diff --git a/packages/engine-ts/src/ClimatePhysics.generated.ts b/packages/engine-ts/src/ClimatePhysics.generated.ts
index 69c77a8f..a9049ecb 100644
--- a/packages/engine-ts/src/ClimatePhysics.generated.ts
+++ b/packages/engine-ts/src/ClimatePhysics.generated.ts
@@ -600,63 +600,71 @@ export class ClimatePhysics {
   }
 
   private stepTerrainEvolution(grid: GridState): void {
-    const { tiles } = grid
-    const up_thresh = this.p('quality_up_threshold', 10)
-    const down_thresh = this.p('quality_down_threshold', 5)
+  const { tiles, width: w, height: h } = grid
+  let up_thresh = Math.floor((this.params as any)["quality_up_threshold"] ?? 10)
+  let down_thresh = Math.floor((this.params as any)["quality_down_threshold"] ?? 5)
 
-    for (let i = 0; i < tiles.length; i++) {
-      const tile = tiles[i]
-      const tid = tile.biome_id
+  for (let i = 0; i < tiles.length; i++) {
+    const tile = tiles[i]
+    const { col, row } = tile
+    let tid = tile.biome_id
 
-      if (tile.is_natural_wonder) continue
+    if (tile.is_natural_wonder) {
+      continue
 
-      // Water freezing/thawing — ice forms below freeze threshold, thaws above
-      const freezeTemp = this.p('water_freeze_threshold', 0.12)
-      const thawTemp = freezeTemp + 0.03  // hysteresis prevents oscillation
-      const isWater = tid === 'ocean' || tid === 'coast' || tid === 'lake' || tid === 'inland_sea'
-      if (isWater) {
-        if (tile.temperature < freezeTemp) {
-          tile.original_biome_id = tid
-          tile.biome_id = 'ice'
+    }
+    // Water freezing/thawing
+    let freeze_temp = (this.params as any)["water_freeze_threshold"] ?? 0.12
+    let thaw_temp = freeze_temp + 0.03
+    let is_water = ( tid === "ocean" || tid === "coast" || tid === "lake" || tid === "inland_sea" )
+    if (is_water) {
+      if (tile.temperature < freeze_temp) {
+        tile.original_biome_id = tid
+        tile.biome_id = "ice"
+        tile.quality = 1
+        tile.quality_progress = 0
+      }
+      continue
+    }
+    if (tid === "ice") {
+      if (tile.temperature > thaw_temp && tile.original_biome_id !== "") {
+        tile.biome_id = tile.original_biome_id
+        tile.original_biome_id = ""
+        tile.quality = 1
+        tile.quality_progress = 0
+      }
+      continue
+
+    }
+    if (tid === "volcano") {
+      continue
+
+    }
+    let ideal = idealTerrain(tile, this.spec)
+
+    if (ideal === tid) {
+      tile.quality_progress += 1
+      if (tile.quality_progress >= up_thresh) {
+        tile.quality_progress = 0
+        if (tile.quality < 5) {
+          tile.quality += 1
+    } else {
+      tile.quality_progress -= 1
+      if (tile.quality_progress <= -down_thresh) {
+        tile.quality_progress = 0
+        if (tile.quality > 1) {
+          tile.quality -= 1
+        } else {
+          tile.biome_id = ideal
           tile.quality = 1
           tile.quality_progress = 0
-        }
-        continue
-      }
-      if (tid === 'ice') {
-        if (tile.temperature > thawTemp && tile.original_biome_id) {
-          tile.biome_id = tile.original_biome_id
-          tile.original_biome_id = ''
-          tile.quality = 1
-          tile.quality_progress = 0
-        }
-        continue
-      }
 
-      if (tid === 'volcano') continue
-
-      const ideal = idealTerrain(tile, this.spec)
-
-      if (ideal === tid) {
-        tile.quality_progress += 1
-        if (tile.quality_progress >= up_thresh) {
-          tile.quality_progress = 0
-          if (tile.quality < 5) tile.quality += 1
-        }
-      } else {
-        tile.quality_progress -= 1
-        if (tile.quality_progress <= -down_thresh) {
-          tile.quality_progress = 0
-          if (tile.quality > 1) {
-            tile.quality -= 1
-          } else {
-            tile.biome_id = ideal
-            tile.quality = 1
-            tile.quality_progress = 0
-          }
         }
       }
     }
+      }
+    }
+  }
   }
 
   private stepGlobalStats(grid: GridState): void {
diff --git a/tools/sprite-generation/sprites.db-shm b/tools/sprite-generation/sprites.db-shm
index c843a1c1..34566726 100644
Binary files a/tools/sprite-generation/sprites.db-shm and b/tools/sprite-generation/sprites.db-shm differ
diff --git a/tools/sprite-generation/sprites.db-wal b/tools/sprite-generation/sprites.db-wal
index 3c1902a8..a129d0c7 100644
Binary files a/tools/sprite-generation/sprites.db-wal and b/tools/sprite-generation/sprites.db-wal differ
diff --git a/tools/transpile-engine/transpile.py b/tools/transpile-engine/transpile.py
index 11da0be9..7a892daf 100644
--- a/tools/transpile-engine/transpile.py
+++ b/tools/transpile-engine/transpile.py
@@ -183,7 +183,7 @@ METHOD_MAP = [
     ("_update_lake_evaporation",     "stepLakeEvaporation",    "private"),
     ("_update_deep_earth_water",     "stepDeepEarthWater",     "private"),
     ("_update_precipitation",        "stepPrecipitation",      "private"),
-    ("_check_terrain_evolution",     "stepTerrainEvolution",   "HAND_WRITTEN"),
+    ("_check_terrain_evolution",     "stepTerrainEvolution",   "private"),
     ("_compute_global_stats",        "stepGlobalStats",        "private"),
     ("_clear_magic_deltas",          "stepClearDeltas",        "private"),
 ]
@@ -918,9 +918,6 @@ def assemble(fns: dict[str, dict[str, str]]) -> str:
         if gd_name == "_apply_aerosol_forcing":
             parts.append(_emit_aerosol_forcing())  # hand-written — too complex for generic transpilation
             continue
-        if gd_name == "_check_terrain_evolution":
-            parts.append(_emit_terrain_evolution())  # hand-written — transpiler mishandles nested if/else
-            continue
         if gd_name in climate_fns:
             body = climate_fns[gd_name]
             ts_body = transform_method_body(body, gd_name, defaults=CLIMATE_DEFAULTS, extra_removals=EXTRA_REMOVALS)