The PhD project is a part of the research center HOBE – Center for hydrology, in which a hydrological observatory will be established in the Skjern River catchment in the western part of Denmark. Precipitation is recognized as one of the most important variables in water balance at a catchment scale, but problems have shown regarding the closure of the water balance at catchment scale due to the significant uncertainty of measuring and estimating the regional of precipitation. Data from rain gauges are commonly used in hydrological applications for stabling the input to a catchment, but the regionalization is complicated by the often short correlation distance of point measurements. Advantages in precision of temporal and spatial resolution can be obtained by application of radar data, which has been proved to have significant improvement to the estimation of precipitation. However, radar data are contaminated by several sources of error therefore needs to be carefully adjusted by using the rain gauge measurement. As radar measures the reflectivity at increasing levels for larger distances, vertical variations of the radar reflectivity is considered to be one of the main causes of differences between radar and rain gauge measurements. Current work on improving precipitation estimates from single polarization radars focuses on corrections using vertical reflectivity profiles. A special profile effect that has been observed is enhancement of radar reflectivity caused by melting hydrometeors falling through the melting layer. Large spatial and temporal variability in the characteristics of precipitation systems contribute substantially to the differences between radar and gauges and the adjustment of radar data should take into account the precipitation type and weather conditions. Knowing the precipitation type the accuracy of the estimates can be significantly improved. Thus a dense network of gauges is required to reliably convert radar data into precipitation. This network will be established in a sub-catchment of Skjern River to support the converting procedure of radar data into precipitation estimates. Attention will be paid to the effects of vertical variations of the reflectivity profile, reflectivity enhancement due to melting of hydrometeors, clutter and anomalous propagation of the radar beam. Furthermore, the impact of new precipitation schemes on the hydrological response will be analyzed using an integrated and distributed hydrological model for the catchment.
