Modelling the statistical dependence of rainfall event variables by a trivariate copula function

In many hydrological models, such as those derived by analytical probabilistic methods, the precipitation stochastic process is represented by means of individual storm random variables which are supposed to be independent of each other. However, several proposals were advanced to develop joint probability distributions able to account for the observed statistical dependence. The traditional technique of the multivariate statistics is nevertheless affected by several drawbacks, whose most evident issue is the unavoidable subordination of the dependence structure assessment to the marginal distribution fitting. Conversely, the copula approach can overcome this limitation, by dividing the problem in two distinct parts. Furthermore, goodness-of-fit tests were recently made available and a significant improvement in the function selection reliability has been achieved. Herein the dependence structure of the rainfall event volume, the wet weather duration and the interevent time is assessed and verified by test statistics with respect to three long time series recorded in different Italian climates. Paired analyses revealed a non negligible dependence between volume and duration, while the interevent period proved to be substantially independent of the other variables. A unique copula model seems to be suitable for representing this dependence structure, despite the sensitivity demonstrated by its parameter towards the threshold utilized in the procedure for extracting the independent events. The joint probability function was finally developed by adopting a Weibull model for the marginal distributions

Land cover changes since the 19th century detected from historic maps for environmental applications: toward a “CORINE 1800” project?

The value of cartographic heritage for environmental applications is demonstrated with a test case in the Central Italian Alps. Land cover changes since the early 19th century are detected from sample maps of the Second Military Survey of the Habsburg Empire in Lombardy (1818-1829), available on the portal www.mapire.eu. They are compared with 1954 areal sur-veys and successive land cover classification until 2018. Issues as land use classes homogeni-zation, data vectorization, georeferencing errors are addressed. The dynamics of main land cover classes (woods, bush, meadows, crops) are investigated on sample areas and the potential use of this exercise for hydrological applications is explored. In fact, the impact of the observed natural afforestation on changes in hydrological losses due to evapotranspiration and its influ-ence as a likely cause for the decrease in runoff monitored since 1845 in the Adda river basin and needs to be assessed in a systematic way. The proposed test case can pave the road for a project extended at European scale, a sort of “CORINE 1800 land cover” Geographic Infor-mation System, which could have several environmental, cartographic and socio-economic ap-plications