Measure of rainfall time structure using the dimensionless n-index

Abstract

The n-index is defined as the exponent of the power law relating the maximum average intensity over given periods of time (e.g. minutes, hours or days) and these periods of averaging. The n-index (between 0 and 1) reports on temporal variability of rainfall behaviour within an event. This study analyses the n-index around the world and its uncertainty according to several criteria of calculation and daily/sub-daily data. The results show that precipitation generally has a nested time structure, i.e. each maximum accumulation of shorter duration is included within a longer one, following a fractal behaviour. The obtained n-index is generally independent of the intensity and the event duration, but is sensitive to the temporal resolution of data. The distribution of the n-index around the world shows that areas with lower n are the coldest regions and zones with marked orography. The highest n-index values are found near the warmest seas.

Daily precipitation concentration around the world according to several indices

“…In other words, the time structure and irregularity of precipitation are reflected in a similar manner at low and high time scales, and this is because the pace of physical processes (evaporation + transport + condensation) is also interconnected at various time scales (the energy of the sensible and latent heat flux is propagated throughout the water cycle). In fact, the n index shows autosimilarity properties on several time scales according to its connection with the fractal dimension of the rainfall events (Monjo, ). In addition and according to the current study, it could be said that n or and the GI reflect characteristics of both the climatic concentration and information entropy of the precipitation, which are related to the physical processes of convection and transport.…”

Spatiotemporal variability of daily precipitation concentration and its relationship to teleconnection patterns over the Mediterranean during 1975–2015

“…The n ‐index ( n ) is a dimensionless indicator that depicts the temporal variability of rainfall behaviour within an event (Monjo, ). The n or index is related to the shape of the Lorenz curve and can reflect the characteristics of both precipitation concentration and precipitation entropy that are connected to the physical process of transport and convection (Monjo and Martin‐Vide, ).…”

Relaciones climáticas entre la fractalidad temporal de los episodios de lluvia y de sequía

“…El primer caso puede ser deducido teóricamente de acuerdo con la interpretación fractal del índice n (Monjo, 2016). Por otro lado, la correlación negativa con h y s implica que una mayor concentración de las rachas está asociada a una mayor regularidad de las precipitaciones.…”

“…les; sin embargo, la intensidad a escala sub-horaria presenta importantes dificultades para ser medida debido a su gran irregularidad (Liu et al 2013, Monjo 2016. Una forma de medir la irregularidad de la precipitación es mediante índices asociados a la curva de Lorenz o la entropía estadística (Monjo y Martin-Vide, 2016).…”

“…En particular, el índice IP establece umbrales variables según el clima: Considera un período de retorno de 5 años y cuatro duraciones, que son 5 minutos, 1, 2 y 24 horas. El índice n de Monjo (2016) se define como el exponente adimensional de las curvas Intensidad-Duración y puede interpretarse como la dimensión fractal de la intensidad de la lluvia. El índice n presenta un umbral teórico que generalmente es independiente de la intensidad y la duración del evento.…”