Summary (details follow)
As of May 18, 85% of Connecticut is rated as no drought on the map of the state published by the US Drought Monitor
(click here for an analysis). 15% of the state remains Abnormally Dry. See the discussion below for a comparison to previous years.
Interagency Drought Workgroup (IDW)
met on May 3 and recommended improving "Drought Watch" to "Drought Advisory" for all counties; continue monitoring
Connecticut Interagency Drought
Workgroup Ends First-Ever Drought Watch, Maintains Statewide Drought Advisory
Some water companies in May were still asking their customers to conserve water;
On Friday, May 19, the Northeast
River Forecast Center reported none of the 20 river gages
they monitor were near flood, and they were all expected to drop in the next three
is generally recovered from its drought conditions, with most wells being near
normal for this time of year and a few being above normal.
On May 19 only the Aspetuck River stream gage in the Aspetuck section of Easton, CT was reporting low flow. By Monday May 22 however, 4 more streams were added to our low-baseflow list. See below for a discussion of how we count low flows.
The USGS's 30-day graphs of streamflow in Connecticut (link below) show similar patterns of the normal rapid jumps in flow during rain events. The rain events have been often enough recently to prevent the flows from receding below the average flows for the date, however. Earlier in the 30-day period, many streams stayed near average without high peaks due to a long interval between storms. See below for further discussion of streamflow patterns.
The USGS's 28-Day Average Streamflow map now categorizes all of Connecticut as having normal or higher-than-normal streamflow.
Your water utility and town web pages are
the best sources of information on water use restrictions that
apply specifically to you.
The CT Department of Public Health (DPH) Monthly Reservoir Status Summary
dated May 3 reports capacity was
at 100% of normal for the end of April, meaning the reservoirs of 34 large water systems averaged
97% of full capacity. More details:
Aquarion maintains on its website a weekly updated water usage report that includes customer usage trends, system transfers, system capacities, days usable storage remaining, and precipitation. They note that as of May 15 their Greenwich Reservoir was 99% full, slightly higher than last year and slightly higher than usual at this time of year based on 30 years of records. Their Stamford system is still a little lower than where it was last year or on average for May 15. Their Bridgeport system reservoirs are at 99.9% full, same as last year and higher than average.
The graphs show that last year their reservoir levels did not begin falling at rates faster than usual until June. That part of the state last year was rated Abnormally Dry by the U.S. Drought Monitor in May and June and was the first area to again be rated Moderate Drought in June 2016. The USGS live-data monitoring well in Greenwich also did not began to fall faster than usual until June 2016.
In Connecticut, the USGS has seven real-time groundwater monitoring wells with multiyear records. Comparing the May 19 water levels with all measurements for that date, 4 were higher than average and 2 were near normal.
The water table at those wells has recovered very well from
previous months' levels. March 30 was the first time in
none of the seven monitoring wells were breaking records for lowest measurement for the date. The water table's
lowest levels occurred last
September, with more stations breaking
low-water-level records than those that were
merely very low until November. The water table usually begins to drop each year in
June. In previous years drought conditions began to show up in groundwater
measurements when the water levels fell at a faster rate than normal. So far
this year levels seem to be pretty steady.
The USGS Groundwater Watch website displays data from 60 wells with monthly measurements along with 10 continuously monitored wells. As of May 12, the most recent monthly measurements were from late April, when 4 of the 60 wells were rated above normal, 45 were normal, and 14 were below normal compared to their records for April measurements.
Groundwater levels influence streamflow. The water level in streams and rivers between storms depends on the flow of water out of the ground into the stream channel. The higher the water table, the more water is available to keep streams flowing. During a drought, smaller upland streams dry up faster than the larger rivers (details below). An occasional brief, powerful rainstorm does not do much to help groundwater levels rise. The rain falls faster than the ground can absorb, and thus much of it becomes stormwater runoff. In that situation, public water supply systems that depend on reservoirs are affected less than those with wells because the runoff is collected by the reservoirs.
There has been an apparent pattern for the last five years in which normal groundwater levels in winter and spring have alternated with well-below-average levels in summer and fall. Click the graph to the right for a larger version in a new tab of a modified USGS graph. There are two trends of great concern. One concern is that the below-normal levels in summer and fall got worse in each of those years. The other concern is that the water table has not recovered yet this year as it did in previous years. Five years is not long enough to make any statistically valid conclusions about climate, however, and those station records only go back seven to 14 years. Click here to see all the USGS graphs for their real-time groundwater measurements that compare levels from the last four years to the median level for each day of the year (lots of data, so it takes a long time to load). USGS manually measures other wells once a month or so, and a quick look at those records verified the possibility that this pattern may apply to all our groundwater.
Watch website is an excellent source of data for examining historic and
current trends. It has a map of Connecticut that is colored to show how the most
recent measurements compare to historical records for each station.
The National Weather Service (NWS) Advanced Hydrologic Prediction Service has detailed maps and data at this link to compare actual precipitation to what is normal for the time of year. Recent rainfall has brought Connecticut's 30-day rainfall totals to near or above average across the state. Just last week the 30-day totals were 25% below normal except for about a quarter of the state along the Rhode Island border and along Long Island Sound.
