COUNTRY BRIEF
June 2019
Projecting future water availability in Lake Malawi and the Shire River basin
Malawi’s development is strongly tied to water availability
Malawi is highly dependent on water from Lake Malawi and the Shire River basin (Figure 1). Over 90% of Malawi’s electricity depends on outflows from the lake into the Shire River which feed three existing hydropower plants – Tedzani, Nkula and Kapichira – with expansion anticipated at the latter two, and plans for additional hydropower stations. Most of the country’s irrigated agriculture is dependent on the river. Regular flows of water are also essential to maintain a wetland system (the Elephant Marsh) and the ecosystem services that it provides.
Pressure on water resources is likely to increase as a result of a growing population, and competing demands for water for energy, agriculture, industrial and domestic purposes. Understanding the scale of potential future changes in water availability under climate change is thus essential to inform socio-economic development planning in Malawi. In this brief we use computer-based water resources models to project future water availability reflecting demand and the effects of water management strategies.
Lake Malawi and the Shire rainfall variability led to low lake levels also affect the ability of Lake Malawi River basin: a dynamic system which resulted in no outflows to the and the Shire River to supply water to Shire River (1910-24). Construction of the different sectors.
Water levels in Lake Malawi fluctuate Kamuzu Barrage in 1965 enabled control 32°0'0"E 34°0'0"E 36°0'0"E throughout the year reflecting the of outflows from the lake into the Shire ´ contribution of lake tributaries, rainfall River. The highest recorded outflows 10°0'0"S and evaporation over the lake, and occurred in 1979-80. However, since outflows to the Shire River. The highest then droughts have significantly reduced outflows usually occur at the end of the water availability on several occasions, rainy season, and the lowest outflows at including in 1992-3 and 2015-16 with 12°0'0"S the end of the dry season. the El Niño events. Malawi Tanzania
Water levels also show change over Decisions to change land use in the basin 14°0'0"S Mozambique time, reflecting a combination of natural – from forestry to agriculture – also play Lake Malawi Shire River factors and management decisions a role in affecting the speed with " Lake Malombe
(Figure 2). In the early 20th century which water drains into the lake from " 16°0'0"S Kamuzu Barrage the catchment. While climate change LMSRB Catchments is expected to be an important driver 2977 m above sea level
About FCFA of changes in rainfall, and therefore 35 m above sea level Future Climate for Africa (FCFA) aims to water availability, decisions regarding generate fundamentally new climate science the management of lake levels will Figure 1: Location, elevation and focused on Africa, and to ensure that this science has an impact on human development across catchments of the Lake Malawi Shire the continent. River Basin www.futureclimateafrica.org Figure 2: Past water levels in Lake Malawi (1921-2018) and Shire River streamflow at the Kamuzu Barrage at Liwonde (1948-2009)
477.0 900 Average Annual Lake Malawi Water Level 476.5 1980, 476.5 Average Annual Streamflow downstream of outflow 476.0 800 475.5 700 475.0 474.5 600 474.0 473.5 500 473.0 400 472.5 472.0 300 Streamflow (m3/s) Streamflow 471.5 1930, 471.4
Annual Lake Malawi levels (masl) levels Malawi Lake Annual 471.0 200 470.5 100 470.0 469.5 0 1921 1931 1941 1951 1961 1971 1981 1991 2001 2011 Year
Pre 1965 1965-1993 Post 1993 Significantly lower in the past Kamuzu Barrage constructed After a drought from 1992-5 with fluctuations and outflow in 1965 allowed management the barrage restricted outflows threshold of 471.5 metres above of lake outflows; historic high to maintain lake levels sea level (masl) crossed in the (477m) reached in 1979-80 early 20th century
Determining water countries. It includes analysis of water Customising the modelling and analysis availability – using the Water demand (water use patterns and to the local context of hydrology Evaluation And Planning allocation) and supply (streamflow, and management decisions is crucial system (WEAP) model groundwater, reservoirs and transfers). to generating stakeholder-relevant Once established, WEAP can be used as a information. decision support tool for assessing water WEAP (Water Evaluation And Planning, availability and supply requirements The UMFULA research team of the Future www.weap21.org) is a software for key sectors. Scenarios can also be Climate for Africa (FCFA) Programme tool for integrated water resources explored to evaluate the implications developed a WEAP model for the Lake planning developed by the Stockholm of different water development Malawi Shire River basin using a four Environment Institute. WEAP is easily and management options on water step process of stakeholder engagement accessible without payment of a software availability and demand. over a three year period (Figure 3). This is licence for users from developing part of UMFULA’s work that aims to
2 support long-term decisions in central • Electricity Supply Corporation of offtakes and irrigation), and priority and southern Africa around resource use, Malawi Ltd (ESCOM) (ESCOM has features of the basin to model (Figure 4). infrastructure investment and cross- recently been split into ESCOM and An iterative development process sectoral growth priorities. Electricity Generation Company Ltd. produced a model that addresses (EGENCO) stakeholder questions and priorities. Stakeholders that were consulted for The model is transferable and, the development of the WEAP model • Shire River Basin Management with further development, could be include: Programme (SRBMP) used by Malawi’s planners and decision • Ministry of Agriculture, Irrigation and makers for scenario analysis, to examine Water Development (Departments • Operators of the Kamuzu Barrage. different combinations of future water, of Irrigation, Surface Water, and energy and food production in the Agriculture Extension Services) Stakeholders informed our country. Further details are available understanding of historical and current in the submitted journal article by water resource management practices, • Department of National Parks Bhave et al. and Wildlife planned infrastructure (new barrages,
Figure 3: The iterative WEAP model development process between UMFULA researchers and local stakeholders
Preliminary Building trust Validate Sector options Communicate one to one with sectoral conceptual and preliminary Stakeholder stakeholder stakeholders model with performance results for Engagement consultations stakeholders metrics feedback Process April 2016 Dec 2016 June 2017 Nov 2017 June 2018
Water De ne Study Future work Understand Develop water Scenarios and Area and based on Resources basin resources robust options Decision stakeholder Modelling hydrology model Context feedback
3 Figure 4: WEAP model schematic for the Lake Malawi Shire River Basin representing the catchments delineated in the map showing elevation (left). This transboundary basin covers parts of Malawi, Tanzania and Mozambique. The WEAP model structure includes lake catchments, Lake Malawi reservoir, flow requirement downstream of the barrage (termed Release) and three existing hydropower stations. Lake Malawi catchments inflow into the ‘Routing River’ which flows to the Lake Malawi reservoir.
