15 July 2019

Denver Is Usually Nearly A Desert; Grand Junction Is In A Desert

Most sources define a desert as a place with an average of 10 inches of precipitation (250 mm) per year, although I've seen 11 inches and 12 inches (in print) also used as definitions.

Denver get an average of 14.30 inches of precipitation per year (although some measurements suggest that the average is a little higher), which is 4.3 inches more than a desert. Grand Junction, where I lived from 1996 to 1999, is a bona fide desert with an average of just 9.4 inches of precipitation per year (probably an overstatement as this average does not appear to include some recent very dry years).

It is also useful, however, to think about the range of precipitation that an area experiences, as the high and the low over a long period of time (the low was 7.48 inches and the high was 20.95 inches since I've lived in Denver) is important for purposes like planning things like landscaping choices, construction specifications, and urban planning considerations like storm sewer capacities. The range is also quite relevant in valuing water rights.

This year in Denver, however, will not be a dry one. We are already at 10.59 inches of precipitation though July 14, 2019, about 2.25 inches above the year to date norm.

Denver has had three years that are below the desert threshold since I've moved here, and five more within under twelve inches of precipitation.

2018: 8.48 
2017: 11.69
2016: 11.59
2015: 18.22
2014: 18.77
2013: 16.60
2012: 10.11
2011: 17.27
2010: 12.86
2009: 18.12
2008: 10.23
2007: 14.00
2006: 8.64
2005: 12.80
2004: 14.67
2003: 13.92
2002: 7.48
2001: 16.55
2000: 14.55
1999: 20.95
1998: 15.93
1997: 19.59
1996: 10.25
1995: 18.27

To some extent, precipitation in Denver is really tri-modal with modes corresponding roughly to years marked by El Niño and La Niña events, and year with neither, respectively, although temperature tracks El Niño and La Niña events more closely than precipitation does.

Since the winter of 1995-1996, eight winters have been El Niño winters (when the central to easter tropical pacific is warmer): 2015-2016 and 1997-1998 (strong), 2009-2010 (moderate), 2002-2003, 2006-2007, 2004-2005, 2014-2015, 2018-2019 (weak).

Seven winters have been La Niña winters (when the central to eastern tropical pacific is cooler): 2007-2008 (strong), 2010-2011, 1995-1996 (moderate), 2005-2006, 2008-2009, 2011-2012, 2018-2019 (weak).

And nine winters have been neither El Niño nor La Niña winters (when temperatures in the central to eastern tropical pacific are normal): 1996-1997, 1998-1999, 1999-2000, 2001-2002, 2003-2004, 2009-2010, 2012-2013, 2013-2014, 2016-2017.

No comments: