ABOUT 35 HOT AIR BALLOONS WERE ENTERED IN THE GREAT WELLSVILLE BALLOON RALLY. AT 0625 EDT, THE PLT (OF C-GDGK) ATTENDED A WX BRIEFING THAT WAS GIVEN TO THE PLTS BY THE BALLOONMEISTER. THE PLT SAID THE BALLOONMEISTER INDICATED THAT THERE WOULD BE SUITABLE FLYING CONDITIONS WITH LIGHT SURFACE WINDS FROM THE SOUTH, & 27 KT WINDS AT 3000 FT, WITH NO CHANGE EXPECTED UNTIL ABOUT NOON. WHEN THE BALLOON LAUNCHED AT 0640 EDT, THE WIND WAS FROM THE NORTH AT 7 TO 10 KTS. ABOUT 40 MIN LATER, THE PLT NOTICED DUST WAS BLOWING & TREES WERE BENDING IN THE WIND. HE DECIDED TO LAND AT THE EARLIEST CONVENIENT TIME. HE STATED THAT THE LANDING WAS HARDER THAN NORMAL DUE TO DIMINISHED ALTITUDE CONTROL. THE 2 PAX RCVD SERIOUS INJURIES. NINE OF THE OTHER PLTS ALSO RPRTD PROBLEMS WITH THEIR LANDINGS. THE WIND WAS RPRTD TO HAVE SHIFTED & WAS BLOWING AT 30 TO 40 KTS.