4 How accurate is the WEAP used to analyse future scenarios. indicator of the utility of the model for model in simulating Model performance is assessed by representing future lake level changes comparing observational data with (Figure 5). The model has less ability variability in Lake Malawi simulated data. to capture monthly flows downstream and the Shire River basin? The WEAP model shows of Lake Malawi. Model performance reasonable ability to simulate is strongly affected by limited data It is important to assess the extent to lake levels, capturing seasonal availability and intermittent records which the model is able to capture the variation, and showing sensitivity of management decisions at the hydrological and water management to changes in rainfall and barrage Kamuzu Barrage. characteristics of the basin before it is operation, which is an important
Figure 5: (a) Observed and simulated monthly Lake Malawi levels for the period 1960-2009 along with inset of table with goodness-of-fit statistics for the entire period. (b) shows observed and simulated average annual streamflow at Liwonde (Kamuzu Barrage) (Bhaveet al. submitted). l
(a) e 477.5 v
e Goodnessof t statistic Performance l
a 477.0 Coe cient of Determination (R2) 0.81 s e
n 476.5 Nash Sutcli e E ciency Coe cient 0.77 a
e Percent Bias -0.01 m
476.0 e v
o 475.5 b a s
e 475.0 r t e 474.5 m
) e
d 474.0 u t i t l 473.5 a (
l Observed Lake Malawi Levels e 473.0 v
e Modelled Lake Malawi Levels l
472.5 k e a L Jan-60 Jan-62 Jan-64 Jan-66 Jan-68 Jan-70 Jan-72 Jan-74 Jan-76 Jan-78 Jan-80 Jan-82 Jan-84 Jan-86 Jan-88 Jan-90 Jan-92 Jan-94 Jan-96 Jan-98 Jan-00 Jan-02 Jan-04 Jan-06 Jan-08 MonthMonth
900 (b) Liwon e serve Streamflow ) 800 s
e Liwon e Simulate Streamflow
m 700 u (
e 600 r
a 500 s h i
400
l a
u 300 n n a 200 e a
r 100 e v
A 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Year
5 How will climate change to the maximum level that can be Shire River as they show a consistent affect future outflows from simulated (480 metres above sea level), reduction over time. Under such Lake Malawi? after which unrestricted downstream conditions, downstream releases would flows occur (effectively reservoir likely need to be constrained, leading to The WEAP model was then run under overtopping) which would likely lead the risk of insufficient water downstream future climate projections from 29 to downstream flooding. Moreover, for to maintain hydropower production and bias-corrected state-of-the-art Global nine models monthly outflows exceed supply for irrigated agriculture and the Climate Models based on the RCP 8.5 1000 m3/s for substantial periods. environment. scenario. The future climate projections Such outflows during the 1979-1981 represent the period 2021-2050. For the period caused extremely high river flows (iii) lake levels falling below the intermediate period of 11 years (from in the Lower Shire. outflow threshold 2010 – 2020), we use observations Reduced rainfall in the Lake Malawi from the 1960-1970 period to run the (ii) lake level behaviour similar to the catchment leads to much lower lake model. The impacts show a wide range recent range levels. Projections from 11 models lead of rainfall-driven changes in lake levels Some climate projections lead to lake to a breaching of the threshold (471.5 that can be grouped into three main levels staying moderately high, meaning metres above sea level) below which no categories (Figure 6): that barrage operation could provide water outflows would occur from Lake consistent flows for downstream Malawi into the Shire River. In such cases (i) high lake levels leading to high requirements. However, for other the Shire River would effectively change Shire River outflows projections, lake levels remain only just from a perennial to a seasonal river. Five models show that lake levels rise high enough to allow outflows into the
Figure 6: Climate change impacts on the Lake Malawi levels based on 29 Global Climate Model projections
481 480 479
l 478 e v
e 477 l
a 476 s e 475 n
a 474 e m
473 t
u 472 o
471 a A SS1-0 A SS1-3 s
e 470 - SM M - SM r t 469 M - M M - MS e
m M- M5 S -Mk3-6-0 468 )
e an SM2 L- M3 467 L- SM2 L- SM2M u
t 466 i a M2-A a M2- t l 465
a a M2- S PSL- M5A-L (
l 464 PSL- M5A-M PSL- M5 -L e
v M - SM M - SM- M
e 463 l
M 5 MP - M3 462
k e MP - SM-L MP - SM-M
a 461
L MP - SM1 or SM1-M 460 - sm1-1 - sm1-1-m 459 inm m4 utflow hreshol 458 Jan-10 Jan-11 Jan-12 Jan-13 Jan-14 Jan-15 Jan-16 Jan-17 Jan-18 Jan-19 Jan-20 Jan-21 Jan-22 Jan-23 Jan-24 Jan-25 Jan-26 Jan-27 Jan-28 Jan-29 Jan-30 Jan-31 Jan-32 Jan-33 Jan-34 Jan-35 Jan-36 Jan-37 Jan-38 Jan-39 Jan-40 Jan-41 Jan-42 Jan-43 Jan-44 Jan-45 Jan-46 Jan-47 Jan-48 Jan-49 Jan-50 Month
