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Summary of Annual Hydrologic Conditions - 2001
Volume 1: Surface Water
Precipitation and Reservoir Contents
Drier than normal conditions continue for water year 2001 from previous water years because of persistent below normal rainfalls. This trend of rainfall deficit began approximately July 1998, possibly as early as 1997. For 32 of 57 months from January 1997 to September 2001, monthly spatially weighted average-precipitation values throughout New Jersey were below the statewide long term monthly means (1895-2000) as shown in figure 1. Precipitation data can be accessed at http://climate.rutgers.edu/stateclim/. For 26 of those 39 months from July 1998 to September 2001, the monthly spatially weighted values were below the long-term monthly means. For water year 2001, the spatially weighted values for 10 of 12 months were below the means (March and June were above their respective means). For water year 2001, the statewide spatially weighted average-precipitation total was 39.12 inches, a 5.68 inch deficit when compared to the long-term annual-mean total (1895-2000). Since 1895, this is the 21st driest water year. The driest water year was 1965 with 32.16 inches of precipitation (David Robinson, New Jersey State Climatologist, Rutgers University, oral commun., 2001). Snowfall was heavy on December 30-31, with as much as 20 inches reported in northern New Jersey. Snow cover was recorded for most of January, mostly in northern New Jersey; several snowfalls added to the cover. Snow cover was maintained for most of February by two snowfalls; the first which occurred on February 5, left as much as 18.5 inches in High Point State Park. On February 22-23, about 7 inches of snow fell but was quickly melted by warm temperatures at the end of the month. March temperatures were above normal and an early March snowfall quickly melted. During the last three weeks in March snow cover was present mainly in northern Sussex County. Snow cover was present near Montague for 91 consecutive days through March 20.
Water year 2001 was devoid of any outstanding hydrologic or weather related events. On May 27, a F2 (Fujita Scale) tornado was reported in Manalapan, and on May 29 a hailstorm was reported in northern New Jersey.
Three National Weather Service (NWS) precipitation stations in Newark, Trenton, and Atlantic City have been selected as index sites for precipitation. During water year 2001, precipitation totals were below normal at all three NWS index stations. The Newark station recorded 34.42 inches, which is 78.3 percent of the 30-year reference-period (1961-90) mean. The Atlantic City station recorded 31.87 inches, which is 76.9 percent of the 30-year mean. The Trenton station recorded 38.60 inches, which is 86.9 percent of the 30-year mean. Monthly precipitation at the three NWS stations, along with the 30-year mean is shown in figure 2. The Atlantic City station recorded a new monthly low of 0.06 inches for October. The previous record low for October was 0.15 inches in 1963.
The October monthly mean temperature determined from spatially weighted average of temperatures recorded throughout New Jersey was 0.3 degrees Celsius above the long-term mean monthly average (1895-2000). Monthly mean temperatures were below average for November through January. The December monthly mean temperature was almost 2.6 degrees Celsius below the December long-term mean monthly average. The February monthly mean was 2.1 degrees Celsius above the average. The March monthly mean was close to average, whereas for April, May, and June the monthly mean averages were about 1 degree Celsius above average. The July monthly mean average was 1.4 degrees Celsius below average. The August monthly mean average was 2.0 degrees Celsius above average, and September ended the water year with monthly mean temperatures 0.2 degrees above average (fig. 3). The long stretch of higher than normal temperatures during the summer increased evapotranspiration, which stressed water supplies.
Combined usable contents of 13 major water-supply reservoirs in New Jersey were 69.9 billion gallons at the end of September 2000, which is 132 percent of the 30-year mean (normal) contents for the end of September and 86.9 percent of capacity. Combined usable contents increased to a maximum of 78.3 billion gallons by the end of March 2001, which is 112 percent of normal contents for the end of March and 97.4 percent of capacity. Reservoir levels experienced a normal decline during the summer because of an increased demand for water supplies. By September 30, 2001, combined usable contents totalled 51.7 billion gallons, which is 97.9 percent of normal contents for the end of September and 64.3 percent of capacity (fig. 4). The term "usable contents" is used here as a measure of the total volume of water that can be removed from a reservoir without pumping, and does not account for the volume of water below the bottom of the lowest outlet or pipe (sometimes referred to as dead storage).
Three gaging stations, located in north, south, and central New Jersey, are considered index stations for statewide streamflow conditions. Streamflow at the index station in northern New Jersey (South Branch Raritan River near High Bridge) averaged 94.8 ft3/s for the water year, which is 77.1 percent of the 1919-2001 average. Streamflow at the index station in southern New Jersey (Great Egg Harbor River at Folsom) averaged 73.0 ft3/s, which is 85.5 percent of the 1926-2001 average. The observed annual mean discharge for the Delaware River at Trenton was 9,069 ft3/s, which is 77.8 percent of the 1913-2001 average. The Delaware River is significantly regulated by reservoirs and diversions. Monthly mean discharge at each of these index gaging stations during the current water year and the long-term normal monthly discharge are shown in figure 5. Annual mean discharge at each of these index gaging stations and the mean annual discharge for the period of record are shown in figure 6.
Annual mean discharges at 46 gaging stations that had 40 years or more of continuous records and mean annual discharge for the period of record at each gaging station are shown in table 1. The difference is listed as percent difference. Discharge at 40 of the 46 gaging stations was below normal for water year 2001. Three of the six gaging stations with above-normal flow recorded flow that was less than 10 percent above normal. Several gaging stations that monitor heavily regulated rivers were not included in this comparison because of large artificial deficits related to regulation. The criterion of assessing gaging stations with 40 years or more of record was used in order to encompass at least one of the approximately 30-year drought cycles that New Jersey has experienced.
The first notable flooding of water year 2001 occurred on December 17, when a thunderstorm dropped more than 3 inches of rain in northern and southern New Jersey and more than 2 inches fell in central New Jersey, flooding some streets. Associated high winds and lightning brought down trees and power lines. Lightning struck close to Mayor Gerald Van Gorden, who said he could feel the heat from the lightning bolt, as he was surveying floodwaters during a local state of emergency near Branchville (New Jersey Herald, Newton, N.J., December 18, 2000). The most notable flooding was caused by rain from Tropical Storm Allison. As much as 5 inches fell on Father's Day, June 17. Several fatalities were linked to the approximately 10 inches of rain that fell in the neighboring Commonwealth of Pennsylvania. Several minor floods also occurred in August throughout New Jersey.