CLIMATE

The climate of TNP, like high altitude areas elsewhere in Lesotho, is characterized by extremes of temperature, precipitation and wind speed. As might be expected from the altitude of the park, temperatures are generally low, even in summer. Considerable variations occur with changes in altitude and aspect. North-facing slopes are generally warmer (and have different slope gradients) than south –facing slopes, which are generally cooler. This is as a result of differences in incoming radiation. Steep south-facing slopes are especially cold in winter because they receive little direct sun and are often shaded by surrounding mountains.

PRECIPITATION

Records maintained over a six year period at Tsehlanyane Transfer Tunnel by LHDA indicate a range of total annual precipitation between a low of 784.6 mm (1992) and a high of 1776.3 mm (1996), with a mean for six year period of 1 100.1 mm.

This measuring station was, however, at one of the lowest points in the park. No data are available for the mean for the park as a whole, but this is likely in the vicinity of 1 500 to 1 700 mm pa.

Similarly, there are no records of the incidence of precipitation from mist; this is likely to be a significant proportion of the total (possibly in the vicinity of 15-20%).

In dry years little snow occurs, but on average, six to eight snowfalls may be experienced. Snow may be expected in any month of the year, but the peak occurrence period is between May and November.

Lesotho falls in the summer rainfall belt of southern Africa. Approximately 80% of the precipitation of the park occurs in the summer, in the form of rain and mist, but occasional snowfalls may also be experienced, even in summer. Summer rains occur from September or October until the end of March. High-intensity thunderstorms are prevalent throughout the summer. The remaining 20% of the precipitation occur in winter (approximately May to July) in the form of rain, mist and snowfalls. The thunders storms referred to are usually associated with occurrences of high intensity lightning strikes. The Drakensberg-Maloti Mountains are known as one of the highest lightning-incidence areas of the subcontinent, and this is likely also to be true for the park.

TEMPERATURE AND WINDS

Temperature records taken for the same six year period at the Transfer Tunnel indicate annual mean minimum temperatures of between 4 and 5°C and mean maximum of between 18 and 20° C. Mean minimum temperatures in summer are in the vicinity of 32° while extreme minimum temperature in the winter are in the vicinity of -9° C.

Frosts may be experienced in any month of the year, but are most frequent in the months March to November.

Wind is a significant meteorological factor at any time of the year. In winter, especially following snowfalls, strong, cold westerly winds are a common occurrence. In spring, strong offshore hot dry winds (so-called “berg winds”) are also regularly experienced. They may reach wind speeds of up to 100 km/h., and cause high fire hazard conditions. These hot winds may blow from early August until early October. They usually occur ahead of cold frontal systems, which may or may not bring relief in the form of rain or snowfalls (Bainbridge et al 1991; Tyson et al., 1976).

IMPLICATION FOR MANAGEMENT

Snowfalls are significant from several points of view. They may be regarded as one of the most beneficial forms of precipitation for the maintenance of stream flow, because water is gradually released as the snow melts. Over relatively protracted periods, ranging from a day or two, to several weeks. This is in comparison to high intensity rainfalls, a high proportion of which either evaporates or is dispersed as surface run-off. Snowfalls may also cause access problems. Heavy snowfalls and the associated icing in sub-zero temperatures may make even surfaced roads impassable, or make access on foot may also be hindered to a greater or lesser extent. Snowfalls may also cause problems for a range of faunal species, either because of the associated low temperatures, or because of problems for a range of faunal species, either because of the associated low temperatures, or because of problem in gaining access to food.

The presence of snow is an obvious tourist attraction. High wind speed may be detrimental to visitor enjoyment and coupled with low temperatures have safely implications. High wind during the dry season increases the risk and intensity of wildfires and may disrupt controlled burning programs.