Kaoyai National Park , southeast of Saraburi and 200 km northeast of Bangkok, is a world of rich and diverse flora from evergreen and rainforest to rolling hills of tropical grasslands. The park has been established in 1962 as the first national park in Thailand. Its area of 2,172 square kilometers spreads across 4 provinces (Saraburi, Nakorn Rachasima, Nakornnayok, and Prachinburi) and a variety of ecological zones including marshlands, tropical forests, and the sandstone mountains that form the Dongrak Range. Kaoyai is regarded as one of the world’s leading parks and has been nominated by UNESCO as a World Heritage Site. It is also a gigantic natural reservoir that produce fresh water resources to the downhill inhabitants. It is the origin of regional major rivers and creeks(Huay) such as Huay Lamtakong, Huay Lampraploeng, Huay Lamprayatharn or Huay Yang, Hanuman River, Sai Yai River, Prachatakham River and Nakornnayok River.
The park is situated near the most westerly part of the Dongrak Mountain Range, with its highest peak, Kao Rom, rising to 1,351 meters. The highest region is located in the north and west of the park, but much of Kaoyai is sandstone plateau with elevations between 600 and 1,000 meters. The plateau slopes gently towards the south and east. By far the largest percentage of the park, from its foothills to altitudes of 1,000 meters, is covered by tropical broadleaved evergreen forest, much of it dense and interspersed with deciduous species. Between 1,000 and 1,500 meters is found submontane broadleaved evergreen. There are also small areas of lowland and submontane scrub.
One of Kaoyai’s great assets is cool, fresh air. Average temperatures range from 28’C in the hottest months of April and May, when daily temperatures may often rise to the mid-30’s. In the coolest months of December and January average temperatures are as low as 17’C but frequently drop much lower. Rainfall is heaviest between May and October during the southwest monsoon. The driest months are December and January, with rain averaging no more than 15 milimeters per month. At park headquarters, the annual rainfall has been measured at 2,270 milimeters, more than 84 percent of which falls during the monsoon, But rain in other areas of the park may average around 3,000 milimeters a year.