weathergeneration: Weather generation

Description

A semiparametric multivariate, multisite weather generator. The algorithm can be interpreted as a way to resample the original data to create synthetic data sets of the same length and similar properties.

Usage

weathergeneration(object, params = defaultGenerationParams(), verbose = TRUE)

Value

An object of the same class as the input object. Generated meteorological series are of the same length as the input.

Arguments

object: An object of class SpatialPointsMeteorology-class, SpatialGridMeteorology-class or SpatialPixelsMeteorology-class.
params: A list with parameters for the weather generator (see defaultGenerationParams).
verbose: Boolean flag to print process information.

Author

Miquel De Cáceres Ainsa, CREAF

Details

The implemented algorithm is based on Apipattanavis et al. (2007) for the non-conditional version, and is similar to Steinschneider et al. (2013) for the conditional one. Part of the code was adapted from package 'weathergen' by Jeffrey D. Walker, whom we are grateful. Conditioning is controlled via the element conditional of params list, which can be:

"none" - The non-conditional version is used, which is based on a first order Markov chain (MC) to simulate weather states (dry/wet/extreme wet) and a K-nearest neighbour (KNN) algorithm to select pairs of days with the same transition and similar weather for the initial state (as in Apipattanavis et al. 2007).
"arima" - Annual precipitation is conditioned using a stationary auto-regressive (ARIMA) model and then a K-nearest neighbour algorithm is used to select a set of years to train the MC-KNN algorithm (similar to Steinschneider et al. 2013). Recommended if low-frequency variation of annual precipitation is to be accounted for in long series.
"window" - The MC-KNN algorithm is trained with the subset of the input data corresponding to a window around the target year. Annual precipitation is conditioned using a lognormal random trial of the precipitation corresponding to the selected years. Recommended to generate stochastic series from climate change projections.

References

Apipattanavis, S., G. Podesta, B. Rajagopalan, and R. W. Katz (2007), A semiparametric multivariate and multisite weather generator, Water Resour. Res., 43, W11401, doi:10.1029/2006WR005714.

Steinschneider S., and Brown C. (2013) A semiparametric multivariate, multisite weather generator with low-frequency variability for use in climate risk assessments. Water Resour. Res., 49, 7205-7220, doi:10.1002/wrcr.20528.