Hydro-Thermo Dynamic Model: HTDM-1.0

1. Hydro-Thermo Dynamic Model: HTDM-1.0 S. Marchenko & V. Romanovsky Geophysical Institute, University of Alaska Fairbanks International Arctic Research Center D. Wisser & S. Frolking Institute for the Study of Earth, University of New Hampshire October 30, 2009. Hydrology Modeling in Alaska Workshop, IARC, UAF, Fairbanks, AK

2. Toward the Coupled Model 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.

3. Outlines • 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

4. Major point We suggest fully coupled Spatially Distributed Model ofSoil 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.

5. 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

6. precipitation run-off base flow evapotranspiration pore space A simple permafrost-hydrology modelM. Rawlins, D. Nickolsky, V. Romanovsky et al., • 1D heat equation with phase change • Two bucket hydrological model

7. 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

8. Hydro-Thermo Dynamic Model - HTDM-1.0 S. 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 WBM plus GIPL equal HTDM-1.0 • Several key parameters: • Field capacity • Wilting point • Infiltration rate • Soil porosity • Soil Thermal Properties • Unfrozen Water Content • Freezing-point depression

9. HTDM-1.0 is afully coupledsoil water balance and heat transfer modelthat simulates: • Vertical water exchange between the land surface and the atmosphere • Horizontal water transport along a prescribed river network • Soil temperature dynamics • Depth of seasonal freezing and thawing by solving 1D non-linear heat equation with phase change numerically • Time of freeze up

10. Seasonality in Freezing/Thawing and Hydrology

11. 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).

12. Modeled distribution of peat depth 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 The peat depth is computed from the the carbon content [kg/m2] of theFAO 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.

13. Modeled distribution of soil thermal conductivity within the upper layer

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

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

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

17. 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.

18. Future Work • Validate predictions of soil moisture and temperature against observed data in Northern Eurasia and Alaska • Reduce uncertainties in peatland locations and parameterization of soil thermal and hydraulic properties • Estimate impacts of thawing permafrost on river discharge and terrestrial carbon transport to the Arctic Ocean

19. Thank you very much !