Storm Tracks: For most of 2015 and 2016, storm centers repeatedly went out to sea to our southeast or passed us by to our northwest, instead of a more usual pattern of random storm paths moving generally west to east. In addition to this unusual pattern, rain that did mange to track over us tended to be fairly heavy. Generally, as our climate changes, heavy precipitation events are becoming more frequent, but heavy rain does not recharge groundwater aquifers as much as the same amount of rain over longer periods would. This means that even when long-term total rainfall returns to normal, streams and rivers could still be afflicted with unusually dry conditions between storms, because flow will drop to unusually low levels due to a lower than normal water table.
Why the unusual storm tracks? Some studies connect a shift in wind systems
such as the jet stream to the unprecedented summertime warming in the north
the loss of Arctic sea ice. For
more information, see these articles about the studies:
Scientists Link California Droughts, Floods To Distinctive Atmospheric Waves (2017-04-06),
Extreme Weather Events Linked to Climate Change Impact on the Jet Stream (2017-03-27), .
Rain? 3 to 5 inches of rain is normal for the month of May in Connecticut, according to the National Weather Service (NWS), based on data from 1981 to 2010. On May 19, the NWS's seven-day forecasts
predicting normal rainfall, and so were the
long-range (16-day) computer models.
Each month, the NWS Climate Prediction Center
issues analyses of global atmospheric conditions that could influence general
temperature and precipitation patterns. Their May 18 analyses for trends through
the end of the calendar year show equal chances for
above-normal, for normal, and for below-normal
precipitation. Above-normal temperatures are a little more
likely than normal temperatures. This is pretty much the same
three-month forecast we have seen for over a year, but actual
precipitation was much lower than normal. Before the April analysis, for three
months in a row, their prognostications for the summer predicted
above-normal rainfall, but that prediction has now disappeared.
The flow between storms is an indicator of drought conditions. We define low flow
as below the 25th percentile for that stream, or below 25% of the mean or below 25% of the median flow
for that stream for the date from the USGS data file at:
at a time when rivers are near their lowest points between storms. The 25th percentile is a flow rate
75% of all average daily flows recorded on that date for that
Why do we count? A count of the number of USGS stream gages reporting low flow at their lowest point between storms is valuable as an indicator of drought conditions. There are only 62 stream gages in Connecticut, so they may not represent the hundreds of streams with no gages. If the number of streams that reach low levels between storms is increasing over time, it raises concern for the recovery of stream ecosystems from the drought. If the count decreases, we can look for continued recovery from drought conditions.
Variable rainfall this spring has greatly affected the count of
low-flow gaged rivers. Instead of the fairly steady increase in the
number of storms and rainfall intensity one expects to see in spring,
there has been wide variation week to week. The double-digit count of low-flow streams
out of the 62
measured by USGS first dropped to single digits (about 15% of
the 62) in mid-February,
lasting until the beginning of March. The count of low-flow
gages jumped in
March but went back to single digits again as storms increased
in early April.
Since mid-April, streamflow has generally been near normal for the time of year,
but there have been stretches of time between
storms during which some stream flows have dropped to low levels.
Here are the recent numbers:
May 22: 7 out of 62 stream gages reporting low flows. List is below.
bottom graph to the right illustrates what can be considered an average
pattern of streamflow, in that the stream shows a flow that peaks above
its average for the time of year but then drops to below average.
Streams in nature maintain healthy flows between storms if the water
table in the watershed of the stream is near or above average for the
time of year.
As of May 18, only 15% of Connecticut remains Abnormally Dry. The 85% of the state with a U.S. Drought Monitor rating of "None" is the largest portion with that rating since December 2014 through April 2015. See the graph below. Most of Connecticut (76%) had finally reached the category of "None" on May 11. More than half the state had been at least Abnormally Dry since April 2016.
Their May 11 narrative for the Northeast said: "Another soaking storm further reduced the coverage of lingering, long-term dryness (D0). Vestiges of dryness, reflected mainly in spotty groundwater shortages, remained in Maryland, Pennsylvania, and Connecticut."
This graph compares the extent of drought
conditions in Connecticut over the past four years. As the graph
below shows, Connecticut has been labeled Abnormally
Dry, Moderate Drought, or worse pretty often over the last few
Last year the state was never completely free of abnormally dry conditions though the area rated None reached 70% during March, two months earlier than this year. The None area then began decreasing again in April 2016 until all of the state was at least Abnormally Dry by mid-June 2016. Two years ago, all of the state had been rated None from December 2014 through April 2015. The 2013 dry period lingered until April 2014 when all of the state was rated None. Abnormally Dry areas began again in July 2014.
The persistent low streamflow levels during the drought had harmful effects on river ecosystems. Last November, for example, fishermen reported long stretches of rivers with no catch at all. How well river ecosystems recover from the drought will depend on flow from groundwater. Where groundwater is near normal, streamflow should remain healthy between storms unless rainfall patterns change in late spring as they did in the past four or five years.
The past U.S. Drought Monitor data for Connecticut used for these comparisons can be found at this link. From the end of January to the beginning of April, Connecticut had the dubious distinction of being the most drought-afflicted state of all 50 based on percentage of area. Click here for details from an archived Know Your Flow! page.
The U.S. Drought
Monitor publishes a weekly analysis of
drought conditions across the entire nation based on a variety of
types of data that include streamflow. The report comes out every
Thursday based on data from that Tuesday. The U.S. Drought Monitor is produced
National Drought Mitigation Center, which is also on Facebook.
Are small and large streams affected by dry conditions equally?
Rivers Alliance of Connecticut