April was unsettled at times but there were also periods of fine, calm and relatively warm weather, Raineffects hydrologist Dave Stewart says.
A series of relatively weak systems prevailed for the first two weeks of the month and only small amounts of rain were recorded from time to time.
About the middle of the month, a complex trough of low pressure brought more significant rain, especially to South and West Otago, and along the east coast, as far north as Dunedin, but only lighter rain occurred elsewhere, he said.
Following this system, two southerly quarter storms occurred, one of which brought winds of record speeds to some parts of the region.
At the end of the month, a depression moving in from the Tasman Sea brought good rainfall to the whole region, except parts of North Otago.
In North Otago rainfall totals varied from well below, to just above average.
More than 60% of the month's rainfall occurred on the last two days of the month so conditions were very dry before that, Mr Stewart said.
Total falls at the indicator sites (average monthly totals in brackets) included: Omarama 47mm (42mm) 12% above average; Waikoura 25mm (45mm) 44% below average; Kauru, the Dasher 52mm (62mm) 16% below average; Palmerston 53mm (49mm) 8% above average; Oamaru Township recorded 46mm.
Significant falls during the month included: April 29-30, Omarama 33mm, Oamaru Township 24mm, Islay Downs 24mm, Palmerston 52mm.
Average monthly river flows remained well below their long-term averages.
Flows became quite low at times causing some restrictions to irrigation, but rose on the last day of the month due to rain.
Farmers reported that although temperatures were good for much of the month, the lack of rain inhibited pasture growth on non-irrigated land, he said.
It was now too late for any more significant growth this season, as frost frequency and severity was cooling ground temperatures.
In Central Otago, rainfall totals were above average but this was mainly because of the heavy rain at the end of the month.
Before that, conditions had been very dry.
Total falls were: Lindis Crossing 44mm (42mm) 5% above average; Alexandra 33mm (30mm) 11% above average; Ranfurly 51mm (40mm) 29% above average; Tima 67mm (48mm) 40% above average; Merino Ridges in the Ida Valley recorded 55mm for the month.
Significant falls included: April 1, Merino Ridges 13mm; April 17-18, Tima 17mm; and April 29-30, Alexandra 29mm, Merino Ridges 37mm, Ranfurly 35mm, Tima 34mm.
River flows remained well below their long-term April averages throughout the month, he said. Rivers began rising due to rain on April 29-30.
Farmers reported some growth on irrigated land during the month and in the more southern areas.
In Lakes Wanaka, Wakatipu and Hawea and surrounding areas rainfall totals were below average.
At the downstream ends of the lakes, conditions were very dry and only the rain at the end of the month gave the totals some respectability, Mr Stewart said.
Total falls were: Makarora Station 147mm (165mm) 11% below average; Glenfinnan 90mm (140mm) 35% below average; Hawea Flat 43mm (57mm) 24% below average; Routeburn Station 90mm (157mm) 42% below average; Queenstown 44mm (74mm) 40% below average; Halfway Bay recorded 28mm.
Significant falls included: April 3-4, Makarora Station 32mm, Routeburn Station 29mm; and April 27-30, Makarora Station 88mm, Hunter Valley Station 57mm, Glenfinnan 62mm, and Queenstown 33mm.
River flows remained low for most of the month.
As a consequence, lakes Wanaka and Wakatipu fell to quite low levels during April.
Lake Wanaka began the month at 276.92m and Lake Wakatipu at 309.71m, 0.35m and 0.2m below average respectively.
Both lakes fell steadily during the month and by April 26-27, Wanaka was at 276.47m, 0.8m below average and Wakatipu at 309.42m, 0.5m below average.
Both rose marginally after that.
Lake Hawea fell steadily during April as Contact Energy continued to release water for power generation.
It began the month at 342.98m, 3m below full and ended the month at 341.72m, 4.3m below full.
Farmers further up the lakes and in the headwaters reported good growth but with cooling conditions. At the bottom ends of the lakes, conditions were too dry for growth on non-irrigated land and the rain late in the month was probably too late to allow growth, as frosts had set in and ground temperatures were cooling quickly, Mr Stewart said.
In Strath Taieri, Lower Taieri and Dunedin, rainfall totals varied from about 40% below average to about 20% above average.
Total falls were: Garthmyl Middlemarch 45mm (38mm) 18% above average; Musselburgh Dunedin 45mm (65mm) 31% below average; Maungatua 56mm (48mm) 16% above average; Dunedin Airport 45mm (49mm) 8% below average; Pine Hill 48mm (65mm) 27% below average; Sullivans Dam 59mm (93mm) 37% below average.
Significant falls during the month included: April 1, Middlemarch 11mm; April 17-18, Lee Flat 21mm, Maungatua 19mm; and April 29-30, Middlemarch 29mm, Dunedin Airport 21mm, Musselburgh 22mm, Lee Flat 21mm, Maungatua 21mm.
Average monthly river flows remained well below their long-term April averages throughout the month.
The rain in the middle of the month resulted in very small rises in some rivers, he said.
Farmers inland reported little growth on non-irrigated land because conditions were too dry.
Closer to the coast, they reported some reasonable growth but it was slowing with the onset of frosts.
In South and West Otago the rainfall was above average with good falls in the middle and at the end of the month.
Total falls were: Tuapeka Mouth 85mm (55mm) 54% above average; Balclutha 56mm (50mm) 12% above average; Waikoikoi 96mm (75mm) 28% above average; Moa Flat 78mm (64mm) 22% above average; Clarks Flat 82mm (54mm) 52% above average.
Significant falls during the month included: April 17-19, Tuapeka Mouth 27mm, Waikoikoi 44mm, Clarks Flat 27mm; and April 29-30, Tuapeka Mouth 44mm, Waikoikoi 36mm, Moa Flat 44mm, Clarks Flat 40mm.
The Clutha River remained below average due to the low levels in Lakes Wanaka and Wakatipu.
Other rivers and streams were below their long-term averages.
The rain in the middle of the month resulted in small rises in all rivers and streams and they began rising again due to the rain on April 29-30.
Farmers reported that there was some growth in the region during April and rain had replenished some of the soil moisture deficit.