Update SOILWAT2 with new SWRC functionality

- SOILWAT2 has now multiple soil water release curves (SWRC) implemented
- updated SOILWAT2 submodule on branch release/devel_v7.0.0 to commit a6c367aef07b746a43b459067ee0ef0139f9f60b "Merge pull request #322 from DrylandEcology/feature_swrc"

-> new SOILWAT2 inputs include: swrc_name (to select a SWRC), ptf_name (to select a pedotransfer function if used), has_swrcp (logical to determine if SWRC parameters are used from new input file or calculated at run-time with selected PTF), and swrc_params (per soil layer parameters of the selected SWRC if used)
-> default values (swrc_name = Campbell1974, ptf_name = Cosby1984AndOthers, has_swrcp = FALSE) re-created previous behavior (except for a small fix for when soil moisture values occur above field capacity and below saturation levels)

testing.sagebrush.master/Stepwat_Inputs/Input/sxw/Input/siteparam.in

@@ -77,6 +77,30 @@ RCP85
 # Are inputs of density representing bulk soil (type 1) or the matric component (type 0)?
 0
 
+
+
+#--- Soil water retention curve (SWRC) ------
+#
+# Implemented options (`swrc_name`/`ptf_name`, see `swrc2str[]`/`ptf2str[]`):
+#   - ptf_name = <other>: SWRC parameters must be provided via "swrc_params.in"
+#   - swrc_name = "Campbell1974" (Campbell 1974)
+#     * ptf_name = "Cosby1984AndOthers" (Cosby et al. 1984 but `swc_sat` by Saxton et al. 2006)
+#     * ptf_name = "Cosby1984" (Cosby et al. 1984)
+#   - swrc_name = "vanGenuchten1980" (van Genuchten 1980)
+#   - swrc_name = "FXW" (Fredlund and Xing 1994, Wang et al. 2018)
+#
+# Note: option "Campbell1974"/"Cosby1984AndOthers" was hard-coded < v7.0.0
+# Note: `rSOILWAT2` may implement additional PTFs
+
+Campbell1974        # Specify soil water retention curve
+Cosby1984AndOthers  # Specify pedotransfer function
+                    # (if not implemented, then provide SWRC parameters via "swrc_params.in")
+
+0     # Has SWRC parameters (see `has_swrcp`)?
+      #    0: Estimate with specified pedotransfer function
+      #    1: Use values from "swrc_params.in"
+
+
 # ---- Transpiration regions ----
 # ndx  : 1=shallow, 2=medium, 3=deep, 4=very deep
 # layer: deepest layer number of the region.

testing.sagebrush.master/Stepwat_Inputs/Input/sxw/Input/swrc_params.in

@@ -0,0 +1,39 @@
+#------ Input for Soil Water Retention Curves (by soil layer) ------
+
+# A table with up to `MAX_LAYERS` rows (soil layers) and 6 columns:
+#   - the soil layers must match `soils.in`
+#   - the interpretation of columns (SWRC parameters) depends on the
+#     selected SWRC (see `siteparam.in`)
+#   - unused columns are ignored (if selected SWRC uses fewer than 6 parameters)
+
+# swrc = "Campbell1974" (default values below, from "Cosby1984")
+#   * param1 = air-entry suction [cm]
+#   * param2 = saturated volumetric water content for the matric component [cm/cm]
+#   * param3 = b, slope of the linear log-log retention curve [-]
+#   * param4 = saturated hydraulic conductivity [cm/day]
+
+# swrc = "vanGenuchten1980"
+#   * param1 = residual volumetric water content for the matric component [cm/cm]
+#   * param2 = saturated volumetric water content for the matric component [cm/cm]
+#   * param3 = alpha, related to the inverse of air entry suction [cm-1]
+#   * param4 = n, measure of the pore-size distribution [-]
+#   * param5 = saturated hydraulic conductivity [cm/day]
+
+# swrc = "FXW"
+#   * param1 = saturated volumetric water content of the matric component [cm/cm]
+#   * param2 = alpha, shape parameter [cm-1]
+#   * param3 = n, shape parameter [-]
+#   * param4 = m, shape parameter [-]
+#   * param5 = saturated hydraulic conductivity [cm / day]
+#   * param6 = L, tortuosity/connectivity parameter [-]
+
+
+# param1  param2   param3   param4     param5   param6
+ 0.0000  0.00000   0.0000   0.000000   0.0000   0.0000
+ 0.0000  0.00000   0.0000   0.000000   0.0000   0.0000
+ 0.0000  0.00000   0.0000   0.000000   0.0000   0.0000
+ 0.0000  0.00000   0.0000   0.000000   0.0000   0.0000
+ 0.0000  0.00000   0.0000   0.000000   0.0000   0.0000
+ 0.0000  0.00000   0.0000   0.000000   0.0000   0.0000
+ 0.0000  0.00000   0.0000   0.000000   0.0000   0.0000
+ 0.0000  0.00000   0.0000   0.000000   0.0000   0.0000

testing.sagebrush.master/Stepwat_Inputs/Input/sxw/files_SOILWAT2.in

@@ -8,6 +8,7 @@ Output/logfile.log	# errors or important info (can also be stdout)
 #Site
 Input/siteparam.in	# site parameters
 Input/soils.in	# soil layer definitions
+Input/swrc_params.in		# Input for soil water retention curve (used if pdf_type = 0, i.e., pedotransfer functions are not used)
 
 #Weather & climate
 Input/weathsetup.in	# weather parameters