Instantaneous PAR estimated using long records of daily temperature and rainfall

Photosynthetically active radiation (PAR) is a key variable needed for running process models that describe the functioning of agricultural crops or forest trees. Actual measured data that covers sufficiently long periods on PAR is usually not available for most research sites. Also, existing data usually consists of temporal averages, which — given the non-linear response of the photosynthetic rate to PAR — are not ideal for estimating photosynthetic production. The range of daily minimum and maximum temperatures is strongly correlated to the intensity of solar radiation. We present a method using a statistical relationship between these variables for generating a long time series of instantaneous PAR values for a given location. The method thus enables one to use photosynthetic production for analyzing growth on sites for which measured PAR is not available.