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Daily stream flow and groundwater dynamics in forested subalpine catchments during spring are to a large extent controlled by hydrological processes that respond to the day-night energy cycle. Diurnal snowmelt and transpiration events combine to induce pressure variations in the soil water storage that are propagated to the stream. In headwater catchments these pressure variations can account for a significant amount of the total pressure in the system and control the magnitude, duration, and timing of stream inflow pulses at daily scales, especially in low flow systems. Changes in the radiative balance at the top of the snowpack can alter the diurnal hydrologic dynamics of the hillslope-stream system with potential ecological and management consequences. We present a detailed hourly dataset of atmospheric, hillslope, and streamflow measurements collected during one melt season from a semi-alpine headwater catchment in western Montana, US. We use this dataset to investigate the timing, pattern, and linkages among snowmelt-dominated hydrologic processes and assess the role of the snowpack, transpiration, and hillslopes in mediating daily movements of water from the top of the snowpack to local stream systems. We found that the amount of snowpack cold content accumulated during the night, which must be overcome every morning before snowmelt resumes, delayed water recharge inputs by up to 3 hours early in the melt season. These delays were further exacerbated by multi-day storms (cold fronts), which resulted in significant depletions in the soil and stream storages. We also found that both diurnal snowmelt and transpiration signals are present in the diurnal soil and stream storage fluctuations, although the individual contributions of these processes is difficult to discern. Our analysis showed that the hydrologic response of the snow-hillslope-stream system is highly sensitive to atmospheric drivers at hourly scales, and that variations in atmospheric energy inputs or other stresses are quickly transmitted and alter the intensity, duration and timing of snowmelt pulses and soil water extractions by vegetation, which ultimately drive variations in soil and stream water pressures. 

Abstract. During spring, daily stream flow and groundwater dynamics in forested subalpine catchmentsare to a large extent controlled by hydrological processes thatrespond to the day–night energy cycle. Diurnal snowmelt and transpirationevents combine to induce pressure variations in the soil water storage thatare propagated to the stream. In headwater catchments these pressurevariations can account for a significant amount of the total pressure in thesystem and control the magnitude, duration, and timing of stream inflowpulses at daily scales, especially in low-flow systems. Changes in theradiative balance at the top of the snowpack can alter the diurnal hydrologicdynamics of the hillslope–stream system, with potential ecological andmanagement consequences. We present a detailed hourly dataset of atmospheric, hillslope, andstreamflow measurements collected during one melt season from a semi-alpineheadwater catchment in western Montana, US. We use this dataset toinvestigate the timing, pattern, and linkages among snowmelt-dominatedhydrologic processes and assess the role of the snowpack, transpiration, andhillslopes in mediating daily movements of water from the top of the snowpackto local stream systems. We found that the amount of snowpack cold contentaccumulated during the night, which must be overcome every morning beforesnowmelt resumes, delayed water recharge inputs by up to 3h early in themelt season. These delays were further exacerbated by multi-day storms (coldfronts), which resulted in significant depletions in the soil and streamstorages. We also found that both diurnal snowmelt and transpiration signalsare present in the diurnal soil and stream storage fluctuations, although theindividual contributions of these processes are difficult to discern. Ouranalysis showed that the hydrologic response of the snow–hillslope–streamsystem is highly sensitive to atmospheric drivers at hourly scales and thatvariations in atmospheric energy inputs or other stresses are quicklytransmitted and alter the intensity, duration, and timing of snowmelt pulsesand soil water extractions by vegetation, which ultimately drive variationsin soil and stream water pressures.