1 Hydrological and climatic data availability and preliminary analysis in Rwanda O. Munyanezaa,b,1, S. Uhlenbrookb,c, S. Maskeyb , U. G. Walia and J. Wenningerb a National University of Rwanda, Department of Civil Engineering, P.O. Box 117, Butare, Rwanda b UNESCO-IHE Institute for Water Education, P.O. Box 3015, 2601 DA Delft, The Netherlands c Delft University of Technology, Department of Water Resources, P.O. Box 5048, 2600 GA Delft, The Netherlands ABSTRACT Proper planning for sustainable development of water resources requires the use of long term meteorological and hydrological data. The main aim of this study is to review the hydro-climatic data availability and to analyze the hydro-climatic variability in Rwanda. This study also presents the assessment of spatial and temporal variability of hydro-climatic data in Rwanda primarily based on pre-1994 period data. Data were collected from many stakeholders in the field of water and environment in Rwanda, such as MINIRENA, MININFRA, ELECTROGAZ, NBDF and NUR-WREM Project. Stream flow data, mainly daily water level measurements, were obtained from 39 gauging stations. Daily rainfall data were obtained from 136 gauges, whereas other climatic variables (temperature, relative humidity, solar radiation, evaporation, sunshine duration, wind speed and direction) were collected from 13 stations. The lengths of these data sets vary significantly, most of them begin in the 1930s and end in early 1994 as a result of the Rwanda Genocide. There are only 11 meteorological stations and 22 hydrological stations that are operating around the whole country after 1994, of which most have resumed operation only recently. Moreover, there are significant amounts of missing data in these data series. The assessment of the data availability shows the severity of the problem currently faced in the country in planning, management and research activities in the water resources sector. Large variability within a year and between the years has been observed for the daily rainfall and stream flows. The average monthly rainfall in Rwandan catchments from 1970 to 1993 is 101 mm/month, with the mean maximum monthly rainfall of 203.8 mm in April and mean minimum of 10.5 mm in July. The hydrograph peaks occur in April and May, roughly one month in lag of precipitation. The minimum flows occur in the months of July and August, summer season. Keywords: Hydrological and climatic data, Rwanda, spatial variability, temporal variability Introduction The world population has tripled in the twentieth century, while, over the same period, water use has increased sixfold. Currently, about 1 billion people live in water-scarce or water-stressed regions, and by 2025 this number is expected to increase by a factor 3.5 (Wagener et al., 2008). The magnitude of this water scarcity and its variations in both space and time are largely unknown because of lack of hydro-climatological data (Oyebande, 2001; Kipkemboi, 2005). Though the needs for hydrological and meteorological information are increasing, there is a decline in technical and human capacities by the reduction in number of hydrological and 1 Corresponding author. Address: National University of Rwanda (NUR), Department of Civil Engineering, P.O. Box 117, Butare, Rwanda. E-mail address: o.munyaneza@unesco-ihe.org ; munyoma2000@yahoo.fr (Omar Munyaneza) 2 meteorological stations in Africa during the last 30 years (Bonifacio and Grimes, 1998). This decline was also observed in Rwanda where only 136 meteorological stations are operational in 1994 out of the 147 existing stations in 1960 to 1990 (Dushimire, 2007). This decline continued during and after the 1994 genocide and at present, only 11 meteorological stations are functioning in the whole country (NWRMP, 2008). The main objective of this work was to presents an overview of the spatial and temporal variability of temperature, precipitation and stream flow data availability in Rwanda. Description of the study area This study was carried out in Rwanda. Rwanda is a small, mountainous country with relatively high rainfall, and is situated in Central Africa, bordered by Burundi in the South, the Democratic Republic of Congo in the West, Uganda in the North and Tanzania in the East. The total area of Rwanda is