Integrated assessment of the climate and landuse change impact on hydrology and water quality in the Songkhram River Basin, Thailand.

The livelihoods of people in the Songkhram River Basin (SRB) rely heavily on river water, especially those involved in the fisheries. Extensive landuse changes in SRB have raised concerns regarding its impacts in water quality in addition to the looming climate change effects. More importantly there is lack of detailed studies on landuse and climate change impact on river water quality for the sustainable water management. Therefore, this study aimed at quantifying the individual and integrated impact of climate and landuse change in streamflows and nitrate nitrogen loadings in the Songkhram River. Future streamflow was simulated using Soil and Water Assessment Tool (SWAT) whereas future climate projections were derived from three Regional Climate Models (RCMs) under two Representative Concentration Pathways (RCPs). A dynamic, spatially explicit, land use change model (Dyna-CLUE) was used to generate two future land use change scenarios namely economic and conservation scenarios. The results show that in future climate change is to be responsible for a 19.5 and 24% decrease in streamflow and 11.25 and 15.25% decrease in nitrate nitrogen loading as projected under RCP 4.5 and 8.5 scenarios, respectively. Whereas landuse change is found to be responsible for a 5.30 and 6.35% increase in streamflow and an 11 and 11.60% decrease in nitrate nitrogen loading under economic and conservation scenarios, respectively in future. Thus, in conjunction, these two agents are seen to play against each other, creating a net effect of decreased future streamflow (16% on average); whereas, in the case of nitrate nitrogen loading, the two work in tandem, leading to an amplified reduction (24.50% on average). Although landuse change is found to be the less afflicting agent, its role should not be overlooked-it may very well further exacerbate the situation if there is a greater unfavourable climatic variation than projected.