Quantifying relative contribution of land use change and climate change to streamflow alteration in the Bengawan Solo River, Indonesia

Figures & data

Table 1. Catchment characteristics of the study area

Id	Catchment	Area (km^2)	Elevation (m)			Avg. slope (%)	Dominant soil	Stream density (km/km^2)
			Min	Max	Av.
S1	Pidekso	234	138	1195	642	15.8	Complex soil	1.9
S2	Madiun	3759	44	3240	1565	9.9	Complex soil	2.5
S3	Kening	837	15	665	294	5.8	Grumusols	1.7

Id- identity; min- minimum; max- maximum; av- average.

Figure 1. Location of the Bengawan Solo catchment and the distribution of gauges. The catchments marked in yellow are part of the study area

Table 2. Hydrological characteristics of the study area

Catchment	Periods	Annual mean P (mm)	Annual mean Q (mm)	Annual mean ET0 (mm)
Pidekso	1982–2013	2719	1379	1819
	1982−1997	2652	1003	1821
	2003–2013	2935	1817	1817
Madiun	1982–2013	2429	919	1762
	1982−1997	2427	803	1836
	2003–2013	2431	1036	1689
Kening	1982–2013	1579	373	1743
	1982−1997	1805	432	1864
	2003–2013	1354	280	1622

Q = discharge; P =  rainfall; ET₀ =  potential evapotranspiration.

Figure 2. Tomer and Schilling’s (2009) framework, adapted after Marhaento (2018), illustrating how the fractions of excess water (P_ex) and excess energy (E_ex) respond to climate change and land use change. The points M₁ and M₂ are the fractions of excess water and energy forir the baseline period (E_ex1, P_ex1) and the altered period (E_ex2,P_ex2), respectively. The resultant length (R) is the magnitude of the combined influence of land use change and climate change

Table 3. Calculation of the contribution of land use change and climate change to streamflow alteration in the study catchments

Catchment	AI	Period	Pex	Eex	R	θ	LUC	CC
Pidekso	0.67	B	0.38	0.09
		A	0.62	0.40	0.39	4.55	92.63	7.37
Madiun	0.69	B	0.33	0.11
		A	0.43	0.17	0.10	23.87	69.33	30.67
Kening	1.03	B	0.24	0.26
		A	0.21	0.34	0.09	65.55	31.25	68.75

AI = aridity index, B = baseline period (1982−1997), A = altered period (2003–2013), P_ex = excess water divided by available water, E_ex = excess energy divided by available energy, R = resultant length (dimensionless), θ = angle of changes (degrees), LUC = relative contribution of land use change (%), CC = relative contribution of climate change (%).

Figure 3. Change of excess water (P_ex) and excess energy (E_ex) from the baseline period (B) to the altered period (A) relative to the aridity index (AI) for (a) the Pidekso catchment, (b) the Madiun catchment, and (c) the Kening catchment

Table 4. The results of the Mann-Kendall trend test and Sen’s slope estimator for annual rainfall and potential evapotranspiration in three catchments

Catchment	Variables	Z	pvalue	Ss
Pidekso	Rainfall	0.82	0.2061	5.9
	ET0	−0.92	0.1788	−3.8
Madiun	Rainfall	−0.87	0.1922	−7.5
	ET0	−1.09	0.1379	−4.1
Kening	Rainfall	−2.44	0.0073*	−23.5
	ET0	−1.09	0.1379	−4.1

Z = standard normal Mann-Kendall test statistic (− indicates a downward trend), * statistically significant at a significance level of 0.05, S_s = Sen’s slope estimator (mm/year).

Table 5. Land use distribution (in km²) in the three catchments for the years 1994 and 2013, and changes (in %)

Catchment	Land use type	1994	2013	∆	%
Pidekso	Agriculture area	114.1	136.3	22.2	19.5
	Forest area	77.5	65.7	−11.8	−15.2
	Settlement	5.6	27.3	21.7	387.5
	Others	36.7	4.7	−32.0	−87.2
Madiun	Agriculture area	1873.4	1781.9	−91.5	−4.9
	Forest area	1474.5	831.1	−643.4	−43.6
	Settlement	307.7	1095.6	787.9	256.1
	Others	103.6	50.6	−53.0	−51.2
Kening	Agriculture area	365.4	526.6	161.2	44.1
	Forest area	455.1	200.8	−254.3	−55.9
	Settlement	14.3	109.2	94.9	663.6
	Others	2.3	0.5	−1.8	−78.3

Figure 4. Land use maps for the study catchments for the years 1994 and 2013

Tomer, M.D. and Schilling, K.E., 2009. A simple approach to distinguish land-use and climate-change effects on watershed hydrology. Journal of Hydrology, 376 (1−2), 24–33. doi:10.1016/j.jhydrol.2009.07.029

 Web of Science ®Google Scholar

Marhaento, H., (2018). Effects of changes in land use and climate on water availability of a tropical catchment. (1 ed.). Ipskamp Printing. doi:10.3990/1.9789036544917

 Google Scholar