This is a work in progress. It is a stub of an article I want to put together which shows how to use several online data repositories together as a showcase of the [Scientific Workflow and Integration Software for Health (SWISH) Climate Impact Assessments](https://github.com/swish-climate-impact-assessment) project.

################################################################
# name:r-code



# aim daily weather for any point location from online BoM weather grids

# depends on some github packages
require(awaptools)
#http://swish-climate-impact-assessment.github.io/tools/awaptools/awaptools-downloads.html
require(swishdbtools)
#http://swish-climate-impact-assessment.github.io/tools/swishdbtools/swishdbtools-downloads.html
require(gisviz)
# http://ivanhanigan.github.io/gisviz/

# and this from CRAN
if(!require(raster)) install.packages('raster'); require(raster)

# get weather data, beware that each grid is a couple of megabytes
vars <- c("maxave","minave","totals","vprph09","vprph15") #,"solarave") 
# solar only available after 1990
for(measure in vars)
{
  #measure <- vars[1]
  get_awap_data(start = '1960-01-01',end = '1960-01-02', measure)
}

# get location
locn <- geocode("daintree rainforest")
# this uses google maps API, better check this
# lon       lat
# 1 145.4185 -16.17003
## Treat data frame as spatial points
epsg <- make_EPSG()
shp <- SpatialPointsDataFrame(cbind(locn$lon,locn$lat),locn,
                              proj4string=CRS(epsg$prj4[epsg$code %in% '4283']))
# now loop over grids and extract met data
cfiles <-  dir(pattern="grid$")

for (i in seq_len(length(cfiles))) {
  #i <- 1 ## for stepping thru
  gridname <- cfiles[[i]]
  r <- raster(gridname)
  #image(r) # plot to look at
  e <- extract(r, shp, df=T)
  #str(e) ## print for debugging
  e1 <- shp
  e1@data$values <- e[,2]
  e1@data$gridname <- gridname
  # write to to target file
  write.table(e1@data,"output.csv",
    col.names = i == 1, append = i>1 , sep = ",", row.names = FALSE)
}

# further work is required to format the column with the gridname to get out the date and weather paramaters.

• Results
  
  • Markus reports:
  • "The R-script worked great once i had set a working directory that did not include spaces. (It may have been a different problem that got solved by changing the wd, but the important thing is it's running now.)"
  • Markus downloaded 70+ GB of gridded weather data from the BoM website to his local computer
  • Also note there is another set of gridded data available from the BOM, which contains pre-computed longterm mean temps, [ready to be extracted with the script](http://reg.bom.gov.au/jsp/ncc/climate_averages/temperature/index.jsp?maptype=6&period=#maps)
  • "Using this file, I only needed to get the 2012 temp grids for a comparison of 2012 vs. 30-year data. I'm going to run the extraction of 1961-1990 data, just to be sure."
  • "When we finished analysis of the long-term temperature from daily means found:
  • While the official, pre-computed long-term mean (i.e. 30-year grid file, analysed with your script) was 22.29 °C for the DRO coordinates (145.4494, -16.1041), the new value from daily means (i.e. daily minave and maxave averaged) is 24.91 °C.
  • We're not sure what causes this discrepancy, but thought we'd note that there is one.
  • For the manuscript, we ended up using the means obtained via BOM's method* to compare 1961-1990 values to 2012, both computed with the above script.
  • (* average of daily min/max temperature for each year, then averaged across the entire 30 year period)

• Dataset discrepancy
  
  • Following up on the interesting a difference between the two BoM datasets.
  • One thing that might cause this might be if you are calculating the average of the annual averages ie sum(annavs)/30 or the average of all the daily averages as sum(dailyavs)/(30 * 365 or 366)? the variance will differ by these methods.
  • looks like the 30 year dataset is the former:
  • "Average annual temperatures (maximum, minimum or mean) are calculated by adding daily temperature values each year, dividing by the number of days in that year to get an average for that particular year. The average values for each year in a specified period (1961 to 1990) are added together and the final value is calculated by dividing by the number of years in the period (30 years in this case)."

  [metadata](http://reg.bom.gov.au/jsp/ncc/climate_averages/temperature/index.jsp?maptype=6&period=#maps)

  • Markus followed the BOM calculation method, and just compared it with two other approaches.
  • average of all 21914 values
  • average of yearly sum(min and max values per year)/(ndays*2)
  • average of yearly sum(daily average)/ndays)
  • where ndays = number of days per year.
  • Differences between these methods show only in the 6th decimal place, far from 2.62 degrees.

################################################################
# This is Markus' comparison script 
# also see the formatted table csv, as well as the SWISH script's raw output csv

setwd("E:\\markus\\ph.d\\aus-daintree\\data-analysis\\climate")
climate <- read.csv("minmaxave-30year-daily.csv", sep=",", dec=".")

climate$year <- substr(climate$file,1,4)
climate$dailymean <- (climate$maxave+climate$minave)/2
head(climate)


#total average across all days and values
annmean <- mean(c(climate$maxave,climate$minave))
annmean


#daily means averaged by year, then total average
annmean1 <- c(1,2)
for(i in 1:30) {
        annmean1[i] <- mean(climate[climate$year==(i+1960),]$dailymean)
        #print(annmean1[i])
}
annmean1
mean(annmean1)


#mean of all values per year, then total average
annmean2 <- c(1,2)
for(i in 1:30) {
        tmpdata <- climate[climate$year==(i+1960),]
        annmean2[i] <- (sum(tmpdata$maxave) + sum(tmpdata$minave))/(length(tmpdata$maxave)+length(tmpdata$minave))
        #print(annmean2[i])
}
annmean2; mean(annmean2)


#differences
annmean - mean(annmean1)
annmean - mean(annmean2)
mean(annmean1) - mean(annmean2)

• Principal findings: Very convenient automated extraction of location-based time series data for the precise period that is requested.
• Weaknesses (whole method, not your script): very long download time for daily grids (~11.000 grids = huge dataset, took several days in my case). Yearly grids would be beneficial (and I believe most others are also looking mainly for data on a yearly (or larger) scale).

• Conclusion
  
  • Take home message: Seems like a perfect case of "double-check the data using one and the same method".