Abstract
In mountain basins, the use of long-range operational weather radars is often associated with poor quantitative precipitation estimation due to a number of challenges posed by the complexity of terrain. As a result, the applicability of radar-based precipitation estimates for hydrological studies is often limited over areas that are in close proximity to the radar. This study evaluates the advantages of using X-band polarimetric (XPOL) radar as a means to fill the coverage gaps and improve complex terrain precipitation estimation and associated hydrological applications based on a field experiment conducted in an area of Northeast Italian Alps characterized by large elevation differences. The corresponding rainfall estimates from two operational C-band weather radar observations are compared to the XPOL rainfall estimates for a near-range (10–35 km) mountainous basin (64 km2). In situ rainfall observations from a dense rain gauge network and two disdrometers (a 2D-video and a Parsivel) are used for ground validation of the radar-rainfall estimates. Ten storm events over a period of two years are used to explore the differences between the locally deployed XPOL vs. longer-range operational radar-rainfall error statistics. Hourly aggregate rainfall estimates by XPOL, corrected for rain-path attenuation and vertical reflectivity profile, exhibited correlations between 0.70 and 0.99 against reference rainfall data and 21% mean relative error for rainfall rates above 0.2 mm h−1. The corresponding metrics from the operational radar-network rainfall products gave a strong underestimation (50–70%) and lower correlations (0.48–0.81). For the two highest flow-peak events, a hydrological model (Kinematic Local Excess Model) was forced with the different radar-rainfall estimations and in situ rain gauge precipitation data at hourly resolution, exhibiting close agreement between the XPOL and gauge-based driven runoff simulations, while the simulations obtained by the operational radar rainfall products resulted in a greatly underestimated runoff response.
Highlights
Natural disasters occurring in mountainous areas worldwide are most often associated with hazards like flash floods, debris flows, and landslides, which are responsible for fatalities, property losses, and environmental degradation [1,2]
The X-band polarimetric (XPOL) radar was operated during rain events first in plan position indicator (PPI) mode taking measurements in a sector scan of 60◦, at 0.5◦, 1.5◦, 2.5◦, 3.5◦, and 5◦ elevation sweeps with a range resolution of 120 m for a total range of 35 km
This section shows a qualitative comparison between XPOL and the two operational radar rainfall products using storm total accumulation maps of two rainfall events (25 August 2012 and 12–13 August 2014) that triggered moderate peak runoff at the Saldur basin outlet
Summary
Natural disasters occurring in mountainous areas worldwide are most often associated with hazards like flash floods, debris flows, and landslides, which are responsible for fatalities, property losses, and environmental degradation [1,2]. Past studies [22,23,24,25,26,27,28,29] have shown that locally deployed dual-polarization X-band radar systems can contribute higher resolution rain rate estimations and improved rainfall quantification accuracies than the lower frequency (C-band and S-band) long-range operational radar systems These short-range radar systems could potentially be used to fill in coverage gaps of operational weather radar networks, which is important for advancing early warning of precipitation driven hydrological hazards (flash floods, landslides, debris flows, etc.) in urban and small mountainous basins [24,25,30].
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