Parameterizing the JULES land surface model for different land covers in the tropical Andes

Figures & data

Figure 1. The location of the iMHEA sites within the major land cover types of the tropical Andes. JTU: Jatunhuaycu; PIU: Piura; HUA: Huaraz.

Table 1. Description of the monitored catchments. BET-Tr: tropical broadleaf evergreen trees; C3: C3 grasses; C4: C4 grasses; ESH: evergreen shrubs; BS: bare soil. The codes JTU, PIU, and HUA refer to the locations shown in Fig. 1.

Code	Ecosystem	Land use	Altitude (m)	Area (km^2)	Soil	Land cover
JTU3	Páramo	Natural	4144–4500	2.25	Andosol, Histosol	0.80 C4, 0.20 ESH
JTU2	Páramo	Grazing	4085–4322	2.42	Andosol	1.00 C4
HUA1	Humid puna	Natural	4280–4840	4.22	Andosol, Histosol	0.75 C4, 0.25 BS
HUA2	Humid puna	Grazing	4235–4725	2.38	Andosol, Histosol	0.70 C4, 0.30 BS
PIU1	Páramo	Natural	3112–3900	6.60	Andosol, Histosol	0.15 BET-Tr, 0.85 C4
PIU2	Páramo	Grazing	3245–3610	0.95	Andosol, Histosol	0.15 BS, 0.85 C4
PIU4	Forest	Natural	2682–3408	2.32	Andosol, Cambisol	0.80 BET-Tr, 0.20 C4
PIU7	Dry puna	Grazing, cultivation	3110–3660	7.80	Andosol	0.35 C3, 0.45 C4, 0.2 ESH

Table 2. Description of soil parameters, as sourced from Best et al. (2011).

Symbol	Description	Unit
b	Exponent in soil hydraulic characteristics
φ	Saturated soil water pressure	m
Ksat	Hydraulic conductivity at saturation	kg m^−2 s^−1
θsat	Soil moisture content at saturation	m^3 m^−3
θcrit	Soil moisture content at the critical point	m^3 m^−3
θwilt	Soil moisture content at the wilting point	m^3 m^−3
hcap	Dry heat capacity	J m^−3 K^−1
hcon	Dry thermal conductivity	W m^−1 K^−1
α	Bare soil albedo

Table 3. Soil parameterization using pedotransfer functions. CL: clay fraction; SA: sand fraction; SI: silt fraction; DBD: dry bulk density (g cm⁻³); SOC: soil organic carbon (% weight); CEC: carbon exchange capacity (cmol kg⁻¹); pH: hydrogen ion activity.

Soil data	Pedotransfer function	Source
1/(n − 1)	$\mathrm{n}=\mathrm{e}\mathrm{x}\mathrm{p}\left(\left(62.986-0.833CL-0.529SOC+0.593pH+0.007C{L}^2-0.014SA\ast SI\right)/100\right)$	Hodnett and Tomasella (2002)
$1/\alpha$	$\alpha =1000\ast 9.80665/\left(1000/exp\left(\left(-2.294-3.526SI+2.440SOC-0.076CEC-11.331pH+0.019S{I}^2\right)/100\right)\right)$
Saturation point (pF = 0)	${\theta }_{sat}=0.01\left(81.799+0.099CL-31.42DBD+0.018CEC+0.451pH-0.0005SA\ast CL\right)$
Wilting point (pF = 4.2)	${\theta }_{wilt}=0.01\left(22.733-0.164SA+0.235CEC-0.831pH+0.0018C{L}^2+0.0026SA\ast CL\right)$
Critical point (pF = 2.5)	${\theta }_{crit}={\theta }_{wilt}+\frac{{\theta }_{sat}-{\theta }_{wilt}}{{\left[1+{\left(\alpha \left|\phi \right|\right)}^n\right]}^{1-1/n}}$	Van Genuchten (1980)
Saturated hydraulic conductivity	${\mathrm{K}}_{sat}=\frac{25.4}{3600}\ast {10}^{\left(-0.60-0.0064CL+0.0126SA\right)}$	Cosby et al. (1984)
Saturated heat conductivity	$\mathrm{h}\mathrm{c}\mathrm{o}\mathrm{n}={\lambda }_{air}^{\theta \mathrm{s}\mathrm{a}\mathrm{t}}{\left({\lambda }_c^{Fc}{\lambda }_s^{Fs}{\lambda }_{si}^{Fsi}\right)}^{1-\theta \mathrm{s}\mathrm{a}\mathrm{t}}$$\lambda \text{s}=\lambda \text{si}=1.57025W{m}^{\text{-1}}{K}^{\text{-1}};\lambda \text{c}=1.16025W{m}^{-1}{K}^{-1}$; $\lambda \text{air}=0.025W{m}^{-1}{K}^{-1}$	Dharssi et al. (2009)
Heat capacity	$\text{Cs}=\text{Csi}=2.133\text{*}{10}^{6}0.7exJ{m}^{-3}{K}^{-1};\text{Cc}=2.373\text{*}{10}^{6}0.7exJ{m}^{-3}{K}^{-1}$

Table 4. Soil parameters used in this study’s JULES set-up.

