Impact of bushfire and climate variability on streamflow from forested catchments in southeast Australia

Figures & data

Fig. 1 Locations of the three study catchments and four validation catchments (I and II); and bushfire extent (III) and logging extent (IV) for the three study catchments.

Table 1 Catchments attributes and calibration and test periods.

Catchment code	Catchment names	Burnt area (%)	Catchment area (km^2)	Burnt area (km^2)	Period of record	Calibration period	Test period
226205	Latrobe at Noojee	18.52	292.9	54.25	1966–2007	1967–1982	1983–2007
229109	Starvation Creek	84.12	31.5	26.47	1973–2004	1974–1982	1983–2004
229214	Yarra River at Little Yarra	45.58	149.4	68.1	1971–2000	1972–1982	1983–2000
405205	Murrindindi River at Murrindindi above Colwells	–	108.2	–	1975–2009	1975–1982	1983–2009
405227	Big River at Jamieson	–	626.3	–	1975–2009	1975–1982	1983–2009
405209	Acheron River at Taggerty	–	627.6	–	1975–2009	1975–1982	1983–2009
227202	Tarwin at Meeiyan	–	1066.7	–	1975–2009	1975–1982	1983–2009

Table 2 Mean annual streamflow, rainfall and areal potential evapotranspiration (APET) for different periods for the three catchments. “start year” is the calibration start year of the streamflow record and “end year” is the end year of the streamflow record.

Catchments	Streamflow (mm/year)				Rainfall (mm/year)				APET (mm/year)
	Start year–1982	1983–1998	1999–end year	1983–end year	Start year–1982	1983–1998	1999–end year	1983–end year	Start year–1982	1983–1998	1999–end year	1983–end year
Latrobe@ Noojee	304	356	217	306	1413	1394	1196	1322	1119	1101	1108	1103
Starvation Creek	417	523	315	464	1621	1604	1400	1549	1092	1073	1079	1075
Yarra River @ Little Yarra	305	341	219	328	1477	1497	1327	1478	1136	1113	1119	1113
405205	218	247	155	212	1017	1082	928	1023	1114	1073	1084	1078
405227	440	541	326	458	1303	1431	1172	1331	1105	1087	1112	1097
405209	393	504	311	430	1292	1408	1108	1292	1121	1102	1122	1110
227202	422	526	329	450	1379	1441	1150	1329	1079	1062	1084	1070

Fig. 2 Cumulative percentage of mortality/regrowth for the three study catchments: (a) mortality/regrowth for ash; (b) mortality/regrowth for all species.

Table 3 Overview of the characteristics for the three hydrological models.

Characteristics	AWRA-L	XAJ	GR4J
Number of free parameters	17	14	4
Interception	An interception store	No interception store	A zero capacity interception store
Evapotranspiration	Rainfall interception evaporation; Soil evaporation; Open water evaporation; Groundwater evaporation; Transpiration	Three-layer evapotranspiration	One layer soil evaporation
Runoff production	Three-layer soil moisture accounting store; Infiltration excess surface runoff and saturation excess runoff; Two hydrological response units	A soil moisture accounting store; Saturation excess runoff	A soil moisture accounting store; Infiltration excess surface runoff and saturation excess runoff
Routing	No routing store	Lag-and-route routing;	Two unit hydrographs;
		A nonlinear routing store	A nonlinear routing store
Source	Van Dijk (2010)	Ren-Jun (1992)	Perrin et al. (2003)

Table 4 Free parameters of the three hydrological models.

