Integrated assessment of future water security: the case of Makassar, Indonesia

Abstract

In many urban areas, population growth and changes associated with climate change are likely to increase pressure on water resources. One such location is Makassar City, located in South Sulawesi, Indonesia, which is experiencing rapid growth, urban sprawling and an increase in freshwater demand but faces a possible reduction in water availability due to climate change. A study, as part of the CSIRO-AusAID Research for Development Alliance, combined climate change, hydrological and resource allocation modelling to examine water security and the resilience of planned infrastructure to climate change impacts. Rainfall and potential evapotranspiration from 5 different Global Circulation Models (GCMs) were statistically downscaled using the CSIRO Conformal Cubic Atmospheric Model, CCAM (McGregor and Dix, 2008). The downscaled rainfall and potential evapotranspiration were used in a hydrological model (SIMHYD) to estimate changes in streamflow for the two rivers which supply Makassar City. As shown in Figure 1 (right), although the CCAM projections show a reasonable variation for the projections of streamflow for both the Maros and Jennebarang catchments, all CCAM based projections of future streamflow agree on a reduction compared to historical records. The future predictions of streamflow indicate a reduction of mean annual streamflow in the order of 0-25 %, with reductions in the mean wet season flow of the same order when compared to the period 1980-1999. The reductions in streamflow for the dry season are projected to be between 5-35%. Figure 1. Predicted average daily runoff for the Puca gauge for the period 2020-2040 (left) and percent changes for mean annual, dry and wet season, number of days with flow below 2m 3 /s and 99 th flow percentile for the periods 2020-2040 (right) at the Puca (red symbols) and Patalikang gauges (blue symbols). The streamflow projections were combined with population projections, infrastructure development plans and water demand estimates to assess future scenarios of water supply capacity for the city, using the REsource ALlocation Model (REALM) software. Results indicate that under the assumed scenarios sufficient inflow for urban water allocation alone will be available during the wet season. However, during the dry season Makassar is likely to face supply problems not only due to reduction in streamflows, but mainly due to infrastructure constraints, population growth and competing water uses. The analysis suggests that the future water security in Makassar will depend on its ability to plan infrastructure and manage water demand despite of climate change. The information generated in this study has allowed key stakeholders to gain greater insight into the future water resource pressures and to re-assess adaptation options.