Canterbury water this season
Our seasonal outlook indicates how much water is in Canterbury's soils, aquifers, rivers and streams, compared against the long-term median for that time of year.
The final days of May saw some of the heaviest three-day rainfall ever recorded in parts of Canterbury, causing severe flooding and significantly changing the outlook for the winter season.
While we would normally report on the water situation as the season begins on 1 June, on this occasion we are reporting from 1 July to give us time to measure the effect of the rainfall on our surface and groundwater systems.
The maps below show the data for June 2021. The dots on the maps represent individual monitoring sites. The colour of each dot represents the groundwater level or stream flow relative to the long-term median June value for the site.
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Heavy rainfall and high river flows in late May significantly changed the groundwater picture across much of Canterbury.
Groundwater levels were at record lows in many places, but recharge from the wet weather has benefited most areas. In most shallower wells, groundwater levels have returned to near median for the time of year. Levels in many deeper wells are still below median.
Water levels are below median in around 58% of the wells we monitor, an improvement from 93% in May.
River and stream flows were very low throughout most of the region through Autumn, but significant rainfall at the end of May changed the picture completely, and floods resulted in central and southern foothill catchments.
A number of foothill sites have recorded higher than the long-term median flow for the month of June, while a number of springfed and lowland streams are still recording below median flows. Banks Peninsula streams are flowing at about normal for June.
Soil moisture over much of the Canterbury plains was exceptionally low until the heavy rainfall event in late May. That rainfall and subsequent precipitation in June mean that soil moisture as of 1 July was slightly above or well above normal levels for this time of year across most of Canterbury, with only South Canterbury and the eastern Banks Peninsula drier than normal.
Soil moisture data and imagery is provided by NIWA.
The extreme rainfall event of late May resulted in rainfall well above the three-month normal for a large section of the mid-Canterbury foothills and a section of the plains. However, when balanced with the proceeding dry months, the rest of Canterbury saw average rainfall levels for the period.
Canterbury had experienced several months with rainfall well below average, until a large amount of rainfall was recorded at many of our monitoring sites between 28 and 31 May.
This was the largest three-day rainfall ever recorded at 28 of our 84 measurement sites. That rain boosted groundwater and soil moisture levels, and river and stream flow. Find out more about the May flooding event.
Many of these indicators were extremely low or dry in May. Although most rainfall ran out to sea, it was enough to improve soil moisture and groundwater in some parts of Canterbury, bringing them more in line with the long-term July average.