Analyzing the impact of thermal stress on vegetation health and agricultural drought – a case study from Gujarat, India

Figures & data

Figure 1. Spatial location of (a) Gujarat within India, (b) districts of Gujarat and location of the nine meteorological stations selected for the study. For full color versions of the figures in this paper, please see the online version.

Figure 2. (a) Isohyetal map showing long-term (1981–2010) mean monsoonal rainfall, and (b) isothermal map showing long-term (1981–2010) mean maximum temperature during the monsoon season.

Table 1. Classification of the VCI, TCI and VHI and corresponding color schemes to depict, respectively, moisture-stress, thermal stress and vegetation health.

Drought	Values	VCI	TCI	VHI
Extreme	<10
Severe	<20
Moderate	<30
Mild	<40
No	≥40

Figure 3. Classified map of land-use/land-cover of Gujarat obtained from 30-m resolution GLC30 (2010) images.

Table 2. Various ranges of the SPI (McKee, Doesken, and Kleist 1993) depicting meteorological drought severity and corresponding color schemes (Bhuiyan et al. 2006) used in this study.

SPI	Color	Drought severity
<−2.0		Extreme
−2.0 to −1.5		Severe
−1.5 to −1.0		Moderate
−1.0 to 0.0		Mild
>0.0		No drought

Table 3. Results of the multiple-regression depicting relative influence of number of heat-wave days (HWD) and monsoon rainfall (P_MON) on average temperature during the monsoon season (T_MON) at selected meteorological stations in Gujarat.

Station		b	β	t	p	R^2
Ahmedabad	HWD	0.079	0.616	3.388	0.120	0.773
	PMON	–0.002	–0.551	–3.034	0.190
Banas Kantha	HWD	−0.051	−0.529	−2.103	0.074	0.598
	PMON	–0.001	–0.746	–2.968	0.021
Bhavnagar	HWD	0.082	0.456	1.483	0.182	0.406
	PMON	–0.001	–0.321	–1.044	0.332
Bhuj	HWD	0.074	0.579	2.540	0.039	0.640
	PMON	–0.001	–0.613	–2.689	0.031
Junagarh	HWD	−0.046	−0.245	−0.713	0.499	0.176
	PMON	0.000	–0.355	–1.034	0.336
Porbandar	HWD	0.054	0.311	1.022	0.341	0.352
	PMON	0.001	0.518	1.701	0.133
Rajkot	HWD	0.077	0.778	2.963	0.021	0.572
	PMON	0.000	0.079	0.300	0.773
Surat	HWD	−0.030	−0.255	−0.661	0.530	0.060
	PMON	0.000	–0.117	–0.303	0.771
Vadodhara	HWD	−0.032	−0.299	−0.925	0.386	0.480
	PMON	–0.001	–0.807	–2.494	0.041

b: non-standardized partial regression coefficient; β: standardized partial regression coefficient; t: tolerance; p: probability; R²: coefficient of determination.

Table 4. Meteorological drought-years, agricultural drought-years (^a), and the years with above-normal temperature (ANT) in Gujarat (shown as Y).

Year	ANT
1982^a
1985^a	Y
1986^a	Y
1987^a	Y
1990
1991^a	Y
1993	Y
1995^a	Y
1998	Y
1999	Y
2000^a	Y
2001
2002^a	Y
2004
2009^a	Y
2010	Y

Figure 4. Frequency plot showing variation of the VCI values in the background of gradual variation of mean maximum aboveground air-temperature during the monsoon season.

Figure 5. Attenuation of the impact of moisture-stress by favorable thermal state in vegetation.

Figure 6. Drought intensification due to the impact of thermal stress in vegetation.

Figure 7. Degradation of vegetation health and development of vegetative drought mainly due to thermal stress.

Table 5. Correlation of the SPI, VCI and TCI with the VHI in the years of vegetative drought and non-drought in Gujarat during 1981–2010.

Year	Pearson correlation coefficient (R)		Pearson correlation coefficient (R)
	SPI-VHI	p	VCI-VHI	TCI-VHI	p
1981	0.17	0.43	0.83	0.56	0.00
1982^a	0.37	0.07	0.58	0.64	0.00
1983	0.06	0.00	0.62	0.59	0.00
1984	0.08	0.69	0.59	0.51	0.00
1985^a	0.76	0.00	0.66	0.59	0.00
1986^a	0.02	0.93	0.75	0.50	0.00
1987^a	0.60	0.00	0.88	0.29	0.00
1988	0.28	0.18	0.66	0.77	0.00
1989	0.15	0.47	0.80	0.35	0.00
1990	0.57	0.00	0.64	0.59	0.00
1991^a	0.02	0.91	0.63	0.64	0.00
1992	0.14	0.50	0.54	0.57	0.00
1993	0.19	0.35	0.78	0.65	0.00
1994	0.23	0.27	0.91	0.33	0.00
1995^a	0.01	0.97	0.72	0.66	0.00
1996	0.21	0.31	0.78	0.63	0.00
1997	0.18	0.40	0.76	0.58	0.00
1998	0.03	0.90	0.79	0.67	0.00
1999	0.06	0.79	0.71	0.75	0.00
2000^a	0.15	0.48	0.72	0.50	0.00
2001	0.23	0.27	0.69	0.55	0.00
2002^a	0.18	0.39	0.72	0.69	0.00
2003	0.12	0.04	0.67	0.50	0.00
2004	0.00	1.00	0.67	0.61	0.00
2005	0.41	0.04	0.72	0.63	0.00
2006	0.12	0.57	0.58	0.53	0.00
2007	0.23	0.26	0.65	0.53	0.00
2008	0.15	0.01	0.59	0.54	0.00
2009^a	0.23	0.28	0.79	0.50	0.00
2010	0.30	0.15	0.65	0.49	0.00

^aYears of vegetative/agricultural drought.

Figure 8. Scatter-plot showing variation of VHI against crop yield (CY) in Gujarat during 2001–2010: (a) in the drought years; (b) in the non-drought years.

GLC30 (2010). http://www.globallandcover.com ( Accessed on 28.April.2016)

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McKee, T. B., N. J. Doesken, and J. Kleist (1993). The Relation of Drought Frequency and Duration to Time Scales. Proceedings of the Eighth Conference on Applied Climatology, American Meteorological Society. Boston, 179–184.

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Bhuiyan, C., R. P. Singh, and F. N. Kogan. 2006. “Monitoring Drought Dynamics in the Aravalli Terrain (India) Using Different Indices Based on Ground and Remote Sensing Data.” International Journal of Applied Earth Observation and Geoinformation 8: 289–303. doi:10.1016/j.jag.2006.03.002.

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