Mapping of maximum snow load values for the 50-year return period for Croatia

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Snow load is an important climatic element that is, together with minimum and maximum temperatures and wind load, a part of the national annex of standards for the design of structures. In particular, the characteristic snow load, defined as the maximum snow load at the ground for the 50-year return period, has to be estimated and a map has to be supplied as part of the national annex. The method for the estimation of this parameter at the station locations is presented, followed by the geostatistical mapping procedure used to estimate this parameter for the whole territory of Croatia. Snow load is defined as a product of snow density, snow depth and gravitational acceleration. Although snow depths are measured at a large number of meteorological stations, snow loads are not easy to estimate because of very few snow density measurements. To overcome this, snow density was fitted to snow depth data using linear regression according to the daily pairs of values from 13 meteorological stations. Since snow density changes with elevations and seasons, the stations are divided into three subsets according to station elevation (lower than 600 m, 600–1000 m high and higher than 1000 m) and the regression equations are also built on a monthly basis. These modelling results allowed the estimation of the snow load at 96 low-elevation stations, eight higher elevation stations and one high-altitude station based on the monthly maximum snow depths and the model estimated snow densities. Based on the monthly maximum snow loads, the series of maximum annual snow loads can be calculated for 118 locations. These series of annual maximum snow loads are the basis for the estimation of the annual maximum snow load values for the 50-year return period, by means of an extreme value distribution.Finally, the estimated annual maximum snow load values for the 50-year return period at 118 stations constitute the input for the geostatistical procedure of mapping this parameter for the territory of Croatia.