diff --git a/pysepal/scripts/gee_interface.py b/pysepal/scripts/gee_interface.py
index c02defab..556f9109 100644
--- a/pysepal/scripts/gee_interface.py
+++ b/pysepal/scripts/gee_interface.py
@@ -682,6 +682,22 @@ def close(self) -> None:
         log.debug(f"Closing GEEInterface... {id(self)}")
 
         try:
+            # Close the EESession HTTP client on the session's own loop BEFORE
+            # stopping it: the httpx AsyncClient (HTTP/2 pool, sockets, TLS
+            # state) must be released deterministically on kernel cull, not
+            # whenever the garbage collector gets to it.
+            if (
+                getattr(self, "session", None) is not None
+                and hasattr(self.session, "aclose")
+                and hasattr(self, "_async_loop")
+                and self._async_loop.is_running()
+            ):
+                future = asyncio.run_coroutine_threadsafe(self.session.aclose(), self._async_loop)
+                try:
+                    future.result(timeout=5.0)
+                except Exception as e:
+                    log.warning(f"Failed to close EESession HTTP client: {e}")
+
             if hasattr(self, "_async_loop") and self._async_loop.is_running():
                 self._async_loop.call_soon_threadsafe(self._async_loop.stop)
                 if hasattr(self, "_async_thread") and self._async_thread.is_alive():
diff --git a/tests/test_scripts/test_gee_interface_close.py b/tests/test_scripts/test_gee_interface_close.py
new file mode 100644
index 00000000..8b7da9cc
--- /dev/null
+++ b/tests/test_scripts/test_gee_interface_close.py
@@ -0,0 +1,66 @@
+"""GEEInterface.close() must release the EESession HTTP client deterministically.
+
+The EESession owns an ``httpx.AsyncClient`` (HTTP/2 pool, sockets, TLS state).
+Before this test existed, ``close()`` stopped the loop and thread but never
+called ``session.aclose()``, leaving the pool to whenever the garbage collector
+ran. Cleanup on kernel cull must be deterministic.
+
+No GEE credentials required: the session is a stub.
+"""
+
+import threading
+
+from pysepal.scripts.gee_interface import GEEInterface
+
+
+class StubSession:
+    """Stands in for EESession — only ``aclose()`` matters here."""
+
+    def __init__(self):
+        """Track aclose() invocations and the thread they ran on."""
+        self.aclose_calls = 0
+        self.aclose_thread = None
+
+    async def aclose(self):
+        self.aclose_calls += 1
+        self.aclose_thread = threading.current_thread()
+
+
+class ExplodingSession(StubSession):
+    async def aclose(self):
+        await super().aclose()
+        raise RuntimeError("boom")
+
+
+def test_close_acloses_session() -> None:
+    """close() awaits session.aclose() on the interface loop, then shuts down."""
+    session = StubSession()
+    iface = GEEInterface(session=session)
+
+    iface.close()
+
+    assert session.aclose_calls == 1
+    # ran on the interface's own loop thread, i.e. BEFORE the loop was stopped
+    assert session.aclose_thread is iface._async_thread
+    assert iface._async_loop.is_closed()
+
+
+def test_close_without_session() -> None:
+    """close() still shuts the loop down cleanly when there is no session."""
+    iface = GEEInterface()
+
+    iface.close()
+
+    assert iface._async_loop.is_closed()
+
+
+def test_close_survives_aclose_error_and_is_idempotent() -> None:
+    """An aclose() failure must not block shutdown; close() twice is a no-op."""
+    session = ExplodingSession()
+    iface = GEEInterface(session=session)
+
+    iface.close()  # must not raise
+    iface.close()  # idempotent
+
+    assert session.aclose_calls == 1
+    assert iface._async_loop.is_closed()