The contribution of soil moisture storage to the water balances of upland forested and grassland catchments

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Abstract
Soil moisture was measured on the Plynlimon catchments, mid Wales, by neutron scattering using networks of access tubes, as a means of estimating the changes in catchment storage for inclusion in the water balance. Reduced networks were used from 1974 to 1982, following an early assessment of their contribution to the water balance from 1970 to 1973. This study assesses the contribution of soil moisture change to both the annual and within-year water balances of the predominantly forested Severn and grassland Wye catchments, during a period of more extreme conditions of wetness, drought and snowfall Soil moisture has a significant impact on the water balance, but with a tendency to give evaporation less than the Penman ET in the summer months and the converse in the winter, a discrepancy explained by the movement of water into and out of stores that are not measured by the soil moisture networks. Losses by evaporation from the forest and grassland areas are estimated and the physical and biological implications for water resources and forestry are discussed.