By Mark Kinver
BBC News science and nature reporter
Concern is growing for flora and fauna in some parts of the UK because rainfall levels are well below the average for winter months.
Low rainfall has raised concerns of a drought this summer
Scientists say trees and fish could suffer in the summer because of the lack of rain to replenish water stocks.
A second successive dry winter has left some areas with groundwater and river levels well down on what they should be for this time of the year.
South-east England is the area worst affected by the lack of rainfall.
Speaking at a briefing in central London, a team from the Centre for Ecology and Hydrology said it was too early to predict an ecological crisis, but warned that only well above average rainfall in the coming weeks would help ease the situation.
"The amount of rainfall over the winter affects how much water is in the soil for plants and animals to draw upon," said Mike Morecroft, an ecologist from the centre.
"If you get dry weather during the summer, how long plants and therefore the whole ecosystem can go on drawing water really does depend on how much is already there at the start of the summer."
Dr Morecroft said the unseasonably dry weather for a second successive winter had led to growing concern.
A hosepipe ban is in force in Kent and Sussex
River flows in Midlands, NE and NW England below 1976 levels
Rainfall in SW England less than half of January average
Ground water levels are below winter average
Some farm reservoirs may not be filled to meet summer needs
(Source: Environment Agency)
"We are seeing a situation where the ecology of Britain is going to be very vulnerable to even quite a dry spell over the summer months.
"The death of trees is possible; beech and birch are particularly susceptible. Even the trees that survive are likely to loose their leaves earlier than normal," he added.
"The drying of water courses can also have an impact on species such as salmon. The small feeder streams where young fish develop may dry out, forcing the juveniles to go more quickly into the main river where they are more vulnerable to mortality."
Dr Morecroft also said low moisture content in soil could increase the risk of forest fires, and grasslands dying, all of which could affect the ecological balance of an area.
But the scientists quickly added that this scenario was not a certainty.
They say the situation is not as bad as in 1976, when millions of trees in England and Wales did succumb to the driest 16 month period on record.
"The 1976 drought is a benchmark drought, not only in the UK but across many parts of Europe," said Terry Marsh, a hydrology expert from the centre.
"While flows in some chalk rivers are fairly similar to levels in 1976, it is only in some, not many."
Average daily consumption per person (in litres):
Midlands - 139
North-west - 142
Eastern - 143
Yorkshire - 145
Northumbria - 146
Wales - 148
Wessex - 155
South-west - 161
Southern - 163
Thames - 170
Mr Marsh pointed out that the focus of their concern was south-east England, not the whole of the UK.
While south-east England was in the grips of a winter drought, receiving only 25% of its average rainfall; he said areas such as west Scotland and North Wales were getting above average rainfall.
Figures from the Environment Agency, responsible for regulating water abstraction in England and Wales, also show that the south-east is facing the toughest challenge to meet demand for supplies.
Groundwater provides 75% of the area's public water supplies, yet some sites are recording levels lower than in January 1976.
River flows are also worryingly low. Many are running at half the level normally expected at this time of year.
About 3.4 million residents in Kent and Sussex are already subject to restrictions on their water use, with 2.7 million of them banned from using hosepipes.
The agency warns that if the amount of rain falling from the skies does not increase, it is likely that more restrictions will be introduced.
A small water firm in Kent feels the problem has already reached the stage where drastic action is required.
Folkestone and Dover Water, which supplies about 160,000 residents, has asked the government to allow it to install compulsory water meters in customers' homes.
It has to convince ministers that it has exhausted all avenues for water sourcing and will have problems with supplies for the next 10 years.
If granted, it will become the first water company in the UK to be granted "water scarcity status".
Climate models forecast drier summers and wetter winters in the UK, but the current lack of winter rain seems to contradict this.
Dr Richard Harding, a climate expert from the Centre of Ecology and Hydrology, said this was to be expected because of increasing variability in rainfall in Britain.
"We are entering a regime the Earth has not been in for 100,000 years or beyond, so we can expect surprises."