diff --git a/src/+equations/calcLambda.m b/src/+equations/calcLambda.m
new file mode 100644
index 00000000..c07c0d54
--- /dev/null
+++ b/src/+equations/calcLambda.m
@@ -0,0 +1,14 @@
+function calcLambda(VPER, POR, Lamda_soc, XSOC)
+    %{
+        Calculate soil hydraulic properties according to equation 6c in
+        Zheng, D., van der Velde, R., Su, Z., Wang, X., Wen, J., Booij, M. J.,
+        Hoekstra, A. Y., and Chen, Y.: Augmentations to the Noah model physics
+        for application to the Yellow River source area. Part I: Soil water
+        flow, Journal of Hydrometeorology, 16, 2659-2676,
+        https://doi.org/10.1175/JHM-D-14-0198.1, 2015
+
+    %}
+
+    Lamda = (2.91 + 0.159 * VPER / (1 - POR) * 100);
+    Lamda = 1 / (Lamda * (1 - XSOC) + XSOC * Lamda_soc);
+end
diff --git a/src/+equations/calcPhi_s.m b/src/+equations/calcPhi_s.m
new file mode 100644
index 00000000..8ea67972
--- /dev/null
+++ b/src/+equations/calcPhi_s.m
@@ -0,0 +1,15 @@
+function Phi_s = calcPhi_s(VPER, POR, Phi_soc, XSOC)
+    %{
+        Calculate soil hydraulic properties according to equation 6b in
+        Zheng, D., van der Velde, R., Su, Z., Wang, X., Wen, J., Booij, M. J.,
+        Hoekstra, A. Y., and Chen, Y.: Augmentations to the Noah model physics
+        for application to the Yellow River source area. Part I: Soil water
+        flow, Journal of Hydrometeorology, 16, 2659-2676,
+        https://doi.org/10.1175/JHM-D-14-0198.1, 2015
+
+    %}
+
+    Phi_s = -0.01 * 10^(1.88 - 0.0131 * VPER / (1 - POR) * 100);
+    Phi_s = (Phi_s * (1 - XSOC) + XSOC * Phi_soc) * 100;
+
+end
diff --git a/src/+init/updateSoilVariables.m b/src/+init/updateSoilVariables.m
index 24706aa5..91e3fa94 100644
--- a/src/+init/updateSoilVariables.m
+++ b/src/+init/updateSoilVariables.m
@@ -28,8 +28,8 @@
             SoilVariables.Lamda(i) = SoilProperties.Coef_Lamda(j);
         else
             VanGenuchten.Theta_s(i) = 0.489 - 0.00126 * SoilVariables.VPER(i, 1) / (1 - SoilVariables.POR(i)) * 100;
-            SoilVariables.Phi_s(i) = init.calcPhi_s(SoilVariables.VPER(i, 1), SoilVariables.POR, SoilConstants.Phi_soc, SoilVariables.XSOC);
-            SoilVariables.Lamda(i) = init.calcLambda(SoilVariables.VPER(i, 3), SoilVariables.POR, SoilVariables.Lamda_soc, SoilVariables.XSOC);
+            SoilVariables.Phi_s(i) = equations.calcPhi_s(SoilVariables.VPER(i, 1), SoilVariables.POR, SoilConstants.Phi_soc, SoilVariables.XSOC);
+            SoilVariables.Lamda(i) = equations.calcLambda(SoilVariables.VPER(i, 3), SoilVariables.POR, SoilVariables.Lamda_soc, SoilVariables.XSOC);
         end
         SoilVariables.XWILT(i) = VanGenuchten.Theta_s(i) * ((-1.5e4) / SoilVariables.Phi_s(i))^(-1 * SoilVariables.Lamda(i));
     end