Sensitivity of SWAT simulated streamflow to climatic changes within the Eastern Nile River basin

Recently Dereje T. Mengistu and Asgeir Sorteberg published a paper on the river flows in the Eastern Nile basin. This study is a part of the EMAPS research.

The paper is published in: Hydrology and Earth System Sciences 2012; 16: 391–407.

The Abstract of the paper is.

The hydrological model SWAT was run with daily station based precipitation and temperature data for the whole Eastern Nile basin including the three subbasins: the Abbay (Blue Nile), BaroAkobo and Tekeze. The daily and monthly streamflows were calibrated and validated at six out- lets with station-based streamflow data in the three different subbasins. The model performed very well in simulating the monthly variability while the validation against daily data revealed a more diverse performance. The simulations in- dicated that around 60 % of the average annual rainfalls of the subbasins were lost through evaporation while the esti- mated runoff coefficients were 0.24, 0.30 and 0.18 for Ab- bay, BaroAkobo and Tekeze subbasins, respectively. About half to two-thirds of the runoff could be attributed to surface runoff while the other contributions came from groundwater.

Twenty hypothetical climate change scenarios (perturbed temperatures and precipitation) were conducted to test the sensitivity of SWAT simulated annual streamflow. The result revealed that the annual streamflow sensitivity to changes in precipitation and temperature differed among the basins and the dependence of the response on the strength of the changes was not linear. On average the annual streamflow responses to a change in precipitation with no temperature change were 19 %, 17 %, and 26 % per 10 % change in precipitation while the average annual streamflow responses to a change in temperature and no precipitation change were

47 temperature and precipitation scenarios from 19 AOGCMs participating inCMIP3 were used to estimate fu- ture changes in streamflow due to climate changes. The cli- mate models disagreed on both the strength and the direc- tion of future precipitation changes. Thus, no clear conclu- sions could be made about future changes in the Eastern Nile streamflow. However, such types of assessment are impor- tant as they emphasise the need to use several an ensemble of AOGCMs as the results strongly dependent on the choice of climate models.

Work during 2011

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The Ethiopian Malaria Prediction System (EMaPS) combines information about weather and water with demographic data to predict mosquito development and malaria risk.

Climate variability and changes may influence socio-economic development in Africa by affecting human health through extreme weather events and by bringing about changes in the ecology of infectious diseases. Malaria is a major climate sensitive public health problem in Ethiopia. Unfortunately, there are no practical tools for predicting malaria epidemics based on weather and climate information. Such tools would be useful in making a more efficient use of the limited resources for malaria control.

The project is a collaborative multidisciplinary research project. Researchers from Ethiopia and Norway work together to develop and validate models for predicting malaria transmission and set up an early warning by combining information on climate, water, epidemiological and entomological data. By the end of the project period, EMaPS will try to provide an implementation approach for early malaria warning. The project also aims to strengthen research, and improve interdisciplinary research capacity in Ethiopia and Norway.

The project contains several disciplines (see figure).

The project combined new population-based malaria transmission data with climate and land use variability data to develop early warning to predict malaria epidemics in Ethiopia. Such information is useful for the public and public institutions about the risk of malaria transmission and thus prevents malaria-related deaths.

Overall, eight PhD candidates (six Ethiopians and two Norwegians) take part in the project. The NUFU project funds four of these students, and four are funded by the University of Bergen. They collaborate and share data between the project parts.

We completed the data collection in 2010. During 2011, we mainly focused on data analysis, write-up and publication of the study findings. We expect all PhD candidates to defend their PhD thesis in 2012, and their works are briefly described below.

Abebe Animut is studying malaria mosquitoes in the highlands. He has described the occurrence of Anopheles arabiensis at altitudes as high as 2200m. He has also described the risk of malaria transmission at varying altitudes between 1700 and 2200 m altitude. His study provides good evidence that malaria transmission often occurs in the Ethiopian highlands.

Dereje Tesfahun has evaluated how rainfall and other factors affect the flow of the major rivers in Ethiopia. He has used a model to assess how sensitive the flows of the major river basins are affected by the weather and by possible land use changes. His research shows that Ethiopian rivers are sensitive to precipitation with a 10% change in precipitation giving a 20-30% response in annual stream flow.

Diriba Korecha has studied seasonal weather forecast for Ethiopia. He has re-classified the climatic zones in Ethiopia, worked on models to improve seasonal weather forecasting and validated the result of 10 years of seasonal forecasting in Ethiopia. His research shows that seasonal weather forecasting in
Ethiopia is difficult.

