difficult to obtain through a network of raingauges. In fact, urban catchments require
rainfall measurements with higher temporal and spatial resolutions [152, 153]. For
example, Berne et al. [154] suggested that hydrological applications for an urban
catchment with a large area (e.g. 1,000 ha) require rainfall measurements at 5 min/
3 km resolutions, whereas smaller urban areas (e.g. 100 ha) require rainfall measurements with resolutions of 3 min/2 km. Ocho-Rodriguez et al. [155] investigated
the impact of the spatial and temporal resolution of precipitation in the hydrodynamic response of urban catchments concluding that the temporal resolution of
precipitation affects the modelling results more strongly than variations in rainfall
spatial resolution. They concluded that resolutions of 1 min/1 km appear to be
sufficient for urban hydrodynamic modelling. Although these resolutions are feasible with small X-band weather radar systems, common operational radar networks
are not able to achieve the temporal resolutions required for small urban catchments.
For instance, the operational weather radar network in the UK provides rainfall
measurements at 5 min/1 km resolutions over the UK. So, it is evident that improvements in radar temporal resolution are required to satisfy urban hydrological applications in particular for smaller urban catchments. This could be achieved by using
nowcasting models to interpolate 5 min radar rainfall measurements to produce
measurements at 1 min temporal resolutions or by performing additional
low-elevation scans within the 5 min radar scanning strategy.
5 Concluding Comments
Precipitation is the main driver of the hydrological cycle and therefore precipitation
is a key input to hydrological models. Raingauges and weather radars are the most
widely used instruments to measure precipitation. Raingauge measurements are
traditionally used as the main input to rainfall–runoff models. In addition, they are
also used for calibrating and validating radar rainfall algorithms [99, 156]. However,
operational raingauge networks are often very sparse and unable to fulfill the density
requirements for real-time hydrological modelling. Rainfall events with high variability in space and time may not be represented accurately by a raingauge network.
The greatest benefit of weather radar is its potential to estimate rainfall rates at high
spatiotemporal resolution (e.g. 1 km/5 min) in real-time and over a large area.
Although radar rainfall measurements can be affected by different error sources,
there are different algorithms to control the quality of radar rainfall that enable its
quantitative use for hydrological and meteorological purposes. Polarimetric weather
radars bring several benefits including improvements in radar data quality, identification of hydrometeors, attenuation correction and radar rainfall estimation. Several
methods to merge radar rainfall with raingauge measurements have also been
developed in the literature. The merging of radar rainfall and raingauge measurements can bring the benefits of both instruments, that is, the accuracy of point
raingauge observations and the spatial distribution of precipitation from radar
measurements.
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rainfall measurements with higher temporal and spatial resolutions [152, 153]. For
example, Berne et al. [154] suggested that hydrological applications for an urban
catchment with a large area (e.g. 1,000 ha) require rainfall measurements at 5 min/
3 km resolutions, whereas smaller urban areas (e.g. 100 ha) require rainfall measurements with resolutions of 3 min/2 km. Ocho-Rodriguez et al. [155] investigated
the impact of the spatial and temporal resolution of precipitation in the hydrodynamic response of urban catchments concluding that the temporal resolution of
precipitation affects the modelling results more strongly than variations in rainfall
spatial resolution. They concluded that resolutions of 1 min/1 km appear to be
sufficient for urban hydrodynamic modelling. Although these resolutions are feasible with small X-band weather radar systems, common operational radar networks
are not able to achieve the temporal resolutions required for small urban catchments.
For instance, the operational weather radar network in the UK provides rainfall
measurements at 5 min/1 km resolutions over the UK. So, it is evident that improvements in radar temporal resolution are required to satisfy urban hydrological applications in particular for smaller urban catchments. This could be achieved by using
nowcasting models to interpolate 5 min radar rainfall measurements to produce
measurements at 1 min temporal resolutions or by performing additional
low-elevation scans within the 5 min radar scanning strategy.
5 Concluding Comments
Precipitation is the main driver of the hydrological cycle and therefore precipitation
is a key input to hydrological models. Raingauges and weather radars are the most
widely used instruments to measure precipitation. Raingauge measurements are
traditionally used as the main input to rainfall–runoff models. In addition, they are
also used for calibrating and validating radar rainfall algorithms [99, 156]. However,
operational raingauge networks are often very sparse and unable to fulfill the density
requirements for real-time hydrological modelling. Rainfall events with high variability in space and time may not be represented accurately by a raingauge network.
The greatest benefit of weather radar is its potential to estimate rainfall rates at high
spatiotemporal resolution (e.g. 1 km/5 min) in real-time and over a large area.
Although radar rainfall measurements can be affected by different error sources,
there are different algorithms to control the quality of radar rainfall that enable its
quantitative use for hydrological and meteorological purposes. Polarimetric weather
radars bring several benefits including improvements in radar data quality, identification of hydrometeors, attenuation correction and radar rainfall estimation. Several
methods to merge radar rainfall with raingauge measurements have also been
developed in the literature. The merging of radar rainfall and raingauge measurements can bring the benefits of both instruments, that is, the accuracy of point
raingauge observations and the spatial distribution of precipitation from radar
measurements.
Precipitation Measurement with Weather Radars
251