Meteorological and hydrological drought assessment in Lake Malawi and Shire River basins (1970–2013)

Figures & data

Figure 1. The study area, Lake Malawi and Shire River basins

Figure 2. Mean annual rainfall pattern and monthly mean rainfall in Lake Malawi and Shire River basins

Figure 3. Lake level and lake outflow. Statistical parameters are from 1970 to 2013 for lake level and from 1976 to 2009 for outflow. The red line is the flow required for maximum hydropower generation

Table 1. Modified standardised precipitation index (SPI) classification. Information source: World Meteorological Organization (2012). (Standardised precipitation and evaporation index (SPEI) and lake level change index (LLCI))

SPI (SPEI, LLCI) value	Explanation	Drought intensity
> 2.0	Extremely wet	No drought
1.5 to 1.99	Very wet	No drought
1.0 to 1.49	Moderately wet	No drought
−0.99 to 0.99	Near normal	No drought
−1.0 to −1.49	Moderately dry	Moderate drought
−1.5 to −1.99	Severely dry	Severe drought
< −2	Extremely dry	Extreme drought

Table 2. Mann-Kendall (MK) test (tau) and Sen’s slope results for precipitation, temperature and lake level at the regional scale. Only Sen’s slopes of significant MK test trends are presented

	Overall		Lake Malawi Basin only
Parameter	Trend, tau	Sen’s slope	Trend, tau	Sen’s slope
Precipitation	−1.3461		−1.1262
Temperature	2.796***	0.02***	2.795***	0.02***
Lake level			−10.278***	−0.0248***

*** significant at p < 0.01.

Figure 4. Mann-Kendall (MK) test results from 1970 to 2013 in Lake Malawi and Shire River basins for rainfall (left) and temperature (right). The significance of the trends is based on p < 0.05

Table 3. Meteorological drought events in Lake Malawi and Shire River Basins between 1970 and 2013 as detected by standardised precipitation and evaporation index and standardised precipitation index at 12-month scale (SPEI12 and SPI12)

SPEI-12				SPI-12
Event	Period	Intensity	Spatial extent (%)	Event	Period	Intensity	Spatial extent (%)
				1	1973–1974	−1.1	25.1
1	1983–1984	−1.51	48.7	2	1983–1984	−131	25.3
2	1987–1988	−1.45	49.8	3	1987–1988	−1.32	38.7
3	1990–1991	−1.32	41	4	1990–1993	−2.65	61.2
4	1992–1996	−2.16	62.5	5	1994–1996	−2.31	53.1
5	1998–1999	−1.02	42.4
6	2004	−1.70	47.6	6	2004	−1.52	41.7
7	2005–2006	−1.92	73.1	7	2005–2006	−1.92	51.8
8	2009–2013	−1.32	37.5	8	2009	−1.02	28.5

Figure 5. Standardised precipitation and evaporation index and standardised precipitation index at 12-month scale (SPEI12 and SPI12) series for Lake Malawi and Shire River basins from 1970 to 2013. Numbers represent drought events

Table 4. Comparison of mean spatial standardised precipitation index and -standardised precipitation and evaporation index at 12 month scale (SPI12 and SPEI12) in terms of the mean drought severity, intensity, duration and frequency and the percentage of total drought months, using t-test

	Severity	Intensity	Duration (months)	Frequency	% of total drought months
SPEI (mean)	19.4	−1.6	18.4	9.4	30
SPI (mean)	18.4	−1.7	17.2	8.9	27.7
Difference (%)	4.7	−6***	6.2	5.4	7.3***

*** significant at p < 0.01.

Figure 6. Mean drought parameters generated from the standardized precipitation and evaporation index (SPEI) and the standardized precipitation index (SPI) in Lake Malawi basin (LMB) and Shire River basin (SRB) for the period 1970–2013. The parameters from left to right are severity, intensity, duration, frequency and percentage of total drought months

Figure 7. Hydrological and meteorological droughts in Lake Malawi basin from 1970 to 2013. Numbers represent drought events. (a) Lake level change index (LLCI) is based on 12-month scale. Meteorological droughts are based on standardised precipitation and evaporation index  at (b) 12-month scale (SPEI12), (c)  24-month scale (SPEI24) and (d) 36-month scale (SPEI36)

Figure 8. Comparison of hydrological drought based on lake level change index at 12-month scale (LLCI12) and meteorological droughts based on standardised  precipitation and evaporation index at (a) 12-month scale (SPEI12), (b) 24-month scale (SPEI24), (c) 36-month scale (SPEI36) in Lake Malawi basin only. (d) The relationship between SPEI36 and LLCI12_t10 (10-month lag). Vertical and horizontal yellow lines mark drought threshold

Figure 9. Comparison of standardised precipitation and evaporation index at 36-month scale (SPEI36), lake level change index at 12-month scale (LLCI12) and LLCI12 at 10-month lag

Figure 10. Meteorological drought trends in Lake Malawi and Shire River basins for the standardized precipitation and evaporation index (SPEI) and the standardized precipitation index (SPI). The significance of the trends is based on p < 0.05. The decreasing trend implies increase in drought

Table 5. Mann-Kendall (tau) and Sen’s slope results for meteorological and hydrological drought parameters. A negative trend for drought intensity signifies an increasing trend of drought. Only Sen’s slopes for parameters with significant trends are presented

	SPEI		SPI
Parameter	Trend, tau	Sen’s slope	Trend, tau	Sen’s slope
Overall – Meteorological drought
SPEI/SPI	−7.91***	−0.018***	−3.86***	−0.0075 ***
Drought area proportion	7.06***	0.02***	1.5
Drought severity	3.81***	0.25***	0.942
Lake Malawi basin only – Meteorological drought
SPEI	−9.3218***	−0.021 ***	–5.4815***	−0.011 ***
Hydrological drought
LLCI	−9.53***	−0.003 ***

*** significant at p < 0.01.

SPEI: standardised precipitation and evaporation index; SPI: standardised precipitation index; LLCI: lake level change index.

Svoboda et al., 2012. Standardized Precipitation Index - user guide. WMO-No, 1090. Geneva: World Meteorological Organisation..

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