about 26 338 km2 out off which about 24,948 km2 is land and 1,390 km2 is covered by water (5.3%). In 2007 the population of Rwanda was estimated to be 9.3 million (NISR, 2008). This gives an estimated population density of about 342 persons/km2, the highest in Africa (NELSAP, 2006). The mean annual rainfall in Rwanda is about 1120 mm and varies from 700 mm in the NorthWest to about 1600 mm/year in the South-West. The mean altitude is 1250 m above sea level with a general slope oriented from west to east (FAO, 2005). The altitude increases progressively from the south-eastern plateau to the north and west where it gets the highest altitudes in the “Congo-Nile Crest” with elevations varying between 2200 m and 3000 m and the chain of volcanoes with the highest point of 4507 m at the Karisimbi volcano (NELSAP, 2006). Rwanda has a moderate climate with an annual average temperature of 190 C. It is divided into three agro-climatic zones: i) high-altitude region, ii) central plateau, and iii) plateau of eastern lowlands and the west (FAO, 2005). The country has an annual cycle of four seasons that are distributed as follows: a short rainy season, locally known as “Umuhindo” runs from September to November, with November characterized by heavy precipitation; a short dry season, locally known as “Urugaryi” runs from December to February; a long rainy season, locally known as “Itumba” runs from March to May, this bringing about 14 to 61% of the total annual precipitation; a long dry season, locally known as “Icyi” runs from June to August. Figure 1 shows the location of Rwanda within the Nile Basin and the distribution hydrological network in the country. 3 Figure 1 The hydrologic networks of Rwanda and the spatial distribution of meteorological stations and River gauging stations Rwanda is head water of the two of the main African Basins: Congo Basin and Nile Basin. Roughly 80 percent of the country is located within the Nile Basin, while the remaining portion forms part of the Congo Basin (MINAGRI, 2000). Two main Rivers, Nyabarongo and Akanyaru and their numerous tributaries, make up the Akagera River which drains most of the Rwandan waters to the Lake Victoria and then the River Nile. Methodology This study presents the baseline information of the spatial and temporal variability of temperature, precipitation and stream flow in Rwanda. Data used in this study were provided by the Ministry of Natural Resources (MINIRENA) and Rwanda Meteorological Office. Some additional data were obtained from other institutions like MININFRA, ELECTROGAZ, REMA, NBDF and NUR-WREM Project. The period of available data records is given in Table 1 for some selected stations, within the period of data availability the data set exhibit some significant discontinuity. In many cases the missing values ranges from several some months to several years. Because of that, a manual screening method was used to select as set of dataset with reasonably long period of time series with minimum missing values, which is presented in Table 1. The locations of these selected stations are presented in Fig. 2. Table 1: Selected stations used for hydro-climatic analysis Station Parameter No Station name Period of data availability Alt. Time series 4 Rainfall Temperature Stream flow 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Rulindo Murehe Kigali Airport Rubilizi Rushashi Nyakibanda Gakoma Butare airport Kansi ENT Kansi Parish Save ETI Cyanika Kaduha Kibeho Kitabi Mbazi Mweya Nyange Muramba Parish Muramba Cyabingo Rwankeri Nemba Remera-Ruhondo Rwesero Gisenyi Airport Kamembe Airport 27 1 2 3 Byimana Kigali Airport Butare Airport Ruhengeri Airport 4 Station No 1 5 Gikongoro River/Former Province Kagitumba/Umutara Ururumanza/Gitara ma Rusumo/Ruhengeri Nyabugogo 3/Kigali Rural Nyabugogo 1/Kigali City 6 Mwogo 1/Butare 2 3 4 1970-1993 1975-1993 1970- 2008 1970-1975; 1978-1993 1979-1993 1970-1993 1971-Jan 1994 1970-1993 1977-Feb 1994 1970-Feb 1994 1974-Feb 1994 1970-1993 1970-Jan 1994 1970-1973; 1975; 1978-1993 1974-Jan 1994 1977-Feb 1994 1977-1993 1970-Feb 1994 1970-1973; 1975-Jan 1994 1970-1973; 1976-1993 1970-1993 1971-1993 1975-1993 1970-Jan 1994 1975-Feb 1994 1971-March 1994; 1998-1999 1970-1989; 1991-1993; 19961999 1971-2000 1971-1993 1977-1992 1990-1993; 