From 75f6433351df6fdcbef9f577bcf8f13610fa7afc Mon Sep 17 00:00:00 2001
From: Daniel Otto <drotto@uw.edu>
Date: Wed, 16 Nov 2022 15:14:37 -0800
Subject: [PATCH 1/2] Updated define_glacier_region to handle a list of DEM
 sources

---
 docs/whats-new.rst |  3 +++
 oggm/core/gis.py   | 11 ++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/docs/whats-new.rst b/docs/whats-new.rst
index 2fae105e3..3ebf20d28 100644
--- a/docs/whats-new.rst
+++ b/docs/whats-new.rst
@@ -69,6 +69,9 @@ Bug fixes
 - corrected a but in ``apparent_mb_from_any_mb``, where only two years of MB
   would be used instead of a range of years (:pull:`1426`).
   By `Bowen <https://github.com/bowenbelongstonature>`_
+- Corrected ``source`` argument in ``tasks.define_glacier_region`` to handle a
+  list of DEM sources. (:pull:`1503`).
+  By `Daniel Otto <https://github.com/d-otto>`_
 
 Migrating guide
 ~~~~~~~~~~~~~~~
diff --git a/oggm/core/gis.py b/oggm/core/gis.py
index 3fe4c03b5..c23a531b3 100644
--- a/oggm/core/gis.py
+++ b/oggm/core/gis.py
@@ -333,7 +333,16 @@ def define_glacier_region(gdir, entity=None, source=None):
 
     # Open DEM
     # We test DEM availability for glacier only (maps can grow big)
-    if not is_dem_source_available(source, *gdir.extent_ll):
+    if isinstance(source, list):  # when multiple sources are provided, try them sequentially
+        for i, src in enumerate(source):
+            source_exists = is_dem_source_available(src, *gdir.extent_ll)
+            if source_exists:
+                source = source[i]  # pick the first source which exists
+                break
+    else:
+        source_exists = is_dem_source_available(source, *gdir.extent_ll)
+        
+    if source_exists is False:
         raise InvalidWorkflowError(f'Source: {source} is not available for '
                                    f'glacier {gdir.rgi_id} with border '
                                    f"{cfg.PARAMS['border']}")

From d4ff09ee2109c50c9bfd922467721e5b84d90430 Mon Sep 17 00:00:00 2001
From: Daniel Otto <drotto@uw.edu>
Date: Wed, 16 Nov 2022 16:22:43 -0800
Subject: [PATCH 2/2] Update PR number in whats-new.rst

---
 docs/whats-new.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/whats-new.rst b/docs/whats-new.rst
index 3ebf20d28..b9aa36cae 100644
--- a/docs/whats-new.rst
+++ b/docs/whats-new.rst
@@ -70,7 +70,7 @@ Bug fixes
   would be used instead of a range of years (:pull:`1426`).
   By `Bowen <https://github.com/bowenbelongstonature>`_
 - Corrected ``source`` argument in ``tasks.define_glacier_region`` to handle a
-  list of DEM sources. (:pull:`1503`).
+  list of DEM sources. (:pull:`1506`).
   By `Daniel Otto <https://github.com/d-otto>`_
 
 Migrating guide