Impact of land use and land cover on the local Climate of Lake Victoria Basin

In the past centuries humans have modified the land use and land cover through different activities, such as urbanization. Although urbanization makes up a small percentage of the total land cover, the accelerated conversion of vegetated land to paved impervious land cover can have profound consequences on the socio-economic livelihoods of people and the ecosystem. Africa is expected to have a surge in urban expansion, with an estimated growth of approximately 590%. The shores of Lake Victoria are among the regions that are expected to have a high growth in urban extent. We hypothesize that the rapid urbanization over Lake Victoria shores will have an impact on the local and regional climate, altering the surface energy balance, temperature and precipitation.

Simulations were conducted with the current land cover and the projected 2030 urbanization levels utilizing the Weather and Research Forecasting model (WRFV3.7 ). Both the control and sensitivity simulations were done with three nested domains. The outer domain which has a resolution of 36 km is over East Africa and parts of the Indian and Atlantic Oceans, the 12 km resolution domain is over East Africa and some parts of Congo, while the 4km domain is over the Lake Victoria Basin. Evaluation for the control simulation was conducted using the Tropical Rainfall Measuring Mission (TRMM) and the following statistics were calculated: root mean square error, mean bias, correlation and standard deviation. Evaluation of the control simulations show that the model has skill with only small biases in temperature and precipitation.

Sensitivity simulations show that increasing the urban fraction over the northern part of the basin modifies physical parameters such as albedo, moisture and surface energy fluxes, aerodynamic roughness and surface emissivity, thereby altering the precipitation and temperature over the region. The change in the physical parameters increases temperature over the urbanized region in all of the domains. The increased temperature over the urbanized region alters the land-lake breeze circulation system and leads to a change in intensity, distribution, and frequency of precipitation. More specifically the results show pronounced increase in rainfall over the north-western crescent of Lake Victoria Basin coinciding with the region of largest urbanization growth. The relative differences between the sensitivity and control simulations are not statistical significantly impacted by domain resolution.