An evaluation of the success of MORECS, a meteorological model, in estimating soil moisture deficits

Abstract

MORECS is an acronym for the Meteorological Office rainfall and evaporation calculation system. In its operational form it uses daily meteorological data to produce weekly estimates of evapotranspiration, soil moisture deficit (SMD) and hydrologically effective rainfall for each square of a 40 × 40 km grid superimposed upon Great Britain. Grid square estimates of meteorological data are found using interpolation methods. A modified version of the Penman—Monteith equation is used to calculate evapotranspiration; a two-reservoir model is used to simulate the extraction of water in the SMD calculations.

The accuracy of SMD estimation by MORECS was investigated, for grassland, by comparing the SMDs with field-measurements made using neutron probes. MORECS was run retrospectively using meteorological data from stations close to the soil moisture measurement sites, to produce point SMD estimates. The effects of the interpolation methods were thus circumvented.

The principal finding was that there was a definite bias in the model towards SMD overestimation in nearly all years except those with very dry summers when underestimation occurred. The reasons for this are explored and areas where improvements might be made are outlined.