Runoff responses to human activities and climate change in an arid watershed of central Iran

Figures & data

Figure 1. An overview of Zayandehrud basin and sub-basins upstream of Zayandehrud Dam

Figure 2. Comparison of area under cultivation in the upstream part of Zayandehrud basin: (a) 1982; (b) 2015. (Isfahan Regional Water Authority (IRWA) 2020)

Figure 3. An overview of the research process

Figure 4. Runoff time series trend (1980–2016): (a) Eskandari station; (b) Ghale-Shahrokh station; (c) Manderjan station

Table 1. Mann-Kendall test results of data collected from the chosen stations (1980–2016)

Variable	Period	Station	p-value^a	Alpha	Var(S)	S	Z
Runoff	1980–2016	Eskandari	< .0001	0.05	5390	−298	−4.20
		Ghale-Shahrokh	.0070	0.05	5390	−200	−2.70
		Manderjan	< .0001	0.05	5390	−398	−5.40
Precipitation	1980–2016	Eskandari	.9570	0.05	5390	−5	−0.05
		Ghale-Shahrokh	.4380	0.05	5390	58	0.77
		Manderjan	.3610	0.05	5390	−68	−0.90
Evapotranspiration	1980–2016	Eskandari	.1170	0.05	5390	116	1.56
		Ghale-Shahrokh	< .0010	0.05	5390	280	3.80
		Manderjan	.0050	0.05	5390	208	2.81

^ap-value determines how likely it is that the data could have occurred under the null hypothesis.

Figure 5. Precipitation time series trend (1980–2016): (a) Eskandari station; (b) Ghale-Shahrokh station; (c) Manderjan station

Figure 6. Evapotranspiration time series trend (1980–2016): (a) Eskandari station; (b) Ghale-Shahrokh station; (c) Manderjan station

Table 2. Pettitt test results of data collected from the chosen stations (1980–2016)

Variable	Period	Station	K	p-value^a	Alpha	Change point
Runoff	1980–2016	Eskandari	231	.0010	0.05	1996
		Ghale-Shahrokh	194	.0120	0.05	1996 and 2007
		Manderjan	285	< .0001	0.05	1996
Evapotranspiration	1980–2016	Ghale-Shahrokh	224	.0010	0.05	1996

^ap-value determines how likely it is that the data could have occurred under the null hypothesis.

Figure 7. Pettitt test results for hydrometric station runoff upstream of Zayandehrud Dam (1980–2016): (a) Eskandari station; (b) Ghale-Shahrokh station; (c) Manderjan station

Figure 8. Pettitt test results for potential evapotranspiration (PET) at Ghale-Shahrokh station (1980–2016)

Table 3. Initial and final intervals of sensitive parameters ofthe SWAT model before and after calibration for the three hydrometric stations in Zayandehrud Dam upstream

Parameter	Description	Initial Range	Calibrated value
			Eskandari	Ghale-Shahrokh	Manderjan
r_CN2.mgt	Initial SCS CN II value	−0.60 to 0.50	−0.49 to −0.37	−0.65 to −0.35	−1.00 to −0.78
v_ALPHA_BF.gw	Baseflow alpha factor (days)	0.00 to 1.00	0.51 to 0.65	0.10 to 0.40	0.11 to 0.16
v_GW_DELAY.gw	Groundwater delay (days)	0 to 500	17 to 105	10 to 80	78 to 192
v_GWQMN.gw	Threshold depth of water in the shallow aquifer required for return flow to occur (mm)	0 to 5000	2154 to 3236	1000 to 2000	0 to 99
v_REVAPMN.gw	Threshold depth of water in the shallow aquifer for “revap” to occur (mm)	0 to 500	225 to 291	80 to 150	202 to 234
v_GW_REVAP.gw	Groundwater “revap” coefficient	0.020 to 0.200	0.045 to 0.064	0.080 to 0.180	0.078 to 0.089
v_RCHRG_DP.gw	Deep aquifer percolation fraction	0.00 to 1.00	0.79 to 0.89	0.60 to 1.00	0.44 to 0.51
r_SOL_K.sol	Saturated hydraulic conductivity	−0.200 to 0.300	−0.060 to 0.144	0.000 to 0.150	0.018 to 0.080
r_SOL_ALB.sol	Moist soil albedo	−0.300 to 0.200	−0.232 to −0.103	−0.300 to −0.150	0.007 to 0.052
r_SOL_AWC.sol	Available water capacity of the soil layer	−0.200 to 0.400	−0.060 to 0.040	−0.200 to 0.000	0.055 to 0.112
r_SOL_BD.sol	Moist bulk density	−0.200 to 0.300	0.217 to 0.315	−0.200 to 0.000	−0.200 to −0.150
v_ESCO.hru	Soil evapotranspiration compensation factor	0.00 to 1.00	0.70 to 0.84	0.70 to 1.00	0.63 to 0.72
v_EPCO.hru	Plant uptake compensation factor	0.00 to 1.00	0.06 to 0.15	0.50 to 0.80	0.13 to 0.19
v_HEAT_UNITS.mgt	Total heat units for cover/plant to reach maturity	1300 to 2500	834 to 1160	1613 to 2000	1834 to 2400
v_IRR_ASQ.mgt	Surface runoff ratio (fraction)	0.000 to 1.000	0.858 to 0.952	0.400 to 0.700	0.935 to 0.966
v_IRR_MX.mgt	Amount of irrigation water applied each time auto-irrigation is triggered (mm)	0.00 to 1.00	0.27 to 0.82	0.45 to 0.70	0.44 to 0.56
v_IRR_AMT.mgt	Depth of irrigation water applied on HRU	0 to 100	16 to 48	0 to 30	9 to 13
v_CNOP.mgt	SCS runoff curve number for moisture condition	0 to 100	45 to 63	55 to 70	82 to 87
v_HUSC.mgt	Fraction of total heat units for the year	0.00 to 1.00	0.12 to 0.28	0.15 to 0.35	0.09 to 0.19
v_AUTO_WSTRS.mgt	Water stress factor of cover/plant	0.00 to 1.00	0.57 to 0.69	0.25 to 0.45	0.89 to 1.00

