A major challenge recently posed to the sub-Arctic and Arctic research community is "to establish the link between permafrost and changes of the boreal forest in response to a warming climate and a changing freshwater system." (McGuire and Chapin 2006). The processes affecting freshwater generation from the boreal forest, such as permafrost and vegetation dynamics, have high spatial and temporal variability. In this study, we seek to understand and quantify the processes, mechanisms, timing and magnitude of water pathways in the sub-Arctic boreal forest ecosystem in an attempt to improve our capability to more correctly simulate ecosystem response to a warming climate, and thus the changes in feedback processes that will ultimately affect the regional arctic climate. This is a truly interdisciplinary study that integrates climatic, ecologic, thermal, and hydrologic processes into a 'hybrid' hydrologic model. Specifically, we aim to quantify and predict the spatial and temporal variation in (1) watershed processes, including the relative importance of vegetation water use and the presence/absence of permafrost and active layer dynamics, (2) the pathways of water in highly heterogeneous (with respect to permafrost and vegetation distribution) sub-arctic watersheds, (3) develop a 'hybrid' hydrologic model this is able to reproduce the major sub-arctic hydrological processes, with specific focus on stream flow, and (4) utilize climate data derived from Regional Arctic System Model (RASM) simulations to provide high resolution sub-grid scale information of vegetation, permafrost, and hydrologic dynamics of selected regions to RASM. Our study focuses on two primary boreal forest types: coniferous or deciduous dominated ecosystems (CDEs and DDEs, respectively) located in three sub-watersheds of varying permafrost distribution in Interior Alaska. In a very general sense, near surface permafrost corresponds to CDEs and permafrost-free areas or areas with deeper permafrost correspond with DDEs. We hypothesize: (1) The water pathway is primarily controlled by vegetation water use in DDEs and by permafrost distribution, active layer dynamics, and topography in CDEs; (2) The primary water pathway is vertical in DDEs and horizontal in CDEs. Our approach is to integrate field measurements (historical and currently funded projects) to develop a "hybrid" hydrologic model. The "hybrid" hydrologic model will be developed within a Bayesian framework in order to quantify and propagate the uncertainty of each model component throughout the simulation. The "hybrid" hydrologic model will also be developed with idea of using flux and climate output from the RASM to make high resolution prediction of ecosystem dynamics in a changing climate. Due to the complexity of the model and the desire to communicate with RASM (or other large scale GCMs), model code will be structured for HPC (using Message Passage Interface) and flux coupling (CPL7) from the outset. We will also work closely with Drs. Wieslaw Maslowski and Dennis Lettenmaier throughout the study period to ensure our efforts will mesh with the RASM framework. The "hybrid" model will be housed within the Arctic Region Supercomputing Center.

The intellectual merit of this proposal lies within the efforts to develop a model that accurately simulates the dynamic sub-RCM grid scale processes that control the dominant feedbacks to climate and provide a viable approach to incorporate those essential feedback linkages to climate into RASM. Incorporating the effects of fine scale processes into coarse scale models has long been an objective of collaborations between field researchers and modelers. Development of a RCM that allows may dynamically accept input from high-resolution watershed models, and vice-versa, may be the ultimate path to achieving that goal. In terms of broader impacts, this proposal will not only yield improved RCM simulations, but will also produce a high quality watershed scale model that accurately incorporates storage dynamics associated with short and long term active layer and permafrost variations. This model will more correctly incorporate sub-hillslope processes, such as influences of vegetation characteristics on runoff pathways, which are essential to correctly simulate runoff and stream chemistry characteristics and change with a warming climate. This project will support one PhD student who will focus her/his research upon methods to incorporate the effects of fine scale ecosystem processes into Regional Climate Modeling.