ABSTRACTThe objective of the present study was to analyse the impacts of climate change on streamflow in the Mae Klong basin in Thailand using improved daily gridded precipitation data of the ECHAM4/OPYC global climate model. Bias correction and spatial downscaling methods are frequently used to improve global climate model precipitation. For bias correction, gamma−gamma transformation and ratio methods were used to correct the frequency and quantity of raw global circulation model (GCM) precipitation data. Spatial disaggregation, based on a multiplicative random cascade, was applied to downscale coarse resolution climate projected precipitation spatially. A rainfall‐runoff model (Hydrologic Engineering Center Hydrologic Modelling System, HEC‐HMS) was used to simulate future streamflow scenarios for three 5 year windows: the 2025s, the 2050s and the 2095s. The downscaling model parameters (β and σ2) were estimated separately for each month using the Mandelbrot−Kahane−Peyrière function. Both methods have proved useful in improving the quality, compared to historical trends and rainfall variability, of raw GCM precipitation data by reducing bias. There will not be much impact on water resources and water availability due to climate change in the coming decades in the Mae Klong River. There is some chance that, in the future, the monsoons will start before their regular period. There is also a chance of an increase in streamflow in the dry period and a decrease of streamflow in the wet period in the basin.