David C. Garen

A spatially distributed energy balance snowmelt model for application in mountain basins

Snowmelt is the principal source for soil moisture, ground-water re-charge, and stream-flow in mountainous regions of the western US, Canada, and other similar regions of the world. Information on the timing, magnitude, and contributing area of melt under variable or changing climate conditions is required for successful water and resource management. A coupled energy and mass-balance model ISNOBAL is used to simulate the development and melting of the seasonal snowcover in several mountain basins in California, Idaho, and Utah. Simulations are done over basins varying from 1 to 2500 km 2 , with simulation periods varying from a few days for the smallest basin, Emerald Lake watershed in California, to multiple snow seasons for the Park City area in Utah. The model is driven by topographically corrected estimates of radiation, temperature, humidity, wind, and precipitation. Simulation results in all basins closely match independently measured snow water equivalent, snow depth, or runoA during both the development and depletion of the snowcover. Spatially distributed estimates of snow deposition and melt allow us to better understand the interaction between topographic structure, climate, and moisture availability in mountain basins of the western US. Application of topographically distributed models such as this will lead to improved water resource and watershed management. Copyright # 1999 John Wiley & Sons, Ltd.

Simulating snowmelt processes during rain-on-snow over a semi-arid mountain basin

Abstract In the Pacific Northwest of North America, significant flooding can occur during mid-winter rain-on-snow events. Warm, wet Pacific storms caused significant floods in the Pacific Northwest in February 1996, January 1997 and January 1998. Rapid melting of the mountain snow cover substantially augmented discharge during these flood events. An energy-balance snowmelt model is used to simulate snowmelt processes during the January 1997 event over a small headwater basin within the Reynolds Creek Experimental Watershed located in the Owyhee Mountains of southwestern Idaho, U.S.A. This sub-basin is 34% forested (12% fir, 22% aspen and 66% mixed sagebrush (primarily mountain big sagebrush)). Data from paired open and forested experimental sites were used to drive the model. Model-forcing data were corrected for topographic and vegetation canopy effects. The event was preceded by cold, stormy conditions that developed a significant snow cover over the sub-basin. The snow cover at sites protected by forest cover was slightly reduced, while at open sites significant snowmelt occurred. The warm, moist, windy conditions during the flooding event produced substantially higher melt rates in exposed areas, where sensible- and latent-heat exchanges contributed 60–90% of the energy for snowmelt. Simulated snow-cover development and ablation during the model run closely matched measured conditions at the two experimental sites. This experiment shows the sensitivity of snowmelt processes to both climate and land cover, and illustrates how the forest canopy is coupled to the hydrologic cycle in mountainous areas.

Evaluation of Official Western U.S. Seasonal Water Supply Outlooks, 1922-2002

Abstract An analysis was conducted of almost 5000 operational seasonal streamflow forecast errors across the western United States. These forecasts are for 29 unregulated rivers with diversity in geography and climate. Deterministic evaluations revealed strong correspondence between observations and forecasts issued 1 April. Forecasts issued earlier in the season were more uncertain yet remained skillful. The average change in forecast performance between January and April was primarily linked to the climatological seasonal cycle of precipitation: regions with climatologically wet winters and dry springs (e.g., California) showed much more forecast improvement between January and April than did regions with dry winters and wet springs (e.g., western Great Plains, Colorado Front Range). Other climatological factors played a secondary role; for example, mixed rain–snow basins in the Pacific Northwest did not show as significant an improvement in skill versus lead time as might otherwise be expected. Mixed t...

A Recent Increase in Western U.S. Streamflow Variability and Persistence

April–September streamflow volume data from 141 unregulated basins in the western United States were analyzed for trends in year-to-year variability and persistence. Decadal time-scale changes in streamflow variability and lag-1-yr autocorrelation (persistence) were observed. The significance of the variability trends was tested using a jackknife procedure involving the random resampling of seasonal flows from the historical record. The 1930s–50s was a period of low variability and high persistence, the 1950s–70s was a period of low variability and antipersistence, and the period after 1980 was highly variable and highly persistent. In particular, regions from California and Nevada to southern Idaho, Utah, and Colorado have recently experienced an unprecedented sequence of consecutive wet years along with multiyear extreme droughts.

A user agency's view of hydrologic, soil erosion and water quality modelling

Abstract The Natural Resources Conservation Service (NRCS) of the US Department of Agriculture provides assistance for land management planning and the use of conservation measures on private farmland in the United States. The NRCS must concern itself with a broad range of issues with regard to models and their application to support the assessments and decision making associated with these activities. These issues include the basic science for the description of physical processes, user issues in the practical application of the model, and software maintenance. In recent years, a significant amount of effort has gone into implementing existing agricultural hydrology/erosion/water quality models. There are, however, some important areas of model development that need to be addressed, including: reconciling the strengths and weaknesses of existing models; accounting for spatial variability of precipitation over the catchment; rectifying weaknesses in the stochastic climate generators currently included in some erosion models; improving the representation of runoff generating processes and water flow paths; and improving our understanding of ephemeral gully (thalweg) erosion and including algorithms to describe it. New model development also needs to follow modern standards of software engineering to ensure code reusability and maintainability. Although the NRCS is primarily a model user agency, it must be involved in all aspects of model development as well as model application to ensure satisfactory results.

Connections between science and spirituality

I would like to continue the discussion of points raised in William Carters response to Robert Frodemans Eos Forum article [Carter, 2006; Frodeman, 2005]. I have appreciated Frodemans work and feel that perspectives on science deriving from humanities, philosophy, and religion can add depth, insight, and meaning to our endeavors. I would like to broaden the discussion beyond just space policy to include the relationship between science in general and these, what I would call, spiritual issues. I can fully understand Carters aversion to including religious people or perspectives in the formation of science policy. In addition to the examples he cites in which religious motivations have led to some scientifically questionable actions and policies by the U.S. government (having to do with medicine and stem cell research), I would also add the continued attempts by religiously motivated people (some with scientific credentials themselves) to discredit Darwinian evolution and instead advocate alternative models, such as ‘intelligent design,’ which make room for supernatural creation instead of, or alongside, evolutionary processes.