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Summary of Annual Hydrologic Conditions - 2002
Volume 1: Surface Water
Precipitation and Reservoir Contents
Drought conditions continued through water year 2002 from previous water years because of persistent below normal precipitation. The State of New Jersey began a drought watch on October 31, 2001. On January 24, 2002, Governor James E. McGreevey declared a drought warning for five of the six drought regions. A state of water emergency (Executive Order No. 11) was then declared on March 4, 2002, after the driest February on record. New Jersey remained under this state of water emergency for the remainder of the water year. Since the drought of the 1960’s, water supply emergencies were declared in 1980 to 1982, 1985, 1995, and 1999. Reservoir levels and ground-water levels reached record lows at times during water year 2002 as a result of the lack of precipitation, water-supply demands, and above average temperatures.
This trend of precipitation deficit began approximately July 1998, possibly as early as 1997. For 38 of 69 months from January 1997 to September 2002, monthly spatially weighted average-precipitation values throughout New Jersey were below the statewide long-term monthly means (1895-2001) as shown in figure 1. Precipitation data can be accessed at http://climate.rutgers.edu/stateclim/. For 32 of those 51 months from July 1998 to September 2002, the monthly spatially weighted values were below the long-term monthly means. For water year 2002, the spatially weighted values for 7 of 12 months were below the means (March through June and September were above their respective means). For water year 2002, the statewide spatially weighted average-precipitation total was 33.99 inches, a 10.73-inch deficit when compared to the long-term meanannual precipitation (1895-2001). Since 1895, this is the third driest water year. The driest water year was 1965 with 32.36 inches of precipitation (David Robinson, New Jersey State Climatologist, Rutgers University, oral commun., 2001). The annual precipitation total for New Jersey is approximately 45 inches. October and November 2001 were the driest October and November on record. More than 3 inches of snow fell on the northern tip of New Jersey on December 8 but quickly melted. Snow cover was as much as 6 inches in northern New Jersey with a trace in southern New Jersey for the second and third week of January. February was mostly devoid of snow and ranks as the driest February on record. September 2001 to February 2002 was the driest 6-month interval on record. The next significant snowfall occurred on March 18 over northern New Jersey; however, it melted quickly. The late snowfall of 3 inches that fell on Cape May on April 6 (a trace in northern New Jersey) did not alleviate the drought. Precipitation from March through June was slightly above the historical average; however, July was the seventh driest July on record, and September 2001 through July 2002 was the third driest September through July on record. A below average August rainfall made the July and August period the ninth driest on record. Precipitation in September was slightly above average, but the water year ended with continuing drought conditions.
Three National Weather Service (NWS) precipitation stations in Newark, Trenton, and Atlantic City have been selected as index sites for precipitation. During water year 2002, precipitation totals were below normal at all three NWS index stations. The Newark station recorded 31.49 inches, which is 68.1 percent of the 30-year reference-period (1961-90) mean. The Atlantic City station recorded 30.95 inches, which is 76.3 percent of the 30-year mean. The Trenton station recorded 32.90 inches, which is 76.7 percent of the 30-year mean. Monthly precipitation at the three NWS stations, along with the 30-year mean is shown in figure 2.
Eleven of the 12 monthly mean temperatures in the 2002 water year (determined from spatially weighted average of temperatures recorded throughout New Jersey) were above the long-term mean monthly average (1895-2001). Monthly mean temperatures ranged from 0.7 to 4.2 degrees Celsius above average for October through April. The winter was the second warmest on record. April had record to nearrecord highs; the temperature on April 17 reached more than 32 degrees Celsius. May was the only month with temperatures below the long-term mean, but only by 0.4 degrees Celsius. June through September temperatures were above the long-term mean (fig. 3). The long stretch of higher than normal temperatures during the summer increased evapotranspiration, which stressed water supplies. Temperature data can be accessed at http://climate.rutgers.edu/stateclim/.
Combined usable contents of 13 major water-supply reservoirs in New Jersey were 51.7 billion gallons at the end of September 2001, which is 97.9 percent of the 30-year mean (normal) contents for the end of September and 64.3 percent of capacity. Combined usable contents declined steadily from the September 2001 to a record low of 28.3 billion gallons at the end of February (1.7 billion gallons below the previous minimum for February). Combined usable contentsclimbed steadily from the record low to a maximum for the water year of 70.1 billion gallons by the end of June 2002, which is 101 percent of normal contents for the end of June and 87.2 percent of capacity. Reservoir levels experienced a normal decline during the summer because of an increased demand for water supplies. By September 30, 2002, combined usable contents totalled 47.2 billion gallons, which is 89.3 percent of normal contents for the end of September and 58.7 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 52.2 ft3/s for the water year, which is 42.8 percent of the 1919-2002 average. Streamflow at the index station in southern New Jersey (Great Egg Harbor River at Folsom) averaged 40.2 ft3/s, which is 47.4 percent of the 1926-2002 average. The observed annual mean discharge for the Delaware River at Trenton was 7,130 ft3/s, which is 61.4 percent of the 1913-2002 average. The Delaware River is significantly regulated by reservoirs and diversions. Monthlymean 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 all 46 gaging stations was well below normal for water year 2002. The percent differences ranged from -38.6 to -94.4. Discharge at 40 of the 46 gaging stations was below normal for water year 2001. The percent differences ranged from -14.5 to -28.7. Discharge at 36 of the 46 gaging stations was below normal for the water year 2000, and the percent differences ranged from 14.3 to -28.7. 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.
No major flooding occurred this water year. Recent major floods are the Sparta Flood in August 2000 and Hurricane Floyd in September 1999.