Thimphu - Geography and Climate

Geography and Climate

Thimphu is situated in the constricted, linear Wang Chuu valley. The river is also known as the Thimphu Chuu (Chuu meaning "river") and the Raidak River. While the surrounding hills are in an altitudinal range of 2,000–3,800 metres (6,600–12,500 ft) (warm temperate zone between 2,000–3,000 metres (6,600–9,800 ft) and cold temperate zone between 3,000–3,800 metres (9,800–12,500 ft)), the city itself has an altitude range varying between 2,248 metres (7,375 ft) and 2,648 metres (8,688 ft). It is these two variations in altitude and climate which determine the habitable zones and vegetation typology for the valley. The valley, however, is thinly forested and is spread out to the north and west. At the southern end of the city, the Lungten Zampa bridge connects the east and west banks of the Wang Chuu which flows through the heart of city.

The Thimphu Chuu or the Wang Chuu raises in the snow fields at an altitude of about 7,000 metres (23,000 ft). It has many tributaries that flow from the Himalayan peaks that largely dictate the topography of the Thimphu valley. The Thimphu valley, so formed, is delimited by a steep eastern ridge that rises from the riverbed and a valley formation with gradually sloping topography, extending from Dechencholing and Simtokha, on the western banks of the Thimphu Chuu. The north-south orientation of the hill ranges of the valley means that they are exposed to moist monsoon winds which engulf the inner Himalayas and its lower valleys. However, the windward and leeward sides of the hill ranges have different vegetation patterns depending on the varying rainfall incidence in the two sides. Thimphu valley lying in the leeward side of the mountains is comparatively dry and contains a different type of vegetation as compared to the windward side. Hence, the coniferous vegetation in the valley is attributed to this phenomenon. Punakha, the old capital of Bhutan, is on the windward side with broad-leaved trees dominating the topography.

The city experiences a southwest monsoon-influenced subtropical highland climate of a warm, temperate climate. The southwest monsoon rainfall occurs during mid-June to September. Lightning and thunder often precedes rainfall in the region with cumulonimbus clouds and light showers dominating the weather. Continuous rainfall for several days occurs resulting in landslides and blockage of roads. Streams and rivers swell up carrying huge amounts of debris from forests. Deep puddles, thick mud, and landslides along roads form barriers to transportation. Cold winds, low temperatures at night, and moderate temperatures during the day, cloudiness, light showers and snowfall mark winter weather in this zone. Fog causes poor visibility, which poses a threat to vehicular traffic in the city. As spring approaches, the landscape is marked by violent winds and relatively dry and clear skies.

Thimphu experiences a wet season, which runs from May through September and a dry season that covers the remainder of the year. Rainfall in the valley varies between 500 millimetres (20 in) and 1,000 millimetres (39 in) per year, the bulk of which is received during the monsoonal wet season. The average temperature recorded during winter varies between 5–15 °C (41–59 °F) while in summer the variation is between 15–30 °C (59–86 °F). The coldest average (minimum) temperature in January is −2.6 °C (27.3 °F) and the average highest temperature recorded during August is 25 °C (77 °F).