  the original CLM.
• This site demonstrates that the runoff
  parameterization plays a critical role in water
  and energy balance prediction.

• Valdai site is a small catchment (0.36 km2) in
  central Russia, mainly covered by grassland.
• CLM and VIC performed similarly in the
  simulation of evapotranspiration except that CLM
  underestimated the peak value.
• Soil moisture contents were poorly simulated by
  CLM with lower peak value than observations.

3
Model evaluation of CLM
The Arkansas-Red basin

• VIC well reproduced observed runoff in terms of
  both magnitude and seasonality.
• CLM well captured the runoff seasonality, but in
  general overestimated runoff, especially in the
  west portion of the basin.

The FIFE Prairie Site (39.0ºN 96.5ºW)
5
Performance testing of Upgraded CLM
The Arkansas-Red basin

• VIC simulated all four energy fluxes quite well,
  while CLM simulated net radiation, sensible and
  ground heat flux reasonably well but
  underestimated the latent heat due to the larger
  runoff estimation.
• VIC simulated soil moisture contents reasonably
  well both at surface and subsurface layer, while
  CLM largely undersimulated the soil moisture
  content at subsurface layer due to larger runoff
  and hence less infiltration.
• The canopy interception for CLM is similar to the
  one for VIC.

• The Upgraded CLM performed significantly better
  than the original CLM in terms of runoff
  prediction.
• The Upgraded CLM better captured the runoff
  peak, which, in general, was overestimated by the
  original CLM.
• The Upgraded CLM performed consistently well in
  both dry and wet areas of the basin, while the
  original CLM considerably overestimated the
  runoff in dry portion of the basin.

Summary of the CLM model evaluation

• From our study
• CLM tends to overestimate runoff peak,
  particularly in the relatively dry
• regions.
• (2) CLM tends to melt snow earlier than
  observation.
• CLM poorly simulates soil moisture profile due
  to poor soil moisture
• plant-water-relation function.
• CLM sometimes may underestimate
  evapotranspiration due to the poor
• parameterization for the soil-water-plant
  relationships.
• (5) CLM has similar canopy interception to the
  one of VIC (in terms of 1-hour time step).
• In general, VIC performs markedly better than
  CLM in terms of
• hydrologic predictions, including runoff,
  soil moisture and snow pack.
• Improvements of CLM are expected by
  incorporating some aspects of
• VIC hydrologic parameterizations into CLM.
• From other studies
• (1) In coupled mode, CLM significantly
  underestimated runoff over
• central U.S., while overestimated runoff
  globally compared to
• observation Bonan et al., 2002.
• (2) The peak snow mass and thus the spring
  snowmelt of CLM lag

The ABRACOS Forest Site (10.1ºS 61.9ºW)

• The Upgraded CLM performed similarly to VIC in
  terms of surface runoff prediction, while the
  difference in the baseflow prediction are due to
  the different parameterization for the rooting
  depth by the Upgraded CLM (3.43m) and VIC (10m).
• The Upgraded CLM significantly improved the soil
  moisture, latent heat and evaportranspration
  prediction.
• Further improvement can be expected if the
  parameterizations are improved for
  soil-water-plant relationships and the rooting
  depth.

The ABRACOS Forest Site (10.1ºS 61.9ºW)
The Torne-Kalix basin

• CLM in general overestimated the sensible heat
  and underestimated the latent heat.
• The poor performance of CLM are attributed to
  the larger estimation of runoff and poor
  simulation of soil moisture content.
• The soil moisture content was very well
  estimated by VIC-10m (10 m rooting depth but
  poorly estimated by VIC-3.43m (3.43 m rooting
  depth), indicating that the 3.43m by CLM is too
  shallow, and 10m is approprirate.
• The evapotranspiration by CLM is extremely low
  (close to 0) in dry seasons, while the
  corresponding soil moisture contents are much
  higher than those simulated by VIC-3.43 in dry
  seasons. This indicates that soil-plant-water
  relationships and thus soil moisture content are
  poorly represented in CLM.
• The canopy interception for CLM is similar to
  the one for VIC.

• The VIC better captured the runoff magnitude and
  seasonality.
• CLM overestimated the runoff peak value for most
  subbasins except Paktfors, Pajala Rumphus and
  Pallo, where runoff peak was largely
  underestimated.

• The runoff peak of CLM, in general, came earlier
  than VIC and observation, implying that the CLM
  snow melt earlier than observation.

5
Conclusions
4
Enhancement of CLM soil hydrology
The Colorado basin

• CLM tends to overestimate runoff, in particular
  in relatively dry areas.
• CLM tends to melt snow earlier, and thus the
  snow-melting dominated
• runoff peak comes one month earlier than
  observation.
• CLM simulates soil moisture contents
  unrealistically due to poor
• parameterization of soil-plant water
  relationships.
• The poor simulation of the latent heat by CLM
  is due to the poor
• runoff parameterization.
• The Upgraded CLM, into which VIC runoff
  parameterization is
• incorporated, performs significantly better
  than original CLM.
• The Upgraded CLM requires only 5 VIC
  parameters, which are
• transferable to CLM without massive
  calibration although some
• systematical adjustment may be required for
  some basins.
• The enhancement of the CLM snow model remains
  to be done.

• Our studies have shown that VIC performs
  significantly better than CLM
• in terms of hydrologic predictions. As shown in
  the below diagram, we
• have upgraded CLM by incorporating the 3-layer
  VIC surface runoff and
• baseflow schemes into the 10-layer CLM. The
  procedures of runoff and
• baseflow calculation in the Upgraded CLM are as
  follows
• In the time order during a model time step
• Surface runoff is calculated based on the 3-layer
  VIC scheme
• Infiltration is based on 10-layers (CLM layer
  scheme) using information for VIC layers
  interpolated to specified CLM layers
• Soil evaporation, root-water-uptake and water
  redistribution (upward and downward), soil
  thermal states and fluxes are based on 10 CLM
  methodology layers

• The Upgraded CLM, in general, performed markedly
  better than the original CLM in the runoff
  prediction.
• The Upgraded CLM largely corrected the runoff
  overestimation by the original CLM in the summer
  period.
• The Upgraded CLM did not largely reduce the
  runoff peak overestimation in the spring time by
  the original CLM, where the runoff peak is
  dominated by snow melting. Further improvements
  for the spring runoff prediction are expected
  when the CLM snow model is enhanced.
• The runoff seasonality is also expected to be
  improved after the CLM snow model is improved.