diff --git a/DESCRIPTION b/DESCRIPTION
index cf417719d8fb14f5d03bf55239ba8e09750246b3..f5abe9b20009f94e6e8608815c1f8aa7fae8da3e 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -7,7 +7,7 @@ Authors@R: c(
   person("Olivier", "Delaigue", role = c("aut", "cre"), comment = c(ORCID = "0000-0002-7668-8468"), email = "airGR@inrae.fr"),
   person("Laurent", "Coron", role = c("aut"), comment = c(ORCID = "0000-0002-1503-6204")),
   person("Pierre", "Brigode", role = c("aut"), comment = c(ORCID = "0000-0001-8257-0741")),
-  person("Guillaume", "Thirel", role = c("ctb"), comment = c(ORCID = "0000-0002-1444-1830"))
+  person("Guillaume", "Thirel", role = c("aut"), comment = c(ORCID = "0000-0002-1444-1830"))
   )
 Depends:
   R (>= 3.6.0),
diff --git a/R/CalGR.R b/R/CalGR.R
index 2ab26dc98869be0a9995d0c7a3b6cec8f9c6018b..04e8e0a5eb865aee84192428aa12ea9a4252f941 100644
--- a/R/CalGR.R
+++ b/R/CalGR.R
@@ -23,18 +23,22 @@ CalGR <- function(PrepGR, CalCrit = c("NSE", "KGE", "KGE2", "RMSE"),
 
   WupInd <- NULL
   if (!is.null(WupPer)) {
-    WupPer <- as.POSIXct(WupPer, tz = "UTC")
-    if (length(WupPer) != 2) {
-      stop("Warm-up period \"WupPer\" must be of length 2")
-    }
-    if (any(is.na(WupPer))) {
-      stop("Non convenient date format for the warm-up period \"WupPer\"")
-    } else {
-      if (!any(PrepGR$InputsModel$DatesR == WupPer[1]) | !any(PrepGR$InputsModel$DatesR == WupPer[2])) {
-        stop("Non convenient date for the warm-up period \"WupPer\"")
+    if (!identical(WupPer, 0L)){
+      WupPer <- as.POSIXct(WupPer, tz = "UTC")
+      if (length(WupPer) != 2) {
+        stop("Warm-up period \"WupPer\" must be of length 2")
+      }
+      if (any(is.na(WupPer))) {
+        stop("Non convenient date format for the warm-up period \"WupPer\"")
       } else {
-        WupInd <- which(PrepGR$InputsModel$DatesR == WupPer[1]):which(PrepGR$InputsModel$DatesR == WupPer[2])
+        if (!any(PrepGR$InputsModel$DatesR == WupPer[1]) | !any(PrepGR$InputsModel$DatesR == WupPer[2])) {
+          stop("Non convenient date for the warm-up period \"WupPer\"")
+        } else {
+          WupInd <- which(PrepGR$InputsModel$DatesR == WupPer[1]):which(PrepGR$InputsModel$DatesR == WupPer[2])
+        }
       }
+    } else {
+      WupInd <- 0L
     }
   }
 
@@ -55,7 +59,7 @@ CalGR <- function(PrepGR, CalCrit = c("NSE", "KGE", "KGE2", "RMSE"),
 
 
   MOD_opt <- CreateRunOptions(FUN_MOD = get(PrepGR$TypeModel), InputsModel = PrepGR$InputsModel,
-                              IndPeriod_WarmUp = WupInd, IndPeriod_Run = CalInd, verbose = FALSE)
+                              IndPeriod_WarmUp = WupInd, IndPeriod_Run = CalInd, verbose = TRUE)
 
 
   MOD_crt <- CreateInputsCrit(FUN_CRIT = FUN_CRIT, InputsModel = PrepGR$InputsModel,
diff --git a/R/SimGR.R b/R/SimGR.R
index fe9183a042722167ac9736a64ad3d796cb59192a..f5d2fc7ffd860f660eb144ee08c7166fb27a6b6e 100644
--- a/R/SimGR.R
+++ b/R/SimGR.R
@@ -39,18 +39,22 @@ SimGR <- function(PrepGR, CalGR = NULL, Param, EffCrit = c("NSE", "KGE", "KGE2",
 
