Abstract

Problems are addressed of inaccuracies and adjustment of the radar data with special attention to the winter precipitation measurements for a hilly area in northwestern European Russia. Calibration of the Valday radar has been done by using a special rain-gauge network over the Polomet' river watershed. The ground network was consisted of 38 gauged sites aggregated in a number of nested groups. Hourly (3-hourly) rates were interpolated into grid cells. The ratio gauge/radar was found varied from 0,5 to 3,8 for 3-hourly rates, and less ranged (from 0,7 to 2,2) for daily amounts. Of particular importance is that the gauge/radar ratios are distributed not randomly. By analyzing their maps, one can infer about specific inaccuracies which are correlated with the terrain features. On winter, when the radar can underestimate those snow amounts fallen onto the hills, there is a considerably scattered ratio between snow water equivalent (SWE) and accumulated radar precipitation estimates. Based upon our experience, the problem seems to be clarified.

Methods are proffered to process the radar-based precipitation data as convenient to be applied just to engineering hydrology. Two main properties of precipitation fields have been examined: (1) spatial coverage, (2) empirical conditional frequency of "at-cell" rain rates by specified spatial average values. Examples of the data processing and analysis are given to expound upon the ideas of how to describe precipitation patterns statistically. For instance, a procedure is proffered to reveal those rain rates exceeding that threshold correlated with antecedent wetness of a drainage basin. A previous classification was done of the radar images using the approach based upon cluster analysis. Two types of rainfall fields with three subtypes each were identified as depending on intensity and preferable localization of heavy rainfall on the area examined.

Two procedures are developed for hydrological calculations with the use of radar precipitation and its spatial characteristics. Both are based on the so-called "extreme intensity" method accepted in Russia for engineering when the maximal (peak) flows and their frequency are to be determined. The peak flow conditions have been simulated and represented as spatial frequency curves for runoff depth on conventional watersheds 10x10 km in area composed of different soils and produced, respectively, different runoff rates. Presented allows us to detect probabilistically on where there would be runoff depth exceeding some specified value, or in opposite, to evaluate what a flow may be expected by given rain rates fallen on given area. An expert outlook is given finally to how to deal with the precipitation space-time series in extended studies of the climate variability and water resources assessment for future water projects.

 

AGU Western Pacific Geophysics Meeting.
Wellington, New Zealand. July 9 - 12, 2002.
A Special Session on Radar Applications in Hydrology and Meteorology

Hydrosphere © 1990 — 2005 Vladimir A. Shutov
Design by Timothy (Azs) Shutov © 2001