# Appendix 1. Statewide maps of selected basin characteristics used to estimate unregulated, daily streamflows

By Lance J. Ostiguy, Peter K. Weiskel, and Stacey A. Archfield

**Figures**

Figure 1-1.   Location of rivers, streams, lakes, reservoirs and large wetlands in Massachusetts.

Figure 1-2.   Average annual precipitation, in inches, for Massachusetts. Average annual precipitation is computed over the period 1971-2000 using the Parameter-elevation Regressions on Independent Slopes (PRISM) model (Daly, 2002).

Figure 1-3.   Average maximum monthly temperature, in degrees Fahrenheit, for Massachusetts. Average maximum monthly temperature is computed over the period 1971-2000 using the Parameter-elevation Regressions on Independent Slopes (PRISM) model (Daly, 2002).

Figure 1-4.   Surficial Geology of Massachusetts (MassGIS, 1999).

**Introduction**

Maps in this appendix show statewide data layers of basin characteristics used as explanatory variables in regression equations developed to estimate unregulated, mean daily streamflow for six selected quantiles in Massachusetts. Sources of the characteristics are located in Armstrong and others (2008). The basin characteristics are listed in table 4 of the report.  

The Strahler stream order is shown on the map of the location of rivers, streams, lakes, reservoirs, and large wetlands in Massachusetts (fig. 1-1). The Strahler stream order is a method of stream ordering designed by Strahler (1952). Stream order only increases when tributaries to the next stream are of the same order. A first order tributary joining a second order tributary will not change a stream to a third order if the latter stream has already been assigned as second order. 

The map of average annual precipitation (fig. 1-2) shows spatially gridded, average-annual precipitation for the 1971-2000 period. At each climate station in the dataset, the monthly precipitation is determined for each of the months in the 1971-2000 period. The point information is then distributed to a spatial grid using the PRISM (Parameter-elevation Regressions on Independent Slopes Model) (Daly, 2002). PRISM integrates point measurements of precipitation, temperature, and other climatic factors, a Digital Elevation Model of the land surface, and an expert system that assigns gridded values of climate variables in accord with the effects of elevation (including rain shadows downwind of mountain ranges), coastal effects, and temperature inversions. PRISM grids are modeled on a monthly basis. The 1971-2000 average grid was obtained by obtaining 12 average-monthly precipitation grids for the 30-year time period, and then summing to obtain an average-annual precipitation grid for the time period.  

The map of average maximum monthly temperature (fig. 1-3) shows spatially gridded, average maximum-monthly temperature for the the 1971-2000 period. At each climate station in the dataset, the monthly-maximum temperature is determined for each of the months in the 1971-2000 period. The point information is then distributed to a spatial grid using the PRISM (Parameter-elevation Regressions on Independent Slopes) model (Daly, 2002). PRISM integrates point measurements of precipitation, temperature, and other climatic factors, a Digital Elevation Model of the land surface, and an expert system that assigns gridded values of climate variables in accord with the effects of elevation (including rain shadows downwind of mountain ranges), coastal effects, and temperature inversions. PRISM grids are modeled on a monthly basis. The 1971-2000 average grid was obtained by averaging the 360 monthly grids of maximum-monthly temperature covering the time period.

The surifical geology map of Massachusetts (fig. 1-4) shows the areas of sand and gravel deposits in Massachusetts (MassGIS, 2009).

# References Cited

Armstrong, D.S., Parker, G.W., and Richards, T.A., 2008, Characteristics and classification of least altered streamflows in Massachusetts: U.S. Geological Survey Scientific Investigations Report 2007–5291, 113 p., plus CD-ROM.

Daly, C., Gibson, W.P., Taylor, G.H., Johnson, G.L., Pasteris, P., 2002, A knowledge-based approach to the statistical mapping of climate. Climate Research, v. 22: p. 99-113. 

MassGIS, 1999, Surficial Geology of Massachusetts, accessed October 28, 2009 at http://www.mass.gov/mgis/sg.htm.

Strahler, A. N., 1952, Hypsometric (area altitude) analysis of erosional topology: Geological Society of America Bulletin, 63, p. 1117-1142. 

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