8 DESCRIPTION OF THE BASELINE ENVIRONMENT 8.1 Introduction A description of the Koeberg biophysical and socio-economic baseline environment is provided hereunder. The description of the baseline environment incorporates all aspects of the proposed development including the laydown areas and the actual site for the proposed PBMR DPP. 8.2 Biophysical Environment (a) Climate The following information was obtained from the meteorological study undertaken by SHE Cape Environmental. This study in included in Appendix Q. Koeberg is situated along the western coast of the South Western Cape. This area is in the Climate Region of Southern Africa that is generally classified as Mediterranean Climate. The main feature of this Climatic Region is that the bulk of the rainfall occurs in winter. It is located between the mid-latitudes and the sub-tropics and is influenced by the quasi-stationary Atlantic anticyclone from which cells migrate eastwards south of the country during the summer months (October - March). This results in steep pressure gradients along the West Coast with a strong southerly airflow, which can typically reach speeds of 100 km/h. These months are characteristically warm to hot and dry. During the winter months, May to September, the westerly belt displaces the Atlantic anticyclone northwards and the area falls under the influence of the westerly frontal weather. The bulk of the annual rainfall recorded occurs during this time. The mountains to the east of this Climatic Region are occasionally snow capped but the snow layer never persists throughout winter. During weak pressure gradients cold dense air descends from the mountains causing a weak north easterly flow in the mornings. This occurs in pre-frontal conditions before the north westerly frontal pressure gradients intensify. Thunderstorms do occur but are limited to the occasional West Coast trough or a strong frontal system. A meteorological factor, which is often disregarded, is the microclimatology of the Koeberg area and specifically the occurrences of land and sea breezes. These occur in the transitional periods between the sub-tropical high and the mid-latitude low. The warm to hot offshore flow is replaced by a cooler onshore flow. The depth of the cooler flow varies. This results in wind shear and the formation of a stable layer. Table 8-1 contains the long term averages and extremes for rainfall, temperature and wind measured at Koeberg Meteorological station from 1980 until 2006. The extreme per parameter is in bold typeset. (b) Rainfall The Mediterranean Climate district, in which Koeberg is situated, has a very low seasonal rainfall variability of below 20%. The pronounced maximum rainfall occurs ESKOM PBMR DPP EIA 8-1 Version 1.0 / October 2009 Environmental Impact Report in winter. The long term average yearly rainfall (27 years) equals 373 mm for the area, with the highest monthly rainfall being July with 65.8 mm and the lowest being February with just 7.9 mm. Table 8-1: Long term averages and extremes for rainfall, temperature and wind measured at Koeberg Meteorological Station Koeberg Meteorological Station Long-Term Averages and Extremes @ 10m agl. - Average period = 1980 to 2006 Temperatures (°C) Rainfall (mm) Wind Month Max. Max Extreme Extreme Avg. Year Year Avg. Highest Year Lowest Year Dir. Gust Gust Year Max. Min. m/s km/hr January 19.5 38.1 2004 10.5 1982 10.3 67.6 1981 0.0 1999 NNW 30.2 108.7 1986 February 19.8 38.0 2005 9.0 1980 7.9 42.0 1996 0.0 2000 NNW 28.8 103.7 1987 March 18.6 36.6 2004 9.0 1989 12.9 51.0 1989 0.0 2001 NNW 32.0 115.2 1987 April 16.8 35.5 1998 5.5 1995 33.5 105.4 1990 2.8 2000 S 37.1 133.6 1987 May 15.1 33.6 1986 5.7 1995 47.3 98.2 1987 1.3 2004 WSW 38.3 137.9 1987 June 13.5 31.4 1985 4.1 1988 64.0 157.4 1994 25.8 1984 E 35.9 129.2 1986 July 13.0 29.0 1980 2.8 1995 65.8 162.4 2001 22.8 2005 WSW 30.6 110.2 2000 August 13.3 32.0 1985 2.2 1981 53.4 134.4 1987 13.8 1991 WSW 31.5 113.4 1985 September 14.3 38.2 2005 2.3 1989 33.3 75.0 1984 2.5 1993 WSW 30.6 110.2 1991 October 15.8 37.2 1985 5.4 1990 19.4 114.8 2004 0.6 1993 NNW 27.2 97.9 1986 November 17.3 36.3 1988 6.3 1998 12.1 52.4 1980 0.4 2003 SSE 27.8 100.1 1991 December 18.8 