Water year
The examples and perspective in this article may not represent a worldwide view of the subject. (September 2016) |
A water year (also called hydrological year, discharge year or flow year) is a term commonly used in hydrology to describe a time period of 12 months for which precipitation totals are measured. Its beginning differs from the calendar year because part of the precipitation that falls in late autumn and winter accumulates as snow and does not drain until the following spring or summer's snowmelt. The goal is to ensure that as much as possible of the surface runoff during the water year is attributable to the precipitation during the same water year.[1]
Due to meteorological and geographical factors, the definition of the water years varies. The
One way to identify a water-year is to find the successive 12-month period that most consistently, year after year, gives the highest correlation between precipitation and streamflow and negligible changes in storage (i.e., soil water and snow).[4] Usually, the time when the variation of storage from year to year is the smallest is the time with the minimum storage level and minimum flow. However, the practical considerations also affect the water year definitions. For example, in Canada the water year starts in October, apparently to coincide with the US one, although better measurement conditions exist in winter.[5]
To accommodate the regional and climatic variations, some researchers use a per-
Classification
Water year types (or indices
- Standardized Precipitation Index (SPI) was proposed by McKee et al. in 1993;[11]
- Reclamation Drought Index;
- deciles.
Many practically used indices were created
All indices by nature reflect the historic values and therefore cannot capture the variations in climate that are known to cause the distribution of water year types to be non-stationary in time.[15]
Uses
Examples of how water year is used:
- Used to compare precipitation from one water year to another.
- Used to define a period of examination for hydrologic modelingpurposes.
- Used in reports by the United States Geological Survey (USGS) as a term that deals with surface-water supply.[2]
- The end of the water year is used by the CoCoRaHSproject as an opportunity for observers to audit and verify data for their site.
See also
References
- ^ a b Johnstone & Cross 1949, p. 103.
- ^ a b United States Geological Survey, "Explanations for the National Water Conditions", http://water.usgs.gov/nwc/explain_data.html, Retrieved 16 October 2011.
- ^ "The hydrological year". Water UK. 31 October 2012.
- ^ Likens, G. E. (2013). Biogeochemistry of a forested ecosystem. Springer Science & Business Media.
- ^ Duncan 1955, pp. 110–111.
- S2CID 225359722.
- ^ a b c Null & Viers 2013, p. 1137.
- ^ a b WEAP 2015, p. 78.
- ^ W. C. Palmer, “Meteorological Drought,” Research Paper No. 45. US Department of Commerce Weather Bureau, Washington DC, 1965.
- ^ Alley 1984, p. 1100.
- ^ McKee, T.B., Doesken, N.J. and Kleist, J. (1993) The Relationship of Drought Frequency and Duration to Time Scales. 8th Conference on Applied Climatology, Anaheim, 17–22 January 1993, 179-184.
- CAWR. Retrieved 7 August 2022.
- ^ Viers 2011, p. 658.
- S2CID 128988784.
- ^ Null & Viers 2013, pp. 1137–1138.
Sources
- Null, Sarah E.; Viers, Joshua H. (February 2013). "In bad waters: Water year classification in nonstationary climates". Water Resources Research. 49 (2): 1137–1148. ISSN 0043-1397.
- WEAP (2015). WEAP User Guide (PDF). Somerville, MA: Stockholm Environment Institute, U.S. Center.
- Alley, W. M. (1984). "The Palmer Drought Severity Index: Limitations and Assumptions". Journal of Applied Meteorology and Climatology. 23 (7): 1100–1109. .
- Viers, Joshua H. (30 March 2011). "Hydropower Relicensing and Climate Change" (PDF). JAWRA Journal of the American Water Resources Association. 47 (4): 655–661. S2CID 3065925.
- Duncan, Craig (1955). The Saskatchewan river basin, Canada: a geographical appraisal of the water resources (PhD). Ohio State University.
- Johnstone, Don; Cross, William Perry (1949). "The Water Year". Elements of Applied Hydrology. Ronald Press Company. pp. 102–103. OCLC 1150788749.