January's heavy rainfalls and thunderstorms may have meant some of the region exceeded its average rainfall, but it was a short-lived benefit for most, hydrologist Dave Stewart says.
"However, Central Otago people were pleased to see the rain as conditions had become extremely dry and the rainfalls in January were the first significant falls in that region for many months," he said.
While the month started off unseasonably cool and wet, it became fine by January 15-19 before the thunderstorms rolled in on January 20-21.
"Unfortunately, such falls are often not very beneficial to the areas they affect, even if those areas are dry because the rain is usually so intense and short-lived that most of it runs off and does not get a chance to soak into the soils."
Rivers showed very sharp rises and usually fell just as quickly, he said.
The last 10 days of the month saw east-northeasterly quarter winds prevailing and while conditions along the east coast were often cloudy and cool, conditions were very hot inland.
Farmers reported more rain was needed urgently to ease the dry conditions that had developed since the rain, which was preventing grass growth, Mr Stewart said.
In North Otago, areas upstream of about Kurow received more rain than areas downstream and other more eastern parts of this region.
Rainfall totals were above average in the northwest area of North Otago but well below average elsewhere.
Average monthly river flows were well below their long-term averages for January.
Irrigation restrictions were in place on the main North Otago rivers by the end of January.
Total rainfalls at the indicator sites (average monthly totals in brackets) were: Tara Hills 63mm (47mm) 36% above average; Waikoura 20mm (52mm) 62% below average; Oamaru Airport 18mm (50mm) 68% below average; Oamaru Town 27mm (47mm) 42% below average; Kauru the Dasher 34mm (83mm) 52% below average; Palmerston 28mm (60mm) 53% below average.
Significant falls included: January 1-3, Tara Hills 17mm; January 9-10, Tara Hills 16mm, Oamaru Town 18mm, Islay Downs 22mm, Palmerston 15mm.
Central Otago received its first significant rainfall in months during January with two good falls.
As a result, rainfall totals were mostly above average except for the Maniototo and Roxburgh.
Average monthly river flows were well below their long-term averages for January although they did improve for a time as a result of the two good rainfalls during the month, he said.
Total rainfalls were: Lindis Crossing 83mm (50mm) 67% above average; Cromwell 83mm (43mm) 92% above average; Alexandra 61mm (42mm) 45% above average; Merino Ridges 90mm (54mm) 66% above average; Ranfurly 41mm (52mm) 21% below average; Tima 51mm (74mm) 32% below average.
Significant falls included: January 10-11, Lindis Crossing 29mm, Cromwell 18mm,Hills Creek 27mm, Ranfurly 21mm; January 23, Lindis Crossing 23mm, Cromwell 47mm, Alexandra 34mm, Hills Creek 24mm, Merino Ridges 63mm.
In Lakes Wanaka, Wakatipu and Hawea and surrounding areas, January was a month of contrasts.
Most of the rain fell in the first 13 days and it was also quite cool and windy.
In the last 17 days it was very dry and very hot.
River flows were close to or above average and rises of up to 1.5m occurred with the heavier bursts of rain in the first half of the month.
River flows generally declined after the 15th.
Lakes Wanaka and Wakatipu levels began the month at 277.73m and 309.31m, 0.05m and 0.1m above average respectively.
Wanaka had risen to 278.16m (0.5m above average) and Wakatipu to 310.59m (0.35 above average by January 11). Both steadily declined after that and they ended the month at 277.22m and 310.10m, 0.45m and 0.1m below average respectively.
Lake Hawea began the month at 343.84m (2.15m below full) and steadily rose to 344.90m later in the month.
Contact Energy then held the lake at about this level for the rest of the month.
In the lakes' headwaters, the cool, wet conditions at the start of the month gave way to warm conditions boosting growth, Mr Stewart said.
At the downstream ends of the lakes, growth was good, but the heat was drying out the area rapidly.
Total rainfallswere: Hunter Valley Station 107mm (94mm) 14% above average; Glenfinnan 166mm (166mm) average; Hawea Flat 75mm (61mm) 23% above average; Routeburn Station 287mm (204mm) 41% above average; Queenstown 86mm (75mm) 14% above average.
Significant falls were: January 1-3, Makarora 63mm, Hunter Valley 30mm, Glenfinnan 70mm, Routeburn 50mm; January 6, Makarora 42mm, Hunter Valley 32mm; January 9-10, Makarora 42mm, Glenfinnan 42mm, Routeburn 143mm.
In the Strath Taieri, Lower Taieri and Dunedin rainfall totals were generally below average and most of the rain occurred in the first 14 days of January.
"The rain did allow some good growth for a time but it has now slowed due to the dry conditions," he said.
Average monthly river flows were well below their long-term averages.
Flows improved by the middle of the month due to rain but they steadily declined after that to end January at very low flows again.
Irrigation restrictions were in place in the Taieri River.
Total rainfalls were: Garthmyl Middlemarch 43mm (63mm) 32% below average; Musselburgh Dunedin 69mm (70mm) average; Maungatua 67mm (77mm) 13% below average; Dunedin Airport 53mm (73mm) 28% below average; Pine Hill 71mm (111mm) 36% below average; Sullivans Dam 65mm (110mm) 41% below average.
Significant falls included: January 7-8, Middlemarch 21mm, Dunedin Airport 15mm, Musselburgh 28mm, Lee Flat 34mm, Pine Hill 21mm.
In South and West Otago, unlike the rest of Otago, there were no problems with lack of moisture and growth.
Apart from the Clutha, other average monthly river flows were generally well above long-term averages, especially the Pomahaka catchment.
Rises of between 1.5m and 2.5m were recorded in some rivers due to heavy rainfalls in the middle of the month and the thunderstorm.
The Waitahuna River was comparatively low.
Total rainfalls were: Tuapeka Mouth 97mm (78mm) 24% above average; Balclutha 91mm (71mm) 28% above average; Waikoikoi 131mm (93mm) 41% above average; Slopedown 163mm (134mm) 21% above average; Moa Flat 120mm (94mm) 27% above average; Clarks Flat 90mm (81mm) 10% above average;Significant falls included: January 8-11, Tuapeka Mouth 53mm, Balclutha 30mm, Waikoikoi 51mm, Slopedown 71mm, Moa Flat 35mm, Clarks Flat 29mm; January 13 Balclutha 23mm, Waikoikoi 20mm, Clarks Flat 19mm; 1 January 21, Tuapeka Mouth 25mm, Waikoikoi 42mm, Moa Flat 57mm.
