hydro-thermo dynamic model: htdm-1.0

Hydro-Thermo Dynamic Model: Hydro-Thermo Dynamic Model: HTDM-1.0HTDM-1.0

S. Marchenko & V. Romanovsky Geophysical Institute, University of Alaska Fairbanks

International Arctic Research Center

D. Wisser & S. FrolkingInstitute for the Study of Earth, University of New Hampshire

October 30, 2009. Hydrology Modeling in Alaska Workshop, IARC, UAF, Fairbanks, AK

The thermal regime and thickness of the active layer affects many important hydrologic processes, including subsurface water storage, runoff generation and fluvial erosion.

Although the GIPL model is helpful tool for understanding the effects of climatic and landscape factors on heat flow and water phase change in soil retrospectively and prognostically, it does not simulate soil moisture dynamics and storage across diverse landscapes.

Toward the Coupled Model

• pan-Arctic Water Balance Model (P/WBM)

• Development of P/WBM

• WBMplus as an extension of a grid based water balance model

• Hydro-Thermo Dynamic Model - HTDM-1.0

• Permafrost dynamics in a changing climate: Implications for Northern Peatlands

• Conclusions

• Future work

Outlines

Major point

We suggest fully coupled Spatially Distributed Model of Soil

Water Balance and Permafrost Dynamics (HTDM-1.0) as a

transient numerical simulator of permafrost and active layer

parameters and components of the hydrologic cycle.

One bucket hydrologic model P/WBM (no temperature profile)Vörösmarty et al., 1998

M. Rawlins, R. Lammers, S. Frolking, B. Fekete & C. J. Vörösmarty, 2003

A simple permafrost-hydrology model

M. Rawlins, D. Nickolsky, V. Romanovsky et al.,

• 1D heat equation with phase change• Two bucket hydrological model

pore space

precipitation

run-off

base flow

evap

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ansp

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ion

WBMplus an extension of a grid based water balance and transport algorithm (still no temperature profile)

Developed by Dominik Wisser et al., 2009

Based on Vörösmarty et al., 1998, Federer et al., 2003, Rawlins et al., 2003

Hydro-Thermo Dynamic Model - HTDM-1.0S. Marchenko, D. Wisser, V. Romanovsky, Frolking, S., and Vörösmarty, C.

We couple a macroscale hydrologic model WBMplus and one of the versions of the GIPL thermo dynamic (permafrost) model

Several key parameters:1. Field capacity2. Wilting point3. Infiltration rate4. Soil porosity5. Soil Thermal Properties6. Unfrozen Water Content7. Freezing-point depression

WBM plus GIPL equal HTDM-1.0

1. Vertical water exchange between the land surface and the atmosphere

2. Horizontal water transport along a prescribed river network

3. Soil temperature dynamics

4. Depth of seasonal freezing and thawing by solving 1D non-linear heat equation with phase change numerically

5. Time of freeze up

HTDM-1.0 is a fully coupled soil water balance and heat transfer model that simulates:

Seasonality in Freezing/Thawing and Hydrology

Permafrost dynamics in a changing climate: Implications for Northern Peatlands

Peatlands cover about 3 Mio km2 north of 40° N (Mathews and Fung, 1987).

It is estimated that about one-third of northern peatlands are in zones of continuous permafrost, with another 40% of northern peatlands in discontinuous, sporadic, and isolated permafrost zones (Smith et al., 2007).

Modeled distribution of peat depth

The peat depth is computed from the the carbon content [kg/m2] of the FAO soil map (Webb et al., 2000, <http://www.daac.ornl.gov>) under the assumption that half of the carbon is in the first upper layer. The peat density is assumed to be 130 kg/m3.

CC – Carbon Content

OC – Organic Content

PD – Peat Depth

PDs – Peat density ~ 130 kg/m3

OC = 2 * CC

PD = OC / PDs

Proposed by Steve Frolking

Modeled distribution of soil thermal conductivity within the upper layer

Modeled peatland area with underlying permafrost at 2 m depth for 2009, 2050, and 2100 using climate forcing from ECHAM5

Mean annual air temperature (ECHAM5) and soil temperature at 0.5 m depth reconstructed for 2001 and predicted for 2050 and 2100

Mean annual soil temperature at 2 m and 5 m depth reconstructed for 2001 and predicted for 2050 and 2100

Conclusions

• HTDM-1.0 gives not bad results, however to capture correct temperature dynamics in the Arctic regions several improvements mostly addressed to soil thermal properties parameterization and input datasets are required.

• Peatlands have unique thermal and hydraulic properties that need to be explicitly considered in coupled permafrost-hydrology models.

• Initial results from the permafrost dynamics simulation over the Northern

Hemisphere permafrost domain, accordingly climate scenario produced by

ECHAM5, indicate a degradation of permafrost over peatland areas

throughout the 21st century.

Future Work

1. Validate predictions of soil moisture and temperature against observed data in Northern Eurasia and Alaska

2. Reduce uncertainties in peatland locations and parameterization of soil thermal and hydraulic properties

3. Estimate impacts of thawing permafrost on river discharge and terrestrial carbon transport to the Arctic Ocean

Thank you very much !