Catchment	n	α	θsat	θcrit	θwilt	hcon	hcap	K
PTF-based
PIU	1.359	2.288	0.463	0.333	0.217	0.219	1 189 944	0.0034
HUA	1.386	2.364	0.422	0.280	0.167	0.264	1 259 371	0.0066
JTU	1.319	1.715	0.565	0.387	0.161	0.149	938 753	0.0052
EXP-based
EXP	1.446	0.850	0.689	0.497	0.221	0.090	668 588	0.0051

Figure 2. Water retention curves obtained from PTF estimation (PIU, HUA, JTU) and in situ investigations in the JTU catchment (EXP)2013.

Figure 3. D8 flow routine in the catchment: (a) JTU2; (b) JTU3.

Figure 4. Left: a comparison of the observed and modelled flows of (a) JTU3, (b) JTU2, (c) HUA1, and (d) HUA2. Right: flow duration curves of the same hydrographs.

Figure 5. Left: a comparison of the observed and modelled flows of (a) PIU1, (b) PIU2, (c) PIU4, and (d) PIU7. Right: flow duration curves of the same hydrographs.

Figure 6. NSE score of the modelling flow in each catchment.

Table 5. Hydrological summary indices as calculated from the observed and modelled flow time series based on a daily time step in this study. OBS: observations; PTF: PTF-based set-up; EXP: EXP-based set-up; RR: rainfall–runoff ratio; BFI: baseflow index; R2FDC: slope of the flow duration curve; NSE: Nash-Sutcliffe efficiency. The codes JTU, PIU, and HUA refer to the locations shown in Fig. 1.

Site	Soil set	RR	BFI	R2FDC	NSE
JTU3	OBS	0.380	0.712	−0.51	n/a
	PTF	0.261	0.266	−1.78	0.057
	EXP	0.325	0.460	−0.80	0.239
JTU2	OBS	0.071	0.577	−1.03	n/a
	PTF	0.189	0.737	−0.76	−1.550
	EXP	0.294	0.858	−0.43	−5.300
HUA1	OBS	0.638	0.674	−3.23	n/a
	PTF	0.528	0.563	−1.09	0.467
	EXP	0.492	0.577	−0.86	0.435
HUA2	OBS	0.579	0.712	−2.93	n/a
	PTF	0.511	0.574	−1.20	0.467
	EXP	0.474	0.579	−0.83	0.416
PIU1	OBS	0.686	0.425	−1.29	n/a
	PTF	0.460	0.424	−1.16	0.620
	EXP	0.461	0.519	−0.91	0.589
PIU2	OBS	0.639	0.598	−1.37	n/a
	PTF	0.550	0.440	−1.33	0.719
	EXP	0.546	0.522	−1.00	0.745
PIU4	OBS	0.360	0.858	−0.99	n/a
	PTF	0.230	0.675	−1.65	0.193
	EXP	0.220	0.752	−1.02	0.160
PIU7	OBS	0.269	0.703	−1.18	n/a
	PTF	0.199	0.709	−1.05	0.474
	EXP	0.142	0.721	−0.73	0.283

Best, M.J., et al., 2011. The joint UK land environment simulator (JULES), model description–Part 1: energy and water fluxes. Geoscientific Model Development, 4 (3), 677–699. doi:10.5194/gmd-4-677-2011

 Web of Science ®Google Scholar

Hodnett, M.G. and Tomasella, J., 2002. Marked differences between van Genuchten soil water-retention parameters for temperate and tropical soils: a new water-retention pedo-transfer functions developed for tropical soils. Geoderma, 108 (3–4), 155–180. doi:10.1016/S0016-7061(02)00105-2

 Web of Science ®Google Scholar

Van Genuchten, M.T., 1980. A closed‐form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal, 44 (5), 892–898. doi:10.2136/sssaj1980.03615995004400050002x.

 Web of Science ®Google Scholar

Cosby, B.J., et al., 1984. A statistical exploration of the relationships of soil moisture characteristics to the physical properties of soils. Water Resources Research, 20 (6), 682–690. doi:10.1029/WR020i006p00682

 Web of Science ®Google Scholar

Dharssi, I. et al., 2009. New soil physical properties implemented in the Unified Model at PS18, Met Office Technical Report 528.

 Google Scholar