Quality metrics in QPE

During the last years, significant advancements have been achieved in improving Quantitative Precipitation Estimates (QPE) by radar. New comprehension of the physics underlying the radar measurements as well as new technological advancements have allowed radar community to propose better algorithms and methodologies to improve QPE. Thus, the essential issues and corrections to be addressed are quite well known and widely recognized, and a number of new insights and ideas have been proposed. However, few of these algorithms and methodologies have been thoroughly tested, and the majority of them are essentially used in scientific studies or just applied by the same institutions that have developed them. So, it is very difficult to have a clear picture of their potential and to be able to fairly compare their performances. This situation leads to practitioners to have serious difficulties to be able to adopt them, even to know what methodologies could be more suited to their particular systems and climates. Additionally, the increase of the number of radars and radar networks available worldwide, and the clear need to merge them to create international networks and to assimilate their data into NWP and GCM models, make that an international agreed procedure to assess the quality of QPE algorithms and correction methodologies are at present a crucial point. Under the WMO impulse, an international group has launched a collaborative network to develop an international inter-comparison program. This inter-comparison program is oriented to establish a set of agreed recommendations based on the comparison of different algorithms and procedures on a number of common reference test-beds. The ultimate aim is to give support to operational services to choose the best correction procedures available worldwide, to make feasible the possibility of having common methodologies for obtaining QPE, and to propose how to characterize in a widely accepted way the uncertainties associated to any QPE procedure. As a first stage, a discussion about how to measure and assess the quality of QPE provided by different algorithms and methodologies in different regions and climates has been initiated. The definition of a quality metrics in QPE, internationally accepted as the reference procedure to measure quality in QPE, is in fact the first step before that the inter-comparison work could be developed. In this paper a first proposition of the proposed quality metrics is presented. It will be also illustrated by its application in selected case studies showing its feasibility, its strengths and its limitations. Finally the rules for a first international inter-comparison experience will be presented and discussed.