Verification of avalanche bulletins by questionnaires
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The paper describes how avalanche bulletins (regional and national) are being verified by means of questionnaires in Switzerland. At the beginning of winter 1996/97 a set of four questionnaires has been introduced: • Questionnaire A: "Personal judgement of avalanche danger" • Questionnaire B: "Observations of avalanches without personal or material damage" • Questionnaire C: "Observations of avalanches with people caught but without material damage" • Questionnaire D: "Observations of avalanches with personal and/or material damage" About 10000 of these questionnaires have been distributed to the public, 500 have been returned during the winter 1996/97. This means twice as many returns as for previous winters. Questionnaires B,C and D can be used for the verification of the higher hazard degrees. Questionnaire A is the most frequently returned and can be used for all degrees of hazard. Therefore it is the subject of our evaluation. The questionnaires are used on a daily basis for the construction of the bulletin if they were returned in time. Therefore we cannot talk of an independent verification in a strict sense. At the end of the winter a comparison between questionnaires and bulletins has been done. The questionnaires allow to define a degree of hazard for 8 expositions and 4 height zones (lSOO-2000m, 2000-2S00m, 2500- 3000m and >3000m). Therefore we compare a set of 32 segments of every questionnaire to the bulletin. The overall estimation for Switzerland shows that about 64% of the feedback are in agreement with the bulletin, 32% differ by l degree of hazard and 4% by 2. The symmetric distribution of differences indicates that the degree of hazard is neither systematically over- nor underestimated. The distribution varies heavily between regions, height levels and expositions. For the region Davos a detailed verification using additional own field observations has been done and is compared to the verification based on questionnaires.