Model	Parameter	Physical meaning	Range
AWRA-L	S0FC (mm)	Accessible top soil water storage at field capacity	5–50
	SsFC (mm)	Accessible shallow soil water storage at field capacity	10–400
	SdFC (mm)	Accessible deep soil water storage at field capacity	100–4000
	Sgref (mm)	Reference gourndwater storage	10–400
	PrefR (mm)	Reference storm size	50–400
	KFC	Drainage fraction at field capacity	0.01–0.5
	Β	Drainage function exponent	0.5–10
	K_gw (d^-^1)	Groundwater drainage coefficient	0.01–0.1
	K_rout (d^-^1)	Surface water drainage coefficient	0.5–2
	cGsmax (m s^-^1)	Maximum sotmatal conductance per unit canopy cover	0.005–0.5
	Vc	Vegetation photosynthetic capacity index per unit canopy cover	0–1
	wslimU	Maximum root water uptake rates from shallow water	0–5
	wdlimU	Maximum root water uptake rates from deep water	0–5
	FsoilEmax	Soil evaporation scaling factor when soil water supply is not limiting evaporation	0–1
	W0limE	Relative top soil water content at which evaporation is reduced	0–1
	ER_frac_ref	Ratio of average evaporation rate over average rainfall intensity during storms per unit canpy cover	0.05–0.5
	S_sls (mm)	Specific canopy rainfall storage capacity per unit leaf area	0.07–0.6
XAJ	UM (mm)	Averaged soil moisture storage capacity of the upper layer	5–100
	LM (mm)	Averaged soil moisture storage capacity of the lower layer	50–300
	DM (mm)	Averaged soil moisture storage capacity of the deep layer	5–100
	B	Representation of the non-uniformity of the spatial distribution of the soil moisture storage capacity over the catchment	1–1.5
	Im (%)	Percentage of impervious and saturated areas in the catchment	0.05–0.4
	C	Coefficient of the deep layer, that depends on the proportion of the basin area covered by vegetation with deep roots	0–0.5
	Sm (mm)	Areal mean free water capacity of the surface soil layer, which represents the maximum possible deficit of free water storage	5–100
	Ex	Exponent of the free water capacity curve influencing the development of the saturated area	0.5–2
	Kg	Outflow coefficients of the free water storage to groundwater relationships	Kg+ Ki = 0.7–0.8
	Ki	Outflow coefficients of the free water storage to interflow relationships	Kg+ Ki = 0.7–0.8
	Cg	Recession constants of the groundwater storage	0.9–0.999
	Ci	Recession constants of the lower interflow storage	0.05–0.95
	Cs	Recession constant in the lag and route method for routing through the channel system within each sub-basin	0.001–0.8
	L (d)	Lag in time empirical value	0–3
GR4J	x1 (mm)	Maximum capacity of the production store	0.05–1500
	x2 (mm)	Groundwater exchange coefficient	–15 to +15
	x3 (mm)	One day ahead maximum capacity of the routing store	1–1000
	x4 (days)	Time base of unit hydrograph UH1	0.05–15

Table 5 Optimal sets of free parameters from three hydrological models for the three study catchments.

Model	Parameter	Optimal set of free parameters
		Latrobe at Noojee	Starvation Creek	Yarra River at Little Yarra
AWRA-L	S0FC (mm)	21.17	46.32	9.94
	SsFC (mm)	83.07	59.01	14.73
	SdFC (mm)	1180.39	969.91	1351.30
	Sgref (mm)	58.85	61.12	30.68
	PrefR (mm)	400.00	397.53	395.55
	KFC	0.33	0.11	0.48
	β	4.61	4.29	3.93
	K_gw (d^-^1)	0.10	0.10	0.10
	K_rout (d^-^1)	1.58	1.00	0.50
	cGsmax (m s^-^1)	0.23	0.14	0.01
	Vc	0.98	0.00	0.00
	wslimU	0.12	2.19	0.96
	wdlimU	0.50	3.16	1.56
	FsoilEmax	0.98	0.59	0.85
	W0limE	0.89	0.76	0.79
	ER_frac_ref	0.43	0.42	0.41
	S_sls(mm)	0.29	0.10	0.08
XAJ	UM (mm)	55.35	64.74	100.00
	LM (mm)	0.56	0.59	0.60
	DM (mm)	0.80	0.80	0.80
	B	1.00	1.00	1.00
	Im (%)	0.93	0.95	0.05
	C	0.80	0.00	0.80
	Sm (mm)	73.58	100.00	100.00
	Ex	300.00	300.00	300.00
	Kg	100.00	100.00	100.00
	Ki	0.10	0.03	0.11
	Cg	0.40	0.27	0.15
	Ci	1.45	1.50	1.50
	Cs	3.00	0.24	0.01
	L (d)	0.15	0.15	0.15
GR4J	x1 (mm)	1499.96	1499.96	1457.25
	x2 (mm)	2.77	3.59	1.05
	x3 (mm)	85.76	428.78	50.35
	x4 (d)	1.74	1.59	1.63

Table 6 Calibration and validation results for the GR4J model in four undisturbed catchments.

