Soil infiltration processes of different underlying surfaces in the permafrost region on the Tibetan Plateau

Figures & data

Figure 1. Location of the study sites on the Tibetan Plateau in China.

Figure 2. Surface vegetation cover at the four monitoring sites: (a) alpine meadow (XDT: AM1); (b) alpine desert steppe (QTB06: ADS); (c) alpine steppe (QTB07: AS); and (d) alpine meadow (QT01: AM2).

Figure 3. Variation of soil initial infiltration rate, and soil moisture and soil texture for different underlying surfaces: alpine meadow (AM1: XDT and AM2: QT01) alpine desert steppe (ADS: QTB06) and alpine steppe (AS: QTB07).

Figure 4. Soil initial infiltration processes for different underlying surfaces: alpine meadow (AM1: XDT and AM2: QT01), alpine desert steppe (ADS: QTB06) and alpine steppe (AS: QTB07).

Figure 5. Variation of soil steady infiltration rate, and soil moisture and soil texture for different underlying surfaces: alpine meadow (AM1: XDT and AM2: QT01), alpine desert steppe (ADS: QTB06) and alpine steppe (AS: QTB07).

Figure 6. Variation of cumulative soil infiltration for different underlying surfaces: alpine meadow (AM1: XDT and AM2: QT01), alpine desert steppe (ADS: QTB06) and alpine steppe (AS: QTB07).

Table 1. Geographical characteristic of the four monitoring sites.

Site ID	Name	Longitude/latitude	Altitude (m a.s.l.)	Vegetation	Vegetation cover (%)	Soil texture
XDT	Xidatan	N: 35.71°; E: 94.09°	4518	Alpine meadow	85	Loamy sand
QTB06	Tedaqiao	N: 35.49°; E: 93.68°	4529	Alpine desert steppe	10	Sand
QTB07	Wudaoliang	N: 35.20°; E: 93.08°	4627	Alpine steppe	65	Sand
QT01	Kekexili	N: 35.13°; E: 93.03°	4740	Alpine meadow	95	Sandy loam

Table 2. Soil physical properties of the four monitoring sites.

Site ID	Depth (cm)	Soil moisture (%)	Sand (%)	Silt (%)	Clay (%)
XDT	10 ~ 20	26.72	79.64	19.02	1.34
QTB06	10 ~ 20	3.76	90.33	8.73	0.94
QTB07	10 ~ 20	5.31	88.80	10.40	0.80
QT01	10 ~ 20	12.89	69.89	28.94	1.61

Table 3. Soil infiltration rate model parameters of the four monitoring sites.

Model	Parameter	XDT	QTB06	QTB07	QT01
KM	a	6.53	7.44	7.60	6.17
	b	0.56	0.49	0.52	0.56
GM	a	1.08	1.22	1.00	0.87
	b	6.88	7.44	7.49	6.22
	n	1.27	0.95	0.85	1.03
HM	k	0.37	0.27	0.24	0.30
MM	a	6.78	7.26	7.30	6.10
	b	1.38	1.11	1.01	1.17

Table 4. Performance of different models for fitted soil infiltration rate against the observations at different sites. R²: standard error of the estimate; RMSE: root mean square error; MAE: mean absolute error. KM: Kostiakov model; GM: general empirical model; HM: Horton model; and MM: Mezencev model.

Site	Index	KM	GM	HM	MM
XDT	R^2	0.756	0.942	0.927	0.939
	RMSE	0.606	0.276	0.387	0.292
	MAE	0.528	0.173	0.169	0.166
QTB06	R^2	0.83	0.936	0.964	0.927
	RMSE	0.561	0.328	0.316	0.372
	MAE	0.498	0.255	0.155	0.273
QTB07	R^2	0.902	0.962	0.977	0.952
	RMSE	0.432	0.254	0.242	0.311
	MAE	0.385	0.210	0.103	0.249
QT01	R^2	0.843	0.947	0.961	0.941
	RMSE	0.45	0.245	0.276	0.275
	MAE	0.393	0.183	0.119	0.192

Figure 7. Comparison between measured and fitted soil infiltration rate for different underlying surfaces: (a) alpine meadow (AM1: XDT); (b) alpine desert steppe (ADS: QTB06); (c) alpine steppe (AS: QTB07); and (d) alpine meadow (AM2: QT01). KM: Kostiakov model, GM: General empirical model, HM: Horton model, MM: Mezencev model.

Table 5. Performance of different models for fitted soil cumulative infiltration against the observations at different sites. PH: Philip model; SW: Swartzendruber model; HO: Horton model; KO: Kostiakov model; MK: modified Kostiakov model; RMK: revised MK model; SCS: SCS model.

Site	Index	PH	SW	HO	KO	MK	RMK	SCS
XDT	R^2	0.957	0.990	0.998	0.981	0.993	0.996	0.981
	RMSE	4.279	2.088	1.498	2.885	1.731	1.322	2.935
	MAE	3.489	1.666	1.086	2.349	1.423	1.151	2.384
QTB06	R^2	0.957	0.990	0.998	0.981	0.993	0.996	0.981
	RMSE	4.279	2.088	1.498	2.885	1.731	1.322	2.935
	MAE	3.489	1.666	1.086	2.349	1.423	1.151	2.384
QTB07	R^2	0.939	0.995	0.998	0.973	0.990	0.977	0.972
	RMSE	4.848	1.672	1.046	3.316	1.962	2.999	3.363
	MAE	4.012	1.227	0.750	2.677	1.690	2.396	2.708
QT01	R^2	0.972	0.992	0.991	0.988	0.995	0.995	0.994
	RMSE	2.695	1.373	1.630	1.761	1.151	1.125	1.808
	MAE	2.271	1.137	1.115	1.516	1.000	0.986	1.552

Figure 8. Comparison between the measured and fitted soil cumulative infiltration under underlying surfaces: (a) alpine meadow (AM1: XDT); (b) alpine desert steppe (ADS: QTB06); (c) alpine steppe (AS: QTB07); and (d) alpine meadow (AM2: QT01). PH: Philip model, SW: Swartzendruber model, HO: Horton model, KO: Kostiakov model, MK: modified Kostiakov model, RMK: Revised MK model, SCS: SCS model.