   WupInd <- NULL
   if (!is.null(WupPer)) {
-    WupPer <- as.POSIXct(WupPer, tz = "UTC")
-    if (length(WupPer) != 2) {
-      stop("Warm-up period \"WupPer\" must be of length 2")
-    }
-    if (any(is.na(WupPer))) {
-      stop("Non convenient date format for the warm-up period \"WupPer\"")
-    } else {
-      if (!any(PrepGR$InputsModel$DatesR == WupPer[1]) | !any(PrepGR$InputsModel$DatesR == WupPer[2])) {
-        stop("Non convenient date for the warm-up period \"WupPer\"")
+    if (!identical(WupPer, 0L)){
+      WupPer <- as.POSIXct(WupPer, tz = "UTC")
+      if (length(WupPer) != 2) {
+        stop("Warm-up period \"WupPer\" must be of length 2")
+      }
+      if (any(is.na(WupPer))) {
+        stop("Non convenient date format for the warm-up period \"WupPer\"")
       } else {
-        WupInd <- which(PrepGR$InputsModel$DatesR == WupPer[1]):which(PrepGR$InputsModel$DatesR == WupPer[2])
+        if (!any(PrepGR$InputsModel$DatesR == WupPer[1]) | !any(PrepGR$InputsModel$DatesR == WupPer[2])) {
+          stop("Non convenient date for the warm-up period \"WupPer\"")
+        } else {
+          WupInd <- which(PrepGR$InputsModel$DatesR == WupPer[1]):which(PrepGR$InputsModel$DatesR == WupPer[2])
+        }
       }
+    } else {
+      WupInd <- 0L
     }
   }
 
diff --git a/man/CalGR.Rd b/man/CalGR.Rd
index 953086d31fde277104ffe31ac35b89fce0fea54c..d511b14d766b1e441d8313b23a1474b456447997 100644
--- a/man/CalGR.Rd
+++ b/man/CalGR.Rd
@@ -21,7 +21,7 @@ CalGR(PrepGR, CalCrit = c("NSE", "KGE", "KGE2", "RMSE"),
 
   \item{CalCrit}{[character] name of the objective function (must be one of \code{"NSE"}, \code{"KGE"}, \code{"KGE2"} or \code{"RMSE"})}
 
-  \item{WupPer}{(optional) [character] vector of 2 values to define the beginning and end of the warm-up period [\code{"YYYY-mm-dd"} or \code{"YYYY-mm-dd HH:MM:SS"}]. See details}
+  \item{WupPer}{(optional) [character] vector of 2 values to define the beginning and end of the warm-up period [\code{"YYYY-mm-dd"} or \code{"YYYY-mm-dd HH:MM:SS"}]; [0L] to disable the warm-up period. See details}
 
   \item{CalPer}{[character] vector of 2 values to define the beginning and end of the calibration period [\code{"YYYY-mm-dd"} or \code{"YYYY-mm-dd HH:MM:SS"}]}
 
@@ -53,11 +53,13 @@ airGR
 functions
 }
 
+
 \details{
-\code{WupPer = NULL} indicates that, if available, a period of one year immediately present before the \code{CalPer} period is used. In order to disable the warm up of the model, users have to make sure not to provide data before \code{CalPer} when preparing the data with \code{\link{PrepGR}}.
+\code{WupPer = NULL} indicates that, if available, a period of one year immediately present before the CalPer period is used. \code{WupPer = 0L} allows to disable the warm up of the model.
 }
 
-\author{Olivier Delaigue}
+
+\author{Olivier Delaigue, Guillaume Thirel}
 
 
 \examples{
diff --git a/man/SimGR.Rd b/man/SimGR.Rd
index 03a5e48d6aee07f96b9d0b52acf2ec196f254bbb..c4a40a6516fc042606226c89d31a03295de6251d 100644
--- a/man/SimGR.Rd
+++ b/man/SimGR.Rd
@@ -25,7 +25,7 @@ SimGR(PrepGR, CalGR = NULL, Param, EffCrit = c("NSE", "KGE", "KGE2", "RMSE"),
 
   \item{EffCrit}{[character] name of the efficiency criterion (must be one of \code{"NSE"}, \code{"KGE"}, \code{"KGE2"} or \code{"RMSE"})}
 
