Title of paper

3.1 Historical climate trends for Namibia

3.1.1 Temperature

There is a clear trend in historic climate data that Namibia is getting warmer, particularly in the latter half of the 20th century.

a	b

Figure 2: Surface monthly air temperature (C) measurements 1901-2000: a) southern Namibia (16-20E, 28-24S); b) northern Namibia (16-20E, 22-18S). Source: Climate Research Unit (Mitchell et al. 2004 in DRFN, 2008).
Figure 2 indicates monthly surface air temperature observed over southern (figure 2a) and northern (figure 2b) Namibia. In both cases there is a clear trend for warmer temperature in the latter half of the 20th century, which is generally 1-1.2⁰C warmer than at the beginning of the century. It is notable that this warming is greater than the global mean temperature change, as noted by (Midgley et al. 2005 in DRFN, 2008), and an increase of 1⁰C.
There is also an indication that, similar to the global record, there was a peak in temperature during the 1940s, which cooled to a minimum in the mid 1970s. Global cooling during this period is mostly attributable to increases in volcanic and sulphate aerosols, after which the impact of anthropogenic emissions dominate the global temperature signal (IPCC, 2007 in DRFN, 2008). This is evident in figure 2 as a rapid increase in temperature between 1975 and 2000, more so in the north of the country. Superposed on the positive temperature trends are decadal-scale fluctuations that suggest climate variability acting at these timescales.
Besides these general trends in temperature an analysis of 7 stations with more than 25 years of recent data (obtained from Meteorological Services of Namibia) indicated that there have been consistent increases in daily maximum temperatures across all stations, with both positive and negative changes in daily minimum temperatures (DRFN, 2008). Approximately 30% of the trends are significant at the 90% level or higher, most notably in the maximum values of daily maximum temperature suggesting that the most consistent change is that the hottest temperatures have been getting hotter (DRFN, 2008).

3.1.2 Rainfall

Figure 3 shows how rainfall has varied between 1901 and 2000 in both southern (figure 3a) and northern (figure 3b) Namibia.

a)	b)

Figure 3: Monthly mean rainfall (mm month-1) measurements 1901-2000: a) southern Namibia (16-20E, 28-24S); b) northern Namibia (16-20E, 22-18S). Source: Climate Research Unit (Mitchell et al. 2004 in DRFN, 2008).

Detecting trends in rainfall is more difficult than detecting trends in temperature, especially in highly variable arid climates such as Namibia (DRFN, 2008). This is mainly because a single extreme rainfall event can contribute a significant proportion of the annual rainfall in some regions. Unlike the temperature record (figure 2) there are no obvious trends during the 100-year period. High levels of rainfall (low temperatures) were observed during the 1970s changing to low rainfall (high temperatures) during the later period. Figure 4 indicates the average monthly rainfall distribution between 1901 and 2000, demonstrating that most of the country is dry (less than 20mm of rainfall) between May and September, with the onset of rainfall in the north typically occurring in November, spreading southward through December and peaking in February. During March and April, average rainfall retreats northward.

Figure 4: Monthly mean rainfall distribution (mm month-1) 1901-2000.

Source: Climate Research Unit (Mitchell et al. 2004 in DRFN, 2008).

There are no obvious trends in rainfall (amount) but there is an indication of change in rainfall season. Analysis of trends at seven² weather stations (since 1960) indicated that there have been statistically significant (at the 90% level) increases in the length of the dry season (defined as the maximum number of days with < 1 mm of rain) and decreases in the number of consecutive wet days (with >= 1 mm of rain) at Lüderitz, Sitrusdal and Hosea Kutako. Additionally there have been statistically significant increases in measures of rainfall intensity at Windhoek.

Overall, it appears as if the northern and central regions of Namibia are experiencing a later onset and earlier cessation of rains, resulting in shorter seasons in most vicinities (DRFN, 2008).

3.2 Future projections for Namibia

Future projections in climate change were projected for Namibia in 2008 by the Desert Research Foundation Namibia through the Vulnerabilty and Adapation Assessment. The projects looked at both historic trends as well as the future, i.e. for the period 2046 to 2065.

3.2.1 Temperature

Figure 5 indicates the minimum, mean and maximum expected change in surface temperature for the 2046-2065 period for both the summer (figure 5 a) and winter (figure 5 b) periods. Changes are a minimum towards the coast and increase further inland during all seasons, with minimum expected increases during summer of 1⁰C - 2⁰C and maximum changes of 2⁰C - 3.5⁰C. Maximum projected increases in temperature are slightly higher during winter (2.5⁰C - 4⁰C) whereas the minimum projected increases are similar to those during summer (DRFN, 2008).

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b)
Figure 5: Minimum (left), mean (middle) and maximum (right) projected change in a) January-March and b) July-September mean surface air temperature (C) from 13 GCMs. Source: DRFN, 2008
It should be noted that downscaling using Regional Climate Models (a higher resolution version of a General Circulation Model) may reduce these estimates of temperature change by a few 10ths of a degree partly because they better resolve complex topography.

It is predicted with a high degree of certainty that Namibia will become hotter throughout the year (DRFN, 2008)

3.2.2 Rainfall

As far as predictions for the future are concerned, it is not obvious whether rainfall will be reduced but there is high likelihood that intensity will increase (DRFN, 2008). Furthermore, the study by the Desert Research Foundation in 2008 indicated that an increase in late summer rainfall over major parts of the country, and a decrease in winter rainfall in the south and west of the country is to be expected. Increases in rainfall are most obvious during the January to April period, especially in the central and north-eastern regions.

It is important to underscore that variability, and stronger variability at that, is likely to remain the key aspect of Namibia’s climate in the future (DRFN, 2008).