Na Hang Nature Reserve, Tat Ke Sector - Frontier-publications.co.uk

Na Hang Nature Reserve, Tat Ke Sector 1997
1.4 Climate and Hydrology
The climate of the Na Hang area is strongly seasonal, with cool, dry winters and
warm, wet summers. Mean climate data for a ten-year period is given by Cox (1994).
The Tat Ke sector is drained by many small streams, although most of these are
seasonal, drying out in the winter dry season. During the survey period in Tat Ke
(which coincided with the summer wet season), the levels of streams within the
reserve varied greatly with recent precipitation (see below). Around the margins of the
reserve, most streams flow directly into the Rivers Nang and Gam, sometimes as steep
waterfalls. In the central area, however, many streams (including the Khau Tinh
stream) disappear into swallow holes in the limestone. A few of the streams in the
sector are said to be permanent, flowing throughout the year, although in the winter
villagers find it difficult to maintain an adequate water supply. Many farmers maintain
small fish ponds amongst their rice paddies, although these too are usually only
seasonal.
During the period of the survey in Tat Ke, rainfall data was collected using a rain
gauge, and the water level of a stream close to the camp (Khau Tinh stream) was
measured. These data are shown in Figure 2, below.
Figure 2. Daily rainfall (mm) and depth of Khau Tinh stream (mm), July- September,
1996
80
70
60
50
40
30
20
10
0
200
150
100
50
0
-50
-100
* = total rainfall not collected
The graph, Figure 2, shows the very short time lag between precipitation and stream
flow. On most occasions, stream flow rapidly increased at the onset of rain. Although
the forest and the limestone geology of the area act as a buffer to some extent,
Frontier-Vietnam Environment Research Report 9 4