Basin Runoff Responses to Climate Change Using a Rainfall-Runoff Hydrological Model in Southeast Australia

Abstract

The effects of climate change have been observed in the Murrumbidgee River basin, which is one of the main river basins in the southeast region of Australia. The study area is the largest and most important agricultural production area within the Murray Darling Basin (MDB). It produces more than AUD 1.9 billion of agricultural products annually and accounts for about 46% of Australia’s total agricultural production. Since Australia’s economy largely depends on its natural resources, climate change adversely impacts the economy in various ways. According to the Intergovernmental Panel on Climate Change’s fifth assessment report (IPCC, AR5), the adaptive capacity and adaptation processes have increased in Australia. The country has implemented policies and management changes in both rural and urban water systems to adapt to future drought, unexpected floods, and other climatic changes. In this study, future catchment runoff has been estimated using the hydrological model, Simplified Hydrolog (SIMHYD), which is integrated with data from three different General Circulation Models (GCMs) and future emission scenarios. Two different representative concentration pathway (RCP) emission scenarios, RCP 4.5 and RCP 8.5, have been used to obtain downscaled future precipitation and evapotranspiration data for the period of 2016 to 2100. Modeling results from the two emission scenarios showed an anticipated warmer and drier climate for the Murrumbidgee River catchment. Runoff in the Murrumbidgee catchment is affected by various dams and weirs, which yields positive results in runoff even when the monthly rainfall trend decreases. The overall runoff simulation result indicated that the impact of climate change is short and intense. The result of the Simplified Hydrolog (SIMHYD) modeling tool used in this study under the RCP 4.5 scenario for the period 2016 to 2045 indicates a significant future impact from climate change on the volumes of runoff in the Murrumbidgee River catchment. For the same period, the climate change prediction showed a decrease in total annual rainfall within the range of 2% to 62%. This reduction in rainfall is projected to decrease river runoff in the upper catchments (e.g., Tharwa, and Yass) by 17% to 58% over the projected periods. However, the runoff trends in the lower sub-catchments (e.g., Borambola) have increased by 137% to 87% under RCP 4.5 and RCP 8.5, respectively. This increasing potential runoff trend in the lower Murrumbidgee catchments gives an indication to build irrigation dams for dry season irrigation management.

Modelling Floodplain Vegetation Response to Climate Change, Using the Soil and Water Assessment Tool (SWAT) Model Simulated LAI, Applying Different GCM’s Future Climate Data and MODIS LAI Data

“…We selected the Burrinjuck sub-catchment, which is part of the Upper Murrumbidgee River catchment in southeastern Australia (Figure 1), for this research. This area is located between 34.53 • S and 148.31 • E and −35.14 • S and −148.55 • E. The Burrinjuck Dam was built on the Murrumbidgee River in 1927 to improve agricultural irrigation in the southern part of New South Wales (NSW) [32]. The Murrumbidgee River begins its journey from Kosciuszko National Park with an altitude of 1500 m and flows around 316 km to enter the Burrinjuck Reservoir.…”

“…Australia is a continent where both arid and semi-arid characteristics can be found in its different regions. Water stress was prominent from 2001 to 2020 in the southeastern part of Australia, and future climate predictions show a decreasing rainfall pattern [32]. The floodplain vegetation response to changing climate is not linear, and it is very important to quantify the influence of various climate-induced factors on floodplain vegetation, considering the spatial and temporal heterogeneity of a given area [33,34].…”

“…This winter precipitation decline has impacted agricultural production by reducing river flow in the Murrumbidgee River, a key watercourse within the Murray-Darling Basin (MDB) (Figure 1) [38]. The summer precipitation trend in this area is highly variable, which makes it difficult to grasp the importance of trends over an extended period in the southeast Australian precipitation [32,38]. Research indicates that there is an anticipated shift in rainfall patterns within the MDB in the coming years, foreseeing a potential decrease in rainfall ranging from 15% to 20% in the Basin region [32].…”

“…is highly variable, which makes it difficult to grasp the importance of trends over an extended period in the southeast Australian precipitation [32,38]. Research indicates that there is an anticipated shift in rainfall patterns within the MDB in the coming years, foreseeing a potential decrease in rainfall ranging from 15% to 20% in the Basin region [32]. Precipitation trends rely on both climate dynamics and thermodynamic changes; thus, it is difficult to understand how anthropogenic forces will influence southeast Australian precipitation [39,40].…”

“…In previous climate studies, Global Climate Models (GCMs) were used to estimate future climate projections in the hydrological modeling [32]. The Coupled Model Intercomparison Project Phase 5 (CMIP5) offers a range of GCMs to address a range of climate-related challenges, which are not always feasible due to the limitation of resources [51].…”