Analysis of Short Term Precipitation in Norway 1967-2010
Total Page:16
File Type:pdf, Size:1020Kb
no. 15/2011 Climate ANALYSIS OF SHORT TERM PRECIPITATION IN NORWAY 1967-2010 Jostein Mamen, Rasmus Benestad and Jan Erik Haugen Photo: Einar Egeland . Contents 1 Introduction 4 1.1 Observation of short term precipitation in Norway . 4 1.2 Types of stations . 4 1.2.1 Tipping bucket rain gauge stations . 4 1.2.2 Weight pluviometer stations . 4 2 Rainfall rate statistics from tipping bucket rain gauge data 5 2.1 Maximum recorded 1 minute values . 5 2.2 Seasonal variations . 8 3 Rainfall rate statistics from weight pluviometer data 10 3.1 Maximum recorded 1 hour values . 10 3.2 Seasonal variations . 12 3.3 Conversion method from 1 hour to 1 minute precipitation . 12 4 Rainfall rate maps 13 4.1 Rainfall intensity exceeded 0.001 % of the time . 13 4.2 Rainfall intensity exceeded 0.01 % of the time . 16 4.2.1 Monthly values . 19 4.3 Rainfall intensity exceeded 0.1 % of the time . 19 4.4 Rainfall intensity exceeded 0.5 % of the time . 22 5 Rainfall rate trends from tipping bucket data and return periods 24 5.1 Rainfall rate trends . 24 5.1.1 Trends of maximum annual 1-minute intensity . 24 5.1.2 Trends of intensity exceeded 0.01 % of the time . 24 5.2 Return periods . 24 6 Methods used to derive rainfall intensity data from long term historical data set 26 7 Appendix - list of stations 33 3 1 Introduction In telecommunication heavy precipitation can lead to outage. [1], [4]. Met.no is therefore asked to analyze short term precipitation in Norway, down to one minute's time resolution. 1.1 Observation of short term precipitation in Norway At traditional weather and precipitation stations, precipitation has been measured twice and once a day, respectively. However, for many purposes, more frequent observations are necessary, and met.no therefore established several tipping bucket rain gauge stations, with time resolution 1 minute, at the end of the 1960s. At the beginning of the 1990s, met.no established a network of weight pluviometer stations with time resolution one hour. Most of the tipping bucket stations were operating only from April to October. During the last 5-10 years some stations have been upgraded to work all-year-round. A more thorough treatment on short term precipitation in Norway is given in [3]. Here regional values for maximum precipitation from 1 minute to 24 hours are given, and also return periods for 1 hour and 24 hours precipitation. 1.2 Types of stations 1.2.1 Tipping bucket rain gauge stations A tipping bucket rain gauge consists of a funnel, two small buckets and a magnet. The rain goes down the funnel and drips into one of the two buckets, balanced on a pivot. The top bucket is held in place by a magnet until it has lled to the calibrated amount (usually 0.1 or 0.2 mm of rain). When the bucket has lled to this amount, the magnet will release its hold, causing the bucket to tip. The water then empties down a drainage hole and raises the other to sit underneath the funnel. When the bucket tips, it triggers a reed switch (or sensor), sending a message to the display or weather station. The display counts the number of times the switch is triggered. By counting the number of buckets tips, the rain intensity within a given time interval (e.g. 1 minute) may be calculated. In Norway the rst tipping bucket stations were established in the spring of 1967. Se table 22 in the appendix for details about the stations. 