The impact of topography on heavy rainfall during two rain seasons was investigated in order to explain their mechanisms on rainfall distribution over Rwanda. Weather Research and Forecasting (WRF-ARW) model was used to study two historical cases of heavy rainfall which took place over Rwanda during two rain seasons, March to May (MAM) and September to December (SOND), from April 7 to 9, 2012 (for MAM) and from October 29 to 31, 2012 (during SOND). The control experiment was done with actual topography, whereas sensitivity experiment was carried out with topography reduced by half. Results show that rainfall distribution over Rwanda significantly changes when topography is reduced. The reduction in topography leads to a decrease in rainfall amounts in both MAM and SOND seasons, with varying magnitudes. This reveals the importance of orography in determining rainfall amounts and distribution over the region. The accumulated rainfall amount from WRF underestimate or overestimate rain gauge stations data by region and by season, but there is good agreement especially in altitude below 1490 m and above 1554 m during April and October respectively. The results may motivate modelling carters to further improve parameterization schemes in the mountainous regions.
KeywordsTopographySeasonal RainfallRwandaWRF Model
Sun, L., Semazzi, F. H. M., Giorgi, F. and Ogallo, L. (1999) Application of the NCAR Regional Climate Model to Eastern Africa: 1. Simulation of the Short Rains of 1988. Journal of Geophysical Research, 104, 6529-6548.
McSweeney, R., Cole, M., Semafara, J.N. and Washington, R. (2011) Rwanda’s Climate: Observations and Projections, Appendix E. Smith School of Enterprise (SSEE) and the Environment, University of Oxford, Oxford.
Gerald, H.R. (2005) Orographic Precipitation. Annual Review of Earth and Planetary Sciences, 33, 645-671. http://dx.doi.org/10.1146/annurev.earth.33.092203.122541
Thomas, K.F. and Gerhard, W.R. (2012) WRF Model Simulation of Two Alberta Flooding Events and the Impact of Topography. Journal of Hydrometeorology, 13, 695-708. http://dx.doi.org/10.1175/JHM-D-11-035.1
Smith, R.B. (1979) The Influence of Mountains on the Atmosphere. Advances in Geophysics, 21, 87-230.
Basist, A., Gerald, D.B. and Meentemeyer, V. (1993) Statistical Relationship between Topography and Precipitation Patterns. Journal of Climate, 7, 1305-1315. http://dx.doi.org/10.1175/1520-0442(1994)007 2.0.CO;2
Anyah, R.O. and Semazzi, F.H.M. (2004) Simulation of the Sensitivity of Lake Victoria Basin Climate to Lake Surface Temperatures. Theoretical and Applied Climatology, 79, 55-69.
Hayward, D. and Clarke, R.T. (1996) Relationship between Rainfall, Altitude and Distance from the Sea in the Freetown Peninsula, Sierra Leone. Hydrological Sciences Journal, 41, 377-384.
Stager, J.C., Reinthal, P.N. and Livingstone, D.A. (1986) A 25,000-Year History of Lake Victoria, East Africa, and Some Comments on Its Significance for the Evolution of Cichlid Fishes. Freshwater Biology, 16, 15-19. http://dx.doi.org/10.1111/j.1365-2427.1986.tb00944.x
King, D., Byamukama, B., Carey, C., Cole, M., Dyszynski, J., Blowfield, Eyre, M.N, Frame, D., Gupta, R., Heffernan, C., Hepburn, C., Inderwildi, O., New, M., Pearce, G., Pickett, J., Rajan, R. and Washington, R. (2011) National Strategy on Climate Change and Low Carbon Development for Rwanda. http://cdkn.org/wp-content/uploads/2010/12/FINAL-Baseline-Report-Rwanda-CCLCD-Strategy -super-low-res.pdf
Khalid, A.A. and Sharaf, A.A. (2013) Rainfall-Altitude Relationship in Saudi Arabia. Advances in Meteorology, 2013, Article ID: 363029.
Bonacina, L.C.W. (1945) Orographic Rainfall and Its Place in the Hydrology of the Globe. Quarterly Journal of the Royal Meteorological Society, 71, 41-45. http://dx.doi.org/10.1002/qj.49707130705
Jimenez, J.A. and Dudhia, J. (2013) On the Ability of the WRF Model to Reproduce the Surface Wind Direction over Complex Terrain. Journal of Applied Meteorology and Climatology, 52, 1610-1617. http://dx.doi.org/10.1175/JAMC-D-12-0266.1
Gamal, E.A., Mostafa, M. and Fathy, E.H. (2012) Heavy Rainfall Simulation over Sinai Peninsula Using the Weather Research and Forecasting Model. International Journal of Atmospheric Sciences, 2013, Article ID: 241050.
Skamarock, W.C. and Weisman, M.L. (2008) The Impact of Positive-Definite Moisture Transport on NWP Precipitation Forecasts. Monthly Weather Review, 137, 488-494. http://dx.doi.org/10.1175/2008MWR2583.1
Obasi, G.O.P. (2005) The Impacts of ENSO in Africa. In: Low, P.S., Ed., Climate Change and Africa, Cambridge University Press, Cambridge, 218-230.
