Water, Water, Everywhere…

Mark Turner, Service Hydrologist

 

Water, water everywhere, nor any drop to drink. That familiar stanza from Samuel Taylor Coleridge’s “The Ancient Mariner” seems apt to describe the state of the water supply here in Northern Maine over the past water year.  (The “water year” is defined as the period between October 1st of one year and September 30th of the next. This interval is often used by hydrologists because hydrological systems are typically at their lowest levels near October 1 and thus begin the process of regeneration.)

 

The question “Are we in/out of a drought?” is not as easy to answer as it may seem.  First, you have to define drought.  There are at least four different ways that drought can be defined:

 

1.    Meteorological - a measure of precipitation departure from normal.

2.    Agricultural - refers to a situation when the amount of moisture in the soil no longer meets the needs of a particular crop.

3.    Hydrological - occurs when surface and subsurface water supplies are below normal.

4.    Socioeconomic- refers to the situation that occurs when physical water shortage begins to affect people.

 

It is also helpful to define an area in terms of “regions” or “divisions” to help more easily describe climatologically homogeneous areas, rather than individual stations or data points.  There are 3 climate divisions in Maine:

 

1.    North

2.    Interior

3.    Coastal

 

In Northern Maine, the latest water year, 2002, began dry, and ended wet.  Division #1 was already in a severe Meteorological/Hydrologic drought, while Division #2 remained in a moderate Meteorological/Hydrologic drought and Division #3 was just considered abnormally dry.  These conditions persisted in the North, and improved slightly in the Interior and Coastal divisions through June.  Two months of note during this period were January and April. January 2003 was among the top 10 coldest and driest Januarys on record, and April refused to provide many of its vaunted showers.

 

Precipitation departed below normal 6 out of the first 9 months of water year 2002 in the North, 5 out of 9 Interior, and 4 out of 9 along the Coast.  For the last 3 months of the water year 2002, there was a significant rebound across the North and Interior Divisions, where near or above normal precipitation was measured, and 3 more months of deficit along the Coast.

 

Below is a breakdown of the month by month precipitation departure from normal for each Climatological Division throughout the water year 2002, the SUM departure and the cumulative percent of normal:

 

 

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

SUM

%

North

-.71

.13

-.42

-1.99

.29

.39

-1.38

-.17

-.26

1.32

1.00

.14

-1.66

96

Interior

-.71

.82

.34

-2.11

.14

.74

-1.62

-.26

-.51

-.67

-.67

1.24

-3.38

91

Coastal

-.87

2.56

1.23

-2.94

.60

2.23

-1.54

-.05

.13

-1.06

-.27

-.47

-.37

100

 

A rule of thumb for meteorological drought is precipitation less than 75% of normal.  For the water year 2002, all 3 Climate Divisions North and East of Route 201 in Maine (The WFO Caribou County Warning Area) were above 90% of normal… still a bit dry, but not in meteorological drought.

 

Of course, precipitation (or lack thereof) alone is not the only measure of drought. In fact, groundwater and stream levels are recharged in part by this precipitation.  Hydrologic conditions can be slow to respond to fluctuations in precipitation.  Across the WFO Caribou area of responsibility, checks of ground water monitoring stations and stream flow gauges showed near normal conditions… yet another indication of no drought.

 

One relatively new tool, available since 1999, is the U.S. Drought monitor.

 

http://www.drought.unl.edu/dm/index.html

 

Tracking drought is a blend science and art. Just as no single definition of drought works for all circumstances, no single monitoring index works under all circumstances. The Drought Monitor is a synthesis of several indices, outlooks and news accounts. This consensus approach seeks to avoid the bias of any one tool or user, and represents a balance that is the consensus of participants. At the beginning of the water year 2002, the Drought Monitor looked like this:

US Drought Monitor

 

And by the end of the water year 2002, it looked like this:

 

US Drought Monitor

Clearly, conditions have improved across Maine, as well as the entire Eastern U.S.

 

So, “Are we in/out of a drought?” 

 

The answer lies in your definition of drought, and by what measure it impacts you and those around you.  But, by conforming to the consensus of the many experts, including:

 

U.S. Department of Agriculture

National Oceanic and Atmospheric Administration

Climate Prediction Center

National Climatic Data Center

National Drought Mitigation Center

U.S. Geological Survey

National Water and Climate Center

Climate Diagnostics Center

Regional Climate Centers

National Weather Service Hydrology

State Climatologists

It is safe to say the drought is over!