diff --git a/mlair/data_handler/default_data_handler.py b/mlair/data_handler/default_data_handler.py
index d85bb4b1233a7324ccda5247cc917f1a847b6363..52835975101f5ce6881b72b127e16c0e299dfb14 100644
--- a/mlair/data_handler/default_data_handler.py
+++ b/mlair/data_handler/default_data_handler.py
@@ -271,7 +271,8 @@ class DefaultDataHandler(AbstractDataHandler):
 
         if multiprocessing.cpu_count() > 1:  # parallel solution
             logging.info("use parallel transformation approach")
-            pool = multiprocessing.Pool(psutil.cpu_count(logical=False))  # use only physical cpus
+            pool = multiprocessing.Pool(
+                min([psutil.cpu_count(logical=False), len(set_stations), 16]))  # use only physical cpus
             logging.info(f"running {getattr(pool, '_processes')} processes in parallel")
             output = [
                 pool.apply_async(f_proc, args=(cls.data_handler_transformation, station), kwds=sp_keys)