Energy balance of a corn residue-covered field during snowmelt

Transport of agricultural chemicals in runoff and recharge waters from snow melt and soil thawing may represent a significant event in terms of annual contaminant loadings in temperate regions. Improved understanding of the me lt dynamics of shallow snowpacks is necessary to fully assess the implicati ons for water quality. The objective of this study was to measure the energ y balance components of a corn (Zea mays L.) stubble field during the melti ng of its snowcover. Net radiation (Rn), soil (G), sensible (H), and latent (Q) heat fluxes were measured in a field near Ames, Iowa, during the winte r of 1994-1995. Energy consumed by melting including change in energy stora ge of the snowpack was determined as the residual of the measured energy ba lance. There was continuous snowcover at the field site for 71 days (maximu m depth = 222 mm) followed by an open period of II days before additional s nowfall and a second melt period. The net radiation and snowmelt/energy sto rage change (S) terms dominated the energy balance during both measurement intervals. Peak daily sensible and latent heat fluxes were below 100 W m(-2 ) on all days except the last day of the second melt period. There was good agreement between predicted and measured values of H and a during the melt ing of an aged snow layer but poorer agreement during the melt of fresh sno w. Both snowpacks melted rapidly and coincident changes in soil moisture st orage were observed. Improved estimates of Q and H, especially for partiall y open surfaces, will require better characterization of the surface aerody namic properties and spatially-representative surface temperature measureme nts.