Table 4. Calibration and validation results of the SWAT model for Zayandehrud Dam upstream stations

Station	Calibration (1980–1991)				Validation (1992–1995)
	NS^a	R^2b	p-factor	r-factor	NS	R^2	p-factor	r-factor
Eskandari (m^3/sec)	0.77	0.79	0.63	0.58	0.63	0.65	0.57	0.62
Ghale-Shahrokh (m^3/sec)	0.78	0.78	0.52	0.35	0.67	0.69	0.49	0.43
Manderjan (m^3/sec)	0.54	0.6	0.51	0.70	0.46	0.52	0.43	0.76

^aNS = Nash-Sutcliffe model efficiency coefficient.

^bCoefficient of determination.

Figure 9. Time series of observed runoff, best runoff simulated by the SWAT model, and total monthly precipitation in the natural period with three years of warm-up (1983–1995) at three stations upstream of Zayandehrud Dam: (a) Eskandari station; (b) Ghale-Shahrokh station; (c) Manderjan station

Figure 10. Time series of observed runoff, best runoff simulated by the SWAT model, and total monthly precipitation in the impact period (1997–2016) at three stations upstream of Zayandehrud Dam: (a) Eskandari station; (b) Ghale-Shahrokh station; (c) Manderjan station

Table 5. Training and validation results of LS-SVM model for Zayandehrud Dam upstream stations

Hydrometric station	Train (1980–1991)			Validation (1992–1995)
	RMSE^a	R^2b	Number of samples	RMSE	R^2	Number of samples
Eskandari (m^3/sec)	2.32	0.85	144	3.24	0.78	48
Ghale-Shahrokh (m^3/sec)	16.36	0.82	144	17.57	0.79	48
Manderjan (m^3/sec)	0.22	0.82	144	0.39	0.75	48

^aRoot mean square error.

^bCoefficient of determination.

Figure 11. Time series of observed runoff, runoff simulated by LS-SVM model, and total monthly precipitation in the natural period (1980–1995) at three stations upstream of Zayandehrud Dam: (a) Eskandari station; (b) Ghale-Shahrokh station; (c) Manderjan station

Figure 12. Time series of observed runoff, runoff simulated by LS-SVM model, and total monthly precipitation in the impact period (1997–2016) at three stations upstream of Zayandehrud Dam: (a) Eskandari station; (b) Ghale-Shahrokh station; (c) Manderjan station

Table 6. Climate change and human activity effects on declining runoff in the studied area as determined by the climate elasticity method

