Comparison of two rainfall–runoff models: effects of conceptualization on water budget components

Figures & data

Figure 1. The Glafkos River catchment in western Greece.

Figure 2. (a) Spatially averaged annual precipitation (P) and measured annual runoff (RO) for the period from 1974/75 to 1992/93. (b) Comparison between the analytically estimated actual evapotranspiration (Turc’s method) and the difference (P − RO).

Figure 3. Schematic representation of the conceptual structure of the ENNS model (Nachtnebel et al. 1993). Asterisks indicate modifications to the original interpretation of the corresponding hydrological processes.

Table 1. ENNS model parameters and their corresponding ranges of variation. Parameters varied during model calibration are shown in bold.

Process	Variable	Value/range
Snowmelting and refreezing	CT (mm/d per °C): degree-day coefficient	2^a
Soil zone (the zone from which evapotranspiration takes place)	M (mm): thickness θfc (–): water content at field capacity θwp (–): water content at wilting point β (–): exponent for infiltration through macropores kSZ (h): time constant of linear reservoir of soil zone	500–2000^b 0.23–0.40^c 0.15^c 1–17 4000–10 000^d
Direct runoff and percolation (reservoir 1 in Fig. 3)	TAB1 (h): time constant for direct runoff TVS1 (h): time constant for percolation Η1 (mm): threshold depth for direct runoff	1–100 1–100 0.0
Slow interflow and deep percolation (reservoir 2 in Fig. 3)	TAB2 (h): time constant for interflow TVS2 (h): time constant for deep percolation Η2 (mm): threshold depth for interflow	100–2500 100–2500 0.0
Baseflow (reservoir 3 in Fig. 3)	TAB3 (h): time constant for baseflow	1500–12000
Runoff smoothing (reservoir 4 in Fig. 3)	TAB4 (h): Time constant for runoff smoothing	0.1

^aModerately forested areas in April (WMO 1983, p. 5.49)

^bThe thickness of the soil zone has been taken as equal to the root depth (see Crow 2005)

^cDingman (2002, p. 225)

^dNachtnebel et al. (1993)

Table 2. Parameter ranges and optimal parameter sets of ensembles 1 and 2, investigated using the ENNS model.

	Parameter ranges ofensemble 1	Optimal parameter set ofensemble 1 PSE1	Parameter ranges ofensemble 2	Optimal parameter set ofensemble 2 PSE2
(1)	(2)	(3)	(4)	(5)
M (mm)	500–2000	1811	1437–1996	1861
θfc (–)	0.23–0.40	0.38	0.28–0.40	0.30
β (–)	1–17	3.8	3.8–16.7	9.5
kSZ (h)	4000–10000	9756	6524–9925	9450
TAB1 (h)	1–100	59.3	18.3–98.9	59.4
TVS1 (h)	1–100	48.4	4.48–82.5	19.0
TAB2 (h)	100–2500	945	345–2312	776
TVS2 (h)	100–2500	1479	127–2471	1530
TAB3 (h)	1500–12000	4700	1550–11934	3605

Table 3. MIKE SHE model parameters and their corresponding ranges of variation. Parameters varied during model calibration are shown in bold.

Process	Variable	Value/range
Snowmelting and refreezing	Degree-day coefficient (mm/d per °C) Min snow storage (mm) Max wet snow fraction	2^a 0 0.5
ET (Vegetation)	Leaf area index (–) Coefficient of interception (mm) Root depth (mm)	5^b 0.05^c 500–2000^d
Overland flow	Initial water depth (m) Μanning number (m^1/3/s) Detention storage (mm) Slope (–) Slope length (m)	0^e 10^f 0–12 0.3^g 700^g
Unsaturated zone (parameters used in Green and Ampt method)	Water content at saturation (–) Water content at field capacity (–) Water content at wilting point (–) Saturated hydraulic conductivity (m/s) Soil suction (m)	0.43–0.47^h 0.23–0.40^h 0.14^h 1.5–2.5 × 10^–7^i 0.16–0.22^j
Simplified macropore flow	Max bypass fraction Water content for reduced bypass flow Min water content for bypass flow	0.3^k 0.35^l 0.14^m
Interflow and deep percolation (reservoir (a) in Fig. 4)	Time constant kha (d) Time constant kva (d)	0.04–4.0^n 0.04–4.0^n
Baseflow (reservoir (b) in Fig. 4)	Time constant khb (d)	4–100^n
Baseflow (reservoir (c) in Fig. 4)	Time constant khc (d)	60–500^n

