Recent changes in climate extremes in Guinea-Bissau

Figures & data

Figure 1. The territory of Guinea-Bissau and its main meteorological stations, with longer climatological series.

Figure 2. Mean monthly temperature (line) and mean monthly precipitation (columns) in Bissau/Observatory station, over the period 1981–2010. Data source: National Institute of Meteorology of Guinea-Bissau.

Table 1. Monthly and daily meteorological observations that were used in this study. Source: National Institute of Meteorology of Guinea-Bissau.

Monthly observation series
Station	Climatic parameters and abbreviation	Period	Latitude (° ´)	Longitude (° ´)	Altitude (m)
Bissau/Observatory	Total precipitation (P)	1960–2020	11.85	−15.6	43
	Maximum temperature (Tx)	1960–2020
	Minimum temperature (Tn)	1960–2020
Bolama	Total precipitation (P)	1981–2020	11.60	−15.48	20
	Maximum temperature (Tx)	1981–2014
	Minimum temperature (Tn)	1981–2014
Bafatá	Total precipitation (P)	1981–2020	12.17	−14.67	20
	Maximum temperature (Tx)	1981–2017
	Minimum temperature (Tn)	1981–2017
Daily observation series
Station	Climatic parameters and abbreviation	Period	Latitude (° ´)	Longitude (° ´)	Altitude (m)
Bissau/Observatory	Total precipitation (P)	1981–2020	11.85	−15.6	43
	Maximum temperature (Tx)	1981–2020
	Minimum temperature (Tn)	1981–2020
Bolama	Total precipitation (P)	1981–2020	11.60	−15.48	20
	Maximum temperature (Tx)	1981–2020
	Minimum temperature (Tn)	1981–2014
Bafatá	Total precipitation (P)	1981–2020	12.17	−14.67	20
	Maximum temperature (Tx)	1981–2017
	Minimum temperature (Tn)	1981–2017

Table 2. Temperature indices used in this study.

Nº	Índices	Description	Unit
1	dtr	Mean annual difference between daily TX and daily TN	ºC
2	su	Annual number of days when TX > 25 degrees_ºC	Days
3	Tmm	Annual mean daily temperature	ºC
4	tnx	Annual warmest daily TN	Days
5	tr	Annual number of days when TN > 20 degrees_ºC	Days
6	TXge30	Annual number of days when TX ≥ 30 degrees_ºC	Days
7	TXge35	Annual number of days when TX ≥ 35 degrees_ºC	Days
8	txx	Annual warmest daily TX	ºC
9	tx90p	Annual percentage of days when TX > 90th percentile	Days
10	wsdi2	Annual number of days with at least 30 consecutive days when TX > 90th percentile	Days
11	tnm	Annual mean daily minimum temperature	ºC
12	tnn	Annual coldest daily TN	ºC

Table 3. Precipitation indices used in this study.

Nº	Índices	Description	Units
1	cdd	Maximum annual number of consecutive dry days (when precipitation < 1.0 mm)	Days
2	cwd	Maximum annual number of consecutive wet days (when precipitation ≥ 1.0 mm)	Days
3	prcptot	Annual sum of daily precipitation ≥ 1.0 mm	Days
4	r10mm	Annual number of days when precipitation ≥ 10 mm	Days
5	r20mm	Annual number of days when precipitation ≥ 20 mm	Days
6	r30mm	Number of days when precipitation ≥ 30	Days
7	r95p	Annual sum of daily precipitation > 95th percentile	Days
8	95ptot	Mean intensity of precipitation events above the 95th percentile	mm
9	rx1day	Maximum annual 1−day precipitation total	mm
10	rx3day	Maximum 3−day precipitation total	mm
11	rx5day	Maximum annual 5−day precipitation total	mm
12	sdii	Annual total precipitation divided by the number of wet days (when total precipitation ≥ 1.0 mm)	mm

Figure 3. Interannual precipitation variability (1960–2020). (a) Bissau/Observatory; (b) Bolama; (c) Bafatá.

Table 4. Estimated trends (by decade) of total monthly precipitation, for the three studied stations, over the period 1960 to 2020.

1960 –2020		Bissau/Observatory		Bolama		Bafatá
Months	Parameter	Mean precipitation (mm)	change by decade (mm; %)	Mean precipitation (mm)	change by decade (mm; %)	Mean precipitation (mm)	change by decade (mm; %)
May	Monthly precipitation	20,2	−0.6 (−3%)	29,3	−0.8 (−2.7%)	25,7	−1.3 (−5.6%)
June	Monthly precipitation	145,5	−4.2 (−2.9%)	193,6	−4.5 (−2.3%)	140,2	−4.7 (−3.4%)
July	Monthly precipitation	393,4	−10.0 (−2.5%)	535,6	−10.2 (−1.9%)	275,9	−8.1 (−2.9%)
August	Monthly precipitation	512,3	−18.6+ (−3.6%)	643,6	−7.1 (−1.1%)	361,4	−3.7 (−1.0%)
September	Monthly precipitation	384,7	2.2 (+0.6%)	417,9	0.7 (+0.17%)	331,3	5.3 (+1.6%)
October	Monthly precipitation	154,5	−1.2 (−0.8%)	191,4	0.2 (+0.1%)	154,7	−4.7 (−3.0%)

+Significant at p < 0.1.

