The NHS is down around 2,000 blood donations in the last two weeks.
Blood donations in Bradford have dropped because of the hot weather and England's fantastic run in the football World Cup.
On normal warm weather days, blood donations have often been around 5% to 10% down on what was forecast.
And around the country, donations have significantly dropped on England's match days, with a maximum drop of around 20% on Saturday as England beat Sweden.
The combined effect has cost the NHS around 2,000 blood donations in the last two weeks.
That has left an urgent need for people with the valuable O negative group to donate at Bradford donor centre in the next few days. Stock levels are low and will fall below three days as the hot weather continues.
NHS Blood and Transplant now urgently needs support to ensure hospital patients get the O negative blood they need.
Mike Stredder, Director of Blood Donation for NHS Blood and Transplant, said: "The long spell of sunshine has been great in many ways but some people have chosen to stay in the sun instead of giving blood, and some people haven't been hydrated enough to donate safely.
"England's excellent world cup has also meant football fans are spending their time enjoying the games rather than donating blood.
"However hospital patients in Bradford urgently need blood every day of the year, whatever the weather.
"Nationally, we aim to have six days of worth of blood stocks but today we only have three days of O negative blood. O negative is especially important because it is the universal donor group which can be given to almost anyone in emergencies. We need donors with other blood groups to keep their appointments usual but this urgent appeal is specific to O negative.
"If you are O negative and you can give blood, please donate now. We have around 75 appointments available at Bradford donor centre over the next few days.
"If you are an existing donor with O negative blood and you can't see a convenient appointment time, you can walk in and donate without needing to make an appointment, or call 0300 1232323, and we will book an appointment for you.
"Please don't delay - we need you today."
NHS Blood and Transplant is asking O negative donors to book appointments or just walk into a donor centre and donate; for all donors to make sure they are well hydrated on the day of donation, if donors need to cancel, to give us 72 hours notice.
Bradford blood donor centre is at
28a Manor Row,