Exploring the impact of climate and land use changes on streamflow trends in a monsoon catchment

Flooding appears to be increasing in Kelantan, Malaysia, in terms of frequency as well as magnitude. This is likely to be due to changes in precipitation, but may also be contributed to by land use change. The Mann-Kendall non-parametric method was used to test for trends in streamflow and precipitation at the 90% significance level. Several significant trends in streamflow were found for the upstream (River Galas) and downstream (River Kelantan) sub-catchments for all variables (annual, seasonal and monthly time-series). In particular, streamflow increased in all seasons in the upstream sub-catchment, but increased in the wet season and decreased in the dry season downstream. Several trends were also observed for precipitation. Precipitation trends were increasing in the wet season and decreasing in the dry season for both upstream and downstream sub-catchments. Analysis of land use change revealed that most changes occurred through conversion of forest to agricultural land (i.e. rubber and oil palm), predominantly in the upstream sub-catchment. The analysis suggests a clear association between streamflow change and precipitation change, but also reveals that land use change may be an important contributing factor, particularly in the upstream sub-catchment. Copyright (c) 2010 Royal Meteorological Society