Assessing Human Impact on the Water Cycle in the Upper Wabash River Basin

A lack of water supplies can pose a serious threat to municipalities, industries, agriculture, and the environment. In order to make more resilient water allocations, it is helpful to quantify water resources. Water abstraction from aquifers, water diversions, and dams that regulate flow are some of the anthropogenic activities that directly affect the water cycle. The evaluation of water resources is complicated by such human alterations. In low-flow months, baseflow cannot be accurately evaluated without separating the impact of reservoir management, since the flow comes not only from groundwater but also slow releases from water management. Streamflow naturalization is required for determining the impact of environmental changes on streamflow trends and better predicting future water availability, so historical daily data were used to estimate daily naturalized streamflow for six sites in the Upper Wabash basin. Based on a comparison of observed and naturalized data for the same period (1968-2014), reservoir management has little impact on annual water levels. The influence of reservoir management is more pronounced seasonally and for the upstream stations. The naturalized mean monthly flow for March of the Salamonie River at Dora (upstream) is 24% higher than the observed mean monthly flow, while the naturalized mean monthly flow for September is 59% lower than the observed mean monthly flow. Long-term (63 to 91 years) unmanaged streamflow statistics for the Wabash River basin revealed statistically significant upward trends in flashiness, mean, flow peaks and low flows. On the other hand, many locations that have traditionally relied on surface water resources, are increasingly utilizing ground water during times of shortage. The increasing use of both surface and groundwater resources requires management tools that can represent these resources at regional scales. In this study, the Variable Infiltration Capacity (VIC) model was modified to account for groundwater storage and withdrawals, and it is referred to as VIC Groundwater (VICGW). In VICGW, aquifer storage is represented through the inclusion of an additional subsurface layer and a new groundwater flow pathway. With the representation of groundwater withdrawals, storage, and a groundwater flow pathway, the baseflow index (BFI) is better represented and increased by 2% in comparison to traditional VIC simulations and the average monthly streamflow is also increased by 23% for the months of August to October. Since water is not always available when and where it is needed, climate trends and changing use patterns require better quantification of future water allocations. To evaluate the impact of projected changes in supply and groundwater demand on watershed scale hydrology, groundwater withdrawals have been projected considering both socioeconomic and climatic factors. From 2020-2060, groundwater withdrawals have been projected for each county in Indiana. Using past trends and the regional growth and decay term, water use efficiency was modeled for different sectors. The projections include not only socioeconomic factors such as population, income, and irrigated land, but also climatic factors such as projected air temperature, precipitation, and evapotranspiration. Domestic and public, industrial and commercial, thermoelectric power, irrigation, livestock, and mining sectors all saw a decrease in water withdrawal per demand unit, while aquaculture was the only sector to see an increase in use. There has been an increase in withdrawals across the state of Indiana, while some counties have projected decreases. Without considering climate change, the projected withdrawals in 2060 will be 3464 million L/d, an increase of 12% over 2015. Climate change is predicted to increase water withdrawals by 20% under a lower representative concentration pathway (RCP 4.5) and 22% under the higher representative concentration pathways (RCP 8.5). Future water supply was projected with VICGW simulations utilizing statistically downscaled climate data. As a result of an increase in future demand, there was a slight reduction in simulated Base Flow Index. Mean annual runoff was estimated to increase by 43 mm annually for 2041-2060, relative to 2015, due to changing supply. Wetter conditions due to changes in climate resulted in an overall rise in the annual mean water table across most of the Upper Wabash basin. Due to changes in demand and supply, the seasonal maximum water table decline across all the grid cells was projected to be 117 cm and 197 cm, respectively. This study evaluates how future water supply and use will affect watershed hydrology and can provide a basis for policymakers and stakeholders to consider future adaptations