| Abstrakt: |
At the beginning of 2021, South Kalimantan suffered from an unusual flood that had never happened within the last five decades. The flood has inundated more than 99,000 houses and caused up to USD 91 million economic losses. Even though it caused significant financial losses and severe damages; however, the main cause of the flood is still unclear and debatable. Several government agencies provided different information related to the cause of the flood. In this preliminary study, to provide more understanding about this problem, we conduct a numerical experiment to assess the effect of land-use changes on floods. We use a well-developed rainfall-runoff inundation model that computes rainfall-runoff processes along with inundation simultaneously based on diffusion wave equations to simulate the 2021 South Kalimantan flood. The flood affects several river basins in the South Kalimantan region; however, we only focus on Martapura River Basin (MRB) due to the limitation of the data. Another reason we selected MRB as the study case is because a significant portion of economic losses was located in the cities within this basin, such as Banjarmasin and Banjarbaru. The primary input of the numerical model includes the Multi-Error-Removed Improved-Terrain Digital Elevation Model (MERIT-DEM) topographic data, the Global Satellite Mapping of Precipitation (GSMaP) gridded precipitation dataset, and the Moderate Resolution Imaging Spectroradiometer (MODIS) land use dataset. The gridded precipitation dataset was selected due to the limited availability of the gage rainfall dataset in the region. The simulation was conducted for 25 days, from January 1st to 25th, 2021. To ensure the quality of the model, simulated river water depth result was compared or calibrated with observational data, i.e., water height at the river from an automatic water level recorder (AWLR). The comparison result showed a reasonably good agreement with the observation dataset so that our model can be used to represent the natural flood process in MRB. The simulated inundation depth using the 2019 MODIS land use dataset ranged from 0.50 to 1.80 m, which corresponds with the observed data gathered by the Regional Disaster Management Agency (BNPB). We then compared the simulation results using the 2010 MODIS land use dataset. We found that the simulation results (inundation depth and river discharge) were not much different from those using the 2019 land use dataset. Therefore, we conclude that the flood may not be caused by land-use change. [ABSTRACT FROM AUTHOR] |
