Predicted Climate Change until 2100 in Maputaland

5.3.1 Temperature

The following data (Table 5-1) are all obtained from the Climate Change Reference Atlas 2017 (SAWS 2017) for the area of the Maputaland Coastal Plain.

Table 5-1: Change of temperature (projection medians) in Maputaland with reference to 1976-2005 as base period.

Climate Change Scenario Period Temperature change

RCP 4.5 “The optimistic scenario” 2036-2065 + 1.5-2°C

2066-2095 + 1.5-2°C

RCP 8.5 “The business as usual scenario” 2036-2065 + 1.5-2°C

2066-2095 + 3-4°C

Both climate change scenarios indicate a slight reduction in seasonal fluctuations, due to a relative temperature increase of about 0.5°C between the cooler months, from June to November, and the hotter summer months, from December to May.

5.3.2 Precipitation

The following data (Table 5-2) are all obtained from the Climate Change Reference Atlas 2017 (SAWS 2017) for the area of the Maputaland Coastal Plain.

Table 5-2: Change of precipitation (projection medians) in Maputaland with reference to 1976-2005 as base period.

Climate Change Scenario Period Precipitation change

RCP 4.5 ”The optimistic scenario” 2036-2065 - 0-5%

2066-2095 - 0-5%

RCP 8.5 “The business as usual scenario” 2036-2065 - 0-5%

2066-2095 - 5-10%

The projections of the two climate change scenarios for the area of the Maputaland Coastal Plain display some differences regarding the development of seasonal precipitation fluctuations. The RCP4.5 model indicates for the period 2065-2095, slightly higher precipitations from December to February (+ ca. 0-5 mm) and from March to May (+ ca. 5-10 mm ). From June to August (- ca. 0-5 mm) and from September to November (- ca. 10-20 mm) precipitation levels could be expected to be slightly lower than they are at present. This implies a slight increase in seasonal variation, and slightly drier conditions overall. The RCP8.5 scenario indicates, for the period 2066-2095, slightly drier conditions from December to March and from June to August (- ca. 0-5 mm), followed by a considerable falling off in precipitation levels between September and November (- ca. 30-50 mm).

Thus, in the RCP8.5 scenario seasonal variation is expected to be more pronounced, while, overall, conditions are significantly drier.

5.3.3 Sea-level

According to the IPCC (2014), the sea-level rose 0.19 m between 1901 and 2010. Scenario RCP4.5 predicts a further rise of 0.26 m for the period 2046-2065 and 0.47 m for the period 2081-2100.

RCP8.5 predicts a further rise of 0.3 m for the period 2046-2065 and 0.63 m for the period 2081-2100 (IPCC 2014). Recent publications indicate that the IPCC (2014) has underestimated the effect of a possible disintegration of large fractions of the Antarctic ice shield (Le Bars et al. 2017; Wong et al.

2017). Wong et al. (2017 and Le Bars et al. (2017) predict sea-level rises, for the RCP8.5 scenario, of 150 cm and 184 cm respectively.

5.3.4 Consequences on the hydrological regime

Two important consequences of climate change will influence the hydrological conditions of the Maputaland Coastal Plain. The first is the projected change of the precipitation and evapotranspiration pattern, and the second is the predicted sea-level rise. These shifts will have opposite effects on the groundwater table (Figure 5-1). The effect of the sea-level rise, however, will diminish with increasing vertical and horizontal distance to the ocean.

The climate scenario projections show a small reduction in precipitation and an increase of temperature. Abtew & Melesse (2013) state: “Evapotranspiration increases with increasing temperature, increasing radiation, decreasing humidity, and increasing wind speed. Decreasing rainfall contributes to increasing evapotranspiration through increase in clear skies, increase in temperature, and lower humidity.” (Abtew & Melaesse (2013) in: Evaporation and Evapotranspiration – Measurements and Estimations; page 197).

This will have a negative effect on the shallow Maputaland aquifer, which is the main water source and the lifeline of the peatlands in Maputaland (Grundling A. 2014). The aquifer is recharged by the precipitation received by the area between the Indian Ocean Coast and the Lebombo Mountains, and so the decrease in rainfall, coupled with the increase in evapotranspiration in this zone will reduce the aquifer’s volume of water.

Figure 5-1: Schematic view of the Maputaland Coastal Plain (proportions exaggerated): shallow aquifer in blue and the expected effects of climate change on groundwater as grey arrows. Blue cross marks the zone where the effects outweigh each other.

According to the conclusions drawn in Chapter 2, the projected sea-level rise will also lead to a rise of the water table, inland. However, the sea-level rise will probably affect only the peatlands on the lowland part of the Maputaland Coastal Plain - for example around Kosi Bay, Lake Sibaya and Lake St. Lucia. As we have seen, peatlands in proximity to the ocean, such as the investigated Matitimani valley, are prone to increased peat accumulation, particularly when they contain peat swamp forest (wood peat exhibited the highest accumulation rates of all peat types). In contrast, due to their vertical distance from the sea-level, peatlands on the upper part of the Maputaland Coastal Plain, such as the Muzi Swamp, are not prone to benefit from a sea-level rise. The great uncertainty in the projections of the sea-level rise make it very to estimate precisely the degree to which the hydrological balance of the peatlands might be positively affected.

Peatlands farther away from the ocean, where the positive effect of sea-level rise peters out, will face stress by the reduction of the water volume in the shallow Maputaland aquifer. The expected effects on peatlands in different hydrogeomorphic wetland types are shown in Figure 5-2. Peatlands in interdune depressions and unchannelled valley-bottoms will probably be the ones most affected, as their water table corresponds directly to the groundwater table. As these water tables are naturally subject to strong seasonal and extra seasonal fluctuations (Grundling A. 2014, Gabriel et al.

2017), the impact of climate change and the resulting water deficit are difficult to estimate, but longer periods of topsoil dryness must be expected, and these could eventually lead to mineralisation.

Unchannelled valley-bottoms with peat swamp forest might be the worst affected, as they do not have the capability of peat surface oscillation to mitigate water table draw-downs. Furthermore,

they have a lower capillary rise as peat substrates originating from non-forest vegetation. Water discharge into seeps might also fall dry, exposing peatland surfaces to aerobic conditions and mineralisation. Peatlands in channelled valley-bottoms, with the characteristic that peatland water tables are lower than the surrounding groundwater table, seem less endangered than peatlands in other hydrogeomorphic settings. However, with a reduction in the water-table, a movement of the discharge zone might occur, shifting the point where the groundwater enters towards the central part of the peatland and allowing desiccation of the fringes.

Figure 5-2: Likely effects of water deficit on peatlands in different hydrogeomorphic wetland types