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[1] The Arctic land surface water balance plays an important role in regulating the planetary heat balance and global ocean circulation. Lakes and wetlands are common features in the low-gradient Putuligayuk River watershed in northern Alaska, with important implications for the annual water balance. Evapotranspiration exceeds precipitation over the summer, and there is a gradual reduction in wetland extent. Total inundated area derived from RADARSAT ScanSAR synthetic aperture radar images throughout 1999 and 2000 varied from 15 to 67 percent of the 471 km 2 watershed. The hydrological system becomes disconnected within 2 weeks of snowmelt, and overland flow largely ceases. End-of-winter snow water equivalent and discharge during the melt period for 1999, 2000, and 2001 were used to estimate that between 30 and 37 mm (24-42 percent) of snow meltwater serves to recharge the evaporation deficit of the previous summer. The percent of snowmelt entering storage is dependent on the available surface storage.

The prediction of methane emissions from high-latitude wetlands is important given concerns about their sensitivity to a warming climate. As a basis for the prediction of wetland methane emissions at regional scales, we coupled the variable infiltration capacity macroscale hydrological model (VIC) with the biosphere-energy-transfer-hydrology terrestrial ecosystem model (BETHY) and a wetland methane emissions model to make large-scale estimates of methane emissions as a function of soil temperature, water table depth, and net primary productivity (NPP), with a parameterization of the sub-grid heterogeneity of the water table depth based on TOPMODEL. We simulated the methane emissions from a 100 km × 100 km region of western Siberia surrounding the Bakchar Bog, for a retrospective baseline period of 1980-1999 and have evaluated their sensitivity to increases in temperature of 0-5 • C and increases in precipitation of 0-15%. The interactions of temperature and precipitation, through their effects on the water table depth, played an important role in determining methane emissions from these wetlands. The balance between these effects varied spatially, and their net effect depended in part on sub-grid topographic heterogeneity. Higher temperatures alone increased methane production in saturated areas, but caused those saturated areas to shrink in extent, resulting in a net reduction in methane emissions. Higher precipitation alone raised water tables and expanded the saturated area, resulting in a net increase in methane emissions. Combining a temperature increase of 3 • C and an increase of 10% in precipitation to represent climate conditions that may pertain in western Siberia at the end of this century resulted in roughly a doubling in annual emissions.

Increasing human appropriation of freshwater resources presents a tangible limit to the sustainability of cities, agriculture, and ecosystems in the western United States. Marc Reisner tackles this theme in his 1986 classic Cadillac Desert: The American West and Its Disappearing Water . Reisner's analysis paints a portrait of region-wide hydrologic dysfunction in the western United States, suggesting that the storage capacity of reservoirs will be impaired by sediment infilling, croplands will be rendered infertile by salt, and water scarcity will pit growing desert cities against agribusiness in the face of dwindling water resources. Here we evaluate these claims using the best available data and scientific tools. Our analysis provides strong scientific support for many of Reisner's claims, except the notion that reservoir storage is imminently threatened by sediment. More broadly, we estimate that the equivalent of nearly 76% of streamflow in the Cadillac Desert region is currently appropriated by humans, and this figure could rise to nearly 86% under a doubling of the region's population. Thus, Reisner's incisive journalism led him to the same conclusions as those rendered by copious data, modern scientific tools, and the application of a more genuine scientific method. We close with a prospectus for reclaiming freshwater sustainability in the Cadillac Desert, including a suite of recommendations for reducing region-wide human appropriation of streamflow to a target level of 60%.

Lakes, ponds, and wetlands are common features in many low-gradient arctic watersheds. Storage of snowmelt runoff in lakes and wetlands exerts a strong influence on both the interannual and interseasonal variability of northern rivers. This influence is often not well represented in hydrology models and the land surface schemes used in climate models. In this paper, an algorithm to represent the evaporation and storage effects of lakes and wetlands within the Variable Infiltration Capacity (VIC) macroscale hydrology model is described. The model is evaluated with respect to its ability to represent water temperatures, net radiation, ice freeze-thaw, and runoff production for a variety of high-latitude locations. It is then used to investigate the influence of surface storage on the spatial and temporal distribution of water and energy fluxes for the Kuparuk and Putuligayuk Rivers, on the Alaskan arctic coastal plain. Inclusion of the lake and wetland algorithm results in a substantial improvement of the simulated streamflow hydrographs, as measured using the monthly Nash-Sutcliffe efficiency. Simulations of runoff from the Putuligayuk watershed indicate that up to 80% of snow meltwater goes into storage each year and does not contribute to streamflow. Approximately 46% of the variance in the volume of snowmelt entering storage can be explained by the year-to-year variation in maximum snow water equivalent and the lake storage deficit from the previous summer. The simulated summer lake storage deficit is much lower than the cumulative precipitation minus lake evaporation (247 mm, on average) as a result of simulated recharge from the surrounding uplands.