Station	Period	${\bar{Q}}^{\mathrm{a}}$	${\bar{P}}^{\mathrm{b}}$	${\overline{PET}}^{\mathrm{c}}$	ε^dp	εPET^e	ΔQtotalf	ΔQCg		ΔQHh
		$(\frac{{\mathit{m}}^3}{\mathit{s}}\times d)$	$\frac{\mathit{m}\mathit{m}}{\mathbf{Y}\mathbf{e}\mathbf{a}\mathbf{r}}$	$\frac{\mathit{m}\mathit{m}}{\mathbf{Y}\mathbf{e}\mathbf{a}\mathbf{r}}$			$(\frac{{\mathit{m}}^3}{\mathit{s}}\times d)$	$(\frac{{\mathit{m}}^3}{\mathit{s}}\times d)$	%	$(\frac{{\mathit{m}}^3}{\mathit{s}}\times d)$	%
Eskandari	1980–1995	1822.2	384.0	1611.3	0.630	−3.2	—	—	—	—	—
	1997–2016	1241.4	372.2	1637.3			580.8	130.0	22.4	450.8	77.6
Ghale-Shahrokh	1980–1995	10,258.6	367.6	1606.5	0.500	−6.3	—	—	—	—	—
	1997–2016	7009.0	392.9	1674.9			3249.7	2401.7	73.9	848.0	26.1
Manderjan	1980–1995	167.0	314.4	1615.4	0.064	−2.6	—	—	—	—	—
	1997–2016	42.7	278.9	1670.3			124.4	15.8	12.7	108.6	87.3

^a$\bar{Q}$ = The average of runoff in each period.

^b$\bar{\mathit{P}}$ = The average of precipitation in each period.

^c$\overline{PET}$ = The average of potential evapotranspiration in each period.

^dε_p = Elasticity coefficient of precipitation.

^eε_PET = Elasticity coefficient of potential evapotranspiration.

^fΔQ_total = Runoff variation during the period (1980–2016).

^gΔQ_C = Climate change participation in runoff variation.

^hΔQ_H = Human activity participation in runoff variation.

Figure 13. Estimation of precipitation elasticity (ε_P) and potential evapotranspiration elasticity (ε_PET) according to relevant alteration in runoff ($\frac{\mathrm{\Delta }Q}{Q}$), precipitation ($\frac{\mathrm{\Delta }P}{P}$), and potential evapotranspiration ($\frac{\mathrm{\Delta }E}{E}$) at three stations upstream of Zayandehrud Dam: (a) Eskandari station; (b) Ghale-Shahrokh station; (c) Manderjan station

Table 7. Climate change and human activity effects on Zayandehrud Dam upstream stations runoff as determined by three different methods

Station	Climate elasticity		Numerical modelling (LS-SVM)		Hydrological simulation (SWAT)		Weighted average coefficient^a
	∆QC (%)^b	∆QH (%)^c	∆QC (%)	∆QH (%)	∆QC (%)	∆QH (%)	(%)
Eskandari	22.40	77.60	32.30	67.70	16.00	84.00	12.80
Ghale-Shahrokh	73.90	26.10	48.68	51.32	41.00	59.00	86.00
Manderjan	12.70	87.30	39.57	60.43	48.00	51.00	1.20
Weighted average^d	66.67	33.33	46.49	53.51	37.87	62.13

^aWeighted average coefficient according to runoff averages of each station over the long term.

^b∆Q_C = Climate change participation in runoff variation.

^c∆Q_H = Human activity participation in runoff variation.

^dParticipation of climate change and human activity impacts on runoff variation in each method for the whole of the watershed, being estimated by weighted average coefficients.

Table 8. Management scenario results for mitigating climate change and human activity effects on runoff reduction

Hydrometric station	Scenario applied	Gross water requirement (MCM)^a	Initial gross water requirement (MCM)^b	Reduction in gross water requirement (%)	Average estimated runoff for scenario (m^3/s)^c	Average estimated runoff for base state (m^3/s)^d	Percentage increase in runoff
Eskandari	I	193.02		37.12	6.53		38.28
	II	274.00	306.97	10.74	4.56	4.03	11.62
	III	246.78		19.60	5.08		20.70
Ghale-Shahrokh	I	129.32		23.31	60.04		25.03
	II	140.77	168.63	16.52	54.99	45.01	18.14
	III	131.16		22.22	58.63		23.23
Manderjan	I	33.65		42.28	0.75		47.01
	II	49.50	58.30	15.09	0.68	0.40	21.56
	III	38.86		33.30	0.70		42.85

^aThe volume of water (MCM) needed for irrigation after applying each scenario.

^bThe volume of water (MCM) needed for irrigation before applying each scenario.

^cRunoff estimated by the SWAT model after applying each scenario.

^dRunoff estimated by the SWAT model before applying each scenario.

Figure 14. Runoff time series for three stations upstream of Zayandehrud Dam before and after the application of three management scenarios using the SWAT model: (a) Eskandari station; (b) Ghale-Shahrokh station; (c) Manderjan station

Isfahan Regional Water Authority (IRWA), 2020. National program of water shortage adaption. Isfahan, Iran: Ministry of Energy.

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