Objectives
1. To develop an improved model for correction of precipitation for wind induced errors and to validate it against Danish climate conditions

2. To improve the estimation of regional precipitation by radar data including spatial dependence of the radar – rain gauges correction factors

3. To analyze the effect of different precipitation estimation schemes on hydrological model predictions

4. To prepare guidelines for precipitation estimation based on commonly available data in Denmark.

Work content
Task 1: Development of correction factors for point precipitation measurements
Test field(s) has been established for intercomparison of rain gauges against an accurate reference gauge. Measurements from the lysimeter (Task 3) provides a basis for comparison of integrated precipitation. An improved model for correction of liquid and solid precipitation will be developed and validated against local climate conditions. A dense network of rain gauges equipped with weather sensors has been established in a sub-catchment to study the effects of local shelter and spatial variability of wind speed, temperature and precipitation type.

Task 2: Precipitation estimation using weather radar
Sub-catchment rain gauges provide support for converting radar data into precipitation estimates. Attention is 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. A survey on radar adjustment methods is being carried out in order to identify the most suitable adjustment technique. The adjustment is being optimized by using meteorological parameters such as temperature and weather type to account for spatial and temporal variations of precipitation type.

Special radar scanning strategies is being adapted to measure the radar radial Doppler winds. This is being used to study their effect on the radar-rain gauges corrections factors in task 1. Data from radars is used to investigate the spatial dependence of the radar derived precipitation estimates and the radar – rain gauges corrections factors.

Task 3: Large-scale lysimeters
To analyze small scale errors, net infiltration is measured with four 12.5 m2 repacked percolation lysimeters. Water storage changes in each lysimeter is estimated with nine TDR probes extending 1 m into the lysimeters from the upper face located at 60 cm soil depth (Crop rooting depth = 60 cm). Automated measurements are collected as 15-min. sums (Bucket tips) for net infiltration and one-hour intervals for water storage (TDR). The tipping buckets (one for each lysimeter) and the self contained TDR system are installed in an observation well with access from the ground surface, approximately 9 m west of the lysimeters.

Task 4: Regionalization of precipitation
The impact of the new precipitation schemes on the hydrological response will be analyzed in WP6 using the integrated and distributed model.