diff --git a/ChangeLog b/ChangeLog
index 6e7cf5d..d419591 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,8 +1,9 @@
-2017-07-03
+2017-07-07
 
         * Bug fix version 1.3.1 released
         ================================
 
+        Reduce computation time of ctmodel and parallelize using OpenMP (#2147)
         Fix csresmap significance computation error (#2136)
         Use MigMatrixNoTheta2cut_offaxis and AngularPSF2DEtrue_offaxis histograms to
           compute PSF and energy dispersion IRFs (#2135)
diff --git a/NEWS b/NEWS
index bdbdbbd..3aa40b1 100644
--- a/NEWS
+++ b/NEWS
@@ -1,6 +1,6 @@
 New Features and Important Changes in ctools 1.3.1
 
-3 July 2017
+7 July 2017
 
 
 Introduction
@@ -58,7 +58,8 @@ None
 
 ctmodel - CTA counts cube modelling
 -----------------------------------
-None
+The efficiency of the model computation has been improved and OpenMP is
+now used to parallelize the model computation (#2147).
 
 
 ctexpcube - CTA exposure cube generation
diff --git a/doc/source/admin/release_history/1.3.1.rst b/doc/source/admin/release_history/1.3.1.rst
index 8c784b2..0110917 100644
--- a/doc/source/admin/release_history/1.3.1.rst
+++ b/doc/source/admin/release_history/1.3.1.rst
@@ -1,7 +1,7 @@
 .. _1.3.1:
 
-ctools 1.3.1 release (TBD)
-==========================
+ctools 1.3.1 release
+====================
 
 Overview
 --------
@@ -21,3 +21,8 @@ The following bugs have been fixed:
   Properly forward working log file pointer in ``ctobssim::set_mc_id_names()``
 * Correct computation of standard deviations in :ref:`cssrcdetect`
 * :ref:`csobsselect` accepts an observation container upon construction
+
+The following improvements have been made:
+
+* [`2147 <https://cta-redmine.irap.omp.eu/issues/2147>`_] -
+  Reduce computation time of ctmodel and parallelize using OpenMP