-  \item{WupPer}{(optional) [character] vector of 2 values to define the beginning and end of the warm-up period [\code{"YYYY-mm-dd"} or \code{"YYYY-mm-dd HH:MM:SS"}]}
+  \item{WupPer}{(optional) [character] vector of 2 values to define the beginning and end of the warm-up period [\code{"YYYY-mm-dd"} or \code{"YYYY-mm-dd HH:MM:SS"}]; [0L] to disable the warm-up period. See details}
 
   \item{SimPer}{[character] vector of 2 values to define the beginning and end of the simulation period  [\code{"YYYY-mm-dd"} or \code{"YYYY-mm-dd HH:MM:SS"}]}
 
@@ -63,9 +63,12 @@ functions
 \details{
 The user can customize the parameters with the \code{Param} argument.
 The user can also use the parameters resulting from a calibration. In this case, it is necessary to use the \code{\link{CalGR}} function.
+\cr\cr
+\code{WupPer = NULL} indicates that, if available, a period of one year immediately present before the CalPer period is used. \code{WupPer = 0L} allows to disable the warm up of the model.
 }
 
-\author{Olivier Delaigue}
+
+\author{Olivier Delaigue, Guillaume Thirel}
 
 
 \examples{
diff --git a/tests/testthat/test-SimGR.R b/tests/testthat/test-SimGR.R
index 9f0ab70b7d338168a13404bad68b9979a5a4aacd..7bf71ba4c819809a1e40cde8116138d6361f71eb 100644
--- a/tests/testthat/test-SimGR.R
+++ b/tests/testthat/test-SimGR.R
@@ -4,10 +4,12 @@ context("SimGR")
 
 data(L0123001, package = "airGR")
 
-BasinObsSubNA <- BasinObs[, c("DatesR", "P", "E", "Qmm", "T")]
+BasinObsUsual <- BasinObs[, c("DatesR", "P", "E", "Qmm", "T")]
+BasinObsSubNA <- BasinObsUsual
 BasinObsSubNA[BasinObsSubNA$DatesR >= "1994-01-01", ]$Qmm <- NA
 BasinObsTotNA <- BasinObsSubNA[BasinObsSubNA$DatesR >= "1994-01-01", ]
 
+PrepUsual <- PrepGR(ObsDF = BasinObsUsual, HydroModel = "GR4J", CemaNeige = FALSE)
 PrepSubNA <- PrepGR(ObsDF = BasinObsSubNA, HydroModel = "GR4J", CemaNeige = FALSE)
 PrepTotNA <- PrepGR(ObsDF = BasinObsTotNA, HydroModel = "GR4J", CemaNeige = FALSE)
 
@@ -18,7 +20,7 @@ test_that("NA on a sub-period", {
     object   = SimGR(PrepGR = PrepSubNA, Param = c(270.426, 0.984, 108.853, 2.149), EffCrit = "KGE2",
                      WupPer = c("1994-01-01", "1994-12-31"), SimPer = c("1995-01-01", "1998-12-31"))
     ,
-    expected = "\"PrepGR\" does not contain any Qobs values on \"SimPer\". The efficiency criterion is not computed",
+    regexp = "\"PrepGR\" does not contain any Qobs values on \"SimPer\". The efficiency criterion is not computed",
   )
 })
 
@@ -29,6 +31,17 @@ test_that("NA on the total period", {
     object   = SimGR(PrepGR = PrepTotNA, Param = c(270.426, 0.984, 108.853, 2.149), EffCrit = "KGE2",
                      WupPer = c("1994-01-01", "1994-12-31"), SimPer = c("1995-01-01", "1998-12-31"))
     ,
-    expected = "\"PrepGR\" does not contain any Qobs values. The efficiency criterion is not computed",
+    regexp = "\"PrepGR\" does not contain any Qobs values. The efficiency criterion is not computed",
+  )
+})
+
+# ----
+
+test_that("Diasle warm-up period", {
+  expect_message(
+    object   = SimGR(PrepGR = PrepUsual, Param = c(270.426, 0.984, 108.853, 2.149), EffCrit = "KGE2",
+                     WupPer = 0L, SimPer = c("1995-01-01", "1998-12-31"))
+    ,
+    regexp  = "No warm up period is used",
   )
 })