Convert negative stock warning to error

docs/CHANGELOG.md

@@ -28,6 +28,7 @@ sections to include in release notes:
 ### Fixed
 
 ### Changed
+- SIPNET will now error instead of warning when an environment pool goes negative. This is a change from previous behavior where SIPNET would log a warning and continue running. (#398)
 
 ### Removed
 

docs/developer-guide/code-structure.md

@@ -65,7 +65,7 @@ Name fluxes by direction and target, e.g., `fluxes.NPP`, `fluxes.soilRespiration
 
 - Apply all additions/removals in a consistent order if constraints require it (e.g., water first if it bounds biochemical rates next step).
 - Enforce invariants:
-  - No negative pools; clamp with tracked deficits and warnings if needed.
+  - No negative pools; enforce with additional `ensureNonNegative()` call(s) in `ensureNonNegativeStocks()`.
   - Mass conservation across linked pools (e.g., C/N stoichiometry) with balanced cross-pool transfers.
 - Centralize any event-specific application here (e.g., harvest removing biomass, adding residues).
 

src/sipnet/sipnet.c

@@ -1348,11 +1348,11 @@ void calculateFluxes(void) {
 //  which var is treated as 0
 void ensureNonNegative(double *var, double minVal, const char *label) {
   if (*var < minVal) {
-    if (fabs(*var) > EPS) {  // Don't print the zeros
-      logWarning(
-          "Non-negative stock constraint applied for %s (value %8.5f set "
-          "to zero) year %d day %d time %6.3f\n",
-          label, *var, climate->year, climate->day, climate->time);
+    if (*var < -EPS) {  // Don't print the zeros
+      logError("Non-negative stock constraint violated for %s year %d day %d "
+               "time %6.3f\n",
+               label, *var, climate->year, climate->day, climate->time);
+      exit(EXIT_CODE_INTERNAL_ERROR);
     }
     *var = 0.;
   }