1997-1999; Sept 2000 24 years 19 years 39 years 22 years 15 years 24 years 23 years 24 years 20 years 24 years 20 years 24 years 24 years 21 years 20 years 17 years 17 years 24 years 23 years 22 years 24 years 23 years 19 years 24 years 19 years 25 years 1800 1575 1495 1400 1620 1750 1500 1768 1650 1670 1750 1950 1900 1894 1900 1700 1700 1600 1950 2200 2250 1675 1850 1475 1554 1591 28 years 30 years 23 years 16 years 1830 1495 1768 1878 7 years 1900 Alt. Period of data availability 1970-1971; 1973-1988 Time series 18 years 1284 1970-1990 1971-1989; 1990; 1999 21 years 20 years 1450 2045 1970-1988; 1995-2000 25 years 1971-1982; 1984-1988; 19951997; 2000 19 years 1970; 1972-1982; 1984-1989; 1995-2000 24 years 1439 1380 1525 5 13 14 Mukungwa 1/Gisenyi Akanyaru 1/Butare Akavuguto/Gikongo ro Nyabarongo 5/Ruhengeri Nyabarongo 4/Gitarama Nyabarongo 3/Kibungo Nyabarongo 2/Kigali City Akagera/Kibungo 15 16 Sebeya 2/Gisenyi Migina/Butare 7 8 9 10 11 12 1971-1985; 1987-1988; 19952000 23 years 1971-1991; 1995-2000 27 years 1400 1406 1971-1993; 1995-2000 29 years 1970; 1974-1984; 1986-1989; 1995-2000 26 years 1700 1971-1990; 1995-1996; 1998 23 years 1475 1971-1990; 1995-2000 26 years 1337 1970-1990; 1995-2000 1970-1990; 1995-1996 1972-1990; 1992; 1995-1997; 1999-2000 1970-1990 27 years 23 years 1352 1325 25 years 21 years 1775 1547 Figure 2 Spatial distributions of selected climate stations and River gauging station Preliminary results of hydrological and climatic data analysis Spatial and temporal variability of daily hydro-climatic data Figure 3 shows daily total rainfall and daily mean stream flows for the year 1985 from several gauging stations. Similarly, Figs 4 and 5 show mean daily temperature for several stations and mean yearly rainfall averaged from selected stations, respectively. 1400 6 The daily rainfall and stream flows show large variability within a year and between the years, as exemplified by Figures 3 and 5. There rainfall and stream flow data are continuous and complete for the year 1985. Because of that, 1985 data were selected for demonstration in this paper. A consistent decrease in summer runoff (June to August) in the upstream was observed on Sebeya River located upstream of the Congo Basin and Ururumanza River for Nile basin (see Figure 3). Butare Airport 12 /1 /8 5 11 /1 /8 5 10 /1 /8 5 9/ 1/ 85 8/ 1/ 85 7/ 1/ 85 6/ 1/ 85 5/ 1/ 85 4/ 1/ 85 3/ 1/ 85 2/ 1/ 85 65 60 55 50 45 40 35 30 25 20 15 10 5 0 1/ 1/ 85 Total daily rainfall (mm/day) Kigali Airport Date Ururumanza Mukungwa 1 Akanyaru 1 Nyabarongo 3 5 /1 /8 5 12 /1 /8 5 11 /1 /8 10 1/ 85 9/ 1/ 85 8/ 1/ 85 7/ 1/ 85 6/ 1/ 85 5/ 1/ 85 4/ 1/ 85 3/ 2/ 1/ 1/ 85 360 330 300 270 240 210 180 150 120 90 60 30 0 1/ 85 Mean dailly discharge (m 3 s-1) Sebeya River Date Figure 3 Intra-annual variability of daily precipitation and mean daily stream flows data in Rwanda primarily based on the pre-1994 period, illustrated for the data of the water year 1985 Akagera 7 Figure 3 shows that there are two rainy periods in Rwanda (March to May and October to December) and two dry periods (June to September and January) in a year. Inter-annual variability of temperature covering the period of 1970-1993 is shown in Figure 4. Butare Airport Ruhengeri Airport Gikongoro 22 21 20 19 18 17 16 15 19 70 19 71 19 72 19 73 19 74 19 75 19 76 19 77 19 78 19 79 19 80 19 81 19 82 19 83 19 84 19 85 19 86 19 87 19 88 19 89 19 90 19 91 19 92 19 93 Mean daily Temperature ( o C/day) Kigali Airport Time (year) Figure 4 Inter-annual variability of temperature, based on selected stations of Rwandan catchments (Kigali, Butare, Ruhengeri and Gikongoro); data covers 1970-1993 Figure 4 shows the record of daily mean temperature data for 1970-1993 with mean yearly temperature of 18.60C. For the selected time series data records, mean maximum daily temperature occurred in 1987 (20.90C, 19.20C and 17.40C at Kigali Airport, Butare Airport and Ruhengeri stations, respectively). The mean minimum daily temperature occurred in 1984 (16.60C at Ruhengeri station). The mean minimum daily temperature in the whole time series at Kigali airport station is 19.4 0C and occurred in 1971. Ruhengeri station present lower temperature values compare to Kigali airport station due to the topography of these two different catchments. The altitude of Kigali airport station is 1495 m whereas the altitude for Ruhengeri station is 1878 m (see Table 1). The impact of topography on temperature variation was also found by Mul et al. in 2008. 