Catchment News

Hydrology Summary Bulletin – December 2022

The Hydrology Summary Bulletin for December 2022 has information on the flows in rivers, rainfall, lake levels, groundwater levels and spring outflows of over 300 stations across Ireland. Rainfall was below the long-term average in most of Ireland last December. River flows, lake and groundwater levels were mostly normal (though some were low) for this time of year.

Overview

Rainfall was below the long-term average in most places this month. Similarly, monthly average river flows were below the long-term average in most rivers across the country, with over half (58%) of river monitoring sites in the normal range and a further 37% below normal for December. Average lake levels also fell during December, with over half (57%) of lakes in the normal range and almost one-third (32%) of lakes with levels below normal for this time of year. There is a similar observation for average monthly groundwater levels, with falling levels since November. Just under half (48%) of monitoring wells were in the normal range for December with a further 36% of wells below normal. Most monitored spring outflows were normal or below normal for December.

Rainfall

The majority of monthly rainfall totals across the country were below their 1981-2010 Long-Term Average (LTA). Percentage of monthly rainfall values ranged from 71% (monthly rainfall total of 93.0 mm) at Finner, Co Donegal to 136% (the month’s highest monthly rainfall total of 187.1 mm) at Belmullet, Co Mayo. Monthly rainfall totals were lowest at Oak Park, Co Carlow with 68.0 mm (81% of its LTA). The month’s wettest day was also recorded at Belmullet, Co Mayo with 41.3 mm on Christmas Day, Sunday 25th . The number of rain days ranged from 15 days at Oak Park, Co Carlow to 28 days at Malin Head, Co Donegal. The number of wet days ranged from 9 days at Ballyhaise, Co Cavan to 22 days at both Malin Head, Co Donegal and Belmullet, Co Mayo. The number of very wet days ranged from 2 days at a few stations to 8 days at Newport, Co Mayo.

River flows

Average river flows for December fell at 91% of monitoring stations compared to average flows observed in November. The monthly average flows at 156 river monitoring sites across the country identified; 1 (1%) as ‘particularly high’ [Glencastle, Co. Mayo], 6 (4%) as ‘above normal’, 90 (58%) as ‘normal’, 52 (33%) as ‘below normal’ and 7 (4%) as ‘particularly low’ for this time of year.

Lake and turlough levels

Average water levels for December fell at 84% of monitored lakes compared to average levels for November. Analysis of monthly average levels at 40 lakes and 4 turloughs were classified as ‘particularly high’ at 3 (7%), ‘above normal’ at 2 (4.5%), ‘normal’ at 25 (57%), ‘below normal’ at 12 (27%) and 2 (4.5%) of monitoring locations for the month of December.

Groundwater levels and spring flows

Average groundwater levels in December fell at 73% of monitoring wells compared to average levels observed in November. December groundwater levels at 42 monitoring locations were classified as ‘particularly high’ at 1 well (2%) [Clarabog. Co. Offaly], ‘above normal’ at 6 wells (14%), ‘normal’ at 20 wells (48%), ‘below normal’ at 11 wells (26%), and ‘particularly low’ at 4 wells (10%) across the country.

Spring outflows were also monitored at 8 EPA monitoring sites for December. The outflows from these springs were compared to previously recorded flows for December and were ‘normal’ at 2 locations, ‘below normal’ at 5 locations and were ‘particularly low’ at 1 [Rockingham Co. Roscommon] monitoring spring location for this time of year.

Learn more:

The monthly hydrology bulletin can be downloaded here: www.epa.ie/publications/monitoring–assessment/freshwater–marine/hydrology-bulletin/hydrology-bulletin/