In response to increasing greenhouse gas (GHG) concentrations, air temperature over Tanzania is projected to rise (Figure 2). Compared to pre-industrial levels, median climate model temperature increases over Tanzania amount to approximately 1.4 °C in 2030, 1.7 °C in 2050 and 1.6 °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 1.4 °C in 2030, 1.7 °C in 2050 and 2.5 °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, in particular over eastern Tanzania (Figure 3). Under the medium / high emissions scenario RCP6.0, the multi-model median, averaged over the whole country, projects 6 more very hot days per year in 2030 than in 2000, 11 more in 2050 and 22 more in 2080. In some parts, especially in eastern Tanzania, this amounts to about 100 days per year by 2080.
Sea level rise
In response to globally increasing temperatures, the sea level off the coast of Tanzania is projected to rise (Figure 4). Until 2050, similar sea levels are projected under both emissions scenarios. Under RCP6.0 and compared to year 2000 levels, the median climate model projects a sea level rise by 11 cm in 2030, 21 cm in 2050 and 41 cm in 2080. This threatens Tanzania’s coastal communities and may cause saline intrusion in coastal waterways and groundwater reservoirs, rendering water unusable for domestic use and harming biodiversity.
Future projections of precipitation are less certain than projections of temperature change due to high natural year-to-year variability (Figure 5). Out of the three climate models underlying this analysis, none of the models projects a clear trend in mean annual precipitation over Tanzania under RCP6.0. Under RCP2.6, two models project a decrease, while for one model, the trend remains unclear. Median model projections for RCP2.6 show a decrease in precipitation by 42 mm until 2080, while median model projections for RCP6.0 show almost no change in precipitation by 2080 compared to year 2000.
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 is also found in climate projections for Tanzania (Figure 6), with climate models projecting a slight increase in the number of days with heavy precipitation, from 8 days per year in 2000 to 9 days per year in 2080 under RCP6.0. Under RCP2.6, the number of days with heavy precipitation does not change.
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 into higher potential evapotranspiration. Annual mean top 1-m soil moisture projections for Tanzania show a decrease of 4 % under both RCP2.6 and RCP6.0 by 2080 compared to the year 2000 (Figure 7). However, looking at the different models underlying this analysis, there is large year-to-year variability and modelling uncertainty, 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 Tanzania indicate a stronger and more continuous rise of potential evapotranspiration under RCP6.0 than under RCP2.6 (Figure 8). Under RCP6.0, potential evapotranspiration is projected to increase by 2.7 % in 2030, 3.8 % in 2050 and 7.1 % 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.