Future hydro-meteorological drought of the Johor River Basin, Malaysia, based on CORDEX-SEA projections

Figures & data

Figure 1. Study area.

Table 1. Summary of climate projections. RCM: regional climate model.

Driving GCM	RCM	RCP	Period	Symbol
CNRM-CM5	RCA4	4.5	2006–2100	CNRM
		8.5	2006–2100
GFDL-ESM2M	RegCM4	4.5	2006–2100	GFDL
		8.5	2006–2100
HadGEM2	RCA4	4.5	2006–2100	Had_RCA
		8.5	2006–2100
HadGEM2	WRF	4.5	2021–2050; 2071–2100	Had_WRF
		8.5	2021–2050; 2071–2100

Figure 2. Framework of the study.

Table 2. Climate index classification.

Index value	Class	Symbol
SPI ≥ 2	Extremely wet	EW
1.5 ≤ SPI < 2	Very wet	VW
1 ≤ SPI < 1.5	Moderately wet	MW
−1 < SPI < 1	Near normal conditions	NC
−1.5 < SPI ≤ −1	Moderately dry	MD
−2 < SPI ≤ −1.5	Very dry	VD
SPI ≤ −2	Extremely dry	ED

Figure 3. Comparison of the climatology cycle between the RCMs and observed data under the (a) original precipitation, Pn; (b) original maximum temperature, Tx; (c) original minimum temperature, Tn; (d) bias-corrected precipitation, Pr_BC; (e) bias-corrected maximum temperature, Tx_BC; and (f) bias-corrected minimum temperature, Tn_BC for the period 1975–2005.

Figure 4. Mean absolute error (MAE) of the RCMs in simulating annual historical (a) precipitation (Pr), (b) maximum temperature (Tx) and (c) minimum temperature (Tn) at the Kluang (48672) and Senai (48679) stations.

Table 3. Annual trends (changes per decade) of observed and RCM precipitation (Pr), maximum temperature (Tx) and minimum temperature (Tn) for the period 1975–2005 at the Kluang (48672) and Senai (48679) stations. MK: Mann-Kendall test; Sen: Sen’s slope. Bold indicates significance at p = 0.05.

		Kluang			Senai
		Pr (mm)	Tx (°C)	Tn (°C)	Pr (mm)	Tx (°C)	Tn (°C)
Gauge	MK	0.24	4.01	5.37	0.99	4.18	5.68
	Sen	13.25	0.40	0.33	55.88	0.23	0.33
CNRM	MK	0.14	2.21	5.03	0.71	2.38	4.76
	Sen	4.20	0.18	0.21	30.67	0.19	0.21
GFDL	MK	0.88	3.09	3.67	0.61	2.86	3.43
	Sen	62.95	0.20	0.25	59.68	0.20	0.24
Had_RCA	MK	−0.44	0.65	3.37	0.10	0.44	2.89
	Sen	−23.28	0.03	0.15	4.22	0.02	0.13
Had_WRF	MK	1.19	−1.29	3.88	0.71	−0.58	3.60
	Sen	104.95	−0.10	0.14	41.50	−0.04	0.15
Ensemble	MK	0.92	2.38	5.30	1.12	2.48	5.03
	Sen	17.90	0.10	0.19	35.84	0.11	0.18

Table 4. SWAT sensitivity analysis and calibration. Parameters are sorted from most sensitive (no. 1) to least sensitive (no. 12). V_ indicates that the original parameter value is replaced by a value, while R_ indicates that the original parameter is multiplied by (1 + a given value).

No.	Parameter name	t-statistic	P value	Min	Max	Fitted value
1	V_ALPHA_BF.gw	9.19	0.00	0	1	0.75
2	R_CN2.mgt	−5.12	0.00	−0.5	0.5	−0.13
3	V_CH_K2.rte	−3.50	0.00	0	500	382.5
4	V_GW_REVAP.gw	−2.87	0.00	0	0.2	0.06
5	V_SURLAG.bsn	−1.42	0.16	0.05	24	3.67
6	R_SOL_AWC(.).sol	−0.97	0.33	−0.5	0.5	−0.17
7	V_CH_N2.rte	–0.74	0.46	0	0.3	0.05
8	V_GWQMN.gw	−0.40	0.69	0	5000	1665
9	V_ESCO.hru	0.32	0.75	0	1	0.73
10	V_REVAPMN.gw	0.10	0.92	0	500	286.5
11	V_RCHRG_DP.gw	0.09	0.93	0	1	0.48
12	V_GW_DELAY.gw	–0.07	0.94	0	500	5.5

ALPHA_BF: baseflow alpha factor; CN2: initial SCS CN II value; CH_K2: channel effective hydraulic conductivity; GW_REVAP: groundwater “revap” coefficient; SURLAG: surface runoff lag time; SOL_AWC: available water capacity; CH_N2: Manning’s n for main channel; GWQMN: threshold water depth in the shallow aquifer for flow; ESCO: soil evaporation compensation factor; REVAPMN: threshold depth of water in the shallow aquifer for “revap” to occur; RCHRG_DP: deep aquifer percolation fraction; and GW_DELAY: groundwater delay.

Figure 5. Comparison of monthly observed and simulated SWAT for calibration (1976–1985) and validation (1986–1989) periods.

Figure 6. Changes in annual precipitation, and maximum and minimum temperatures under (a) RCP4.5 and (b) RCP8.5 scenarios against the historical mean (1976–2005).

Figure 7. Monthly changes in precipitation, and maximum and minimum temperatures under the RCP4.5 and RCP8.5 scenarios for the 2021–2050 and 2071–2100 periods against the 1976–2005 historical period. The shading indicates the ensemble range by all climate projections.

Figure 8. Probability density function (pdf) of the historical (1976–2005) and future (2021–2050 and 2071–2100) SPI-3 under the (a,b) RCP4.5 and (c,d) RCP8.5 scenarios.

Figure 9. Comparison of the number and duration of the historical and future (a,c) meteorological and (b,d) hydrological droughts of the JRB under the RCP4.5 and RCP8.5 scenarios.

Figure 10. Relative changes in the future annual streamflow against the historical period under various climate projections and RCP scenarios.

Figure 11. Probability density function (pdf) of the historical (1976–2005) and future (2021–2050 and 2071–2100) SSI-3 under the (a,b) RCP4.5 and (c,d) RCP8.5 scenarios.