add combination of temp and precip sd correctly

ncsu-landscape-dynamics · Sep 24, 2023 · ae4891d · ae4891d
1 parent c8107cb
commit ae4891d
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Showing 2 changed files with 10 additions and 1 deletion.
diff --git a/R/configuration.R b/R/configuration.R
@@ -367,7 +367,10 @@ configuration <- function(config) {
 
       weather_coefficient_stack <- weather_coefficient_stack * precipitation_coefficient
       if (config$weather_type == "probabilistic") {
-        weather_coefficient_sd_stack <- weather_coefficient_sd_stack * precipitation_coefficient_sd
+        # compute sd from combined sd of the two rasters hard coded 10 years as our current
+        weather_coefficient_sd_stack <-
+          combined_sd(temperature_coefficient_sd, precipitation_coefficient_sd,
+                      temperature_coefficient, precipitation_coefficient, 10, 10)
       }
     }
   } else if (config$precip == TRUE) {

diff --git a/R/helpers.R b/R/helpers.R
@@ -264,3 +264,9 @@ output_from_raster_mean_and_sd <- function(x) {
   x2 <- suppressWarnings(terra::app(x, fun))
   return(x2)
 }
+
+# Combine two standard deviation spatRasters
+combined_sd <- function(v1, v2, m1, m2, n1, n2) {
+  (((n1 - 1) * v1 + (n2 - 1) * v2) / (n1 + n2 -1)) +
+    (((n1 * n2) * (m1 - m2)^2) / ((n1 +n2) * (n1 + n2 -1)))
+}