Water balance, flow duration and frequency in a small experimental watershed in Kinabalu Park, Sabah

We examined the water balance and hydrological characteristics of tropical montane forests in Kinabalu Park. A small experimental watershed, named Mempening (KM), was established and continuous monitoring of rainfall and discharge was conducted from January 2006 to December 2007. Annual rainfall in 2006 and 2007 was 3,203 and 3,109 mm, respectively. Annual discharge at KM in 2006 and 2007 was 2,350.5 and 2,022.3 mm, respectively. Rainfall and flow duration curves in KM were compared with those observed in two other experimental watersheds in Sabah (Sapulut; SP and Ulu Kalumpang; UK.). The probability of daily rainfall greater than 1 mm in KM, SP and UK.was 83%, 73% and 68%, respectively. The probability of a daily discharge less than 1 mm in KM, SP and UK. was zero, 34% and 2.5%, respectively. In KM and UK, discharge did not cease during the year, whereas in SP the flow frequently ceased. The difference between daily discharge when the probability of occurrence exceeded 80% (D80) and 20% (D20) in KM, SP and UK. was 13.7, 5.6 and 2.2 mm, respectively; showing that the fluctuation of daily discharge was the smallest in UK. and the greatest in KM. This difference can be explained by the watershed bedrock geology, which is Tertiary Sedimentary Rock in KM and SPbutvolcanic ash in UK..