1.2.2 Weight pluviometer stations A weighing-type precipitation gauge consists of a storage bin, which is weighed to record the mass. Certain models measure the mass using a pen on a rotating drum, or by using a vibrating wire attached to a data logger. The advantages of this type of gauge over tipping buckets are that it does not underestimate intense rain, and it can measure other forms of precipitation, including rain, hail and snow. These gauges are, however, more expensive and require more maintenance than tipping bucket gauges. In Norway, the Geonor precipitation gauge is prevailing. A bucket is suspended by three cylinders, each housing a vibrating wire. The vibrating wires are driven by a spectrum of frequencies and vibrate at their resonance frequencies. The resonance frequency of each wire depends upon the tension in the wire, which is directly related to the amount of weight in the bucket. Information is processed by three signal conditioning boxes and sent to a data logger where average accumulations are stored. The rst station was established in December 1991. See table 23 in the appendix for details about the stations. 4 2 Rainfall rate statistics from tipping bucket rain gauge data At rst, only stations with more than 10 years of operation were included. Geographical considerations saw the need for some stations with only 8 years of operation. The total number of stations are therefore 77. See table 22 in the appendix for details about the stations. The following stations have been in operation all-year-round: 3810, 17980, 18020, 18210, 18320, 18420, 18701, 18815, 18920, 19020, 26999, 27020, 27564, 39150, 44190, 44580, 44620, 44640, 44660, 44730, 47240, 50480, 50490, 64300, 68230, 68863. These stations are marked with an A in the rst column of table 22. 2.1 Maximum recorded 1 minute values The analysis includes almost 5 000 000 observations of rainfall intensities. Table 1 gives the highest 1-minute rainfall intensities (parameter RR_01) registered at Norwegian pluviometer stations. Only three times the intensity has exceeded 4 mm/minute. In the period 1967-2010 a total of 35 observations exceeded 3 mm/minute. The table also shows that very heavy precipitation is not restricted to the Southeastern part of Norway, but can occur in Western Norway and Northern Norway as well. STNR NAME MUNICIPALITY COUNTY RR_01 DATE AND TIME (UTC) 4781 GARDERMOEN SØR Ullensaker Akershus 4.3 08.07.1973 09:32 62290 MOLDE - NØISOMHED Molde Møre og Romsdal 4.3 01.08.1986 17:12 18701 OSLO - BLINDERN PLU Oslo Oslo 4.1 17.06.1980 14:38 32100 GVARV Sauherad Telemark 3.8 16.07.1982 01:30 62290 MOLDE - NØISOMHED Molde Møre og Romsdal 3.8 01.08.1986 17:11 62290 MOLDE - NØISOMHED Molde Møre og Romsdal 3.8 01.08.1986 17:13 82090 FAUSKE Fauske Nordland 3.6 19.07.1988 18:21 17980 OSLO - LJABRUVEIEN Oslo Oslo 3.6 12.07.2010 22:20 18020 OSLO - LAMBERTSETER Oslo Oslo 3.6 12.07.2010 22:24 18269 OSLO - HAUGENSTUA Oslo Oslo 3.5 12.07.2010 