^aModerately forested areas in spring during snowmelt (WMO 1983, p. 5.49)

^bValue for mixtures of broadleaf forest and shrub (Dingman 2002, p. 297)

^cSee MIKE SHE User Manual (2009, p. 295)

^dCrow (2005)

^eNo initial water depth at the soil surface at the beginning of the hydrological year (1 October)

^fMIKE SHE User Manual (2009, p. 115)

^gEstimated from the digital elevation model of the catchment (see Athanasiadou 2011)

^hDingman (2002, p. 225)

ⁱDingman (2002, p. 331)

^jDingman (2002, p. 235)

^kBeven and German (1982)

^lEqual to the mean value of the field capacity

^mEqual to the wilting point

ⁿRanges as those used for the corresponding reservoirs of the ENNS model (see Table 2). The threshold depths H_a, H_b and H_c in Figure 4 have been set to zero for the reasons discussed in Section 4.2 regarding ENNS.

Figure 4. Similar to Figure 3, but for the MIKE SHE model.

Table 4. Optimal parameters for the MIKE SHE model.

Parameter	Value
Depth of soil zone (mm)	1000
Detention storage (mm)	10
Water content at saturation (–)	0.47
Water content at field capacity (–)	0.35
Saturated hydraulic conductivity (m/s)	2.0 × 10^−7
Soil suction (m)	0.22
Time constant kha of reservoir (a) in Figure 4 (d|h)	2.5|60
Time constant kva of reservoir (a) in Figure 4 (d|h)	0.4|9.6
Time constant khb of reservoir (b) in Figure 4 (d|h)	27|648
Time constant khc of reservoir (c) in Figure 4 (d|h)	250|6000

Figure 5. Criteria values for the ENNS simulations using parameter sets PSE1 and PSE2, and for the MIKE SHE simulations. (a) CrWB, (b) CrQ, (c) $\mathrm{C}\mathrm{r}\sqrt{\mathrm{Q}}$ and (d) CrlogQ.

Figure 6. (a)–(e) Comparison of measured and simulated hydrographs using the ENNS and MIKE SHE models for the period from 1984/85 to 1988/89. (f) Annual runoff (RO) and change of storage.

Figure 7. Comparison of the actual evapotranspiration simulated by ENNS and MIKE SHE: (a) and (b) daily values for year 1984/85, (c) annual values.

Figure 8. Comparison of the total infiltration and its components simulated by ENNS and MIKE SHE: (a) total infiltration, (b) infiltration through the macropores, (c) infiltration through the soil matrix and (d) annual values.

Figure 9. Comparison of (a, b) daily values and (c) annual values of the direct runoff simulated by ENNS and MIKE SHE.

Figure 10. Comparison of daily and annual values of the baseflow simulated by ENNS and MIKE SHE.

Figure 11. Values of criteria CrWB, and $\mathrm{C}\mathrm{r}\sqrt{\mathrm{Q}}$ for the ENNS and MIKE SHE simulations for the years from 1975/76 to 1992/93.

Figure 12. Comparison of the annual depths of (a) direct runoff and (b) baseflow simulated by ENNS and MIKE SHE for the period from 1975/76 to 1992/93.

Table A1. Spearman’s rank correlation coefficients (SRCCs) of criteria CrQ, $\mathrm{C}\mathrm{r}\sqrt{\mathrm{Q}}$, CrlogQ and CrWB, calculated independently for each year in the calibration period.

Year	SRCCCrQ, $\mathrm{C}\mathrm{r}\sqrt{\mathrm{Q}}$	SRCCCrQ, CrlogQ	SRCCCrQ, CrWB	SRCC$\mathrm{C}\mathrm{r}\sqrt{\mathrm{Q}}$, CrlogQ	SRCC$\mathrm{C}\mathrm{r}\sqrt{\mathrm{Q}}$, CrWB	SRCCCrlogQ, CrWB
1984/85	0.93	0.63	0.13	0.83	0.33	0.28
1985/86	0.96	0.76	0.42	0.88	0.54	0.51
1986/87	0.94	0.74	0.18	0.90	0.35	0.35
1987/88	0.89	0.55	0.16	0.82	0.41	0.41
1988/89	0.85	0.33	0.36	0.68	0.52	0.21

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