Appendix 2: Hydrometeorology and Hydroclimatology of Baseflow Page 1 of 19
A time series of end of month soil moisture data was developed for each climate division in the United States from 1931 to present using a nonlinear water balance (Huang, van den Dool and Georgarakos 1996). This data is available from the National Centers for Environmental Prediction (NCEP). The components in this balance were precipitation, evaporation, runoff, and groundwater loss. dw () t P( t) E( t) R( t) G( t) dt Page 2 of 19 Where: W(t) is the soil water content at time t P(t) is the mean areal precipitation over area A And so on Runoff, or net streamflow divergence, is composed of two components, surface runoff and baseflow. m Wt () S( t) P( t) Wmax B( t) W ( t) 1 Where: W max is the soil s water holding capacity in mm m is a parameter with a value >1 (typically in the range of 2-4) α is the inverse of the response time of baseflow µ is the portion of subsurface flow that becomes baseflow Groundwater loss is also a function of these parameters, and evapotranspiration is estimated from the temperature, an estimate of radiation, and the W max Huang et al. calibrated this water balance to match observed runoff values by applying search optimization algorithms to the parameters until the model s estimates of hydrologic processes (runoff, baseflow, etc) showed the smallest deviation from real world, long term, and large scale data of these processes.
Figure 1 - Map of Climate Divisions with Maryland highlighted Page 3 of 19
This soil moisture data set was used to control for hydroclimatological variability when analyzing trends in streamflow. Page 4 of 19
Annual Inches of Baseflow Page 5 of 19 16 14 12 10 8 6 4 1935 1945 1955 1965 1975 1985 Calendar Year 1985 1975 1965 1955 1945 Seasonal Kendall Tau on Monthly Baseflow for Linganore Creek Frederick 5 5 5 1935 1935 1945 1955 1965 1975 Figure 2 - Baseflow Timeseries and Seasonal Kendall Tau Plot for Linganore Creek at Frederick, MD
Soil Moisture (mm) Page 6 of 19 Time Series of Climate Division Soil Moisture for CD 125 1935 1945 1955 1965 1975 1985 1985 1975 1965 1955 1945 Seasonal Kendall Tau on Monthly Soil Moisture for Climate Division 125 5 5 5 1935 1935 1945 1955 1965 1975 Figure 3 - Timeseries and Seasonal Kendall Tau for end of month soil moisture for Climate Division 125
Ending year Page 7 of 19 A comparison of the Kendall Tau plots for monthly baseflow and end of month soil moisture values suggests that the trends seen in baseflow for Linganore Creek are explained almost entirely by climatological variation for Climate Division 125. Diff. Of SKT Z score(monthly BF) - SKT Z score(monthly SM) for LinganoreFrederick and CD125 1985 1975 Z 1.6 1.4 1.2 1965 1 1955 1945 Positive Difference Negative Difference 0.8 0.6 1935 Figure 4 - "Difference Surface" comparing the difference in Z scores (computed from the probability of trend for each sub-period) between Linganore Creek's Monthly Baseflow and Climate Division 125's end of month soil moisture
Ending year Page 8 of 19 Diff. Of SKT Z score(monthly BF) - SKT Z score(monthly SM) for LinganoreFrederick and CD125 1985 1975 Z 1.5 1 1965 1955 1945 0.5 0-0.5 1935 Beginning year -1 Figure 5 Shows the same Difference Surface as Figure 4, but with the same symbol and Z scores being represented by the color gradient
Page 9 of 19 Additional Figures below for the Soil Moisture and associated trends of the other climate divisions used in this research: Monthly Soil Moisture for CD: 120 Seasonal Kendall Tau on Monthly Soil Moisture for CD 120 5 5 5
Page 10 of 19 Monthly Soil Moisture for CD: 121 Seasonal Kendall Tau on Monthly Soil Moisture for CD 121 5 5 5
Page 11 of 19 Monthly Soil Moisture for CD: 122 Seasonal Kendall Tau on Monthly Soil Moisture for CD 122 5 5 5
Page 12 of 19 Monthly Soil Moisture for CD: 123 Seasonal Kendall Tau on Monthly Soil Moisture for CD 123 5 5 5
Page 13 of 19 Monthly Soil Moisture for CD: 124 Seasonal Kendall Tau on Monthly Soil Moisture for CD 124 5 5 5
Page 14 of 19 Monthly Soil Moisture for CD: 125 Seasonal Kendall Tau on Monthly Soil Moisture for CD 125 5 5 5
Page 15 of 19 Monthly Soil Moisture for CD: 126 Seasonal Kendall Tau on Monthly Soil Moisture for CD 126 5 5 5
Page 16 of 19 Monthly Soil Moisture for CD: 127 Seasonal Kendall Tau on Monthly Soil Moisture for CD 127 5 5 5
Page 17 of 19 Monthly Soil Moisture for CD: 255 Seasonal Kendall Tau on Monthly Soil Moisture for CD 255 5 5 5
Page 18 of 19 Monthly Soil Moisture for CD: 307 Seasonal Kendall Tau on Monthly Soil Moisture for CD 307 5 5 5
Page 19 of 19 Huang, J., H. M. van den Dool & K. P. Georgarakos (1996) Analysis of Model-Calculated Soil Moisture over the United States (1931-1993) and Applications to Long-Range Temperature Forecasts. Journal of Climate, 9, 1350-1362.