Fix ALMaSS.growcrop! to use daily growing-degree days and not total gdd

src/crop/almass.jl

@@ -201,10 +201,10 @@ function stepagent!(cs::CropState, model::SimulationModel)
     # (https://www.eea.europa.eu/publications/europes-changing-climate-hazards-1/heat-and-cold/heat-and-cold-2014-mean)
     basetemp = cs.croptype.mingrowthtemp
     ismissing(basetemp) && (basetemp = 5.0)
-    gdd = (maxtemp(model)+mintemp(model))/2 - basetemp
-    gdd > 0 && (cs.growingdegreedays += gdd)
+    delta_gdd = bounds((maxtemp(model) + mintemp(model)) / 2 - basetemp)
+    cs.growingdegreedays += delta_gdd
     # update crop growth
-    growcrop!(cs, gdd, model)
+    growcrop!(cs, delta_gdd, model)
 end
 
 
@@ -248,14 +248,18 @@ end
 #TODO till!()
 
 """
-    growcrop!(cropstate, gdd, model)
+    growcrop!(cropstate, delta_gdd, model)
 
-Apply the relevant crop growth model to update the plants crop state
-on this farm plot.  Implements the ALMaSS crop growth model by Topping
-et al. (see `ALMaSS/Landscape/plant.cpp:PlantGrowthData::FindDiff()` and
+Update the crop state on this farm plot for a given daily change in
+growing-degree days `delta_gdd` (units of 'Kelvin Days').
+
+Implements the ALMaSS crop growth model by Topping et al. (see
+`ALMaSS/Landscape/plant.cpp:PlantGrowthData::FindDiff()` and
 `ALMaSS/Landscape/elements.cpp:VegElement::DoDevelopment()`).
 """
-function growcrop!(cs::CropState, gdd::Float64, model::SimulationModel)
+function growcrop!(cs::CropState, delta_gdd::Real, model::SimulationModel)
+    total_gdd = cs.growingdegreedays
+    # TODO: logic the wrong way around for fertiliser?
     fertiliser in cs.events ?
         curve = cs.croptype.lownutrientgrowth :
         curve = cs.croptype.highnutrientgrowth
@@ -270,17 +274,11 @@ function growcrop!(cs::CropState, gdd::Float64, model::SimulationModel)
             cs.LAIgreen = curve.LAIgreen[cs.phase][p]
             return
         else
-            gdd = cs.growingdegreedays
             # figure out which is the correct slope value to use for growth
-            if p == length(points) || gdd < points[p+1]
-                #FIXME it appears to me from the ALMaSS source code that the curve value
-                # for the day is multiplied with that day's growingdegreedays to give the
-                # diff, which is then added to the previous values. However, this results
-                # in values that are staggeringly too large. I'm not quite sure what the
-                # issue is here...
-                cs.height += bounds(curve.height[cs.phase][p]*gdd)
-                cs.LAItotal += bounds(curve.LAItotal[cs.phase][p]*gdd)
-                cs.LAIgreen += bounds(curve.LAIgreen[cs.phase][p]*gdd)
+            if p == length(points) || total_gdd < points[p+1]
+                cs.height += curve.height[cs.phase][p] * delta_gdd
+                cs.LAItotal += curve.LAItotal[cs.phase][p] * delta_gdd
+                cs.LAIgreen += curve.LAIgreen[cs.phase][p] * delta_gdd
                 return
             end
             #XXX To be precise, we ought to figure out if one or more inflection