In response to increasing greenhouse gas (GHG) concentrations, air temperature over Uganda is projected to rise by 1.5 to 3.5 °C (very likely range) by 2080 relative to the year 1876, depending on the future GHG emissions scenario (Figure 2). Compared to pre-industrial levels, median climate model temperature increases over Uganda amount to approximately 1.4 °C in 2030, 1.7 °C in 2050 and 1.8 °C in 2080 under the low emissions scenario RCP2.6. Under the medium / high emissions scenario RCP6.0, median climate model temperature increases amount to 1.3 °C in 2030, 1.5 °C in 2050 and 2.3 °C in 2080.
Very hot days
In line with rising mean annual temperatures, the annual number of very hot days (days with daily maximum temperature above 35 °C) is projected to rise substantially and with high certainty over most parts of Uganda (Figure 3). Under the medium / high emissions scenario RCP6.0, the multi-model median, averaged over the whole country, projects 13 more very hot days per year in 2030 than in 2000, 26 more in 2050 and 39 more in 2080. In some parts, especially in northern Uganda, this amounts to about 150 days per year by 2080.
Future projections of precipitation are less certain than projections of temperature change due to high natural year-to-year variability (Figure 4). Out of the three climate models underlying this analysis, two models project an increase and one model projects no change under RCP6.0, while under RCP2.6, two models project no change and one model projects a decrease in mean annual precipitation over Uganda. Median model projections show no change under RCP2.6 and an increase of 67 mm under RCP6.0 until 2080.
Heavy precipitation events
In response to global warming, heavy precipitation events are expected to become more intense in many parts of the world due to the increased water vapour holding capacity of a warmer atmosphere. At the same time, the number of days with heavy precipitation events is expected to increase. This tendency can also be found in climate projections for Uganda. Under RCP6.0, median climate model projections show an increase in the number of days with heavy precipitation from 8 in the year 2000 to 10 in the year 2080. Under RCP2.6, the number of days with heavy precipitation is projected to not change (Figure 5).
Soil moisture is an important indicator for drought conditions. In addition to soil parameters and management, it depends on both precipitation and evapotranspiration and therefore also on temperature, as higher temperatures translate to higher potential evapotranspiration. Annual mean top 1-m soil moisture projections for Uganda hardly show any change under both RCPs by 2080 compared to the year 2000 (Figure 6). However, there is considerable modelling uncertainty as different hydrological models project different directions of change, which makes it difficult to identify a clear trend.
Potential evapotranspiration is the amount of water that would be evaporated and transpired if sufficient water was available at and below the land surface. Since warmer air can hold more water vapour, it is expected that global warming will increase potential evapotranspiration in most regions of the world. In line with this expectation, hydrological projections for Uganda indicate a stronger and more continuous rise of potential evapotranspiration under RCP6.0 than under RCP2.6 (Figure 7). Under RCP6.0, potential evapotranspiration is projected to increase by 1.6 % in 2030, 2.2 % in 2050 and 4.9 % in 2080 compared to year 2000 levels.
3 Changes are expressed relative to year 1876 temperature levels using the multi-model median temperature change from 1876 to 2000 as a proxy for the observed historical warming over that time period.