Catchment code	Area (km^2)	Calibration NSE (1975–1982)	Validation NSE			Calibration B	Validation B			B Difference (validation – calibration)
			1983–2009	1983–1998	1999–2009		1983–2009	1983–1998	1999–2009	1983–2009	1983–1998	1999–2009
405205	109	0.58	0.73	0.72	0.58	0.13	0.07	0.07	0.06	−0.06	−0.06	−0.07
405227	632	0.83	0.84	0.85	0.77	0.07	0.11	0.08	0.16	0.04	0.01	0.09
405209	633	0.82	0.85	0.85	0.82	0.09	0.12	0.08	0.20	0.03	−0.01	0.11
227202	1080	0.85	0.78	0.76	0.83	−0.01	−0.08	−0.07	−0.10	−0.07	−0.06	−0.09

Fig. 3 Variation of annual rainfall, observed and simulated annual streamflow at the three study catchments for the AWRA-L model: (a) Latrobe@Noojee, (b) Starvation Creek, and (c) Yarra River@Little Yarra. The two dashed vertical lines indicate the years 1983 and 1998.

Fig. 4 Variation of annual rainfall, observed and simulated annual streamflow at the three study catchments for the XAJ model: (a) Latrobe@Noojee, (b) Starvation Creek, and (c) Yarra River@Little Yarra. The two dashed vertical lines indicate the years 1983 and 1998.

Fig. 5 Variation of annual rainfall, observed and simulated annual streamflow at the three study catchments for the GR4J model: (a) Latrobe@Noojee, (b) Starvation Creek, and (c) Yarra River@Little Yarra. The two dashed vertical lines indicate the years 1983 and 1998.

Fig. 6 Comparison of observed and simulated daily streamflow for the Latrobe@Noojee catchment using the GR4J model: (a) Calibration, 1977–1978, and (b) Simulation, 1991–1992.

Table 7 Hydrological model calibration results for the three catchments.

Catchment code	Catchment name	AWRA-L		XAJ		GR4J
		NSE	B (%)	NSE	B (%)	NSE	B (%)
226205	Latrobe at Noojee	0.78	–0.76	0.78	0.66	0.71	–0.57
229109	Starvation Creek	0.84	–0.20	0.80	2.65	0.67	2.29
229214	Yarra River at Little Yarra	0.85	0.39	0.85	1.80	0.83	–0.31

Table 8 Effects of bushfire and climate variability on the mean annual streamflow for the three catchments.

Catchment	Period (post-bushfire)	ΔQtot (relative to pre-bushfire)		AWRA_L				XAJ				GR4J
				ΔQfire		ΔQclim		ΔQfire		ΔQclim		ΔQfire		ΔQclim
		(mm year^-1)	(%)	(mm year^-1)	(%)	(mm year^-1)	(%)	(mm year^-1)	(%)	(mm year^-1)	(%)	(mm year^-1)	(%)	(mm year^-1)	(%)
Latrobe@Noojee	1983–1998	52	17	95	31	–44	–14	79	26	–28	–9	66	22	–15	–5
Starvation Creek	1983–1998	107	26	155	37	–48	–12	110	26	–4	–1	143	34	–36	–9
Yarra River@Little Yarra	1983–1998	36	12	38	12	–2	–1	20	7	16	5	33	11	3	1
Latrobe@Noojee	1999–2007	–87	–29	30	10	–117	–39	48	16	–135	–44	4	1	–91	–30
Starvation Creek	1999–2004	–101	–24	48	12	–149	–36	27	7	–129	–31	21	5	–122	–29
Yarra@Little Yarra	1999–2000	–86	–28	–25	–8	–60	–20	8	3	–94	–31	–29	–10	–57	–19

ΔQ_tot: difference in observed streamflow between post- and pre- bushfire periods; ΔQ_clim: impact of climate variability on streamflow, calculated from the difference in simulated streamflow between the post- and pre- bushfire periods (equation (3)); ΔQ_fire: impact of bushfire on streamflow, calculated from the difference between ΔQ_tot and ΔQ_clim.

Fig. 7 Summary of bushfire impact on annual streamflow (in mm) from 1983 to the end year of streamflow record for the three catchments. White boxplots: 1983 to 1998; grey boxplots: 1999 to the end year of record. For each catchment, the three white/grey boxplots represent total streamflow (mm) change relative to the pre-bushfire period (horizontal line), bushfire impact on streamflow (mm) (without notch), climate change impact on streamflow (mm) (with notch), respectively.

Fig. 8 Summary of bushfire impact on annual streamflow (%) from 1983 to the end year of record for the three catchments. White boxplots: 1983 to 1998; grey boxplots: 1999 to the end year of record. For each catchment, the three white/grey boxplots represent total streamflow change (%) relative to pre-bushfire period (horizontal line), bushfire impact on streamflow (%) (without notch), and climate change impact on streamflow (%) (with notch), respectively.

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