Aerial view of Accomplishment Creek and the Sagavanirktok River in the Brooks Range of Alaska.  Photo by D.L. Kane

The Role of Spatial and Temporal Variability of Pan-Arctic River Discharge and Surface Hydrologic Processes on Climate

Dennis P. Lettenmaier (, University of Washington
Eric F. Wood (, Princeton University
Andrew John Weaver (, University of Victoria

Riverine inflows to the Arctic Ocean play a key role in climate, both regionally and globally. Low net radiation over the pan-Arctic drainage area and the ocean/sea ice surface results in low evaporative demand, and hence a large net export of freshwater from the Arctic Ocean. This export of freshwater has important implications for the thermohaline circulation of the global ocean. Snow plays a major role in the water balance of the region's land surface, and is the dominant source of streamflow. Nonetheless, notwithstanding the importance of land processes to arctic and global climate, relatively little is known about the interaction of land surface hydrological variability in the Arctic and climate.

The central science question around which our work is focused is "How will the coupled arctic climate system respond to changes in riverine discharge of freshwater, and how do the temporal and spatial variability of freshwater discharge and changes therein interact with the dynamics of high latitude climate?". Although numerous studies have hypothesized effects on the global climate system of changes in the arctic freshwater balance, the more specific effects of temporal and spatial changes in river discharge have yet to be examined. One argument holds that because the transport time for sea ice out of the Arctic Ocean is several years, changes in seasonality and the spatial distribution of river discharge would be damped out in terms of their broader scale effects on climate. However, changes in freshwater discharge such as those that have been observed over the last few decades in several large Russian rivers almost certainly will affect the distribution of sea ice in the estuaries and continental shelf waters, and in turn energy exchanges over larger areas. Whether such local changes, when integrated over the major rivers and numerous smaller ones discharging to the Arctic could affect climate at regional and global scales is an unknown that we intend to address. Similarly, the effects on the arctic climate system of changes in the space-time distribution of snow cover over land are poorly known. Earlier ablation of snow cover has a large effect on the albedo of the land surface, and hence a direct effect on land-atmosphere energy exchanges, but it also affects the seasonality of river flows with consequent possible effects outlined above.

The project experimental design is based on a series of uncoupled, partially coupled, and fully coupled simulations with a combination of sea ice, atmosphere, and ocean models that are currently components of the University of Victoria's Earth System Climate Model, and the University of Washington and Princeton University's Variable Infiltration Capacity (VIC) land surface model. Both sets of models have been designed for, and extensively tested with, arctic data. The science questions will be posed through a combination of model runs in which sea ice, ocean, and land surface models are run in off-line mode, and various aspects of the off-line climatologies (for a retrospective period ranging from 20 to 50 years) will be prescribed in partially coupled ensemble runs of the fully coupled model system. These partially coupled model results will be compared with results of fully coupled ensemble climate simulations to isolate the effects of interactions among the land, sea ice/ocean, and atmosphere. The project represents a collaboration between three PIs and institutions: Lettenmaier (University of Washington), Weaver (University of Victoria), and Wood (Princeton University). Lettenmaier and Wood have extensive experience in land surface modeling at regional and global scales, and have been active in land surface model validation studies, including the recent PILPS-2e Arctic Hydrology Model Intercomparison Project. Weaver has extensive experience with arctic and global climate studies, including coupled sea ice, ocean, and atmospheric modeling at regional and global scales. Support is requested for Lettenmaier and Wood's participation in the project. Direct support is not requested for Weaver and his group, who are funded from Canadian sources. However, interaction with Weaver will be facilitated by the physical proximity of the University of Victoria and the University of Washington. Local support is requested for a University of Victoria post-doctoral research associate for the time (approximately 20 weeks per year) he or she will spend at the University of Washington, and one or more University of Washington researchers are likewise expected to spend time at the University of Victoria.

Arctic CHAMP
Science Management Office

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Photo: Aerial view of Accomplishment Creek and the
     Sagavanirktok River in the Brooks Range of Alaska.  Photo by D.L. Kane