Surface Water | Trends
Summary
Trends in streamflow continue to be dominated by increases over the last 30 water years, with 70% of all reporting stations experiencing increases in annual average streamflow, and 4 out of 110 stations (3.6%) experiencing statistically significant increasing trends (α = 0.10). This is, however, a decrease from WY 2022 when 90% of stations had increasing trends and 14% were statistically significant. Two years of drier conditions (WY 2023 and 2024) are affecting the 30-year trends in annual average streamflow, but only one station (near Michigan City) had a statistically significant decrease. Annual maximum flows were found to be decreasing for 74% of reporting stations, with statistically significant decreases at 8 of 110 stations. Annual minimum flows are increasing for 73% of stations, fifteen of which were statistically significant.
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Layers Present in Webmap
Rate of Change of Maximum Flow Rate [in/yr] – The rate of change of the annual maximum flow rate over the last 30 years based on the Theil-Sen trend slope estimator. The flow rates were normalized based on the drainage area of each station’s corresponding watershed. Statistically significant trends were defined based on a 10% significance level using the Mann-Kendall statistical test.
Rate of Change of Mean Flow Rate [in/yr] – The rate of change of the annual mean flow rate over the last 30 years based on the Theil-Sen trend slope estimator. The flow rates were normalized based on the drainage area of each station’s corresponding watershed. Statistically significant trends were defined based on a 10% significance level using the Mann-Kendall statistical test.
Rate of Change of Minimum Flow Rate [in/yr] – The rate of change of the annual minimum (7 day moving average minimum) flow rate over the last 30 years based on the Theil-Sen trend slope estimator. The flow rates were normalized based on the drainage area of each station’s corresponding watershed. Statistically significant trends were defined based on a 10% significance level using the Mann-Kendall statistical test.
Note: Discharge flow rates for trend analysis are normalized by the watershed area and presented as inches per unit area. This makes the trend magnitudes comparable between watersheds; however, those small magnitude trends can still represent substantial changes in annual water volume, especially in larger watersheds, such as along the Wabash River.