
%0 Journal Article
%A Sadras, Víctor O. 
%T Influence of size of rainfall events on water-driven processes. I. Water budget of wheat crops in south-eastern Australia
%J Australian Journal of Agricultural Research
%D 2003/04/17
%V 54
%N 4
%P 341-351
%K climate, fractals, power laws, self organised criticality, self-similarity, drainage, runoff, soil evaporation, transpiration.
%R https://doi.org/10.1071/AR02112
%U https://www.publish.csiro.au/paper/AR02112 
%X Power laws relating the number of events N (s) and their sizes s, i.e. N (s) &#126; s&#8211;&#964;, are widespread in natural and social systems. Two hypotheses were tested: (1) power laws can be used to characterise rainfall patterns irrespective of the amount, seasonality, and rainfall mechanisms; and (2) crop water budget components favoured by large rainfall events, i.e. runoff and drainage, are negatively associated with &#964;, whereas soil evaporation, which is favoured by small rainfall events, is positively associated with &#964;. Hypothesis 1 was tested using long-term records of daily rainfall in 114 geographically widespread Australian locations from 12 to 43°S, and from 115 to 154°E, with median annual rainfall from 113 to 3437 mm, and Walsh and Lawler&#39;s seasonality index from 0.07 (very equable rainfall regime) to 1.1 (most rain in 3 months or less). Coefficients of determination of the linear regression between log-transformed number and size of rainfall events ranged from 0.90 to 0.98 (P &#60; 0.0001). A single value of &#964; described well the rainfall patterns in 50 out of the 114 locations, whereas some degree of curvilinearity suggested that a multidimensional model would be more suitable in the other locations. Hypothesis 2 was tested in a factorial modelling experiment combining 44 years and 39 southern Australian locations in a latitudinal band (33&#8211;36°S) between 134 and 147°E. Simulated water budget components of wheat crops on a sandy loam soil included runoff (R), drainage beyond the root-zone (D), and evapotranspiration (ET) and its components. Seasonal rainfall (range from 176 to 381 mm) and &#964; (range from 2.84 to 3.76) were unrelated. Simulated ET, R, and D increased, and the soil evaporation : ET ratio (E/ET) decreased with increasing rainfall. For a given amount of seasonal rainfall, processes favoured by large rainfall events, including runoff and drainage, were more frequent and more intense in locations with smaller &#964;, whereas E/ET increased with larger &#964;. Despite some limitations, power laws provided a statistical description of rainfall patterns that is agronomically meaningful, with parameter &#964; accounting for the effect of size of rainfall events on the fate of water in crops. 
