A study on the impact of climate change on streamflow at the watershed scale in the humid tropics

Figures & data

Fig. 1 Map of the study area: Chaliyar watershed, India.

Fig. 2 Chaliyar watershed—land-use/land-cover classification (from SWAT).

Fig. 3 Chaliyar watershed—soil texture classification (from SWAT).

Fig. 4 Chaliyar watershed with weather stations and river gauge station (from SWAT).

Fig. 5 DEM of the Chaliyar watershed in grid format.

Table 1  Summary of input data for the SWAT model

Data type	Source	Scale	Data description/properties
Topography	Survey of India	1:50 000	Elevation, spot height, drainage, boundary
Soil	Kerala State Land Use Board	1:250 000	Soil classification and physical properties
Land use	Kerala State Land Use Board	1:50 000	Land-use classification—cropland, forest, pasture, etc.
Weather	Meteorological observatory of the CWRDM at Kottaparambu	–	Daily precipitation (1981–2006); pan evaporation (1981–2006); maximum and minimum relative humidity (1981–2006); maximum and minimum temperature (1981–2006)
Streamflow, water quality	Gauging station of the CWC at Kuniyil	–	Daily discharge (1981–2006); water level (1981–2006); water quality (1981–2006); sediment load (1981–2006)

Table 2  Details of land-use/land cover classifications from SWAT

Area		Land-use/land cover	Land cover defined in SWAT database
(%)	(ha)		Definition	Symbol
0.54	1366.72	Residential area (rural)	Residential – medium/low density	URLD
0.68	1721.06	Residential area (urban)	Residential – medium/low density	URMD
8.20	20753.95	Double crop (kharif and rabi)	Rice	RICE
3.19	8073.79	Agriculture plantation – arecanut	Agricultural land – generic	AGRL
14.71	37230.57	Agriculture plantation – rubber	Agricultural land – close grown	AGRC
3.54	8959.63	Agriculture plantation – banana	Agricultural land – row crops	AGRR
2.35	5947.78	Agriculture plantation – cashew	Orchard	ORCD
2.54	6428.66	Grass land	Range – grasses	RNGE
4.21	10655.38	River/water bodies	Water	WATR
21.23	53732.49	Forest evergreen – dense	Forest – evergreen	FRSE
22.22	56238.15	Forest deciduous – dense	Forest – deciduous	FRSD
16.59	41988.79	Forest mixed	Forest – evergreen	FRST

Table 3  Crop growth values linked to SWAT database

Common name	SWAT crop code	Crop type	Crop growth parameter values used in SWAT
Rice	RICE	Warm season annual	Orysa sativa
Range grasses	RNGE	Perennial	Values of Little Bluestem
Agricultural land – generic	AGRL	Warm season annual	Values of Grain Sorghum
Agricultural land – row crops	AGRR	Warm season annual	Values for corn
Agricultual land – close-grown	AGRC	Cool season annual	Values for winter wheat
Orchard	ORCD	Trees	Values for apples
Forest – mixed	FRST	Trees	Values for oak
Forest – deciduous	FRSD	Trees	Values for oak
Forest – evergreen	FRSE	Trees	Values for pine

Fig. 6 Location of Kerala and the Chaliyar River basin in the PRECIS domain.

Fig. 7 Comparison of present and bias-corrected future scenario daily precipitation during the monsoon season.

Fig. 8 Comparison of present and bias-corrected future scenario maximum and minimum temperatures.

Fig. 9 Plots of (a) observed and (b) simulated streamflow for the calibration period.

Fig. 10 Plots of (a) observed and (b) simulated streamflow for the validation period, 2002–2006.

Table 4  Overview of parameter changes for calibration of SWAT

Rank*	Parameter description	Parameter code	File	Change from the SWAT database default value
1	SCS curve number	CN2	.mgt	Increased
2	Soil available water capacity	SOL_AWC	.sol	Increased
3	Soil evaporation compensation factor	ESCO	.hru	Increased
4	Average slope steepness	SLOPE	.rte	Increased
5	Effective hydraulic conductivity of the soil layer	SOL_K	.sol	Decreased
6	Effective hydraulic conductivity in main channel	CH_K2	.rte	Decreased
7	Average slope length	SLSUBBSN	.rte	Increased
8	Surface runoff lag coefficient	SURLAG	.bsn	Decreased
9	Baseflow alpha factor	ALPHA_BF	.gw	Decreased
10	Soil depth	SOL_Z	.sol	Increased
11	Threshold level for baseflow in shallow aquifer	GWQMN	.gw	Decreased
12	Deep aquifer percolation fraction	RCHRG_DP	.gw	Increased
13	Maximum canopy storage	CANMX	.hru	Decreased
14	Moisture soil albedo	SOL_ALB	.sol	Decreased
15	Groundwater revap coefficient	GW_REVAP	.gw	Increased
* Rank of most sensitive model parameters.

Fig. 11 (a) Observed and projected monthly streamflow and rainfall—A2 scenario; and (b) observed and projected monthly average temperature and ET—A2 scenario; average of 25 years.

Fig. 12 (a) B2 scenario—observed and projected monthly streamflow and rainfall; and (b) observed and projected monthly average temperature and ET, average of 25 years.