Adugna Woyessa has studied the prevalence and risks for malaria using prospective community-based surveys in Butajira in the south central Ethiopian Highlands. His study confirms that malaria is present at altitudes as high as 2200 m, and the malaria prevalence increases towards the lowlands. Malaria occurs throughout the year, but mainly after the main rains. One important finding is that he shows that malaria varies much between villages and within households at all altitudes.

Eskindir Loha studies malaria in the holoendemic Arba Minch area. One of his studies shows that models of climate-malaria link vary from place to place, and one model cannot fit all locations. Malaria modelling may need the inclusion of non-climatic causes. In a follow up study he shows that risk of getting malaria varies much both in time and space within villages. He now works on a paper to describe the influence on rainfall, temperature, socioeconomic factors on the incidence on malaria in these lowlands.

Fekadu Massebo is describing the association between resting behaviour, human blood index and entomological inoculation rates of Anopheles arabiensis in south Ethiopia. The studies include analysis on how mosquito density is associated with malaria cases and how it is influenced by temperature and rainfall. He also assesses insecticide resistance pattern, and if simple house screening will reduce risk of malaria infection.

Torleif Markussen Lunde works on the malaria prediction model. He uses information collected from several disciplines of our project. He has developed a validated malaria prediction model. In the coming months, he will produce malaria distribution maps for Ethiopia, and try to estimate how the new IPPC climate scenarios will affect malaria in the coming years.

Ellen Viste has used weather analysis to describe and analyse from where moisture to Ethiopia comes from. The Indian Ocean, the Congo Basin and the Red Sea are important moisture source regions. The results suggest that most of the air – humid or not – that enters the Ethiopian highlands from the south has travelled through the Indian Ocean, by the African continent, reaching the Ethiopian highlands from the south-west, or through the Turkana channel.

Some conclusions:
The research will reach its research objectives by the end of 2012, and will have produced eight PhDs and over 20 master theses. Based on our experience we conclude the following challenges remain:

Research challenges include:
• Improve seasonal weather forecasting for Ethiopia
• Further develop and field-test malaria prediction in close collaboration with national meteorology and health authorities
• Possibly add new disciplines such as studies on climate – food production and nutrition.

Educational challenges include:
• Strengthen PhD training in advanced epidemiology and mathematical modelling (both in geophysics and in health research)
• Strengthening training in medical entomology (masters level)

These are parts we wish to include in plans for a possible extension of our project.


EMAPS 2011 Annual Meeting

The EMAPS Annual Meeting will be on Monday and Tuesday January 10 and 11 at Ghion Hotel in Addis Ababa.

We plan the meeting as an open scientific meeting, and a closed session for EMAPS to discuss administrative matters and to discuss possible strategies to continue the EMAPS programme for another project period.

We will have one or two lectures at the start of the workshop. Our main emphasis is on forecasting malaria epidemics, and we aim to build our scientific meeting around our modelling efforts.

We shall discuss this in thematic areas such as: mosquito dynamics and behaviour, human host infection (highland, and lowland areas), environmental (hydrology and climate/meteorology), and modelling (captures the whole or part of the information collected so far).

It is difficult to forecast malaria epidemics

Malaria transmission is complex and is associated with climate. However, simple attempts to extrapolate malaria incidence rates from averaged regional meteorological conditions have proven unsuccessful. This study from the EMAPS research group describes P. falciparum malaria incidence models linked with meteorological data in south Ethiopia.

Variability in the models was principally attributed to regional differences, and a single model was not found that fits all locations. Past P. falciparum malaria incidence appeared to be a superior predictor than meteorology. The study concludes that future efforts to model malaria incidence may benefit from inclusion of non-meteorological causes.

This study is agrees with a recent Nature paper by Gething and colleagues. They describe the malaria decline takes place during global warming. The reasons for decline might be non-climatic causes such as better treatment and prevention. The paper by Loha and Lindtjørn shows that factors affecting malaria incidence also varies with a region.

Locally, we are examining possible associations between temperature, rainfall, mosquito development and malaria in both lowlands and highlands in Ethiopia. Through this research, we hope to improve our understanding of the local variations in malaria epidemiology.

Loha, E., & Lindtjørn, B. (2010). Model variations in predicting incidence of Plasmodium falciparum malaria using 1998-2007 morbidity and meteorological data from south Ethiopia. Malaria Journal, 9 (1) DOI: 10.1186/1475-2875-9-166

Gething, P., Smith, D., Patil, A., Tatem, A., Snow, R., & Hay, S. (2010). Climate change and the global malaria recession Nature, 465 (7296), 342-345 DOI: 10.1038/nature09098

Some prelimary results

In a recent scientific conference in Tromsø, Eskindir Loha and Torleif Markussen Lunde presented some preliminary results of our research on climate and malaria.

You can download their presentation here. Tromso2010 EMAPS