Flaounas, E., Basin, S. and Janicot, S. (2010) Regional Climate Modeling of the 2006 West African Monsoon: Sensitivity to Convection and Planetary Boundary Layer Parameterization Using WRF. Climate Dynamics, 36, 1083-1105. http://dx.doi.org/10.1007/s00382-010-0785-3
Hession, S.L. and Moore, N. (2011) A Spatial Regression Analysis of the Influence of Topography on Monthly Rainfall in East Africa. International Journal of Climatology, 31, 1440-1456. http://dx.doi.org/10.1002/joc.2174
Teixeira, J.C., Carvalho, A.C., Luna, T. and Rocha, A. (2014) Sensitivity of the WRF Model to the Lower Boundary in an Extreme Precipitation Event—Madeira Island Case Study. Natural Hazards and Earth System Sciences Discussions, 1, 5603-5641. http://dx.doi.org/10.5194/nhessd-1-5603-2013
Mohan, M. and Sati, A.P. (2016) WRF Model Performance Analysis for a Suite of Simulation Design.
Megan, S.G. and Lackmann, G.M. (2010) Sensitivity of Simulated Tropical Cyclone Structure and Intensity to Horizontal Resolution. Monthly Weather Review, 138, 688-704. http://dx.doi.org/10.1175/2009MWR2976.1
National Centre for Atmospheric Research (NCAR) (2014) ARW Version 3 Modeling System’s User’s Guide. NCAR, Boulder.
Michalakes, J., Dudhia, J., Gill, D., Henderson, T., Klemp, J., Skamarock, W. and Wang, W. (2004) The Weather Research and Forecast Model: Software Architecture and Performance. Proceeding of the 11th ECMWF Workshop on the Use of High Performance Computing in Meteorology, Reading, 25-29 October 2004, 156-168.
Skamarock, W., Klemp, J., Dudhia, J., Gill, D. and Barker, D. (2008) A Description of the Advanced Research WRF version 3. NCAR Technical Note NCAR/TN-475+STR, 113 p.
Maussion, F., Scherer, D., Finkelnburg, R., Richters, J., Yang, W. and Yao, T. (2011) WRF Simulation of a Precipitation Event over the Tibetan Plateau, China—An Assessment Using Remote Sensing and Ground Observations. Hydrology and Earth System Sciences, 15, 1795-1817. http://dx.doi.org/10.5194/hess-15-1795-2011
Benjamin, P.C.J. and Pierre, C. (2011) Testing WRF Capability in Simulating the Atmospheric Water Cycle over Equatorial East Africa. Climate Dynamics, 37, 1357-1379. http://dx.doi.org/10.1007/s00382-011-1024-2
Jessica, E.T., Jason, E.S., Kevin, J.A. and Richard, S. (2013) Multidecadal Variability in East African Hydroclimate Controlled by the Indian Ocean. Nature, 493, 389-392. http://dx.doi.org/10.1038/nature11785
Anyamba, E.K. (1984) Some Aspects of the Origin of Rainfall in Deficiency in East Africa. Proceedings of the WMO Regional Scientific Conference on GATE, WAMEX and Tropical Meteorology, Dakar, 10-14 December 1984, 110-112.
Black, E., Slingo, J. and Sperber, K.R. (2003) An Observational Study of the Relationship between Excessively Strong Short Rains in Coastal East Africa and Indian Ocean SST. Monthly Weather Review, 131, 74-94. http://dx.doi.org/10.1175/1520-0493(2003)131 2.0.CO;2
Browning, K.A., Hill, F.F. and Pardoe, C.W. (1974) Structure and Mechanism of Precipitation and the Effect of Orography in a Wintertime Warm Sector. Quarterly Journal of the Royal Meteorological Society, 100, 309-330. http://dx.doi.org/10.1002/qj.49710042505
Johansson, B. and Chen, D. (2003) The Influence of Wind and Topography on Precipitation Distribution in Sweden: Statistical Analysis and Modeling. International Journal of Climatology, 23, 1523-1535. http://dx.doi.org/10.1002/joc.951
Anders, A.M., Roe, G.H., Hallet, B., Montgomery, D.R., Finnegan, N.J. and Putkonen, J. (2006) Spatial Patterns of Precipitation and Topography in the Himalaya. In: Willett, S.D., Hovius, N., Brandon, M. and Fisher, D.M., Eds., Tectonics, Climate, and Landscape Evolution: GSA Special Paper 398, Geological Society of America, Boulder, 39-53. http://dx.doi.org/10.1130/2006.2398(03)
Argent, R., Sun, X., Semazzi, F., Xie, L. and Liu, B. (2015) The Development of a Customization Framework for the WRF Model over the Lake Victoria Basin, Eastern Africa on Seasonal Timescales. Advances in Meteorology, 2015, Article ID: 653473. http://dx.doi.org/10.1155/2015/653473