37.4 2002 9.6 1988 12.9 32.8 1984 0.3 2005 ESE 36.9 132.8 2002 The maximum rainfall occurs in July and the highest rain-day frequency is also observed in July. The winter rains occur mostly out of Cumulus and Nimbostratus cloud formations during the winter months as pre- and post frontal precipitation. During summer, unstable and hot conditions can result in thunder activity which is rare, less than 5 times per year, causing thundershowers out of Cumulonimbus cloud formations. Coastal lows passing the Cape from west to east, sometimes causes drizzle and light rain out of low cloud. ESKOM PBMR DPP EIA 8-2 Version 1.0 / October 2009 Environmental Impact Report Koeberg Weather Station - Monthly Rainfall 1980 - 2006 180 160 140 120 100 80 60 Rainfall(mm) 40 20 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average 10.3 7.9 12.9 33.5 47.2 64.1 65.9 53.4 33.3 19.3 12.1 12.9 Max Rain 67.6 42.0 48.4 107.8 98.2 157.4 162.4 134.4 75.0 114.8 52.4 32.8 Min Rain 0.0 0.0 0.0 2.8 1.3 12.0 22.8 12.8 2.5 0.6 0.4 0.3 Figure 8-1: Monthly rainfall figures from Koeberg Weather Station (c) Temperature Figure 8-2 shows a typical Mediterranean Climate temperature graph with warm summers and cool winters. The reason for the mildness is the close proximity of the Atlantic Ocean. The cold Benguella Current off the coast at Koeberg has a moderating effect on the diurnal temperature. The coldest temperature measured at Koeberg is 2.2°C while the hottest has been 38.2°C. In winter, during times of weak pressure gradients, there is a temperature inversion present in the morning. Inversions also take place when cooler maritime air replaces warm air during onshore flow synoptic conditions. AVERAGE MONTHLY TEMPERATURE (1980-2005) VS 2006 22 20 18 16 14 DegreesCelsius 12 10 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1980 - 2005 19.5 19.7 18.6 16.8 15.1 13.5 13.0 13.3 14.2 15.8 17.2 18.8 2006 20.0 20.4 18.4 16.8 14.4 14.4 12.8 13.0 15.3 15.9 18.1 18.1 Figure 8-2: Average monthly temperature figures from Koeberg Weather Station ESKOM PBMR DPP EIA 8-3 Version 1.0 / October 2009 Environmental Impact Report (d) Wind In the summer months of October to March the prevailing winds are from the south to south east, while in the winter months of May to August the prevailing wind is from the north east to north west. During April and September, transitional months, the frequencies of the 2 prevailing wind directions are about equal. Refer to Figure 8-3 for the quarterly wind roses. During summer, when the winds from the southerly sector prevail, a high percentage (approximately 30%) of the velocities are in the range from 25-50 km/hr. Winds are frequently strong and can attain gale force (>70km/hr) at times especially in the afternoons. Velocities exceeding 100 km/hr have been recorded. A change in weather from sunny, usually associated with southerly winds, to cloudy cooler conditions with northerly to north westerly winds is frequently associated with the passage of a coastal low pressure system. Once the low pressure system has passed, the onshore north westerly flow increases in strength dependant on the intensity of the cold front. A strong cold front with its active depression passing over or close to the area results in stormy turbulent conditions. During these times wind velocities exceeding 125 km/hr have been recorded. Once the cold front has passed, the wind backs to the south west bringing in cold, moist and unstable conditions. Occasionally “Bergwinds” or moderate north easterly winds affect the area. These occur mainly during autumn, winter and spring. These winds are offshore and flow from the interior. As it flows towards the coast it is warmed adiabatically resulting in warm to hot weather at Koeberg. Figure 8-4 shows very clearly the strongest winds in summer are the south east to south south easterly winds while in winter the weak offshore and the strong north westerly winds predominate. ESKOM PBMR DPP EIA 8-4 Version 1.0 / October 2009 Environmental Impact Report Average Wind Rose - January 1980-2006 KOEBERG N 20 NNW NNE NW 15 NE 10 WNW ENE >12 m/s 5 8-12 m/s W 0 E 4-8 m/s 0-4 m/s WSW ESE SW SE SSW SSE S Radial scale = 0 to 20% in 5% intervals.