Quantifying the impact of climate variables on reference evapotranspiration in Pearl River Basin, China

Figures & data

Figure 1. Location of the Pearl River Basin study area.

Figure 2. Relationship between the observed annual pan evaporation, ET_pan, and calculated annual reference evapotranspiration, ET_o.

Table 1. Correlation coefficients between interpolation result and observation data. IDW: inverse distance weighting; Ke: ordinary kriging with exponential variograms; Kl: universal kriging with linear drift variograms; Ks: ordinary kriging with spherical variogram. ET_o: reference ET; RH: relative humidity; SD: sunshine duration; TAV: average temperature; WS: wind speed.

	Method
Factor	IDW	Ke	Kl	Ks
ETo	0.827**	0.824**	0.809**	0.817**
RH	0.755**	0.466**	0.752**	0.749**
SD	0.947**	0.951**	0.938**	0.950**
TAV	0.318*	0.850**	0.857**	0.851**
WS	0.343**	0.366**	0.283*	0.349**

**indicates significance at the 0.01 probability level; *indicates significance at the 0.05 probability level.

Figure 3. Variation of the annual ET_o in the Pearl River Basin in the period 1960–2016.

Figure 4. Spatial distribution of the annual ET_o in the Pearl River Basin.

Figure 5. Monthly ET_o in the Pearl River Basin.

Table 2. Percentage of positive (PS) and negative (NE) trend region of basin and the change trend of ET_o and climate variables in the PRB in the period 1960–2016. See Table 1 for climate variable abbreviations./dec: per decade.

		Jan.	Feb.	Mar.	Apr.	May	Jun.	Jul.	Aug.	Sep	Oct.	Nov.	Dec.	Annual
ETo	PS	10.23	76.61	8.00	58.91	9.85	44.26	7.92	28.80	26.11	85.87	68.83	55.14	27.15
	NE	89.77	23.39	92.00	41.09	90.15	55.74	92.08	71.20	73.89	14.13	31.17	44.86	72.85
	mm/dec	−0.81	0.51	−0.94	0.19	−0.72	−0.18	−1.00	−0.25	−0.83	0.58	0.31	0.14	−2.96
	mm	51.08	56.49	79.04	96.69	114.33	113.91	131.66	125.60	107.16	87.36	64.11	53.12	1080.55
RH	PS	67.27	4.48	15.37	5.30	0.45	12.47	0.00	0.00	0.01	0.00	1.68	3.22	0.00
	NE	32.73	95.52	84.63	94.70	99.55	87.53	100.00	100.00	99.99	100.00	98.32	96.78	100.00
	/dec	0.08	−0.48	−0.33	−0.57	−0.52	−0.32	−0.57	−0.86	−0.69	−0.87	−0.58	−0.82	−0.55***
SD	PS	2.16	31.29	0.00	19.51	5.65	10.16	0.00	0.06	0.00	29.04	29.62	6.67	1.06
	NE	97.84	68.71	100.00	80.49	94.35	89.84	100.00	99.94	100.00	70.96	70.38	93.33	98.94
	h/dec	−0.20	−0.02	−0.15	−0.06	−0.13	−0.11	−0.19	−0.15	−0.20	−0.03	−0.06	−0.09	−0.12***
TAV	PS	79.45	100.00	93.43	99.19	94.67	99.65	94.58	96.11	93.03	99.23	100.00	98.50	99.55
	NE	20.55	0.00	6.57	0.81	5.33	0.35	5.42	3.89	6.97	0.77	0.00	1.50	0.45
	℃/de	0.07	0.33	0.06	0.21	0.07	0.15	0.08	0.12	0.10	0.23	0.24	0.10	0.14***
WS	PS	15.91	18.05	16.64	17.99	28.40	53.89	41.50	90.46	64.58	40.11	28.89	32.00	35.23
	NE	84.09	81.95	83.36	82.01	71.60	46.11	58.50	9.54	35.42	59.89	71.11	68.00	64.77
	m/dec	−0.05	−0.07	−0.08	−0.06	−0.04	0.01	−0.00	0.03	0.01	−0.02	−0.03	−0.03	−0.03**

***indicates significance at the 0.001 probability level; **indicates significance at the 0.01 probability level.

Figure 6. Spatial change trend of the ET_o in the Pearl River Basin.

Figure 7. Relative change, RC, of climate variables in the Pearl River Basin. RH: relative humidity; SD: sunshine duration; TAV: average air temperature; WS: wind speed.

Figure 8. Monthly relative change, RC, sensitivity coefficient, Sen, and contribution, Con, of the climate variables in the Pearl River Basin.

Figure 9. Sensitivity coefficient (absolute) between ET_o and climate variables in the Pearl River Basin. RH: relative humidity; SD: sunshine duration; TAV: average air temperature; WS: wind speed.

Figure 10. Contribution between ET_o and climate variables in the Pearl River Basin. RH: relative humidity; SD: sunshine duration; TAV: average air temperature; WS: wind speed.

Table 3. Percentage of area influenced by each dominant variable to ET_o (%).

	Jan.	Feb.	Mar.	Apr.	May	Jun.	Jul.	Aug.	Sep.	Oct.	Nov.	Dec.	Annual
RH	1.43	0.00	3.14	7.86	7.59	4.10	0.73	2.23	5.24	17.04	1.24	45.22	4.61
SD	68.66	0.00	66.19	28.40	76.16	65.48	98.61	94.67	92.81	7.28	16.31	23.79	72.70
TAV	10.85	84.14	2.11	42.72	0.60	26.75	0.55	1.52	0.15	63.47	63.96	3.41	6.56
WS	19.05	15.86	28.56	21.02	15.66	3.67	0.11	1.59	1.80	12.21	18.49	27.57	16.13

Figure 11. Variation of ET_o and climate variables in the Pearl River Basin. RH: relative humidity; SD: sunshine duration; TAV: average air temperature; WS: wind speed.