Precipitation fields in an alpine Mediterranean catchment: inversion of precipitation gradient with elevation or undercatch of snowfall?

Abstract

The mean precipitation measurements in a Mediterranean Alpine catchment in Sierra Nevada show an inversion of the gradient with the altitude beyond a certain threshold. Is it due to a real pattern or it can be explained by systematic error of solid precipitation measurement in gauges? Can we assess climatic fields in an alpine catchment from gauge measurement? This article describes a research developed to answer both questions in the Alto Genil Basin. As commonly happens in most of the basins, the spatio-temporal information from climate gauges is limited; therefore to reduce uncertainty in estimates of climatic fields, some secondary information should be introduced. Since orographic conditions clearly influence precipitation, the relationship between this climatic variable and elevation is usually included as secondary information into the estimates. However, while there is a clear relationship between temperature and elevation, the relationship between precipitation and elevation is not so simple. In this article the analysis of the data performed allow us to demonstrate that there is a real inversion of the gradient within this Mediterranean Alpine area as other authors previously pointed in some tropical and subtropical zones. The intensity of this phenomenon and the altitude threshold from which it appears can be altered as a consequence of the undercath of the solid precipitation. To estimate precipitation fields, we have used different hypotheses about the intensity of the undercatch taking into account empirical corrections obtained for nearby mountain ranges. An analysis of the sensitivity of the results to the assumed undercatch hypothesis shows that it is not possible to estimate properly precipitation fields (the sensitivity of the results to the adopted hypothesis is high) in these alpine areas if we only have information about the precipitation measurements at the stations.