diff --git a/climax/main/downscale_train.py b/climax/main/downscale_train.py
index 4689781aa7ad5efdd26c4e2ab4e4b42023b51bca..749257c602a450a29051157a889e2fbacbfb43ee 100644
--- a/climax/main/downscale_train.py
+++ b/climax/main/downscale_train.py
@@ -69,7 +69,7 @@ if __name__ == '__main__':
     LogConfig.init_log('Initializing ERA5 predictors.')
     Era5 = ERA5Dataset(ERA5_PATH.joinpath('ERA5'), ERA5_PREDICTORS,
                        plevels=ERA5_PLEVELS)
-    Era5_ds = Era5.merge(chunks=-1)
+    Era5_ds = Era5.merge(chunks={'time': 365})
 
     # initialize OBS predictand dataset
     LogConfig.init_log('Initializing observations for predictand: {}'