CLIMATE-The Bat Dai Son Mountain area

CLIMATE

The climate of the studied area has distinct wet and dry seasons, following the typical seasonality of northern Vietnam and SE China. The most significant rainfall originates from the summer monsoons coming from the SW from May to September and is characterized by frequent torrential rainfall. The winter NE monsoon coming from the Gulf of Tonkin in the period from October until April. In the studied area, this monsoon brings cold dry air and infrequent light rain, accounting usually for less than 5–10% of the annual rainfall.

The climate pattern within the Bat Dai Son Mountain area is classified as a monsoon tropical climate with cold winter and summer rains (Nguyen Khanh Van et al. 2000). Very humid, hot summers with torrential rains and dry winters are typical of the area (Fig. 5, 6).

The minimal night temperatures at elevation 800–900 m a.s.l. in studied area decline during December and January, reaching as low as 5–8°C and the hottest time are March – May when the temperatures can reach an average of 30–35°C (Fig. 5). The annual precipitation here is 1100 mm in a year with a maximum in June, July, and August (Fig. 5). At higher elevations and within specific orogenetic microclimates the mean annual rainfall may rise considerably and average temperatures can be essentially lower. Cool foggy and misty weather all around the year is very typical of in studied area at elevations 1000 m a.s.l. and higher. Meanwhile, a strongly seasonal climate with dry, almost rainless period from November until April identifies specific vegetation of habitats particularly on rocky limestone at low elevations.

The climate observed in lowlands particularly associated with Song Lo and Song Mien Rivers valleys at elevations 100–400 m a.s.l. is warmer. Common summer temperatures here 35–38°C, with winter temperatures normally between 15–20°C. Night temperature during the coldest winter nights is usually higher than 10C° (Fig. 6). The lowlands around Ha Giang Town in Song Lo Valley is one of the dampest places in the area with a total

rain of 2860 mm in a year, in which Bac Quang District stands out from the rest with 4000 mm/year. Drizzle and mist occur quite often, especially in the early morning. Another noticeable feature of Ha Giang weather including Quan Ba District is high humidity at 85% on average (Lotusia, 2020).

Soure: Averyanov L.V., K.S. Nguyen, T.H. Tran, A.L. Averyanova, T.V. Maisak, H.T. Nguyen. – Plant diversity, flora and vegetation of Bat Dai Son Mountain area, northern Vietnam –– Saint-Petersburg, STRATA, 2020 — 561 p