1. Measurements and models of cold region hydrology (with a focus on hydrology of the pan-arctic region)
Dennis P. Lettenmaier
Department of Civil and Environmental Engineering
University of Washington
CLIC
First Science Conference China Meteorological Administration
April 12, 2005
Beijing, China

2. Outline of this talk Science focus
Modeling as a synthesis approach – reproduction and diagnosis of observations
Illustrative results
Some comments on observations
In situ
Remote sensing
Role of reanalysis

3. 1) Science questions
What is the riverine flux of freshwater to the Arctic Ocean (ACSYS)
What have been the (recent) changes in riverine discharge to the Arctic, and what are their causes?
Changes in precipitation and its seasonality
Anthropogenic effects (reservoir storage)
Permafrost
What are the role of other changes in the terrestrial hydrology of the pan-arctic domain, and what are their impacts on regional climate?
Snow cover extent, and seasonal patterns
Lake and wetland dynamics (freeze-thaw patterns; spatial extent)
Vegetation change

4. 2) Modeling approach

5. River routing networks
Columbia River at 1/8 degree lat-long
Pan-arctic region at 100 km

6. Investigation of forest canopy effects on snow accumulation and melt
Measurement of Canopy Processes via two 25 m2 weighing lysimeters (shown here) and additional lysimeters in an adjacent clear-cut.
Direct measurement of snow interception

7. VIC energy balance model of canopy effects on snow accumulation and melt – forested and open conditions

8. Summer 1994 - Mean Diurnal Cycle
Point Evaluation of a Surface Hydrology Model for BOREAS
SSA Mature Black Spruce
NSA Mature Black Spruce
SSA Mature Jack Pine
-100
100
300
Rnet
-50 50
150
250 H 60
120 LE 3 6 9 12 15 18 21 24
Rnet H LE 3 6 9 12 15 18 21 24
Rnet H LE 3 6 9 12 15 18 21 24
Flux (W/m2)
Local time (hours)
Observed Fluxes
Simulated Fluxes
Rnet
Net Radiation H
Sensible Heat Flux LE
Latent Heat Flux

9. Range in Snow Cover Extent
Observed and Simulated –
Eurasia
North America J F M A S O N D
Month
Observed
Simulated 4 8 12 16 20
snow cover extent (106 km2) 2 6 10

10. Mean Normalized Observed and Simulated Soil Moisture
Central Eurasia,
20°E
30°E
40°E
50°E
60°E
70°E
80°E
90°E
100°E
110°E
120°E
130°E
140°E
40°N
50°N
60°N A B C D E F G H
100
200
Soil Moisture (mm) J M S O N
Normalized
Observed
Simulated

11. Cold Season Parameterization -- Frozen Soils
Key
Observed
Simulated
5-100 cm layer
0-5 cm layer

12. 3) Illustrative results
Arctic Ocean freshwater flux – VIC and previous estimates
from Su et al, JGR 2005

13. Simulated and observed streamflow – Lena River and major tributaries
from Su et al, JGR 2005

14. Simulated and observed snow cover extent, 1980-99
from Su et al, JGR 2005

15. Modeled and observed dates of lake freeze-up and break-up for Primrose Lake (upper) and 13 Canadian lakes (lower),
from Su et al, JGR 2005

16. Predicted and observed (CALM station) permafrost active layer depth
from Su et al, JGR 2005

17. Observed and modeled (reconstructed) trends in Arctic river discharge
Yukon (at Pilot Station): 831,000 km2
Lena (at Kusur): 2,430,000 km2
Ob (at Salekhard): 2,950,000 km2
Yenisei (at Igarka): 2,440,000 km2
Observed
Simulated

18. Multi-model ensemble – preliminary results for pan-arctic domain
Annual simulated discharge
Simulated and observed snow areal extent

19. Monthly P , E, and R from ERA40 and VIC over the Lena River basin
VIC/OBS
ERA40

20. Monthly P , E, and R from ERA40 and VIC over the Yenisei River basin
VIC/OBS
ERA40

21. Monthly P , E, and R from ERA40 and VIC over the Ob River basin
VIC/OBS
ERA40

22. Monthly P , E, and R from ERA40 and VIC over the Mackenzie River basin
VIC/OBS
ERA40

23. Annual average precipitation (P, mm), evaporation (E, mm), and runoff (R, mm) from the observations (OBS), VIC model, and ERA-40 reanalysis for the Lena, Yenisei, Ob, and Mackenzie from 1979 through 1999

24. Estimates of the fraction of annual total discharge into the Arctic Ocean for each 5° latitude zone from Eurasia and North America based on the VIC R, ERA-40 R, and P-E fields.

25. 4) Some comments on observations in the framework of pan-arctic land surface water and energy balance studies
Key hydrologic observation is precipitation (main forcing of the land surface water budget). Streamflow is also a critical variable for estimating the water budget (evapotranspiration is extremely difficult to estimate directly, usually done by closure).
Surface solar radiation (main surface energy forcing) is poorly observed as well
Decorrelation length of precipitation is longer than that of most other water and energy balance variables, and its measurement by gauges is subject to various errors, most notably solid precipitation catch deficiencies (also orographic effects, which are not well captured by gage networks
Precipitation gage networks (at high latitude especially, but also in other inaccessible parts of the globe, and underdeveloped countries, have been in a state of decline.
A pragmatic strategy is a) assure that observations of river discharge are taken (and ideally reported in near-real time for the mouths of major rivers); and b) in situ measurements of other variables are linked to a broader framework of remote sensing and/or reanalysis with specific targets for estimation error

26. Remote sensing framework for key hydrologic variables at high latitude
Precipitation – Global Precipitation Measurement mission (GPM) – specifically includes high frequency (HF) channels on GPM microwave imager (GMI) for estimation of low intensity and solid precipitation. GPM is an approved international mission
Snow (water equivalent) – Cold Land Processes mission proposal – passive-active, specifically targeted at estimation of SWE at high resolution, and in regions of complex topography. Also MODIS, AMSR, other (existing) sensors for estimation of snow areal extent.
Inland water altimetry (WatER – Water Elevation Recovery) – evolving ESA-U.S. proposal for high resolution, inland water altimetry (would allow estimation of storage change in lakes and wetlands, river discharge through use of data assimilation methods
Other existing (and planned) sensors for, e.g., topography, vegetation, other land cover characteristics

27. Reanalysis is central to a more coherent basis for water and energy balance synthesis
Latest reanalysis results (ERA-40) are promising basis for estimation of high latitude water balance variables (especially precipitation)
Reanalysis efforts to date have not considered (very carefully) how best to utilize land surface observations, and (perhaps more importantly) have not been used as the basis for observing system design
Reanalysis furthermore has not been designed for use in trend diagnostics (which introduces a number of difficult questions about which observations to assimilate
Nonetheless, the reanalysis concept may well be the best hope for a coherent framework of integrating in situ and R/S observations, and advanced land surface modeling method. There is a need for some creative energy in this area

28. Conclusions
Land surface models offer a viable approach for synthesizing observations, and knowledge of physical processes, over high latitude land regions
There remain gaps in our representation of key processes (e.g., permafrost) at these scales, and we are severely data limited. Furthermore, downscaling to regional scales is complicated.
Reanalysis results from ERA-40 at the scale of large Arctic rivers is promising, especially for precipitation. Results for other variables (especially runoff) are not as good, but likely are due at least in part to model deficiencies
We need a more coherent framework for integration of existing and planned satellite sensors, especially in the context of sparse in situ observations. Possibly in situ observations could be viewed more in the context of tie points for R/S Cal-Val, and/or reanalysis