6 What other factors affect water extraction from Lake Malawi. Both future or the operation of infrastructure future water supply? countries are also cooperating to share like the Kamuzu Barrage that would water resources of the Songwe River, critically affect future lake level and Inflows which forms their border, to expand outflow behaviour. Since the catchment area of Lake irrigated agriculture. Malawi covers parts of Malawi, Sustainability of future investments will Tanzania and Mozambique, changes in Outflows require more effective and extensive water availability from neighbouring Water management decisions, especially data collection and use. Lake Malawi/ countries can affect inflow to the lake. how the outflows are regulated by Shire River development plans need The model shows that, over the long the Kamuzu Barrage, have major to address uncertainty in future water term, land-based catchments in Malawi implications for existing and planned availability and demand changes, have contributed 55%, Tanzania 41% downstream infrastructure. New including how multi-year shifts in lake and Mozambique 4% to the total Lake hydropower plants are planned to levels would affect water trade-offs Malawi inflow. increase electricity generation to meet between hydropower, irrigation and rising demand, while plans for canal- the environment. The wide range of Tanzania’s contribution of water to Lake based irrigation in the Lower Shire have potential future lake level changes and Malawi is substantial, and therefore been identified to promote food security impacts on outflow suggest a need lake levels will be sensitive to future and socio-economic development. for decision making under uncertainty management decisions in Tanzania that approaches. Such approaches can affect water availability. Historically help identify management decisions much of Tanzania’s contribution has Implications and (particularly for the Kamuzu Barrage) come from the Ruhuhu basin, which recommendations that work effectively across a range of has relatively high rainfall but a low future climates (dry and wet conditions) population density and limited water use The model performance is highly and basin development scenarios. for irrigation. However, this catchment constrained by data availability and The WEAP model is intended to be a is included in irrigation expansion plans knowledge of past operating decisions, useful tool to assess such options, and under the Southern Agricultural Growth but demonstrates good ability to allow stakeholders to explore scenarios Corridor of Tanzania (SAGCOT). Malawi simulate Lake Malawi levels. The results and thereby support robust decision also has plans to expand irrigation show a wide range of impacts due making. The UMFULA research team is along the lake coast through its Green to large differences in climate model working with stakeholders to do exactly Belt Initiative and other irrigation projections in this region of Africa. this, and a subsequent brief will be schemes which will reduce water The impacts presented here assume published later this year. inflows to the lake or lead to direct no change in lake evaporation in the
7 Reference Bhave, A.G., Bulcock, L., Dessai, S., Conway, D., Jewitt, G., Dougill, A.J., Kolusu, S.R. and Mkwambisi, D. Lake Malawi’s threshold behaviour: A stakeholder-informed model to simulate sensitivity to climate change, Submitted to Journal of Hydrology.
About Future Climate for Africa
Future Climate for Africa (FCFA) aims to generate fundamentally new climate science focused on Africa, and to ensure that this science has an impact on human development across the continent. This brief was written by members of the UMFULA research team: Ajay Bhave ([email protected]), Katharine Vincent ([email protected]) and David Mkwambisi ([email protected]). It is based on the journal article by Bhave et al., as referenced above. The authors are immensely grateful to the stakeholders who took out time from their busy schedule to attend meetings to engage in discussions, help develop the model, and provide valuable feedback. This includes representatives of the Ministry of Agriculture, Irrigation and Water Development (Departments of Irrigation, Surface Water, and Agriculture Extension Services), Department of National Parks and Wildlife, Electricity Supply Corporation of Malawi Ltd (ESCOM), Electricity Generation Company Ltd. (EGENCO), Shire River Basin Management Programme (SRBMP) and operators of the Kamuzu Barrage.
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