Rates of snowmelt distributed across Emerald Lake watershed, an alpine basin located in the Sierra Nevada, California, were estimated for water year 1987 using a point snowmelt model applied to regions that were classified based on distributed snow water equivalence and net solar radiation (NSR). A 5-m resolution digital elevation model (DEM) and a 5-m classified digital terrain model of snow water equivalence (SWE) were resampled to coarser resolutions (25-m, 30-m, 50-m, and 100-m) using the nearest neighbor approach. These images were used to define other snowmelt physical parameters and the initial state of the snowpack before melting. Topographic parameters calculated at 50-m and 100-m resolution exhibited significant differences in their histogram distribution as compared to the 5-m DEM. The most important were variations in slope, aspect, sky view factor, and terrain configuration factor, which influenced radiation calculations and the definition of distributed parameters for snowmelt calculations. Elevations, however, did not change significantly from one resolution to the other. The distribution of topographic parameters modeled at 25-m and 30-m, remained almost unchanged. Four, seven and ten classes of snow water equivalence and net solar radiation were combined using a band interleave process to determine the maximum number of combined classes. The point snowmelt model was then applied to these areas, which shared similar SWE and NSR characteristics, to obtain hourly melt rates. Modeled snowmelt rates were compared to the total daily discharge observed at the outlet of Emerald Lake watershed. There was good agreement for resolutions S-, 25-, 30-, and 50-m but not for the 100-m OEM, as modeled net solar radiation was too high and water was released from the basin too early. Model performance using three tests (Nash-Sutcliffe criteria, sum of squares of the deviations and the sum of the absolute differences between observed discharge and computed melting) showed that the 30-m resolution OEM with combined classes of 7 SWE and 7 NSR provided the best snowmelt performance for this distributed approach. Finally, fractional snow cover area at one month intervals were estimated, showing that this approach offers the potential to model spatially distributed snow covered area in alpine regions.

The influence of climate and antecedent moisture conditions on hydrological and biogeochemical fluxes was studied and contrasted in three nested, high-elevation, snowmelt-dominated catchments in the Sierra Nevada, California and one basin-floor, semi-arid catchment in southeastern Arizona. Investigations were completed within a different two-year period at each site, with the second year being climatically different (typically drier) than the first. Spring snowmelt, widespread winter frontal precipitation, and episodic summer rains induce surface water flow in these catchments, though the timing and magnitude of nutrient redistribution among soil and stream compartments varies in each. Surface water flow from spring snowmelt in high-elevation catchments travels through the subsurface or across the surface as direct runoff A more typical process producing surface water flow in semi-arid catchments is flooding during episodic or widespread rainfall. Hydrograph separations at Emerald Lake, Topaz Lake and Marble Fork catchments in Sequoia National Park, California, revealed that the majority of snowmelt flowed through soil before entering the stream in both average and highsnow years. The Emerald Lake watershed had a higher fraction of old water in its outflow in the average accumulation year because of the previous year's high accumulation and longer melt season. A mixing model analysis performed of the upper San Pedro River, Arizona, for wet and dry years showed that summer flood hydrographs were composed mainly of precipitation and surface runoff in both years, though a higher soil-water input occurred in the wetter year and in early season floods in the dry year. Stream and soil water nitrate concentrations were higher during floods in the dry year. Early season floods in the dry year exhibited more variability in stream water nitrate and sulfate, whereas late season flood concentrations reflected a well-mixed system and therefore less variation of these species during flood hydrographs. These data showed that periods of below average precipitation preceding major runoff periods result both in less soil water and solute export during summer floods in basin-floor catchments and less direct snowmelt in high-elevation catchments. Hydrologic and solute export in each catchment, despite their differing geographical locations, responds in similar ways to climate variability.