Water Usage and Water Availability Under Changing Land Use and Climate Within Toowoomba Region , Queensland Australia

Water Usage and Water Availability Under Changing Land Use and Climate Within Toowoomba Region , Queensland Australia

This study aimed to quantify the water usage of eight sectors of users in the Toowoomba Region and to identify the significant factors affecting their consumption. The sectors are residential, agriculture, livestock, mining, industrial, commercial, institutional, parks, and gardens. Land Change Modeler (LCM) in TerrSet was employed to analyze land use change and predict the future "business as usual" scenarios for 2038 and 2058. The data used in the analysis were land-use, socioeconomic, and geophysical data of 1999, 2010, and 2018. Land Change Modeler (LCM) in TerrSet was employed to analyze land use change and predict the future "business as usual" scenarios for 2038 and 2058. Future land use changes were simulated using the Multi-Layer Perceptron Neural Network and Markov chain model, considering various influencing factors, such as distance from roads and anthropogenic disturbances, elevation, slope, rainfall, and temperature. Using the land prediction output, the demand and water supply were simulated for years 2038 and 2058 using the Water Evaluation and Planning (WEAP) System to determine future unmet water demands of the different water user sectors, including the Environmental Flow as an additional sector. The area of each sector was expressed in hectares. Water usage of each sector used in WEAP was based on the 2018 Toowoomba Region’s land-use map. The water use coefficient of each sector per hectare was quantified to determine the current water consumption, which was subsequently inputted in WEAP as the demand side.

Agriculture, residential, commercial, and industrial sectors were the top four major water users in the Region with annual average water usage of 39 million kl, 5.3 million kl, 930 thousand kl, and 550 thousand kl, respectively. Mining with 76 thousand kl and electricity generation with 380 kl were the least at 7th and 8th place, respectively. Regression analysis showed that the different sectors have varying significant factors affecting water usage. For the residential sector, it was observed that surface water and annual access charge were the dominant factors with R2 = 79.5%. Surface water was the only dominant factor in the commercial sector with R2 = 83%. On the other hand, Agriculture, Livestock, and Mining were significantly influenced by Tier 1 and December temperature with R2 = 96.7%, access charge and annual rainfall with R2 = 86.7%, and Toowoomba population and December temperature with R2 = 89.6%, respectively. Moreover, the sole sector affected by Toowoomba bores was the institutional sector with R2 = 85.1%. In terms of parks-gardens and energy generation, these sectors were significantly affected by surface water supply and temperature with R2 = 93%, respectively.

Land use change projection showed an expansion of farmlands and mining area by 2038 and 2058, followed by a reduction in the area for livestock production for the base scenario (1999-2018). On the contrary, the first alternative scenario (1999-2010), which simulates the "Big Dry" period, showed a steady increase in the area for livestock production and a gradual decrease in mining area while farmlands may increase until 2058. Meanwhile, the second alternative scenario (2010-2018) predicted a general decline and/or stable expansion in farmland and mining areas until 2058. There was no difference in the water usage projection under land use and climate change scenarios. The overall comparison of the long-term annual average unmet water demands for 2038 and 2058 revealed no difference in values under normal years and very dry water years. Simulations of unmet water demand under climate trends 2038 and 2058 for very dry water years revealed that there would be a total water deficit of approximately 590 million cubic meters in both years. Conversely, in a very wet water year, there would be a total deficit of 462 million cubic meters and 525 million cubic meters in 2038 and 2058, respectively.

There were limited studies that have been conducted about the nexus between water consumption and land-use change under different climate scenarios. The implications of these studies, as mentioned, extend to addressing this significant issue by identifying the various sectors affecting water consumption. This study found that land use and its future changes are good factors to consider in managing the current and future water demands either in wet or dry climate conditions. This is especially important in a society, such as Toowoomba, because it is an example of a vastly growing regional city in Australia, where sustainable water management is one of its primary concerns. This study generated information and knowledge to help in addressing the region’s current and water consumption issues, with wider applications not only to other regions in the country but also worldwide.

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