Estimation of the spatial pattern of surface relative humidity using ground based radar measurements and its application to disease risk assessment

Temperature, precipitation and moisture play a major role in many agricultural and biological processes, particularly in the occurrence and propagation of plant diseases. In southern Quebec, hourly relative humidity (RH) data are provided by automated weather stations located 30–50 km apart. Since RH varies considerably in space and time, there is a lack of reliable information on moisture in between weather stations. By using information provided by weather radar, RH data could become available on an hourly basis with a spatial resolution of a few kilometres. In this study, we compared RH measured at three weather stations to RH calculated from weather radar measurements using time interval of 240 h in 1997 and 336 h in 1998. A valid t-test designed for simple linear regression analysis with two time series as dependent and explanatory variables, and based on the first difference ratios (FDRs) of the time series clearly showed that RH calculated from radar measurements is comparable to the one measured at weather stations. The possibility of using weather radar measurements to map the variability of Cercospora carotae (Pass.) Solh. in a geographic information system (GIS) is discussed.