Lam Sieo Yai basin is located at the heart of the Isaan plateau in
Northeastern Thailand (Fig. 1) with an elevation that ranges between
100 and 200 m above sea level. It overlaps with three
different provinces (Mahasarakam, Roi Et, Sisaket), and 7 districts
of Northeastern Thailand, which are among the poorest of Thailand.
Its area is 2875 km2. The Sieo Yai River is the main river of Lam Sieo
Yai basin. It joins the Mun river, then ultimately flows into the
Mekong River. The area is exposed to a tropical savanna climate. Its
average annual temperature is 18 C. As shown in Tables 1 and 2,
the area is exposed to two contrasted seasons: the dry season between
November and April, which commonly includes severe
drought conditions, and the monsoon-affected wet season between
May and October, which features floods on occasions. Also, the
period between December and February is significantly cooler.
Annual rainfall amounts to approximately 900 mm on average yet
with high inter-annual variability.