22:31 Table 1: Maximum l rainfall intensities. Unit: mm/minute Figure 1 shows all 1-minute rainfall intensity observations from 18701 Oslo - Blindern in the period 1968-2010. Intensities over 4 mm/minute has occured only once, 3 mm/minute has been exceeded 5 times and 2 mm/minute 12 times. We also notice the change of instrument in 2004, when the volume of the tipping bucket was reduced from 0.2 mm to 0.1 mm, giving more accurate observations. Table 2 to 5 gives maximum annual 1 minute intensities for all stations. As can be seen, both from this table and gure 1, the maximum intensity varies a lot from year to year. Intensities over 2 mm/minute do not occur often. However, the average of the highest intensity each year for the whole period is as high as 2.8 mm/minute, indicating that very heavy showers occur almost on an annual basis. 5 Figure 1: One minute rainfall intensities recorded at 18701 Oslo - Blindern 1968-2010 YEAR/STNR 200 1220 2840 3030 3810 4220 4781 11620 12290 12670 15720 17260 17870 17980 18020 18210 18270 18320 18420 18640 1967 1.9 1.0 1968 1.0 1.2 1.5 1.9 0.2 1969 0.4 1.0 1.0 1.7 0.6 0.6 1970 0.6 3.1 2.4 1.0 2.4 1.7 0.4 1971 0.6 1.9 0.6 0.8 0.4 1972 2.6 2.1 1.2 1.2 1.9 1.9 1.0 0.4 1973 0.8 1.9 1.9 1.9 4.3 2.6 1.9 0.2 0.4 1974 1.0 1.0 1.0 0.8 1.2 1.0 0.8 0.8 0.6 0.4 3.1 1.7 1.5 1.2 1975 1.5 1.5 1.5 1.7 2.1 1.9 1.2 0.8 0.8 0.2 1.2 0.8 2.4 2.1 1976 0.8 1.5 0.6 0.6 1.5 1.9 1.7 1.9 0.8 0.2 0.6 0.8 0.8 1.2 1977 1.0 1.5 1.0 0.8 1.0 1.5 1.5 1.2 1.0 0.4 1.0 1.5 1.9 0.8 1978 1.7 0.8 1.9 1.2 1.5 1.2 1.0 1.0 1.2 0.6 1.0 0.8 1.0 1.7 1979 1.5 1.7 1.9 1.5 1.2 1.9 1.5 1.5 1.2 0.4 1.2 1.9 2.1 1.0 1980 1.2 1.9 2.1 0.8 2.6 1.0 1.2 1.0 1.2 1.0 2.4 1.5 1.2 1.7 1981 0.8 2.8 1.0 1.0 1.0 1.7 1.2 1.0 0.6 1.5 1.2 3.1 2.4 1982 1.0 2.4 1.0 1.0 1.7 0.8 0.6 1.0 1.2 0.6 1.9 1.2 1.2 1.9 1983 1.7 0.4 1.0 1.2 2.6 0.2 0.4 0.8 1.7 1.2 1.0 1984 1.0 1.7 1.5 2.8 1.2 0.8 0.6 0.6 1.7 0.4 1.5 2.8 1.5 1.2 2.4 1985 1.9 2.8 1.2 2.6 0.8 2.6 1.9 1.5 1.7 0.6 1.9 2.1 1.3 1.9 0.4 0.4 1986 1.7 1.9 2.1 0.6 1.0 1.5 1.0 1.2 1.7 0.4 1.9 1.7 0.4 1.5 2.4 1.5 1987 1.2 0.8 0.8 0.6 0.8 1.7 0.8 0.6 0.4 1.0 0.9 1.2 1.5 1988 1.9 1.9 1.7 1.0 0.8 1.2 1.9 1.0 1.3 1.4 1.5 1989 2.6 1.2 1.9 2.1 1.7 0.2 1.0 1.5 1.5 0.3 1.3 1990 0.8 1.7 0.2 0.8 1.9 0.2 0.6 1.2 0.8 1.3 0.2 1991 1.0 1.7 1.2 1.5 1.7 0.8 1.7 0.6 1.0 1.6 1.4 1992 1.2 0.4 1.5 1.2 1.7 1.0 1.5 1.1 1.6 1993 1.9 1.2 1.7 0.8 0.9 0.5 1994 0.8 0.8 1.7 1.2 0.8 0.4 0.8 0.4 1.3 0.8 1995 1.0 1.2 1.2 1.9 1.0 2.1 2.8 1.4 1.0 1.2 1996 1.2 1.0 1.0 1.2 2.0 0.4 2.1 1997 1.9 2.0 0.9 1.8 0.8 1998 1.0 0.8 1.6 0.6 0.6 0.6 0.6 0.6 1999 0.9 1.0 1.5 2.0 1.6 1.1 0.4 1.2 2000 0.7 1.7 2.1 2.0 1.6 0.8 1.2 1.8 1.0 2.1 2001 1.3 2.8 1.2 1.2 1.3 0.6 2.2 1.8 2.6 1.3 2002 3.2 2.8 1.7 2.2 3.2 1.4 2.2 2.2 1.9 2.7 2003 1.4 2.1 0.2 1.4 2.3 1.8 1.8 2.1 1.6 2004 1.4 2.0 0.2 2.8 1.1 1.4 1.2 1.6 0.8 1.4 2005 1.5 0.8 1.1 2.6 1.4 1.0 0.8 1.4 2006 2.1 1.9 1.8 1.7 1.7 2.0 1.6 1.4 1.5 2007 0.6 1.0 1.5 1.9 1.1 2.2 1.8 1.3 1.4 2008 2.0 1.0 0.2 0.9 1.9 1.5 2.2 2.2 2.0 2009 1.6 1.2 0.7 2.2 1.3 0.8 2 2.2 2.0 2010 2.3 1.9 1.5 3.6 3.6 2.5 2.3 2.9 Maks 2.6 2.6 2.8 3.1 3.2 2.6 4.3 1.9 2.6 1.9 1.0 3.1 2.8 3.6 3.6 2.5 3.1 2.6 2.9 2.4 Table 2: Maximum annual rainfall intensities for station numbers 200 to 18640.