Modelling the impacts of land-used and climate change in Skudai river watershed

Predicting the impact of land-use, climate change and Best Management Practices (BMPs) on a watershed is imperative for effective management of aquatic ecosystems, floods, pollutant control and maintenance of water quality standard in a tropical climate. Based on the prediction, unique information can be derived that is critical to the watershed management under dynamic environmental conditions. The study seeks to evaluate how land-use and climate change influences the hydrology, sediments, and water quality of an urbanized tropical watershed in which the land-use is controlled by urban development as observed from historical and projected land covers. Therefore, the response of a tropica l watershed and its river system under climate and land-use changes were evaluated using Skudai River watershed as a case study. Seven land-use scenarios from the year 1989 to 2039 were developed using remote sensing teclmiques, and nine projected climate change scenarios were derived using dynamically downscaled model from the based projection under representative concentration pathways (RCPs) scenarios. These scenarios were integrated into the Hydrological Simulation Program FORTRAN (HSPF) model to determine the impact of land-use , climate change, and pollutants control via best management practices in a tropical watershed system. The model was calibrated and validated from 2002 to 2014, and the performance coefficients showed a good correlation between simulated and observed streamflow, water temperature, dissolved oxygen (DO), biochemical oxygen demand (BOD), ammonia nitrogen (NH3-N), nitrate nitrogen (N03-N), and orthophosphate (P04) concentrations. The output of the validated model under land-use changes showed that the hydrological water balance of the watershed changes with total runoff as the primary source of water loss. For streamflows and in-stream concentrations (NH3-N, N03-N, and P04) , as the streamflow increases, NH3-N and P04 concentrations increase while N03-N concentration showed low response as compared to the other two concentrations. As urban development increased from 18.2% to 49.2%, nutrient influx such as total nitrogen (TN) and total phosphorus (TP) loads increased from 3080 to 4560 kg/yr and from 130 to 270 kg/yr, respectively. Furthermore, TN to TP ratio changed from 8.3:1 to 7:1, an indication that the rivers are receiving excess nutrients flows which might result in eutrophication at the downstream of the watershed . The amount of sediment load produced in the watershed decreased by approximately 17.8% as a result of the changes in land-use derived from urban development. Further analysis ofthe results showed that climate change with high rainfall and increase in air temperature do not affect DO concentration and water temperature in comparison to climate change with low rainfall. Implementation of multiple detention pond BMPs in identified Critical Source Areas (CSAs) reduced pollutant loads by 14% to 27% as compared to watershed without any BMPS, independent ofclimate and landuse changes. Analysis ofBMPs using existing and future land-use is very important to ensure their effectiveness to control and maintain water quality. This study provides a basis to develop water resource management in an urban watershed and be resilient to land-use and climate changes