8 Total annual Rainfall (mm/yr) 1450 1350 1250 1150 1050 950 850 750 3 19 2 35 19 38 19 41 19 44 19 47 19 50 19 53 19 56 19 59 19 6 19 2 65 19 68 19 71 19 74 19 77 19 80 19 83 19 86 19 89 19 9 19 2 95 19 98 20 01 20 04 20 07 19 16 19 19 19 19 19 10 13 650 Time (year) Figure 5 Inter-annual variability of rainfall, based on selected stations in all Rwandan catchments; the first meteorological station was installed in 1910 at Save, southern Province of Rwanda, currently 11 meteorological stations are operating in the whole country, years time series records (1910–2008) with cut-off periods of 1920 to 1930 and 1994 Figure 5 shows that the maximum annual rainfall in Rwandan catchments from 1910 to 2008 is 1450 mm/a in 1951 and minimum is 677 mm/a in 1919. The years of 1995, 1996 and 2001 presented drought period in Rwanda. During these drought years, remarkable decrease in water level was also observed in some lakes like Bulera and Ruhondo located in the northern of Rwanda (MINITERE, 2005). Spatial and temporal variability of monthly hydro-climatic data Intra-annual variability of total monthly rainfall and mean monthly temperature from selected climate stations, illustrated for the data of 1970–1993, is presented in Fig. 6. Kigali Airport Butare Rirport Byimana Kansi Parish Rulindo Rushashi Nyakibanda Total Monthly Rainfall (mm/month) 250.0 225.0 200.0 175.0 150.0 125.0 100.0 75.0 50.0 25.0 0.0 Jan Feb Mar Apr May Jun Jul Time (month) Aug Sept Oct Nov Dec 9 Kigali Airport Butare airport Gikongoro Ruhengeri Mean Monthly Temperature ( o C) 21.5 21.0 20.5 20.0 19.5 19.0 18.5 18.0 17.5 17.0 16.5 16.0 Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec Time (month) Figure 6 Intra-annual variability of total monthly rainfall and mean monthly temperature, illustrated for the data of 1970–1993 Mean monthly Discharge (m 3 s-1) Figure 6 shows the summer rainfall (June-July-August) and winter rainfall (March-April-May) across the whole country. The average monthly rainfall in Rwandan catchments from 1970 to 1993 is 101 mm/month, with the mean maximum monthly rainfall of 203.8 mm in April and mean minimum of 10.5 mm in July. The rains are mainly concentrated between November and April. Intra-annual variability of mean monthly stream flows for selected stations in 1985 is shown in Fig. 7. Sebeya Ururumanza Nyabugogo 3 Mwogo 1 Mukungwa 1 Akanyaru 1 Nyabarongo 3 Akagera Aug Oct 11000 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 Jan Feb Mar Apr May Jun Jul Sept Nov Month of 1985 Figure 7 Intra-annual variability of mean monthly stream flows for selected stations in 1985 The hydrograph peaks occur in April and May, roughly one month in lag of precipitation. The minimum flows occur in the months of July and August. Dec 10 Conclusions Hydrological and climatic data availability in Rwanda has been reviewed and analyzed. Hydroclimatic data in Rwanda are scarce in time and space with around one station per 30km x 30km, and many data gaps (duration often more than one year) within the record 1910-2008 were detected. The data in Rwanda is not all compiled in data bases. Some data sets can be found as hard copy and others can be found with private persons according to the research they were doing for their personal interests. Large variability within a year and between the years has been observed for the daily rainfall and stream flows. A consistent decrease in summer runoff (June to August) in the upstream of Rwandan catchments was observed and the hydrograph peaks occur in April and May. In order to address some of these problems, the data reconstruction and the build up of an updated complete Rwanda data base are needed. It is strongly recommended that more of these hydro-climatic stations are urgently rehabilitated and new installed in different catchments of Rwanda. Acknowledgements This study was supported by a grant from the National University of Rwanda (NUR) through NUR-Sida-Research Commission. A Nuffic/NPT Fellowship provided support to facilitate the research. 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