Estimation of the climate impact on water resources in Nyabugogo Swamp in Kigali, Rwanda.

1. “ESTIMATION OF CC AND VARIABILITY IMPACTS AND
MITIGATION MEASURES ON WATER RESOURCES IN
THE NYABUGOGO SWAMP IN RWANDA”
By
Eng. Omar MUNYANEZA, PhD
omarmunyaneza1@gmail.com/ +250 788560783
Department of Civil & Environmental Engineering
CST/University of Rwanda
24th March 2016
IPAR 5th ANNUAL RESEARCH CONFERENCE

2. Presentation outline
• Introduction
• Study Area Description
• Objectives
• Research Methodology
• Results and Discussions
• Conclusion and Recommendations

3. Introduction
 Water is a finite resource vital for sustaining life on
earth;
 While water is a cross-cutting resource;
 The entire food production chain depends on water;
 Water resources support economic growth through,
industrial processing, energy, transportation, agriculture
and tourism;
 Water resources are under pressure from population
growth and rapid economic development in Rwanda;
 However, water resources is directly linked to the
climate which is highly variable;

4. Introduction (Cont’d)
 The climate variability have a great impact on
sustainable WRM in the world;
 Water resources in the Nyabugogo catchment
is seriously affected by the climate
variability;
 Consequently, nowadays the Nyabugogo
swamp is being flooded due to the global
phenomena and intensive human activities;
 This increases the danger of sudden
flooding of rivers in a catchment.

5. Example of recent flood case due
probably to Climate Change
 The recent floods occurred in Feb 2013
affected Nyabugogo wetland and caused
loss of properties, loss of 4 human lives
through a car which was drawn by the
water, and
 Disruption of socio-economic activities,
through the business in the area and other
issues related to transport facilities.

6. Loss of 4 human lives through this car

7. Introduction (End)
An integrated and coordinated
management approach is
needed to provide answers to
water resources in the
Nyabugogo swamp.

8. Nyabugogo catchment boundaries
Study Area
 Total area of 1,647 km2
 Nyabugogo river, total length
of 42.7 km
 Main Inflow is lake Muhazi

9. RESEARCH OBJECTIVES
 To investigate the recent trends and
variability of climatic data and
streamflow trend in the Nyabugogo
catchment, and
 To propose possible mitigation with the
goal of estimating the impact caused by
this trend on water resources in the
Nyabugogo swamp (220 ha).

10. Methodology
 Trends analysis of data set of daily maximum,
minimum temperatures, rainfall and evaporation
of Kigali airport station (1981-2012) from
Rwanda Meteorology Agency (RMA).
 And Nyabugogo River Discharge data
collected from Rwanda Natural Resources
Authority (RNRA).

11. Methodology (Cont’d)
 In this study, the Mann Kendal (MK) non-
parametric trend test has been performed
using XLSTAT to detect trends;
 The time series from each parameter was also
subjected to the Pettitt Test (Pettitt, 1979) to
detect abrupt changes in hydrological series;
 In addition, SPSS software was used to assess
a non-parametric correlation between climate
variables.

12. Methodology (Cont’d)
Trend Analysis
 The test statistics Z is computed as:
A positive (negative) value of Z signifies an upward/
downward) trend.

13. Correlation between climate variables
 The Kendall’s tau_b and Spearman rank test
were used to determine the correlation coefficient;
 It helps us to know the magnitude of the
correlation between climatic variables;
 The Spearman rank test, is a simple measure of
correlation between 2 data series and is a special
case of the Pearson product-moment coefficient
(Myers and Well, 2003).
Methodology (End)

14. Results and discussions
Mann-Kendall trends results on temperature

15. Discussion on temperature trends Results
 The Kigali Airport station shows a slight decrease, then
a significant increase in trend in the period 1987-
1994;
 Though, most of the part of the period 1991-2012
corresponds to a significant increase in To trends;
 The observed warming was supported by Collins
(2011) who demonstrated that significant increasing
temperature trends were found on average all over the
African continent.
 Pettitt tests revealed that abrupt change points was
observed in the years 1985, 1987,1989, 1993,1998,
2001, 2008 and 2009.

16. Mann-Kendall trends results for rainfall

17. Discussions on rainfall trends results
 The results of the Mann-Kendall for rainfall shows
that there is in general a significant decrease in
rainfall.
 Pettitt tests for rainfall revealed that abrupt
change points was observed in the years 1981, 1998,
2008 and 2010.
 Nevertheless, Nyabugogo wetland has been prone to
heavy floods and this may be explained by
increase in urbanization which results in increase
of impermeable areas.

18. Mann-Kendall trends results for evaporation

19. Discussions on evaporation trends results
 The results showed that there is a significant
increase trend in evaporation in the Nyabugogo
catchment,
 The increasing temperature results in an increase in
potential evaporation largely because water holding
capacity of the air is increased,
 Pettitt tests for evaporation revealed that abrupt
change points in the years 1991, 1995, 1998, 2001, 2008
and 2009, 2010.

20. Mann-Kendall trends results for discharge
 The trend analysis of the mean annual discharge
of the Nyabugogo river was performed using Mann-
Kendall test statistic;
 Due to the large data gap discharge data, it was
difficult to analyze and draw a conclusion;
 The % value of missing streamflow data is
greater than 50% (1984 to 1994 and 2001 to2009),
thus we cannot rely on the results of such a poor
data;
 Long records of runoff are essential to determine
whether runoff of a river is changing over time.

21. Correlation between climate variables

22. Correlation between climate variables
 Streamflow was slightly correlated with the
total rainfall;
 Positive relationship between rainfall and
streamflow was observed;
 The significance test (2-tailed) was performed at
10% and the higher significance was found to be
between temperature and rainfall (0.435).
 In fact, rainfall and temperature are physically
related through the dependence of atmospheric
moisture on temperature.

23. Facts impact of climate variability and/or change
on water resources in the Nyabugogo swamp

24. Facts impact of climate variability and/or change on
water resources in the Nyabugogo swamp

25. Facts impact of climate variability and/or change
on water resources in the Nyabugogo swamp

26. Summary of climate variability impact on water
resources in the Nyabugogo swamp

27. Conclusions
 A strong correlation between temperature and
evaporation was detected; but the correlation
between rainfall and discharge was found to be
weak;
 The results showed a significant decrease in rainfall;
 The analysis of discharge data did not show
significant results due to a large gap observed in it.
 Holistic approach need to be implemented to address
the challenges related to climate variability and change
by applying integrated methods for a good
sustainable water resources management in the
Nyabugogo catchment.

28. Recommendations
 More research on how the severity of storms and
other extreme hydrologic events might change is
necessary.
 Increased and widespread hydrologic monitoring
systems are needed
 A regular data record should be given a careful
attention for future research by installing enough
equipment with continuous data collection in the
catchment.
 There should be a systematic reexamination of
engineering design criteria and operating rules
of existing dams and reservoirs under conditions
of climate change.