Environmental Science and Engineering Seminar

Rainfall is a complex field, highly variable both in space and time, whose satisfactory description requires taking into account several aspects such as intensity, timing, seasonality, extremes, etc. Here I discuss some recently introduced  seasonality indicators of precipitation based on a probabilistic interpretation of the monthly rainfall fractions and  information theory -- relative entropy (RE),  dimensionless seasonality index (DSI)  and centroid -- to describe the  time-concentration, monsoonality and timing of rainfall. Their application on a global scale to precipitation gridded datasets and coupled atmosphere-ocean general circulation models is discussed. Global regions with different precipitation regimes are classified and characterized in terms of RE and DSI. The RE characterizes the concentration of rainfall throughout the year and has an easy interpretation in terms of number of dry/wet days. Global monsoon areas are generally characterized by large values of the DSI, which may serve as a precipitation-based monsoon index. Model biases and future projection changes of rainfall seasonality are analyzed with the new set of indicators.