Figure 4. Interannual variability of precipitation indices in Guinea-Bissau over the period 1981 to 2020. (A: Bissau/Observatory; B: Bolama; C: Bafatá; PRCPTOT: Annual sum of daily precipitation ≥ 1.0 mm; CDD: Maximum annual number of consecutive dry days (when precipitation < 1.0 mm); RX5DAY: Maximum annual 5−day precipitation total; SDII: Annual total precipitation divided by the number of wet days (when total precipitation ≥ 1.0 mm).

Table 5. Estimated trends (by decade) of precipitation indices, for the three studied stations, over the period 1981 to 2020.

1981 –2020	Bissau/Observatory	Bolama	Bafatá
Indice	change by decade (days; mm)	change by decade (days; mm)	change by decade (days; mm)
cdd	3.7	0.42	5.17*
cwd	0.0	2.35**	−0.56
prcptot	42.0	51.58	82.6**
r10mm	0.4	0.59	1.57*
r20mm	0.5	0.65	2.31***
r30mm	0.4	0.00	2.22***
r95p	29.5	55.67	52.70*
r95ptot	1.5	2.57	2.92*
rx1day	0.4	11.72	9.79**
rx3day	0.7	8.17	11.94 ***
rx5day	7.7	10.07	15.85***
sdii	0.6	−0.14	1.91***

*Significant at p < 0.05; **Significant at p < 0.01; ***Significant at p < 0.

Table 6. Summary of the trends of temperature indices for the period 1960–2020. TX: monthly average of maximum temperature; TN: monthly average of minimum temperature.

Months	Parameter	Meteorological stations
		Bissau/Observatory change by decade (ºC)	Bolama change by decade (ºC)	Bafatá change by decade (ºC)
January	TX	0.22***	−0.03	0.013
	TN	0.11+	0.19+	0.34*
February	TX	0.30***	0.08	0.010
	TN	0.28**	0.18*	−0.07
March	TX	0.32***	−0.03	0.000
	TN	0.25*	0.27***	0.11
April	TX	0.11+	−0.05	0.019**
	TN	0.17*	0.08	0.07
May	TX	0.14*	−0.03	0.011
	TN	0.08	−0.06	0.00
June	TX	0.26***	0.11**	0.022*
	TN	0.22***	−0.05	0.20**
July	TX	0.33***	0.08+	0.017**
	TN	0.24***	−0.10*	0.22**
August	TX	0.32***	0.07+	0.024***
	TN	0.16**	0.00	0.00
September	TX	0.34***	0.08*	0.017**
	TN	0.15*	0.04	0.09+
October	TX	0.26***	0.09*	0.015**
	TN	0.21***	0.12	0.12+
November	TX	0.26***	0.00	0.020**
	TN	0.12*	0.00	0.27**
December	TX	0.36***	0.05	0.007
	TN	0.22**	0.22*	0.05
Year	TX	0.26***	0.03	0.16 **
	TN	0.18**	−0.01	0.15**

+Significant at p < 0.1; *Significant at p < 0.05; **Significant at p < 0.01; ***Significant at p < 0.

Figure 5. Interannual variability of temperature indices in Guinea-Bissau over the period 1981 to 2020. (A: Bissau/Observatory; B: Bolama; C: Bafatá; TXge30: Annual number of days when TX ≥ 30°C; TXge35: Annual number of days when TX ≥ 35 degrees_ºC; dtr: Mean annual difference between daily TX and daily TN.

Table 7. Summary of the trends of daily temperature indices for the period 1981–2020.

1981 –2020	Bissau/Observatory	Bolama	Bafatá
Indice	change by decade (days)	change by decade (days)	change by decade (days)
dtr	0.31*	−0.14	0.56*
su	0.00	0.00	0.00
tmm	0.18*	−0.19***	−0.09
tnx	0.15	−0.16	−0.6*
tr	−3.39	−24.96***	−18.68
TXge30	13.82***	5.00	3.83**
TXge35	8.00*	0.00	5.00*
txx	0.19	−0.25	−0.17
tx90p	3.18***	0.50	1.14
wsdi2	6.67***	1.03	3.41
tnm	0.03	−0.39***	−0.30
tnn	−0.83*	−1.30***	0.00

*Significant at p < 0.05; **Significant at p < 0.01; b ***Significant at p < 0.